October 25, 2012
Factors to Consider with Fall Fertilization in a Dry Year
With harvest finishing early and the potential for some nice fall weather ahead, producers may be tempted to get a jump on spring field work by doing tillage and fertilization this fall. There also may be financial incentives such as product discounts or moving expenses from one year to another.
The following agronomic concerns, briefly described here, also should be considered:
- Soil nitrates may be higher than normal this fall, especially in rainfed fields. Take soil samples and determine residual soil nitrate levels before deciding on fertilizer N application rates.
- Dry soils are difficult to sample and may affect results. Soil organic matter and soil nitrate results should be fine, but some soil pH and potassium may be affected by the dry conditions.
- Dry soil conditions may make tillage difficult.
- Knife applications, including sealing of anhydrous ammonia injection tracks, also may be more difficult in dry soil conditions.
- Wait to apply nitrogen until soil temperatures drop below 50°F since the conversion of anhydrous to nitrate is much slower below 50°F. Leaching is more likely on sandy ground. (See the CropWatch Soil Temperature page for daily updates of soil temperatures.) Currently, average soil temperatures across the state range from 50.8°F to 57.0°F.
- Fall application of other forms of nitrogen is discouraged due to potential nitrogen loss between application and when the crop needs the nitrogen.
- If soil conditions are not conducive to soil sampling, use historical trends and make adjustments based on recent fertilizer application and yield history. Corn removes about 70 lb N, 35 lb P2O5, and 30 lb K2O for every 100 bushels. Soybeans remove about 37 lb P2O5 and 60 lb K2O for every 50 bushels.
- Monitor rain and snow infiltration between now and the next growing season and make fertilizer adjustments next spring if excessive rain may have caused leaching.
Charles Shapiro, Extension Soils Specialist, Haskell Ag Lab
Charles Wortmann, Extension Soils Specialist