Fertilizing Irrigated Grain and Oilseed Crops

Introduction

Soil fertility is an important aspect of irrigated crop production. On nutrient deficient soils, applying fertilizer increases yields and improves crop quality. To achieve optimum crop yields, producers should use soil tests to develop an economical and environmentally responsible soil fertility program.

It is necessary to understand how the amount and availability of soil nutrients can limit crop growth before management practice are changed to improve crop production. This factsheet contains fertilizer recommendations for irrigated small grain and oilseed crops based on field research conducted by the Soil and Crop Management Branch of Alberta Agriculture, Food and Rural Development.

Nutrient Requirements of Crops

Crops need many nutrients to grow properly. Nutrients needed in larger amounts are called macronutrients. Nutrients required in smaller amounts are known as micronutrients.

The macronutrients include: nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg). In Alberta, nitrogen and phosphorus limit crop production the most. Potassium and sulphur are occasionally limiting, while Ca and Mg rarely limit crop growth.

The micronutrients, also called trace elements, include: chlorine (Cl), boron (B), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and molybdenum (Mo). These elements limit growth on certain soils and under some crop conditions. Do not over-fertilize because the range between deficient and toxic levels of some micronutrients is narrow.

The nutrients removed by some crops are shown in Table 1. The amount of each nutrient removed varies with crop cultivar, environmental conditions during the growing season and the amount of nutrient available in the soil. Crops may take up some elements in greater quantities than required when there is an abundance of the element in the soil. This is referred to as luxury consumption.

Table 1. Level of nutrients removed by irrigated crops.

Crop
Crop
Part
Nitrogen
(N)
Phosphate
(P₂O₅)
Potassium
(K₂O)
Sulphur
(S)
Chlorine
(Cl)
Boron
(B)
Copper
(Cu)
Iron
(Fe)
Manganese
(Mn)
Zinc
(Zn)

lb/acre

Spring
wheat
80 bu/ac Seed
120
50
30
8
6
.06
<.l
.50
.20
.20

Straw
50
10
100
12
2
.02
<.l
.20
.30
<.10

Total
170
60
130
20
8
.08
<.2
.70
.50
<.30

Barley
120 bu/ac Seed
120
45
40
10
8
.10
<.l
.30
.10
.10

Straw
60
15
130
12
1
.02
<.l
.10
.70
.10

Total
180
60
170
22
9
.12
<.2
.40
.80
.20

Canola
60 bu/ac Seed
115
55
25
20

Straw
60
20
115
15

Total
175
75
150
35

Flax
45 bu/ac
Seed
90
40
35
7

Straw
35
10
70
7

Total
125
50
105
14

To obtain satisfactory yields, plants must receive optimum quantities of nutrient elements from the soil or from applied fertilizer.

Nutrient Uptake and Accumulation

In many crops, most of the N, P, S, and Mo is found in the seed, while stalks and leaves contain most of the K, Ca, Mg, Zn, Fe, Mn, B and Cu. At first, nutrient uptake is faster than growth. For example, when a crop reaches 40 per cent of its final dry weight, 60 to 75 per cent of the total N, P and K have been accumulated within the plants.

Plants continuously take up nitrogen. As plants mature, they translocate N from the leaves and stem to the grain for protein production. By maturity, the grain contains 60 - 70 per cent of N in the plant.

Phosphorus is also taken up continuously during the growing season. However, within 40 days of emergence, grain crops have taken up as much as 70 per cent of the P they require. Much of the P accumulated by the leaves and stems is translocated to the grain at maturity.

Uptake of K begins when rapid plant growth starts and continues until grain starts forming, at which time the uptake of K is nearly complete. The K in the plant is found mostly in the leaves and stems.

Irrigated crops grown on nutrient deficient soils can only reach optimum yields with the application of fertilizer. But, fertilization may not increase yields or quality if other management inputs are not at optimum levels. A fertilizer program should be based on soil tests to determine the nutrient status of the soil and coupled with knowledge of the previous cropping history, fertilizer prices, estimated crop value at harvest, target yield and the management level of the producer.

Soil Sampling

Soil tests help to determine the type and amount of fertilizers needed to correct a nutrient shortage. Soil samples should be taken randomly at 15 to 20 locations in each field. Sample large fields (over 80 acres) separately. Sample unusual soil areas separately (machine leveled, eroded, saline or wet areas) or avoid them completely. Divide each soil core into 0-6, 6-12 and 12-24 inch depths (0-15, 15-30 and 30-60 cm). Samples must be air dried before they are sent to a soil testing laboratory for analysis. Contact a district agriculturalist, a soil specialist or see Agdex 533-4, Soil Sampling Guide, for detailed information on soil sampling.

Deficiency Symptoms and Plant Tissue Analysis

Visual deficiency symptoms
Some nutrient deficiencies have characteristic symptoms. Visual symptoms cannot be relied upon alone to identify a nutrient problem because they may signal the presence of other problems such as restricted root growth or disease. But visual symptoms are helpful when used with other diagnostic tools. Usually, by the time visual symptoms of a nutrient deficiency appear, significant yield losses have already occurred.

Nitrogen: Nitrogen is readily transferred from older to newer leaves as soil nitrogen is depleted. As a N deficiency develops, older leaves appear pale yellow, while younger leaves remain a darker green.

Phosphorus: A deficiency is most noticeable in young plants, which have a high demand for this nutrient. Phosphorus is readily transferred from older to younger leaves. Purple stems and dark yellow tips on older leaves are characteristic symptoms of a severe deficiency.

Potassium: Potassium is readily transferred from older to younger leaves when a deficiency occurs. Yellowing first appears on the tips of older leaves and advances toward the base of the leaf. Younger leaves usually remain a darker green.

Sulphur: Leaves on both S and N deficient plants appear light green or pale yellow. However, S does not move readily from older to younger leaves. In the early stages of a deficiency, younger leaves first appear light green or pale yellow, while older leaves remain green. The opposite occurs with a N deficiency. If a S deficiency persists or becomes severe, upper leaves may turn yellow and older leaves turn light green.

