The Effect of N Fertilizer Placement and Timing on Soil Profile Dynamics of Available Phosphorus and Exchangeable Potassium at Different Growth Stages of Spring Wheat (Triticum aestivum L. cv. Spectrum) on Leached Chernozem*

摘要

The maintenance of optimum levels of nitrogen (N), phosphoms (P) and potassium (K) in the soil encourages vigorous growth of spring wheat root systems, which in turn significantly enhances uptake of other nutrients in the soil. A study was carried outto determine the effect of N fertilizer placement and timing on accumulations and distributions of available P and exchangeable K in the soil profile at different phenological stages of the wheat crop at Krasnodar Agricultural Research Institute in Krasnodar County (45°5'N, 38°50'E, >400 m elev.) in Eastern Europe. The experiment was designed as Randomized Complete Block with four replicates, which were subjected to six N fertilizer treatments (T_1-T_6). Spring wheat was grown under rainfed conditions with treatments varying in N fertilizer placement and timing. N treatments (T_1-T_6) triggered an available P bulge of 2.7-6.4 mg 100 g~(-1) soil when compared with accumulations in the control plots during the first season. In the second season, available P build-ups of 2.7-6.3 mg 100 g~(-1) soil were observed. This was attributed to increased concentration of ions associated with the use of anunoniacal fertilizers, which promoted the solubility of immobile P into relatively available forms. There was a bulge of available P content in the topsoil of about 0.1-2.8 mg 100 g~(-1) soil and 0.2-3.0 mg 100 g~(-1) soil compared with its content in the upper subsoil in the first and second seasons, respectively. This was largely due to the rapid fixation ofP, which curtailed its mobility to lower layers of the soil. Peak build-ups of available P (11.0-17.3 mg 100 g~(-1) soil) and exchangeable K (19.1-28.1 mg 100g~(-1) soil) in the soil profile were observed at tillering stage before rapidly dwindling to as low as 9.0 and 16.6 mg 100 g~(-1) soil, respectively at anthesis in the first season of the study. In the second season this trend was largely distorted by excessive rainfall. This pattern was attributed to the peak P uptake by wheat plants between stem elongation and anthesis, which caused the P depletion in the soil profile. Comparatively high potassium requirement by wheat plants between seed germination and anthesis accounted for corresponding depletion of exchangeable K in the soil profile at anthesis.