| | Introduction | Background of research study | Importance of soil sampling and testing | Inoculant and nitrogen fixation | Nitrogen and inoculant recommendations | Recommendations for phosphorus fertilizer | Potassium requirements | Sulphur recommendations | Micronutrient fertilizer requirements | Summary
Introduction
Irrigation farmers in southern Alberta have found that dry beans fit well into their overall farm management program. Dry beans yield very well under irrigation, providing excellent economic returns.
Other benefits include greater residual nitrogen levels for subsequent crops and expanded crop rotations. These factors help break weed, disease and insect cycles.
A three-year agronomic research study was conducted in southern Alberta to develop up-to-date agronomic information for Alberta bean growers. This factsheet summarizes the research results to help producers maximize the profitability of beans on their farms and to be competitive on the world markets.
Background of Research Study
The study had three objectives:
- to examine the responsiveness of different types of commercial bean cultivars to rhizobium bacteria and to determine the need for additional nitrogen fertilizer for optimum crop production
- to correlate bean cultivar response to phosphate fertilizer and to correlate response with a number of new soil test methods for determination of plant available soil phosphorus
- to determine the potential extent of zinc deficiency of beans in Southern Alberta.
The bean types and varieties used in each component were Pinto (Othello), Pink (Viva), Red Mexican (NW-63) and Great Northern (GN-1140).
Importance of Soil Sampling and Testing
Soil sampling and testing can give an excellent inventory of plant available nutrients and other soil chemical factors important for crop production. This inventory is a basis for recommending additional nutrients for crop production on an individual field basis.
Soil nutrient levels vary from year to year and, frequently, will vary within fields, even on fields that seem to be uniform. So producers need to follow certain recommended steps for soil sampling and testing to develop a sound ongoing soil fertility management program. Poor soil sampling technique is a major problem, which causes variation in fertilizer recommendations.
Soil testing is only as good as the quality of the soil samples. Soil sampling should be done on an individual field basis. Samples from different fields should not be mixed.
Begin by evaluating each field to determine representative areas. Major areas within fields that have distinctly different soil properties, such as texture, should be sampled and fertilized as separate fields because of different nutrient requirements. Samples should be taken at 0 - 6, 6 - 12 and 12 - 24 inch depths from 15 to 20 locations within each field and then bulked into composite samples.
Inoculant and Nitrogen Fixation
Rhizobia bacteria infect bean roots and form nodules. The bacteria use energy from the plant and in return, provide nitrogen to the plant. As a result, much of the nitrogen (N) required by beans can be provided from the soil and bacterial fixation, which can greatly reduce, and at times eliminate, the need to add nitrogen fertilizer. Inoculation with the proper strain of Rhizobium phaseoli bacteria is essential to ensure fixation. There are three main types of inoculants:
Powdered - fine peat containing the rhizobium, applied directly to the seed.
Liquid - contains the rhizobium in a buffered liquid, applied directly to the seed and is held in place using a sticker.
Granular - small peat-based granules contain the rhizobium, applied in the seed row.
The powdered and liquid forms have been the most commonly used, but granular inoculants are gaining popularity because of their convenience and effectiveness.
It takes three to five weeks after seeding for the bacteria to infect plant roots and form nodules. The effectiveness of the inoculation process can be assessed by simply digging up plants and observing the number, size, color and distribution of the nodules.
Nodules on roots close to the original location of the seed that are reddish or pink inside indicate the bacteria are functioning and fixing nitrogen. Nodules are likely not fixing nitrogen when they appear white, grey or greenish when cut in half. Nodules widely distributed through the root system would indicate that native soil bacteria have also infected the roots. These bacteria may or may not function effectively in fixing N to meet plant requirements.
Soil tests are important in deciding whether or not fertilizer should be applied. Generally, if soil tests are above 20 lb N/ac in the 0 - 12 inch depth, no additional N fertilizer is required for most pulse crops, with the exception of beans. Beans are only able to fix 30 to 40 per cent of their total N requirements, with the remaining N supplied by the soil or from fertilizer.
When growing beans in soils testing less than 80 to 100 lb N/ac, there are times when the addition of some N fertilizer can be beneficial. In a cool wet spring, when nodules are slow to develop, plants may not be able to obtain sufficient N from the soil, resulting in a nitrogen deficiency. Therefore, in soils very deficient in soil N, a modest application of N fertilizer may be a good investment.
Remember that excess N fertilizer may reduce the amount of N fixed by a legume crop and delay crop maturity. Mid-season N applications are normally not recommended. An exception would be under conditions of failed inoculation and obvious N deficiency.
Nitrogen and Inoculant Recommendations
The research study's first objective was to examine the responsiveness of four different types of commercial bean cultivars (Pinto, Red Mexican, Pink, Great Northern) to rhizobium bacteria and to determine the need for additional nitrogen fertilizer for optimum crop production.
In the study, inoculant generally did not result in a marked yield increase of any of the bean types. However, most fields had a history of inoculant use from past bean production, resulting in a build-up of rhizobia in the soil. Therefore, the history of legume crops in the crop rotation likely had a strong effect on the reduced benefit of the inoculants. Most sites showed improved root nodulation, so the practice of adding the rhizobium inoculant with the seed at the time of seeding is still an important management practice.