Canola yields may be reduced even if the sulphur deficiency is marginal and there are no obvious visual symptoms. Sulphur deficiency causes younger leaves to yellow in the initial stages, and eventually affects all leaves. In some cases, leaves are poorly developed and cupped, and the backs of leaves are purple. The flowers may be paler than normal. Sulphur deficiency delays and prolongs flowering, delaying maturity. Pods form slowly and are small and poorly filled, and the seeds are shrunken or shrivelled. If S deficiency symptoms are noticeable in canola, S is severely lacking.

Boron: A Boron deficiency results in stunted growth of young plants. The youngest leaves are affected first. They are deformed, thick, brittle and small because B is not easily transferred from old to young leaves. Older leaves usually remain green and appear healthy. Often dark brown, irregular lesions appear, followed by pale yellow chlorosis of young leaves. Stems are short and growing points may die. In canola, symptoms of a B deficiency can be confused with a S deficiency. When a B deficiency is moderate, seed yield is often reduced without evidence of severe deficiency symptoms during vegetative growth.

Chlorine: Chlorine deficiencies are very rare. Symptoms of a deficiency may include stubby roots, some chlorosis of new leaves and plant wilting. Research has shown that chloride added at rates higher than required to meet nutritional needs is associated with suppression of root and leaf diseases in some cereal crops. The reason why added chloride may aid in disease suppression in some soils is poorly understood.

Copper: Copper is not readily transferred from older to younger leaves. When a deficiency occurs, older leaves remain darker and relatively healthy and symptoms develop on younger leaves. In wheat, Cu deficiency symptoms include yellowing of younger leaves, limpness. wilting, pigtailing of the upper leaves, kinking of the leaf tips, excessive tillering, aborted heads, delayed maturity and poor grain filling. Copper deficiency can also resemble frost damage. On Cu deficient soils these symptoms tend to occur in irregular patches. Copper deficiency is often associated with the disease stem or head melanosis and an increased incidence of ergot. For barley, symptoms include yellowing, pigtailing, awn kinking, excessive tillering and weak straw. Oats will also show pigtailing. Copper deficiency symptoms are not well documented for canola but may include: stunted plants, slow pod development, reduced seed set, and increased amounts of green seeds.

Iron: An Fe deficiency is characterized by chlorosis of the younger leaves. The tissue between the veins gradually turns yellow, while the veins tend to stay green. The tips and margins of some leaves may turn brown and become dry and brittle.

Manganese: Oats are an excellent indicator of Mg deficiency because Mg is partly mobile in oats. White to grey flecks or specks first appear and become more severe on mature leaves about halfway up the shoot. If a deficiency persists, symptoms spread to old leaves then to the youngest leaves. The specked condition, known as "grey speck", appears in interveinal area on the lower half of older leaves and extends toward the tip as symptoms develop.

Manganese is not readily transferred from old to young leaves in wheat and barley. In wheat and barley, affected leaves turn pale green and appear limp or wilted. Leaves develop a rapidly spreading interveinal chlorosis in the mid-section of the leaf. Small white to grey spots, specks or stripes appear near the end of the leaf tip on young leaves, and leaves have a limp or wilted appearance.

Molybdenum: Molybdenum deficiencies are rare. Deficiency symptoms are similar to those of N.

Zinc: Zinc is partly mobile in wheat and barley. Deficiency symptoms appear in these crops as pale yellow chlorotic areas on middle leaves, halfway up the stem. Chlorosis develops on the lower half or mid-section of the leaf followed by grey or dark brown necrosis of the leaf. Generally, stems are short and often fan shaped with leaves crowded together at the top. In flax, deficiency can cause grayish-brown spots in the younger leaves, shortened internodes and a stunted appearance.

Tissue sampling and testing
Plant tissue tests are helpful for determining which nutrients are responsible for poor crop growth and choosing a fertilizer program to correct a problem. Tests involving plant tissue must be calibrated with field fertilizer trials. Calibration of tissue tests is complex because the measured nutrient concentration, which is the basis of the tests, varies with the stage of plant development, crop variety and the portion of the plant sampled.

Take representative plant tissue samples early in the growing season to assist with interpretation of soil tests. For small grain crops, sample all the above ground portion just before heading. For flax and canola, sample all the above ground portion just before or during early flowering. Normally, a sample of 25 plants from a field is sufficient for a tissue analysis. Do not contaminate plant tissue samples with soil. Do not include root material with tissue samples. Place fresh samples in clean paper bags and air-dry them to remove excess moisture before shipment to a laboratory. For most crops, the concentration of nutrient elements found in plant parts can be used to determine the nutritional status of the plant. The quality of the analysis depends on the sampling procedure and interpretation of the results.

Tissue samples taken from a normal crop growth area and poor growth area in a field can provide a useful comparison.
Table 2 gives typical nutrient values in tissue of cereals, canola and flax. For more specific range values for various crops, as well as interpretation of test results, contact the Soils and Animal Nutrition Laboratory of Alberta Agriculture, Food and Rural Development in Edmonton or a soil and crop specialist.

Table 2. Levels of nutrients in small grains, canola and flax.

