How do drought and flood conditions affect the release of nitrogen from ESN?
Water is part of the release mechanism needed to dissolve the urea inside the ESN coating. But it does not regulate the rate of release except when the soil becomes dry enough to limit the process. This occurs near the wilting point of soil moisture. Above that, as long as the fertilizer is in good contact with the soil, there is little or no difference in the release rate with differences in soil moisture. Soil temperature is the primary regulating factor.
In other words, the release rate will be similar in saturated soil to that in unsaturated conditions. This is one of the benefits of ESN. While conventional fertilizers and even inhibitors may be affected by excess moisture, ESN continues to protect N in very wet conditions as well as in dry conditions.
Do you have a release chart showing the relationship between N release from ESN and soil temperature?
We would typically describe the release of ESN to be about 50 to 70 days, but temperature and moisture can alter the timing of its release.
The attached figure shows the effect of temperature on the release as measured in the laboratory in water. This is not to be interpreted as a prediction of exactly what will happen in the field, but it will give you an idea of the temperature effect.
Moisture has little effect on the rate of release as long as there is adequate moisture to maintain the process. If ESN is incorporated into the soil and there is sufficient moisture to grow a crop, there would be little effect of moisture. Moisture only becomes a concern when it is surface applied and not incorporated in areas with limited or infrequent rainfall.
As an example, let’s compare a couple of different environments. In the Midwest US, we have many no-till corn growers who use ESN as a top dress with no incorporation with great success. Rainfall in these areas is typically sufficient to provide intermittent moisture to continue the release. By comparison, in the Great Plains, we would not recommend top dress applications for dryland cropping because rainfall is too infrequent.
Will a heavy rainfall within 24 hours of ESN application compromise the longevity of the product or change the results?
No, the ESN polymer is still there, working to keep your nitrogen protected. The ESN coating is designed to release over 50 to 70 days, and protect your nitrogen for that period of time. One large rainfall does not compromise the ESN coating or cause all of your nitrogen to release very quickly. However, any nitrogen that was released from the coating and not used by the crop before the rain came is subject to losses.
How do temperature and moisture level impact the speed of release of ESN?
We would typically describe the release of ESN to be about 50 to 70 days, but temperature and moisture can alter the timing of its release.
Moisture has little effect on the rate of release as long as there is adequate moisture to maintain the process. If ESN is incorporated into the soil and there is sufficient moisture to grow a crop, there would be little effect of moisture. Moisture only becomes a concern when it is surface applied and not incorporated in areas with limited or infrequent rainfall.
As an example, let’s compare a couple of different environments. In the Midwest US, we have many no-till corn growers who use ESN as a top dress with no incorporation with great success. Rainfall in these areas is typically sufficient to provide intermittent moisture to continue the release. By comparison, in the Great Plains, we would not recommend top dress applications for dryland cropping because rainfall is too infrequent.
How long does it take ESN to be released after application (on average)?
The attached document shows the typical ESN release at different temperatures. It provides an approximation of the typical release timing.
There will be some nominal amount of N that becomes available within the first week – typically about 15 to 25% – due to normal imperfections in the coating of some granules. The release of the remainder of the N will proceed according to soil temperature. At a soil temperature of about 20°C, we would expect the N to release over about 50 to 70 days. Typical release in soil at this temperature would be about 25 to 30% in the first two to three weeks.
If applying ESN in a situation where some immediately available N is needed, we suggest blending ESN with sufficient soluble N – such as urea or ammonium sulfate – to cover the immediate needs for the first two to three weeks. If for example, the soil has little or no residual N from the previous crop, no P fertilizer containing N is applied, soil is low in organic matter, and the crop needs some N immediately, you can apply a blend supplying about 20 to 25% of your N as a soluble form and the balance as ESN.
How much N is available when ESN is first applied?
Typically, most users are using ESN in a blend with other soluble fertilizers such as urea, MAP or DAP, ammonium sulfate, etc. This accomplishes several other objectives such as supplying other needed nutrients and making sure the crop has some immediately available nitrogen for early growth. The following link provides recommendations for various regions and indicates the appropriate amounts of ESN to include in the blend for some different application strategies. Typically, we expect some immediately available N from ESN, as the effects of normal handling and blending processes will produce some immediate release. The normal range of immediately available N when ESN is first applied would be about 15 to 25% if proper care is taken during handling.
