| Scope and Method of Study. For chapter one, a field experiment was conducted to evaluate cotton's ability to recover from earlier season N stress. The treatments included 4 rates of preplant (0, 33, 67 and 101 kg N ha-1) and side dress (0, 33, 67, 101 and 134 kg ha-1) N fertilizer applied at early pinhead square, white flower and 30 days after white flower. For chapter two, field studies were established to evaluate application of midseason (V8 to V10) variable liquid UAN (28%) at 4 rates (45, 90,134, and 224 kg N ha-1) applied at different distances (0, 10, 20, 30 and 38 cm) away from the row, on maize grain yield and nitrogen use efficiency.;Findings and Conclusions. For chapter one, the results indicated that, cotton suffered N deficiency if 0 kg N ha-1 preplant N was applied. However, regardless of location and cropping season, cotton recovered from early season N deficiency and attained near maximum lint yield, as long as side dress N fertilizer application was done by EPHS cotton growth stage. Delaying N application to 30 DAWF lint yields were significantly (P<0.05) reduced. The increase in NDVI with preplant N application showed that sensor based nitrogen rate calculator (SBNRC) could be used to make precise sidedress N recommendation for cotton at EPHS or WF growth stages. For chapter two, maize grain yields increased the closer N was applied to the row. Increased N rate led to a general decline in NUE to as low as 4%, 26%, 45%, 43% at Hennessey, Efaw, LCB (2009), and LCB (2010) respectively. Regardless of cropping season and location, the best sidedress N application distance, was between 0 and 10 cm. Application of N at distances >10cm away from the row resulted in reduced grain yield, N uptake and NUE. |