Cereals,
whole plant prior to filling
Low
Marginal
Sufficient

Percent (%)

Nitrogen
<1.5
1.5 - 2.0
>2.0

Phosphorus
<0.15
0.15 - 0.25
>0.25

Potassium
<1.0
1.0 - 1.5
>1.5

Sulphur
<0.1
0.1 - 0.15
>0.15

Parts per million (ppm)

Boron
<3.0
3.0 - 5.0
>5.0

Copper - barley
<2.3
2.3 - 3.7
>3.7

- wheat
<3.0
3.0 - 4.5
>4.5

- oats
<1.7
1.7 - 2.5
>2.5

Iron
<15.0
15.0 - 20.0
>20.0

Manganese
<10.0
10.0 - 15.0
>15.0

Molybdenum
<.01
0.01 - 0.02
>0.02

Zinc
>10.0
10.0 - 15.0
>15.0

Canola at early flowering
Low
Marginal
Sufficient

Percent (%)

Nitrogen
<2.0
2.0 - 2.5
>2.5

Phosphorus
<0.15
0.15 - 0.25
>0.25

Potassium
<1.2
1.2 - 1.5
>1.5

Sulphur
<0.20
0.20 - 0.25
>0.25

Parts per million (ppm)

Boron
<20.0
20.0 - 30.0
>30.0

Copper
<1.7
1.7 - 2.7
>2.7

Iron
<15.0
15.0 - 20.0
>20.0

Manganese
<10.0
10.0 - 15.0
>15.0

Molybdenum
-
-
-

Zinc
<12.0
20.0 - 30.0
>30.0

Flax at early flowering
Low
Marginal
Sufficient

Percent (%)

Nitrogen
<1.25
1.25 - 1.75
>1.75

Phosphorus
<0.2
0.2 - 0.25
>0.25

Potassium
<1.0
1.0 - 1.5
>1.5

Sulphur
<0.1
0.1 - 0.15
>0.15

Parts per million (ppm)

Boron
<3.0
3.0 - 5.0
>5.0

Copper
<2.4
2.4 - 3.5
>3.5

Iron
<15.0
15.0 - 20.0
>20.0

Manganese
<10.0
10.0 - 20.0
>20.0

Molybdenum
-
-
-

Zinc
<12.0
12.0 - 15.0
>15.0

Source: Alberta Agriculture, Food and Rural Development and Manitoba Agriculture.
Critical levels have not been established for chlorine.

Determining Fertilizer Requirements

Nitrogen (N)
All crops require nitrogen in large amounts ( Table 1). Nitrogen is often the most limiting nutrient in irrigated production in Alberta. Crops normally take up nitrogen from the soil in the form of nitrate nitrogen (NO_³-N). When N is adequate it promotes vigorous growth and a larger leaf area with a deep green color. Crops obtain nitrogen from:

inorganic nitrate nitrogen (NO_³-N) and ammonium nitrogen (NH₄+-N) in the soil solution or attached to soil particles,
ammonium and nitrate nitrogen released from breakdown of soil organic matter, manure or residual N from legume crops during the growing season,
applied nitrogen fertilizer (NH₄+ and NO_³-N),
from rainfall associated with lightning.

Most of the N stored in the soil is found in soil organic matter. One per cent of organic matter represents a thousand pounds of N per acre, but less than 1 per cent of the N tied up in organic matter is released each year. Soil micro-organisms are responsible for releasing the N. Several factors influence the activity of these micro-organisms including: environmental conditions, particularly the carbon to nitrogen ratio in plant residue; soil temperature; soil moisture; and organic matter content. Normally only 1 0 to 20 per cent of the total N required for high crop yields is supplied by N released by soil organic matter decomposition. Fertilizer must supply the remaining N. If the previous crop was a legume, an additional 1 0 to 30 lb/ac of available N is added to soil from plant residue. The amount of N fertilizer required depends on the level of soil nitrate-nitrogen (NO_³-N). Less fertilizer will be needed if the level of plant available soil nitrogen is high.

Crops respond dramatically to N fertilizer on deficient soils. Under irrigation, high rates of N fertilizer can be economical, but they should only be applied when soil test levels of nitrate-nitrogen are very low.

Fertilizer recommendation tables have been developed under field conditions for crops irrigated at three management levels: optimum, intermediate and average. The total water required for crops grown under these production conditions includes available spring soil moisture, growing season precipitation and effective irrigation water (see Table 3).

Optimum production is achieved when total water use is between 450 and 500 mm per season. Soil moisture must not drop below a 50 per cent safe depletion point during the growing season, which occurs when half of the readily plant available water in the root zone has been depleted. Once soil moisture drops below 50 per cent safe depletion, a plant cannot take up water at a sufficient rate to meet transpiration needs, causing the plant to undergo stress. The longer the period of stress, the greater the potential yield reduction.

Intermediate production conditions occur when total water use is between 375 and 425 mm per season. Soil moisture will drop below a 50 per cent safe depletion point for a few days, several times during the growing season.

Average production conditions occur when total water use is between 300 and 350 mm per season. Soil moisture will drop below a 50 per cent safe depletion point for a number of days, two or more times during the growing season.

Table 3. Total amounts of water required for optimum, intermediate and average crop production conditions.

	Moisture level
Production level	inches	millimetres
Optimum	18-20	450-500
Intermediate	15-17	375-425
Average	12-14	300-350

Figures 1 to 5 provide predicted yields for soft white spring wheat, hard red spring wheat, durum wheat, prairie spring wheat, feed barley, malting barley, canola, flax and oats. The curves show the effect of banding increasing rates of N fertilizer at a depth of 7.5 to 10.0 cm (3 to 4 inches) in the late fall or spring. The effect of nitrogen fertilizer on yield is significantly affected by method of placement.

Figure 1 Predicted yield increase for soft white spring wheat and hard red spring wheat to added nitrogen fertilizer, when soil test nitrogen (0-24)inches is 30 lb/ac.

. Figure 2 Predicted yield increase for durum wheat and prairie spring wheats to added nitrogen fertilizer, when soil test nitrogen (0 - 24)inches) 30 lb/ac

Figure 3 Predicted yield increase for malt and feed barley to added nitrogen fertilizer, when soil test nitrogen (0 -24 inches) is 30 lb/ac.

Figure 4 Predicted yield increase for flax and canola to added nitrogen fertilizer, when soil test nitrogen (0 - 24 inches) is 30 lb/ac.

Figure 5 Predicted yield increase for oats to added nitrogen fertilizer, when soil test nitrogen (0 -24) inches) is 30 lb/ac.

The amount of N fertilizer required for maximum economic yield can be estimated by using the cost of N fertilizer per pound and the expected value of the crop per bushel at harvest. If the combined soil and fertilizer N level used exceeds 150 lb/ac severe lodging may occur with varieties that have limited lodging resistance. Generally, the combined level of soil N and fertilizer N should not exceed 180 lb/ac to avoid problems of lodging, excessive vegetative growth and delayed maturity. Under high fertility conditions selection of lodging resistant varieties is important.