A significant response to nitrogen fertilizer occurred at most sites. Traditionally, beans have not been considered very responsive to nitrogen fertilizer when seeded with the proper viable rhizobium inoculant. Close examination of the data from all sites showed that optimum yield was generally achieved when the soil N in the 0 - 12 inch depth plus fertilizer N totalled between 100 and 120 lb N/ac. The mean and medium soil N plus fertilizer N levels were 102 and 109 lb N/ac. From this information, nitrogen fertilizer response information was developed for bean growers.
The use of a seed-placed inoculant along with modest nitrogen fertilizer application has proven to be the best method to optimize bean yields under irrigation in southern Alberta. From the research results, a nitrogen fertilizer response chart was developed (Table 1).
The information in Table 1 forms the basis for making fertilizer recommendations for southern Alberta bean growers. Generally, most irrigated fields have soil N levels that are greater than 40 lb N/ac and therefore, most bean growers would not have to apply more than about 50 lb N/ac.
Table 1. Nitrogen fertilizer response chart for irrigated beans in southern Alberta.
Soil Test N Level
(lb/ac - 0 to 12 inches) | Recommended N Fertilizer Level
(lb/ac) |
| 0 - 10 | 90 |
| 10 - 20 | 80 |
| 20 - 30 | 70 |
| 30 - 40 | 60 |
| 40 - 50 | 50 |
| 50 - 60 | 40 |
| 60 - 70 | 30 |
| 70 - 80 | 20 |
| 80 - 100 | 10 |
| >100 | 0 |
Recommendations for Phosphorus Fertilizer
All sites had medium to high soil test levels for soil phosphorus (P). Most sites only responded slightly to phosphate fertilizer, partly as a result of high soil P test levels. Based on the research data, phosphate (P205) fertilizer recommendations were developed (Table 2). The recommendations in Table 2 are based on banded phosphate fertilizer. Broadcast-incorporated rates should be increased by 1.5 to 2 times to be equally effective.
Table 2. Banded phosphate fertilizer recommendations for beans at various soil test levels based on the Kelowna P soil test method.
Soil Test P Level
(lb/ac - 0 to 6 inches) | Recommended P205
(lb/ac) |
| 0 - 10 | 50 |
| 10 - 20 | 45 |
| 20 - 30 | 40 |
| 30 - 40 | 35 |
| 40 - 50 | 30 |
| 50 - 60 | 25 |
| 60 - 70 | 20 |
| 70 - 80 | 15 |
| >80 | 0 |
Potassium Requirements
Beans tend to have a higher requirement for potassium (K) than cereal crops and often require almost as much potassium as nitrogen. However, only 20 to 25 per cent of the plant K is in the seed, while the rest is in the leaves and stems, which are normally returned to the soil.
Many southern Alberta soils are medium to high in exchangeable potassium, often ranging from 400 to 1000 lb of K/ac in the 0 - 6 inch depth of soil. Generally, when soils test greater than 300 lb K/ac, potassium fertilizer is not required. Table 3 provides general recommendations for potassium fertilizer requirements when soils are less than 300 lb K/ac.
Table 3. General potassium fertilizer recommendations for beans
Soil Test K Level
(lb/ac - 0 to 6 inches) | K2O Recommendations (lb/ac)
Irrigated Brown & Dark
Brown Soils |
| 0 - 50 | 130 |
| 50 - 100 | 110 |
| 100 - 150 | 90 |
| 150 - 200 | 60 |
| 200 - 250 | 50 |
| 250 - 300 | 40 |
| >300 | 0 |
Generally, K deficiencies are most likely to occur on intensively cropped sandy soils. When potassium fertilizer is required, banding K is the most efficient method of application. Therefore, if potassium is required, it may be best to either band it before seeding or sideband it at the time of seeding. Broadcast incorporated K should be increased by 1.5 times to be as effective as banded K application.
Sulphur Recommendations
Sulphur (S) deficiencies are rarely a problem on irrigated soils in southern Alberta. Irrigation water normally contains enough sulphate sulphur to meet crop requirements. Soil sampling and testing can help determine if sulphur may be deficient in a field. Soil samples should be taken from the 0 - 6, 6 - 12 and 12 - 24 inch depths to determine the amounts of S at each depth.
There are times, however, when sulphur deficient areas are found in a small percentage of a field. This finding makes it rather difficult to determine if sulphur fertilizer is really needed. If sulphur deficient areas are suspected within a field, sample and test different soil areas separately to confirm if a potential deficiency exists.
If soil S levels are less than 20 lb/ac, Table 4 can be used as a guide to assist in interpreting your soil test, deciding if sulphur fertilizer is required and what rates to use. If sulphur is required, apply a sulphate containing fertilizer such as ammonium sulphate (21-0-0-24) to correct the deficiency.
Table 4. General sulphate sulphur fertilizer recommendations for beans.
