M. A. Newman

NITROGEN FERTILIZATION OF CONSERVATION-TILLED WHEAT. I. SOURCES AND APPLICATION RATES

ABSTRACT Selection of the nitrogen (N) source and rate for application is critical to ensure profitable wheat (Triticum aestivum L.) yields. The research objective was to evaluate several N sources and spring application rates for conservation tillage wheat production. Research was initiated in the fall of 1997 and continued through 2000 on Collins silt loam (Aquic Udifluvents). A different cultivar was seeded each of the three years. The experimental design was a split-plot with 0, 34, 67, 101, 134, and 168 kg N ha−1 rates the main plots and N sources (ammonium nitrate, urea, urea-ammonium nitrate, ammonium sulfate and UAN+Ca(NO3)2 co-mixture) the sub-plots. The yield response to N rate varied with year and N source. For the three years, yields were increased by applying either 67 or 101 kg N ha−1. Broadcasting AN produced higher yields than urea-containing N sources (urea or UAN) for two of the three years. Broadcasting urea or UAN restricted yields approximately 12% apparently due to N volatilization losses. Broadcasting AS was as effective as AN one of the two years while broadcasting the UAN+ Ca(NO3)2 co-mixture resulted in higher yields at a lower N rate than AN for one of two years. Yield differences due to N source were small when rainfall occurred within two days of soil application. Take-all root rot affected yield one of three years with AN and AS being more efficient N sources. Sulphur fertilization was not needed for wheat production on this soil.

DESIGN OF A SEED-SPECIFIC APPLICATION SYSTEM FOR IN-FURROW CHEMICALS

In-furrow chemical inputs such as fungicides, insecticides, and nematicides are generally applied at planting as a continuous band of material. Focusing these applications at the seed and minimizing the amount of chemical applied between seeds has potential to significantly reduce in-furrow inputs. An in-furrow seed-specific application system was developed to apply discrete bands of liquid chemical to individual seeds during planting. Each seed was detected in the seed tube, seed arrival time at the furrow was estimated, and a chemical band was applied as the seed landed in the furrow. The seed-specific applicator was evaluated at three field speeds and four spray band lengths during corn and cotton plantings. Accuracy of spray band placement, measured as percent of seeds observed within a sprayed band of soil, ranged from 63% to 97% in corn and from 56% to 98% in cotton, depending on field speed and spray band length. As spray band length increased from 3.8 to 7.6 cm, accuracy (averaged across speeds) increased from 76% to 91% in corn and from 72% to 95% in cotton. Accuracy and field speed were inversely related, with highest accuracies observed at the slowest speed. While the applicator performed well, further improvements may be possible, especially when operating at high field speeds. Substantial in-furrow material savings are feasible and depend on desired seeding rates and spray band lengths.

Seed-Specific Placement of In-Furrow Chemicals

In-furrow chemical inputs, such as fungicides and insecticides, are currently applied as a continuous band at planting. Focusing these applications at the seed, and minimizing the chemical applied between seeds could reduce in-furrow inputs significantly. The University of Tennessee Sensors and Controls Laboratory has developed a seed-specific applicator to apply discrete bands of liquid chemical to individual seeds at planting. First, seeds are detected in the seed tube, then tracked from the point of detection to the point of chemical application, and finally sprayed with a variable length chemical band as the seed lands in the furrow. Accuracy of the prototype applicator has been evaluated under various field conditions using cottonseed. In 2002, the applicator was calibrated using a trial-and-error method; 55 to 98% of planted seeds were adequately sprayed, depending on planter speed [3.2, 6.4, 9.7 km/hr (2, 4, 6 mph)] and spray band length [2.5 to 6.6 cm (1.0 to 2.6 in.)]. The calibration process was automated in 2003, and similar results were observed. Assuming a seeding rate of 9.8 sd/m (3 sd/ft), material savings of 35-75% are expected (depending on band length).