How long does it take to decay crop residue?

The time required to complete the residue decay process depends on several factors, including temperature, soil moisture, the amount and type of residue present, and the amount of available nutrients to support the decay organisms. For example, we have seen heavy corn residue that was treated soon after harvest under ideal conditions (adequate moisture and high temperatures), and most of the leaves and stalk centers (pith) were decayed in about 40 days. Also, the outer shell of the stalks remained to protect the soil over winter, and the remaining residue was fully decayed by planting time. However, as the temperature or moisture levels decline, the decay process slows and takes longer to complete.

Why accelerate the residue decay process?

As decay activity increases and the number of microbial colonies grows, the fungi and other microbe species require nitrogen and other nutrients to build their cell structure (just like humans). As these soil resources are gathered by the microbes, the nutrients are temporarily unavailable for crop production. This figure illustrates the relationship between the residue decay process (brown line) and nutrient availability (green line).  The amount of available nitrogen and other nutrients is lowest when the decay process is at its peak. If the decay process is still underway when the next crop is growing, then the nutrients in the soil and the residue are tied up. By speeding up the completion of the decay process, Chandler Biocat 1000 helps to make sure these nutrients are available for the next crop.

What is the nutrient content of crop residue?

CropDry tons of residueNP2O5K2O
Corn (150 BPA or drought damaged)5 tons/A100 #/A37 #/A145 #/A
Corn (over 200 BPA)10 tons/A200 #/A74 #/A290 #/A
Soybeans2 tons/A90 #/
20 #/A50 #/A
Oats2 tons/A25 #/A15 #/A80 #/A
Wheat3 tons/A40 #/A10 #/A70 #/A

How do temperature and soil moisture influence decay activity?

To make sure the decay process is completed quickly, we recommend that you apply Biocat 1000 as soon after harvest as possible. The residue will decay as long as there is ample moisture and the temperature is above 38° F. As illustrated in the figure below, the amount of biological activity in the soil doubles for each 10 degree increase in the temperature, so the decay process will be completed sooner if Biocat 1000 is applied when temperatures are warmer.

If the residue is very dry or the soil temperature is low, the decay organisms become dormant. As the soil conditions improve, the microbe colonies are quickly regenerated, and the decay process continues. So, you can apply Biocat 1000 late in the fall or early in the spring when the weather is cool, and the product helps the decay organisms work whenever the temperatures increase. However, if your soil is very dry or frozen, you should wait to apply Biocat 1000 at a later time.

Do I need to add extra nitrogen to decay my residue?

The short answer to this question is “maybe” — based on our calculations, the microbial decay process requires about 12-13 pounds per ton of corn residue. So, if you expect to decay about 1.5 tons of residue per acre in the fall after harvest, then you may need about 20 pounds per acre of available N. In most years, this amount of nitrogen should be left after the crop season, and you will not need to apply any additional N in the fall.

However, you may need more nitrogen in some cases. First, if you had heavy rainfall during the season, much of the residual N may have leached away and cannot help with residue decay. Second, if you sow fall cover crops, these plants will need extra nitrogen for fall growth. When available N is limited, the cover crop will compete with your microbes for the residual nitrogen, and the residue decay process and the early cover growth will both suffer.

The amount of N required to generate fall cover growth depends on the crop. For example, annual rye may need 25-30 pounds per acre for emergence and fall growth. To support residue decay and the cover crop, you may need about 50 pounds of available nitrogen after harvesting the cash crop. In this case, you may want to apply some additional fall nitrogen.