Precision agriculture means using variable rates based on management zones, and it has been gaining popularity over the past decade. Variable rate planting and commercial fertilizer application are the most common types of precision agriculture, but manure may soon be joining their ranks.
Many research studies show that variable rate manure application works, and that it’s economical; but there are also imperfections that make it complex. Luckily, in addition to the constant improvements of precision manure applicator technology, there are some practical methods that can increase the success of variable rate manure applications.
Precision application of manure is tricky
Manure itself is not precise. It can be difficult to be certain exactly what nutrients are present in manure for a couple reasons. For one, some of the nutrients in manure are in organic forms, meaning they are not immediately available to the crop. Over time, those organic forms will break down into forms that can be used by plants; but the pace of that transformation is difficult to estimate since it is a microbial process that varies based on the environment. While tools and calculators exist to help estimate how quickly organic forms will become plant-available, they can never be 100% accurate.
Another issue is that manure nutrient content is not uniform. This is especially true for solid manures as the nutrient content in one area of a stockpile will certainly vary from another area. And no matter how well a liquid manure pit is agitated, some variability will still exist. In addition to spatial variations, manure nutrient content varies over time. Nutrient content from storage and handling to what is actually applied can drastically vary.
Also, using variable rates might be a challenge because manure application sometimes occurs during a time crunch. Perhaps harvest was late, or planting was early, or the ground was too wet, or impending ground freeze came too soon; or perhaps storage was in danger of overflowing. Whatever the case, when application must be done on a tight schedule, it is easier to have a “just get it on the field” mentality; which leaves no time for the planning and that precision agriculture takes.
What can be done about these challenges?
Properly sampling manure for testing is a practical way to better understand the actual nutrients applied. To get the best representation of the manure, many samples should be taken during application and mixed well. Keeping detailed records of sample analyses will ensure planning for future applications is done with the most accurate information possible. Speaking of sampling, soil should also be sampled regularly to determine which areas of a field are in need of different nutrient management.
Source: umn.edu
Categories: Minnesota, Crops