When N fertilizer levels are increased, the protein content of the seed produced increases. This can be a serious problem for malting barley and soft wheat. As long as adequate water is available, good irrigation management will help keep protein levels at an acceptable level.

Leaching of nitrate-nitrogen through the root zone into the groundwater is an environmental concern, which demands careful management when large amounts of N fertilizer or manure are applied to achieve maximum yield. Studies in Alberta have shown high fertility used to improve crop yield resulted in a marked increase in soil nitrate-nitrogen content after only four years. High fertility coupled with other intensive management inputs also resulted in a substantial increase in soil nitrate-nitrogen. Suggested maximum amounts of soil and fertilizer N to avoid serious agronomic and quality problems are presented in Table 4.

Table 4. Suggested maximum levels of soil nitrogen (0-24 inches) plus fertilizer nitrogen.

	Irrigation level Average Intermediate Optimum
Crop	Max N (lb/ac)
Soft white spring wheat	120	150	180
Hard red spring wheat	100	130	160
Durum wheat	110	140	170
Prairie spring wheat	120	150	180
Feed barley	120	150	180
Malting barley	100	130	160
Canola	120	150	180
Flax	100	130	160
Oats	120	150	180

To determine the economic application rate of N fertilizer, the following factors must be evaluated: soil N level, previous crop, price of N fertilizer, crop value, ratio of marginal economic return and level of irrigation management. Examples of estimating the economic rate of N fertilizer required for canola are provided in Tables 5 and 6. Each example is based on soil test N (0-24 inches) of 50 lb/ac and uses two fertilizer price scenarios. In Table 5, the first scenario used a lower nitrogen fertilizer cost ($0.22/lb) and a higher value for canola ($6.00/bu). In this scenario it would be economical to apply N fertilizer at a rate of up to 150 lb/ac, which is the top end of the chart. The second scenario used a higher nitrogen fertilizer cost ($0.30/lb) and a lower value for canola ($4.00/bu). An economic N fertilizer rate of 140 lb/ac is predicted at a 2:1 ratio, where a two dollar return is expected from the last dollar spent on fertilizer. At a 3:1 ratio, 80 lb/ac of N fertilizer would be economical. Producers frequently use a 2:1 ratio, but can select any cost-benefit ratio to suit their situation and yield goal.

Table 5. Determination of economic nitrogen fertilizer response of canola using the optimum irrigation chart when soil test nitrogen is 50 lb/ac (0-24 inch depth) using two scenarios.

N Fertilizer Added (lb/ac)	0	10	20	30	40	50	60	70	80	90	100	110	120	130	140	150
Expected Yield	31.5	36.2	40.1	43.6	46.8	49.7	52.4	54.9	57.1	59.2	61.2	63.0	64.7	66.3	67.7	69.1
Added Yield Increase /10 lb/ac N	0	4.7	3.9	3.5	3.2	2.9	2.7	2.5	2.3	2.1	1.9	1.8	1.7	1.6	1.5	1.4
Scenario 1:
Fertilizer Cost $0.22/lb		2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20
Canola @ $6.00/bu		28.20	23.40	21.00	19.20	17.40	16.20	15.00	13.8	12.60	11.4	10.80	10.20	9.60	9.00	8.40
Scenario 2:
Fertilizer Cost $0.30/lb		3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00
Canola @ $4.00/bu		18.80	15.60	14.00	12.80	11.60	10.80	10.00	9.20	8.40	7.60	7.20	6.80	6.40	6.00	5.60
									3:1						2:1

In Table 6, with average production conditions, the same two price scenarios were used. With a lower nitrogen fertilizer cost ($0.22/lb) and a higher value for canola ($6.00/bu) the maximum rate that is economical is at the 120 lb/ac of N fertilizer. At this point the yield increase table shows no additional predicted yield increase. The second scenario used a higher N fertilizer cost ($0.30/lb) and a lower value for canola ($4.00/bu). The economic N fertilizer rate occurs at 90 lb/ac at the 2:1 ratio. In each case, the same crop and soil test levels were used.

Table 6. Determination of economic nitrogen fertilizer response of canola using the average irrigation chart when soil test nitrogen is 50 lb/ac (0-24 inch depth) using two scenarios. Fertilizer added is in lb/ac and yields are in bu/ac. The boxed numbers indicate the point where marginal economic return is 2:1 or 3:1.

N Fertilizer Added (lb/ac)	0	10	20	30	40	50	60	70	80	90	100	110	120	130	140	150
Expected Yield	27.8	31.1	33.9	36.4	38.6	40.6	42.4	44.0	45.4	46.7	47.9	49.0	50.0	50.0	50.0	50.0
Added Yield Increase /10 lb/ac N	0	3.3	2.8	2.5	2.2	2.0	1.8	1.6	1.4	1.3	1.2	1.1	0	0	0	0
Scenario 1: Fertilizer Cost $0.22/lb		2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20	2.20
Canola @ $6.00/bu		19.80	16.80	15.00	13.20	12.00	10.80	9.60	8.40	7.80	7.20	6.60	0	0	0	0
												3:1
Scenario 2: Fertilizer Cost $0.30/lb		3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00
Canola @ $4.00/bu		13.20	11.20	10.00	8.80	8.00	7.20	6.40	5.60	5.20	4.80	4.40	0	0	0	0
					3:1					2:1

Predicted yield increase should be used for economic analysis. A target yield must be realistic and based on long-term averages and the management ability of the producer and conditions such as climate that are expected in the coming year.

Added N fertilizer will increase yield and protein content, while high rates of N fertilizer may decrease oil content of oilseed crops (Figure 6). Although the percentage of oil may decrease with added N fertilizer, the total oil produced per acre can be dramatically increased.

Figure 6 Effect of N fertilizer on protein and oil content of irrigated canola.

