Cotton yield and nitrogen requirement is modified by crop rotation and tillage method

Abstract

This experiment evaluated alternative methods of soil preparation for cotton ( Gossypium hirsutum L.) on a clay soil prone to compaction from traffic or tillage of wet soil. The treatments compared were: (1) a cotton-wheat rotation, where soil was maintained in good physical condition; (2) continuous cotton with soil preparation by minimum tillage (min-till); (3) continuous cotton with complete soil disturbance (max-till). In addition, as nitrogen (N) fertilizer application rates and application strategies may change with the method of soil preparation, we evaluated different methods of N application (anhydrous ammonia or urea applied before or after sowing, and placed under the crop row or between rows) with rates from 0 to 225 kg N ha −1. The experiment was repeated in 3 consecutive years. Max-till decreased soil nitrate, increased soil bulk density, reduced root development and, in some years, reduced water extraction in comparison with min-till and rotation cotton. Overall, soil under the max-till treatment was the most compacted; this was the result of soil preparation under wet conditions in the last two seasons. Cotton grown in rotation with wheat gave a yield that was, on average, 1.3% greater than that for min-till and 7.1% greater than for max-till. The difference between rotation and min-till was small in the third year of the experiment, indicating that min-till may take time to show production advantages. Optimum N fertilizer rates averaged 145 kg ha −1 for rotation, 189 kg ha −1 for min-till and 210 kg ha −1 for max-till. Crop maturity was delayed slightly and micronaire reduced slightly in rotation cotton. Continuous cotton had a lower level of nitrogen uptake than did cotton grown in rotation with wheat; this is consistent with soil nitrate tests taken before sowing. The best fertilizer application strategy was to apply anhydrous ammonia under the crop row 2–4 months before sowing. The response to urea was similar, but side-dressing all N fertilizer after sowing was the worst method of application, particularly under max-till. We conclude that min-till is a viable option for soil preparation on this soil type, particularly under wet conditions. Weed, insect and disease factors may affect the decision to change rotation and tillage practice.