Spring Forage Nitrogen Management
by Amy Shober, Sydney Riggi, and Jarrod Miller; University of Delaware Extension
Early Spring Nitrogen Application Strategies
Nutrient loss potential is still high during the late winter and early spring, especially when conditions are as wet as we have seen in the last few weeks. Here we quickly outline some strategies for getting maximum return on your spring nitrogen (N) applications, while minimizing the potential for losses to the environment. These strategies will ensure you are ready to go when soils dry out and conditions are more favorable for plant growth.
Grasses or Grass-legume Mixes
Consider a spring topdress application N to pastures to promote growth, especially if pastures have thinned and were not fertilized in the fall. Early spring application can help extend hay supplies. We recommend N applications of 30 lb/A to stimulate growth in pastures with <25% clover in the stand. For stands with 25-50% clover, reduce the N application to 15 lb/A. Apply N when additional tillers start forming and before stem elongation Nitrogen applications are not recommended for pastures with >50% clover or legume.
Early spring manure applications are not best for quick greenup of grass species. Manure N availability will be delayed with cool temperatures due to low microbial activity. Microbes must be active to break down organic matter and release N in a plant available form; microbial activity is slow until soil temperatures reach around 50-55 F (late April to early May). Instead, apply commercial N fertilizers (either liquid or granular), which are immediately available to crops coming out of dormancy. Walk the fields about 30 days after the first application of N in the spring to determine if more N is needed.
Skip P and K fertilization at this time. Winter breakdown of plant tissues due to freeze and thaw events should provide enough P and K to support spring growth, unless soil test levels are LOW (<25 FIV). Save P and K applications for early summer after the first hay harvest.
Once fields green up, avoid grazing too early; wait until grasses are 4 inches tall to prevent overgrazing and animal health issues (e.g., grass tetany).
Cereal crops provide excellent feed for livestock when grazed or cut for silage or hay. Cereal crops grown for forage will benefit from spring N applications of 60-90 lb/A. As with grasses, apply N in early spring (late February to early March) to stimulate growth. A single N application is ok. However, splitting the spring N application can reduce lodging and improve yield and protein levels. We highly recommend splitting spring N applications if the crop will be grazed to prevent nitrate poisoning of livestock. For split N applications, apply approximately 30 lb/A of N at green up. Terminate grazing and apply the remainder of the N just prior to joining (Feekes 5).
If you plan on growing cereal crops for grain (with or without grazing), more intensive N management is recommended. Research out of Virginia Tech supports splitting N applications to wheat or barley in the spring to achieve higher yields. The first application of N is recommended at green up, around Feekes growth stage 2-3 based on tiller counts (Table 1). The second N application is recommended at jointing (approximately Feekes 5) based on a whole plant total N tissue test (Table 2); cut the whole plant ½ inch above the soil line and submit the sample to a reputable laboratory.
If only a single spring application is possible, we recommend applying N at jointing (Feekes 5) if tiller counts at green up are >105 tillers per square foot for wheat and >150 tillers per square foot for barley. If tillering is below these thresholds, apply N at Feekes 2-3. Virginia Tech researchers recommend that this single early season N application be based on the results of a soil nitrate test (to a 3 foot depth). If collecting a 3 ft soil sample is infeasible, use the tiller count guidance in Table 1 and double the N rate.
Instructions for completing early season tiller counts:
Lay a yard stick (3 feet long) on the ground and count the tillers along the length of the stick.
Multiply the number of tillers by 4 and divide that number by your row width. This will give you tiller density in tillers/sq. ft.
Repeat these counts in five locations in the field and average the values.