Effects Of N Rates And Cultivation On Growth And Nutrient Utilization Of Winter Wheat On Dryland In Northwestern China

Water and soil nutrients are the key factors restraining the yield of winter wheat on dryland in northwestern China. Reasonable N application and cultivation methods have been approved played an important role in creasing crop yields and nutrient use efficiency. Field experiments, with winter wheat as test crop, were carried out to study the effects of N application and cultivation methods on crop growth and nutrient utilization at different N rates and under different methods of cultivation. The main results obtained from the experiments are as follows: 1. The biomass of winter wheat increased with the prolongation of the growth stage, and reached the maximum values at the grain filling stage, which was 11941, 16999 and 17484 kg/ha at 0, 120 and 240 kg N/ha. However, an obvious decrease of biomass was observed from grain filling to harvest for the crop at each N rates, and this meant that loss of biomass happened during late growth stages. Application of N had increased the allocation of dry matter from vegetative parts to heads, and elevated the grain yields, but over application of N had led to decrease of heading rate, harvest indexes, allocation of dry matter to heads, as well as the crop yields. At stage from elongation to heading, the water content in plant was found more sensitive to N rate, and application of N had significantly increased the water content in the plant at this stage. Water use efficiency at each stage was found significantly increased by N fertilization, but it did not continuously increase with the increase of N rates. 2. The uptake of N, P and K was also found increased with the extension of growing seasons, with the N uptake maximized at heading (Apr. 19) at 240 kg N/ha and early filling (May 9) at 0 and 120 kg N/ha, the P uptake at early filling, and K uptake at heading (obviously earlier than N and P). Increase of N rates had increased uptake N, P and K, and their accumulation in plant. However, the uptake of N, P and K was found obviously decreased after flowering and grain filling, with N decreased by 65.6 –101.2 kg N/ha, P by 4.7 -15.5 kg P/ha and K by 65.3 -118.2 kg K/ha. This meant that loss of nutrient happened at late growth stages. Further analysis also showed that N released from vegetative parts could not be totally moved to heads. Apart from the stem and leaf, N accumulated in grain was found also from the soil at high N rates, while loss of N and P was increased with the increase of N rate during late growth stages. After harvest, the residual nitrate N from N fertilizer was found mainly in the 0-80 cm soil layers. 3. The biomass of winter wheat was all maximized at late grain filling stage (May 29) under each cultivation condition, with the maximum biomass of 17269, 18396, 15978 and 16874 kg/ha for the ridge-furrow (RF), supplemental irrigation (SI), straw mulching (SM) and conventional style (CS) cultivation, respectively. Then the biomass was found to decrease continuously till harvest, with the lower decreasing percentages (8.1% and 7.8%) for the RF and SI cultivation, and the higher decreasing percentages (13.3% and 15.8%) for the SM and CS cultivations. The highest grain yield was obtained for the SI cultivation, and then was for the RF one, while it was decreased by 6.6% by SM cultivation. No significant difference was found for water contents and its changes with growth stages between different cultivations. However, supplemental irrigation could significantly increase the water content in the plant at heading stage, and this may be the main reason for the increased grain yield by SI cultivation. 4. The uptake of N, P and K was all found increased with the extension of growing seasons under each cultivation, with the N and P uptakes maximized at late grain filling (May. 29) and K at heading (Apr. 19). The maximum uptake value was 266, 299, 203 and 256 kg N/ha for N, 34, 48, 28 and 30kg P/ha for P, and 238, 261, 217 and 218 kg K/ha for K with the RF, SI, SM and CS cultivation, respectively. This indicated that the RF and SI cultivation could significantly increase the nutrient uptake by plant. However, the uptake of N, P and K was found obviously decreased after the stage with maximum nutrient uptake. Comparisons between the decrease of nutrient uptake in stems and leaves and the increase of that in heads showed that N and P released from vegetative parts were obviously increased by RF and SI cultivation, and that of K was only increased by SI cultivation. The residual nitrate N in 0-200 cm soil layers was found lowest for SI, and highest for the SM cultivation.