Identifying the Best Tillage Tool For the Job

The use of manure in a fertilizer rotation has been increasing in recent years. While advances are being made in broadcast application, incorporation of solid livestock manure into the soil shortly following application is recommended in order to maintain ammonia levels and minimize odours and runoff.

Five years ago, the AgTech Centre completed research on the most effective tillage methods for incorporating manure. Little has changed in terms of tillage tools and how they operate. The research measured the percentage of manure incorporated using different tools and took a frank look at how much disturbance each tool made.

The case for incorporation
For this study a number of commonly used tillage methods were compared on both tilled and untilled wheat stubble. While there were different results depending on the type of tillage method used, soil conditions had virtually no effect on manure incorporation.

There are a number of concerns with the broadcast application of manure, despite the fact that it is a common and accepted practice. The biggest concern is the impact in terms of odour and runoff into water sources. These concerns can be somewhat mitigated by incorporating manure into the soil.

When manure is turned into the soil, a greater amount of usable nitrogen is available. Liquid manure spread over a field and not incorporated can lose up to 90 percent of its ammonia. Once injected, those ammonia losses can be as low as five percent. Similarly, a broadcast application of manure can lose up to 80 percent of the ammonia while the losses range from 10-15 percent if the manure is incorporated.

Weighing the benefits
Each plot was replicated four times. A strip was left between each replication for machine turning and operation. Half the plots were tilled prior to manure application and the rest of the plots were left as untilled wheat stubble. Fresh solid cattle manure was evenly broadcast at a rate of 30 tonnes/ha (12 tons/ac) using a manure spreader.

Tillage methods tested included a heavy tandem disk and a chisel plow with spikes at a depth of 15 cm (6 in), a heavy harrow and a combination deep ripper and disk at a depth of 41 cm (16 in) on the ripper and 20 cm (8 in) on the disk. Speeds were consistent with the exception of the heavy harrow, which was 2 km/hr (1.2 mph) faster.

After visual incorporation measurements had been taken the plots were packed using a heavy roller. Soil samples were then taken in 3 cm (1.2 in) increments for lab analysis to test manure incorporation. The different incorporation tillage methods showed quite a difference in the percentage incorporated. The difference was as much as 10 percent from the highest to the lowest average incorporation.

The highest incorporation came from a combination deep ripper and disk, with the offset disk providing similar results. The heavy harrows had the lowest percentage of surface incorporation. However these benefits have to be measured against the effect on trash cover and loss of soil moisture.