Field experiments were conducted to standardize protocols for site-specific fertilizer nitrogen (N) management in Bt cotton using Soil Plant Analysis Development (SPAD) chlorophyll meter. Performance of different SPAD-based site-specific N management scenarios was evaluated vis-à-vis blanket fertilizer N recommendation. The N treatments comprised a no-N (control), four fixed-time and fixed N doses (60, 90, 120, and 150 kg N ha-1) including the recommended dose (150 kg ha-1), and eight fixed-time and adjustable N doses based on critical SPAD readings of 45 and 41 at first flowering and boll formation stages, respectively. The results revealed that by applying 45 or 60 kg N ha-1 at thinning stage of the crop and critical SPAD value-guided dose of 45 or 30 kg N ha-1 at first flowering stage resulted in yields similar to that recorded by applying the recommended dose of 150 kg N ha-1. However, significantly higher N use efficiency as well as 30–40% less total fertilizer N use was recorded with site-specific N management. Applying 30 kg N ha-1 at thinning and SPAD meter-guided 45 kg N ha-1 at first flowering were not enough and required additional SPAD meter-guided 45 kg N ha-1 at boll formation for sustaining yield levels equivalent to those observed by following blanket recommendation but resulted in 20% less fertilizer N application. Our data revealed that SPAD meter-based site-specific N management in Bt cotton results in optimum yield with dynamic adjustment of fertilizer N doses at first flowering and boll formation stages. The total amount of N fertilizer following site-specific management strategies was substantially less than the blanket recommendation of 150 kg N ha-1, but the extent may vary in different fields.

Living mulch is a cover crop which is intercropped with a cash crop to protect against soil erosion and structural deterioration without taking land out of production. To avoid interference which reduces cash crop yield, the mulch requires management techniques which minimize resource utilization during the critical period of crop development without killing the mulch outright. The experiments reported here examine non-chemical management innovations in a sweet corn-white clover intercrop system which allow for clover regrowth and also contribute to the N requirement of the corn. In 1986 clover was suppressed by mowing or partial rototilling. Yields of corn in plots where clover was rototilled were comparable to yields of clean cultivated corn and superior to yields from plots where clover was mowed or unsuppressed. In 1987 rototilling was compared at 3 timings after corn emergence. Highest corn yields were obtained by rototilling the well-established clover at 2 rather than 4 or 6 weeks after emergence. Yields from rototilled plots in 1987 exceeded those from clean cultivated plots or plots where clover was unsuppressed. After rototilling, the clover reestablished via stoloniferous growth emanating from a narrow strip of roots which passed between the tiller tines. In both years corn leaf N concentrations were highest in the rototilled plots. In 1987 clean cultivated corn appeared N deficient and had a greater incidence of corn smut than corn from the rototilled clover plots. Multiple corn row arrangements which facilitate access to the mulch were compared at a constant plant population to conventional single rows on 76 cm centers. There were no differences in yield between single and double rows (152 cm centers) in either year, while the triple-row arrangement (228 cm centers) reduced yield in 1987 due to the low productivity of the plants in the middle row of the 3 rows.