Wheat Production in Mississippi
Nitrogen recommendations for wheat
In the Midsouth, nitrogen application timing typically has a significant effect on wheat productivity. This is primarily because the mid-south's warm, wet winter climate is conducive to substantial nitrogen loss by leaching and denitrification, and can also cause wheat growth problems. This necessitates applying the bulk of supplemental nitrogen during the spring, rather than the fall, to minimize these problems.
Growers managing for high wheat yields should time nitrogen application according to wheat growth stage and needs, rather than merely applying a given number of pounds of nitrogen fertilizer. Wheat nitrogen requirements are greatest during rapid growth stages in the spring. Thus, nitrogen application timing must closely coincide with wheat needs to optimize productivity.
Wheat generally requires about 1.5 to 2 pounds of N for each bushel of grain it produces. However, wheat yield is rarely limited strictly by nitrogen rate. In fact, wheat is capable of producing 1 bushel of grain per pound of nitrogen under ideal conditions.
Wheat needs a small amount of nitrogen during the fall to stimulate tiller growth and promote establishment. However, since wheat's fall nitrogen requirement is relatively small (15 to 25 lbs. of N), supplemental nitrogen application primarily depends upon the previous crop and date of planting. Wheat planted following corn, sorghum and rice, and cotton may require about 30 to 40 pounds of supplemental nitrogen. This will help compensate for nitrogen tied up by decomposing grain crop residue. However, if the yield level of these crops did not meet the yield goal which nitrogen application was based upon, particularly during a droughty season, supplemental nitrogen may not be needed. If wheat follows a legume, such as soybeans, or fallow land, supplemental fall nitrogen fertilizer needs are less and may not be needed. Supplemental nitrogen (30 lbs. N) is recommended when planting late link to (Optimum wheat planting dates), to promote fall tillering and establishment.
Spring nitrogen application should normally commence shortly after wheat breaks winter dormancy during tillering stages link to (Feekes growth stages 3 or 4) and be complete at the time stem elongation or jointing begins (Feekes growth stage 6). Rapid wheat vegetative growth and nitrogen uptake begins at stem elongation.
Nitrogen sufficiency during tillering is very important because potential head number, which is generally the most important yield component, is determined by tillering success. After jointing begins, the plant no longer directs nitrogen into more tillers. The potential head size will also suffer if nitrogen application to correct a deficiency is applied after stem elongation begins. However, the nitrogen requirement when stem elongation begins is only about 30-35% of the total season uptake. Thus, split nitrogen applications often produce better results due to high likelihood of denitrification and possibly volatization during wet spring conditions. Split applications may also reduce coverage problems resulting from a single nonuniform application.
The initial topdress of a split application should be applied when dormancy breaks in late-winter (Feekes growth stage 3 or 4) and not exceed 50% of the total seasonal amount. This normally occurs during early-February. The purpose of this application is to promote tillering and head size. The final topdress application should be applied by the time the first node appears at the beginning of stem elongation (jointing, Feekes growth stage 6). This application delivers the main nutritional needs of the crop. This generally occurs in early-March.
Growers who choose to apply spring nitrogen in a single application should time it at Feekes growth stage 4 or 5.
Recommended spring nitrogen rates generally vary from 90 to 140 lbs./a. with higher rates within this range recommended on heavy, clay soils, rather than light, sandy soils. Rates may often be reduced if the wheat's spring visual appearance is dark green, resulting from considerable carryover nitrogen from the previous crop or fall nitrogen application.
Urea-ammonium nitrate solution (N-sol 32%) topdress applications should be limited to a maximum of 50 pounds N per acre to prevent considerable leaf burn.