Phosphorus (P)
Soil tests determine the amount of phosphorus (P) in the soil and fertilizer recommendations are made in terms of phosphate (P_²O₅). The price of the fertilizer is based on the percentage of (P_²O₅)in the fertilizer. To convert P to (P_²O₅), multiply by 2.3 (e.g., 1 0 lb/ac of P = 23 lb/ac of (P_²O₅).

Soils in southern Alberta are fairly high in total P, often containing over 1200 lb/ac in the surface soil. However, the portion of plant-available P in soil is frequently low.

Much of the unavailable P is contained in soil minerals and soil organic matter.

Crops often respond to phosphate fertilizer on soils that are low in available P. However, the response to P is generally much smaller than with N fertilizers.

Soil tests are used to estimate the P-supplying power of soils. These tests attempt to measure the plant-available portion of the total P supply in the soil. In the past two decades, some soils that received P fertilizer have benefited in a build-up of residual fertilizer P, most of which remains plant-available.

Phosphorus soil tests and fertilizer recommendations in Alberta are not always effective in predicting when a crop will respond to P fertilizer application. Soils that have accumulated fertilizer P over the years may still test deficient in plant-available P, particularly on high pH calcareous soils, yet crops may not respond to added P fertilizer. Some soils that test high in plant-available P still respond to added P. A further problem occurs when soil sampling fields. Because P fertilizer is normally seed- placed or banded, soil P levels differ widely over short distances within a field, necessitating extreme care in obtaining a representative sample of the field. These problems cause serious concerns for farmers trying to optimize their P fertilizer use through the interpretation of soil tests. The phosphorus fertilizer recommendations used by the Alberta Soils and Animal Nutrition Laboratory at various soil test levels are presented in Table 7.

Table 7. Phosphorus fertilizer recommendations at various soil test levels

Soil test level P (lb/ac)	P₂O₅ recommendation (lb/ac)
(0 - 6 inch depth)	Grains	Canola	Flax
> 80	0	0	0
50 - 80	20	20	10
40 - 50	20	20	20
30 - 40	20	30	20
20 - 30	30	40	25
10 - 20	40	50	30
0 - 10	50	60	35

Note: Miller Axley method used to determine soil P.

For greatest efficiency, phosphate fertilizer should be either seed-placed or banded. Germination and emergence can be substantially reduced if more than 20 to 30 lb/ac of P_²O₅ is seed-placed with canola or 10-20 lb/ac of P_²O₅ is seed-placed with flax (see page 13 for additional information).

Research has shown that P uptake efficiency was only 12 to 15 per cent when N (108 lb/ac) and P_²O₅ (54 lb/ac) were dual banded. When N and P were banded separately, P uptake efficiency was 30 to 35 per cent. Apparently, nitrogen can radiate out from the dual-banded fertilizer while the P does not. At high concentrations of N fertilizer, plant roots may be unable to penetrate the band to take-up P fertilizer. When high rates of N fertilizer (>70 lb/ac) are used, deep-banding N and seed-placing P generally gives a better response than dual deep-banded N and P.

Recent studies have compared residual effects of P fertilizer with repeated annual seed-placed applications. Investigations of the forms of applied P remaining in soil showed that after five years, less than 15 per cent had been converted to unavailable forms. This remaining fertilizer P should be available for subsequent crops for many years.

Moderate to large one-time applications of fertilizer P on some soil types may be an alternative to the traditional approach of applying small amounts of P annually. Such a practice offers several agronomic advantages. A large, single application of P can supply the future P needs of a crop such as canola, which has a high P requirement but does not tolerate high rates of seed-placed P. Residual P applications also provide a means of overcoming the variable P deficiency that is often associated with machine levelled or eroded land. The negative factors of this practice include: high initial cash costs and potential for inducing zinc or copper micronutrient deficiencies.

The fundamental concern farmers have is how much phosphate fertilizer to apply to a crop. When soil test P levels are low and limited amounts of P fertilizer have been applied in previous years, follow the recommendations of soil test report. If soil test P levels are medium to high and significant P fertilizer has been applied in the past 10-20 years, an annual application of phosphate fertilizer is recommended to meet crop requirements and replenish the soil P that is removed. A maintenance application is the amount of P_²O₅ removed by a crop in a growing season ( Table 1).

Potassium (K)
Soil tests determine the amount of potassium (K) in the soil and fertilizer recommendations are made in terms of potassium oxide (K²O). The price of K fertilizer is based of the percentage K²O in the fertilizer product. To convert K to K²O, multiply by 1.2 (e.g., 10 lb/ac of K =12 lb/ac of K²O). The potassium fertilizer sold in Alberta is potassium chloride (KCI) and is often referred to as muriate of potash or simply as potash.

Crops have a high K requirement, taking up nearly as much potassium as nitrogen. The seed contains 20 per cent of the K. The remaining K is contained in leaves and stems, which is often returned to the soil. Generally, southern Alberta soils have high levels of exchangeable K primarily because of abundance of K-bearing soil minerals' Soil test K levels frequently range from 400 to over 1000 lb/ac. In K fertilizer research plots across southern Alberta, application of K has not resulted in a yield response, reduced lodging or reduced disease. Existing recommendations ( Table 8) suggest K be applied when soil test levels are less than 300 lb/ac for canola. Few southern Alberta fields test less than 300 lb/ac. Potassium may be required on sandy soils with low K levels.

Table 8. Potassium fertilizer recommendations for irrigated grains and oilseed crops in Alberta.

Soil test level K (lb/ac)	K₂O recommendation (lb/ac)
(0 - 6 inch depth)	Grains	Canola	Flax
> 300	0	0	0
250 - 300	0	15	0
200 - 250	15	45	15
150 - 200	45	60	30
100 - 150	60	80	60
50 - 100	100	100	100
0 - 50	120	120	120

Potassium is less mobile in soil than nitrate-nitrogen but more mobile than phosphate. Potassium fertilizers are more efficient when seed-placed or banded. However, even small amounts of seed-placed potassium with canola or flax may reduce germination and emergence. If potassium is required, banding or broadcast- incorporation should be used.