Soil Test S Level
(lb/ac - 0 to 12 inches) | Sulphate-Sulphur
Recommendations (lb/ac)
Irrigated Brown and
Dark Brown Soils |
| 0 - 5 | 25 |
| 5 - 10 | 20 |
| 10 - 15 | 15 |
| 15 - 20 | 10 |
| >20 | 0 |
Elemental S fertilizer products are available, but often the S will not convert to a plant available form rapidly enough to meet crop requirements in the first year it is applied. Therefore, a fall broadcast application of elemental S, followed by spring incorporation, is best used in a longer term program to build soil S levels.
Micronutrient Fertilizer Requirements
Beans require all the essential micronutrients. Some micronutrient research work was conducted with beans; however, only zinc (Zn) has been identified as being occasionally deficient on coarse textured soils.
From the research data, Zn fertilizer recommendations have been developed (Table 5). Note that Zn recommendations are based on a very limited amount of field data. Recommendations are based on a combination of soil texture and soil analysis of a 0 - 6 inch soil sample using the DTPA extractable zinc method.
Table 5. Zinc fertilizer recommendations for beans based on soil texture and DTPA extractable zinc.
Soil Texture | Zinc Soil Test
Level in ppm
(0 - 6 inches) | Zinc Recommended |
| Medium to Fine | >1.5 | No zinc recommended* |
 | 1.0 - 1.5 | 3 lb Zn/ac soil applied
or one foliar application |
| <1.0 | 5 lb Zn/ac soil applied
or 1 - 2 foliar applications |
| Coarse | >3.0 | No zinc recommended* |
(Sandy loam to
loamy sand) | 1.5 - 3.0 | 3 lb Zn/ac soil applied
or one foliar application |
| <1.0 | 5 lb Zn/ac soil applied
or 1 - 2 foliar applications |
* Foliar zinc application may be necessary at soil test levels above the critical level when soil conditions are very cool and wet, reducing Zn availability to the plant.
On medium to fine textured soil types, zinc is not recommended above a critical level of 1.5 ppm. Between 1.0 and 1.5 ppm, 3 lb of soil applied Zn/ac is recommended, and below 1.0 ppm, 5 lb of soil applied Zn/ac is recommended. On sandy soils (sandy loam to loamy sand), zinc is not recommended above a critical level of 3.0 ppm. Between 1.5 and 3.0 ppm, 3 lb of soil applied Zn/ac is recommended and below 1.5 ppm, 5 lb of soil applied Zn is recommended.
Banding the zinc before or at the time of seeding is the preferred method of application. However, soil applied zinc sulphate could be substituted for one or two foliar applications. Zinc deficiency can be partially induced by cool, wet soil conditions, which may reduce soil zinc availability to the crop.
Beans grown in soils that have soil test Zn levels above the critical level may still show visual symptoms of Zn deficiency during wet, cool conditions in June. Beans will often grow out of the deficiency as the weather warms up. However, if cool weather conditions are prolonged, a foliar application could result in a yield benefit.
Previous work with boron (B) and beans in southern Alberta did not result in improved crop growth or yield. In fact, several locations resulted in a 5 to 15 per cent bean yield reduction to a 3 lb B/ac banded application. Even small applications of B can be potentially toxic to a sensitive crop like beans. Growers should consult with either a soil or crop specialist before using boron fertilizer with beans.
Summary
Producers can benefit from using inoculant with beans. However, to reach the full yield potential, additional nitrogen fertilizer is recommended on fields that have less than 80 to 90 lb N/ac in the 0 - 12 inch depth of soil. A nitrogen fertilizer recommendation chart (Table 1) has been developed for soil testing labs, fertilizer dealers and farmers to fine tune nitrogen fertilizer recommendations. The response to phosphorus fertilizer is generally small, usually due to higher soil test P levels in irrigated soils. However, phosphorus is very important in bean production, and a maintenance application can be quite beneficial. A phosphorus fertilizer recommendation chart (Table 2) was developed from the research data. Beans showed no response to potassium fertilizer so, an updated potassium fertilizer recommendation chart could not be developed. However, an estimated recommendation chart was developed (Table 3), based on theoretical assumptions. Generally, as long as soil test K levels (using the modified Kelowna method) are above 300 lb K/ac, response to K fertilizer is unlikely, based on these trials.
Although zinc deficient soils are not common in southern Alberta, bean response to Zn fertilizer was observed and was clearly more prevalent on coarse textured soils. From these trials, a Zn fertilizer recommendation chart (Table 5) was developed.
Acknowledgments
The authors gratefully acknowledge funding support from DowAgro Sciences and Philom Bios during the first two years of the study and support from the Alberta Agriculture Research Institute, Alberta Pulse Growers Commission, Westco and Agrium over the three years of the study.
Prepared by:
Dr. Ross H. McKenzie and Kevin Seward
Agronomy Unit, Plant Industry Division, AAFRD, Lethbridge (403) 381-5842
Dr. Refe Gaudiel, (retired)
New Crop Development Unit, Plant Industry Division, AAFRD, Brooks
Beata Lees Westco, Lethbridge
Source: Agdex 142/532-1. May 1999. |
|