Nitrogen Application to Cotton on Clay Soil: Timing and Soil Testing

With the aim of improving utilization of N fertilizer and the flexibility of N application strategies in cotton ( Gossypium hirsutum L.), five field experiments examined the response of cotton to N fertilizer, either applied before sowing or as applications before or after sowing, or both. The soils were Pellusterts with a high pH. Anhydrous ammonia was used as the N fertilizer throughout. Soil nitrate N, N uptake, and lint yield were measured in all experiments. There was a linear increase in N uptake with increased application of N fertilizer, with an average of 30% of applied N being taken up by the crop 120 d from sowing. Compared to a single presowing application, N recovery was increased by split application on two occasions, but on a further two occasions it was decreased. Split application increased lint yield on one occasion only—when compaction, waterlogging, and a long growing season allowed better utilization of sidedressed N. On all other occasions the two methods of N application produced similar yields. Therefore, sidedressing can be considered a viable practice on these soils and in this climate. Maximum yield was obtained when crop uptake was about 108 kg N/ha at 120 d from sowing, and was only partially affected by yield level. Soil nitrate N, sampled to a depth of 30 cm 4 wk before sowing, was closely correlated ( r =0.86) with subsequent plant N uptake in nil fertilizer treatments. Therefore, N fertilizer requirement can be accurately determined by applying moderate levels of N before sowing, then subsequently testing for soil N on nil fertilizer strips to determine if any sidedressing is necessary. It was concluded that recovery of N fertilizer was generally poor, and improvement of this parameter has the potential to increase fertilizer use efficiency and productivity of cotton in this environment.