Sulphur (S)
Canola and flax have a higher requirement for sulphur than cereal crops. Fortunately S levels in irrigated soils of southern Alberta are usually adequate for crop growth. Much of the S in the topsoil is contained in the organic matter (200 to 600 lb/ac) and is slowly released as sulphate-sulphur (SO₄-S), the form that crops require, through break down of organic matter by soil micro-organism activity. Sulphate-sulphur, like nitrate-nitrogen, is very mobile in soil. The topsoil of some irrigated fields is deficient in plant-available sulphate-sulphur, but the subsoil has enough S in the form of gypsum salts (calcium sulphate) to meet crop requirements. Irrigation water also contains substantial amounts of sulphate-sulphur. Approximately 30 lb/ac of sulphate-sulphur is added to the soil with each 12 inches of applied irrigation water.

A soil test for S can help to determine if S fertilizer is required. Samples should be taken separately from the 0-6, 6-12 and 12-24 inch depths to determine the level of S at various depths. Use Table 9 as a guide to determine if S fertilizer is required.
Research conducted in southern Alberta found that irrigated crops did not respond to S fertilizer, even at low S sites. There are several explanations for this:

Soils with low levels Of S04-S in the surface soil often were underlain by subsoils containing adequate levels of sulphate.
Sulphate-sulphur in irrigation water provided ample S to growing crops.
Rainfall provided about 5 lb/ac of S annually.

Table 9. Sulphur fertilizer recommendations for irrigated crops in Alberta.

Soil test level S (lb/ac)	(S recommendation (lb/ac)
(0 - 24 inch depth)	Grains	Canola	Flax
30	0	0	0
20 - 30	0	10	5

15 - 20	5	15	10

10 - 15	10	20	15

5 - 10	15	25	20

0 - 55	20	30	25

Micronutrients
Soil tests for micronutrients have not been well calibrated to southern Alberta conditions. Soil tests are based on American methods and deficiency standards have been modified for southern Alberta conditions ( Table 10).

Table 10. Range levels of micronutrients in soils.

Nutrient	Low	Medium	Adequate
Boron	0.0 - 0.4	0.5 - 1.2	> 1.2
Chlorine*	0.0 - 8.0	-	-
Copper	0.0 - 0.2	0.3 - 1.0	> 1.0
Iron	0.0 - 2.0	2.0 - 4.5	> 4.5
Manganese	0.0 - 1.0	-	> 1.0
Zinc	0.0 - 0.5	0.5 - 1.0	> 1.0

*This level is used by some labs as a critical level for recommending Cl for disease suppression in cereals.

Micronutrient deficiencies have not been observed in irrigated grain or oilseed crops and yield increases have not been recorded in research plots. Fertilizer trials conducted from 1983 to 1991 have not shown responses to any micronutrients by small grains, canola or flax. Responses to zinc have been obtained with some special crops such as dry beans.

Micronutrient fertilizers may be required on land that is severely eroded or that has been machine levelled, thus exposing subsoil. In these cases, maintenance applications of micronutrients may be necessary to prevent future deficiencies. Normally, micronutrient fertilizers are not required by crops in southern Alberta.

Growers who are concerned about micronutrient deficiencies should consult their district agriculturalist or Agdex 531 - 1, Micronutrient Requirement of Crops in Alberta. Producers who wish to try micronutrient fertilizers should soil test first, leave test strips and carefully evaluate the results.

Fertilizer Application

Crop response to various fertilizers differs, thus the choice of products should be governed by the crop, type of fertilizer, method of application, the cost per unit of the nutrient and the relative convenience in using the product.

Nitrogen - Anhydrous ammonia (82-0-0) is the most concentrated (highest analysis) and least expensive form of N fertilizer. It can be applied in fall or early spring when soil conditions are suitable. Gaseous losses should not be significant if the fertilizer is spiked into moist soil to a depth of 7 to 12 cm (3 to 5 inches).

Of the granular products, urea (46-0-0) is the highest analysis and generally the least expensive. Surface- applied urea can be lost to the air by changing from urea to gaseous ammonia (volatilization). Once urea is well incorporated into soil, volatilization losses normally are minimal. Incorporate urea as soon as possible after surface application. When broadcasting urea, air temperatures should be less than 10&3176C or soil temperatures should be less than 5°C to minimize losses of N.

Ammonium nitrate (34-0-0) contains half of its N in the mobile nitrate form and half in the ammonium form, which is not mobile. This can be an advantage when rapid N uptake is important.

Urea-ammonium nitrate (UAN) liquid fertilizers (28-0-0, etc.) contain urea and ammonium nitrate dissolved in water. Pumping liquids may be convenient since less time and labor is required if the producer has the necessary equipment. Liquid fertilizers are especially suited to fertigation. Urea in the liquid fertilizer is subject to the same volatilization losses as granular urea and must be managed carefully to prevent gaseous losses.

Blended granular or liquid fertilizers (27-14-0, 24-17-0, 27-27-0, etc.) are physical mixes of urea or ammonium nitrate, phosphate and at times other nutrient fertilizers. They can be custom blended to a producer's specification and can include K, S or micronutrients if required. They are more convenient to use than the basic products applied separately.

Phosphorus - Monoammonium phosphate is the form of granular phosphate fertilizer sold in Alberta. It contains 1 1 to 12 per cent N and 51 to 55 per cent phosphate (P205). The commercial liquid phosphate fertilizer sold is ammonium polyphosphate and usually contains 10 per cent N and 34 per cent phosphate (P205). Ammonium phosphate is the form of P generally used. Research has shown it to be slightly more available than triple superphosphate (0-45-0) or diammonium phosphate (1 6-48-0), particularly on high pH soils. The liquid polyphosphates (1 0-34-0) are applied in a solution form. They break down rapidly in the soil to forms that are available as ammonium phosphate.

