Characteristics of N,P and K uptake at different growth stages of spring wheat in irrigating region of Ningxia

Three field experiments were conducted independently at three places in Ningxia irrigated region by Yellow River water to investigate the characteristics of N,P and K uptake of spring wheat at different growth stages.All the test soil was irrigation-silting soil with middle fertility level.Two fertilization treatments were set up(N 225 kg/ha,P2O5 120 kg/ha,K2O 60 kg/ha and CK)with three replicates for each place.The results showed that application of N,P,K fertilizers remarkably increased grain yields,weights of dry matters,and N,P and K contents and accumulates.Whatever fertilization levels,the above-ground dry matter accumulate increased with the growth stage and showed a typical S-shape.There were two peaks of dry matter accumulation occurred at jointing and filling stages separately and each account for about 30% of total accumulation.The contents of N,P,K in plants showed a downward tendency with growth stages;in which a sharply declined from jointing to middle of filling stage and a slowly declined both in the earlier times of tillering and after middle filling stage were observed.Under all experimental condition,N,P and K accumulation increased with both growth stages and fertilization rates,and the proportion of nutrient accumulate at different growth stages was almost same.On average,N,P,K uptake accounted for 4%5%,20%23% of the total uptake at seedling and tillering stages.During jointing period,the absorbed rates accounted for 30%,41%,34%,respectively,which was highest at this stage comparing with the others.The absorbed rates accounted for 14%,12%,10% at heading stage,for 29%、20%、26% at filling stage,for 1%3% at ripening stage.The uptake rates of N,P,K by plants were significantly positive correlated with the accumulated rates of dry matters,but were significantly negative correlated with the contents of N,P,K in plants either high fertility or low fertility.