Potassium - Potassium chloride (KCl), often referred to as muriate of potash, is the form of potassium fertilizer sold in Alberta. Potassium chloride (0-0-60, 0-0-62) is the form of K used as fertilizer.

Sulphur - If S is deficient in soil and is needed by the crop immediately, fertilizer containing sulphate-sulphur such as ammonium sulphate [21-0-0-(24)1, which contains 24 per cent SO₄-S are best. These fertilizers contain sulphate, which is immediately available to the crop. Other fertilizers, which contain elemental (pure) S (0-0-0-90) or urea S [30-0-0-(20)], are only recommended if S levels need to be built up over time. Elemental S must be converted by micro-organisms to the sulphate form before it can be used by the crop. Conversion to sulphate requires several months to several years under warm, moist conditions. Conversion is too slow to fully satisfy crop needs in the year of application on deficient soils. Elemental forms can be used for long-term S building over several years.

Micronutrients - For specific information on micronutrient recommendations, sources and methods of application for specific crops on problem soils, consult a regional soil or crop production specialist.

Micronutrient fertilizers are available in organic and inorganic forms. Table 11 lists some common inorganic micronutrient fertilizers. The inorganic forms are the most economical. The organic sources are synthetic chelates, which are considered to be more available in some soil types.

Table 11. Common inorganic micronutrient fertilizers

Nutrient	Form	% of Nutrient in product
Boron	Borate	14-20
Boron	Borax	11
Copper	Copper sulphate	25
Iron	Iron sulphate	19
Manganese	Manganese sulphate	26
Zinc	Zinc sulphate	18-23

Manure - The composition of manure varies widely. The differences are due to the type of animal, the type of feed and the conditions under which the manure is collected and stored. Storage conditions affect the moisture content. The quantity of bedding materials contained in manure affect the composition of nutrients such as N, P and K. Table 12 gives average values, but considerable deviations will occur. The best way to determine nutrient levels is to send samples to a soil and feed testing laboratory.

Table 12. Approximate nutrient content of animal manure.

		Nutrient (Ib/ton raw waste)
Type of manure	Waste handling system	Dry matter (%)	Nitrogen available*	Total nitrogen**	P₂O₅	K₂O
Swine	Without bedding	18	6	10	9	8
Swine	With bedding	18	5	8	7	7
Beef Cattle	Without bedding	15	4	11	7	10
Beef Cattle	With bedding	50	8	21	18	2
Dairy Cattle	Without bedding	18	4	9	4	10
Dairy Cattle	With bedding	21	5	9	4	10
Poultry	Without bedding	45	26	33	48	34
Poultry	With bedding	75	36	56	45	34
	Deep pit (compost)	76	44	68	64	45

Source: Sutton et al. Purdue Univ. 1D-1 01 (1975).
* Primarily ammonium N which is available to the plant during the growing season.
* Ammonium N plus slow releasing organic N.

Storage and handling are important because they determine the ease with which the nutrients are released for plant use. Storage of manure for a long time can affect the retention of the nutrients. Loss of N in the urea form is the most critical. The hydrolysis of urea and formation of volatile ammonia (NH₃) gas can be hard to avoid. Improper storage of manure in loosely stacked piles will lead to rapid evolution of the gas. Good aeration encourages microbial activity that causes the pile to heat excessively and dry rapidly. Any handling of manure that contributes to heating or drying will hasten the loss of NH₃. Therefore, storage of manure in a compacted state is desirable. Compaction retards heating and drying as well as promotes anaerobic decomposition and the production of various organic acids capable of neutralizing and converting NH₃ to non-volatile salts.

The two best methods used for field application of manure are spreading of solid or liquid material followed by immediate incorporation when weather, soil and crop conditions permit. Injection of slurry or liquid manure into soil is very effective. The method of application greatly affects nitrogen loss ( Table 13). Immediate incorporation of manure will minimize N volatilization. In liquid systems, the addition of nitrification inhibitors has been used with some success.

Table 13. Effect of method of application of manure on nitrogen volatilization losses.

Method of application	Type of waste	*Nitrogen loss(%)**
Broadcast without incorporation	Solid	21
Broadcast without incorporation	Liquid	27
Broadcast with incorporation**	Solid	5
Broadcast with incorporation**	Liquid	5
Knifing	Liquid	5
lrrigation	Liquid	30

Source: Sutton et al. Purdue Univ. 1D-101 (1975).
* Percentage of total N in waste that was lost within four days after application.
** Cultivation immediately after application.

Winter application is normally not recommended due to very high potential nitrogen volatilization losses and potential run-off losses in spring.

From Table 12, under beef cattle with bedding, if N is assumed to be worth $0.25/1b, phosphate is $0.25/Ib and potash is $0.15/1b, a ton of manure would be worth about $13.65 on a wet basis. Aiberta research has shown that less that 50 per cent of feedlot manure decomposes in the first year. Researchers have observed responses to manure four years after the last application and residual effects will persist for many decades.

Feedlot manure weighs from 30 to 40 lb/cubic foot, depending on amount of bedding and moisture content. A reasonable estimate of tons per acre of applied manure can be determined by calculating the capacity of the manure spreader, number of loads spread and number of acres fertilized. An analysis of the manure for nutrient and moisture content would make the estimate of nutrient application much more accurate.

Manure is sometimes better than commercial inorganic fertilizer:

Manure is a slow release fertilizer that contains nutrients in organic form that slowly change to inorganic forms over the growing season to supply nutrients to the crop.
Manure increases the water holding capacity of the surface soil.
Manure helps to bind soil particles together to reduce soil erosion potential. This improves soil structure and helps prevent soil crusting problems.

Rate, placement and time of fertilizer application
Nitrogen fertilizers perform equally well when banded at a depth of 3 to 4 inches and with a shank spacing of not more than 12 to 14 inches wide. If ammonium nitrate (34-0-0) fertilizer is broadcast and incorporated into soil, increase the application rate by 5 to 10 per cent due to the slightly reduced efficiency of broadcast versus banded application. If urea (46-0-0) is broadcast and incorporated into the soil, increase the application rate by 10 to 15 per cent due to reduced efficiency of broadcast versus banded application and potential volatilization (loss of nitrogen to the atmosphere). Volatilization losses are greater when:

soil temperatures are greater than 50° C,
air temperatures are greater than 100° C,
less than 12 mm (1/2 inch) of rain or irrigation is received,
surface soil is coarse textured,
soil is low in organic matter content,
surface soil is high in lime,
day versus night humidity is variable.
Incorporate urea fertilizer immediately after broadcasting to minimize volatilization losses.

The relative effectiveness of fall versus spring applications of N fertilizer is also a consideration. Fall fertilization can range from very effective to disastrous, depending on soil type, form of N fertilizer used and how it is applied. Table 14 gives a general summary of the relative effectiveness of methods and times of nitrogen application.

Table 14. The effect of different nitrogen application methods and dates on crop yield.

Application method	Effectiveness	Variability
Spring broadcast and incorporated	100%	Slight
Spring banded	110%	Little to none
Fall broadcast and incorporated	95%	Moderate to high
Fall banded	110%	Slight

Source: Agdex 542-7

In all cases, spring-banded N is superior to spring- broadcast N, but the differences at times are relatively small. Fall-broadcast N is the least effective method of application and its efficiency declines with the length of time a soil is saturated with water. Finally, fall-banded N is just as effective as spring-banded N except when N is applied early in the fall or if soils are saturated with water for an extended period in early spring.

The maximum rates of N and P fertilizers that can be safely placed with seed with conventional hoe drill seeding equipment is provided in Table 15. These rates can be increased if the fertilizer is banded further away from the seed. For conventional seeding equipment, do not apply more than 10-20 lb/ac of N in the ammonium nitrate form when placed with canola, however, up to 30 - 40 lb/ac can be placed with grains at seeding time. Urea based fertilizers should not be applied at rates greater than 20 - 30 lb/ac in grain crops and should not be seed-placed with oilseed crops. The salt effects of seed-placed monoammonium phosphate are less than for N fertilizers. Up to 70 lb/ac of phosphate can be seed-placed with grains at seeding time, however, rates should not exceed 20 to 30 lb/ac for canola and 10 to 20 lb/ac for flax.

Table 15. Maximum rates of actual nitrogen (N) that can safely seed placed.

Crop	Soil texture	Seedbed soil moisture	Phosphate	*Double disc or narrow hoe drill		**Pneumatic seeder 50% spread
Crop	Soil texture	Seedbed soil moisture	Phosphate	Urea	Ammonium nitrate	Urea	Ammonium nitrate
				lb/ac	lb/ac of Nitrogen (N)
Wheat Barley Oats	Medium to fine	Good Poor	70 70	30 20	45 30	45 30	65 45
	Coarse	Good Poor	70 70	20 15	30 20	35 25	55 35
Small seeded crops	All textures	Good Poor	10-20 0-10	10 0	20 10	20 10	35 25

*Conventional seeder- double disc or narrow hoe opener (1 -2 inch spread of seed and fertilizer)
** Pneumatic seeder- cultivator with sweeps at 12 inch spacing giving 50% spread of seed and fertilizer

Fertigation
Fertigation is the application of fertilizer through an irrigation system. it can be an excellent method of making in-season adjustments on soil nitrogen levels. Under normal fertilizer management, fertigation is not necessary on medium and fine textured soils. On these soil types, where leaching is not a problem, all nitrogen fertilizer be can be applied before seeding to allow the crop to take up N as it is required. However, on sandy soils where leaching and downward movement of nitrate is a potential problem, fertigation of nitrogen fertilizer may be beneficial.

Fertigation works best with pivot irrigation systems, which can apply water lightly and frequently to avoid leaching water below the crop root zone. Even then, not more than 20 to 30 per cent of required N should be applied by fertigation. Generally, all fertigation applications of N should be completed by mid to late June. Problems can occur at the seedling stage if nitrogen is deficient, soils are wet and crop moisture use is relatively low.

If a N deficiency develops in early July, it takes time to apply the fertilizer and up to 7 to 10 days for the majority of the urea and ammonium nitrogen in the liquid fertilizer (28-0-0) to be converted to nitrate-nitrogen form that crops can use. This delay could substantially reduce potential yields.

Computerized Fertilizer Recommendations

Irrigation farmers in Alberta can take advantage of a computer program called FERT-92, which was developed to assist with determining optimum economic fertilizer recommendations. District agriculturists in the irrigated areas have the program. Farmers who want to use the program should contact their district agriculturalist. A user simply has to input soil analysis results, previous crop, crop to be grown, irrigation level, fertilizer price and estimated crop value at harvest. With this information, the program will calculate prices similar to that shown in Tables 5 and 6. This will assist with selection of the most economic nitrogen fertilizer level for each crop. Recommendations are also made for P, K and S. Producers are welcome to make use of this program when developing their fertilizer management plans.

Summary

Nitrogen fertilizer will dramatically increase crop production and yield increase charts can be used to assist with determining economic nitrogen rates. District agriculturists have a computer program available to quickly do these calculations.
Crops respond to P fertilizer, but responses are not always well predicted by soil tests. A maintenance application of phosphate fertilizer annually is useful in maintaining good levels of soil P.
Potassium and S normally are not limiting factors in yield of crops. The naturally high levels of these elements in most southern Alberta soils are generally sufficient for optimum crop production.
Irrigated grain and oilseed crops rarely need additional micronutrients. More research is needed to improve micronutrient soil testing, calibration and interpretation.

Prepared by:
Dr. Ross H. McKenzie
Soil Fertility Specialist
Alberta Agriculture, Food and Rural Development
Lethbridge, AB

Len Kryzanowski
Crop Nutrition Agronomist
Alberta Agriculture, Food and Rural Development
Edmonton, AB

Source: Agdex FS100/541-1.

For more information about the content of this document, contact Ross McKenzie or Agriculture Information Services.
This information published to the web on April 1, 2003.