Potassium acquisition by soybean affected by stratified soil potassium, growth stage, and soil water content.

摘要

A 2-year field study on a silt loam, no-till soil was designed to test the hypothesis that temporal variability and vertical stratification of soil water---having the greatest effect---and K through the profile of no-till soil will lower plant-available K and reduce soybean [Glycine max (L.) Merr.] growth and yield. The objectives of this study were to (1) quantify the impact of distribution and quantity of soil K and water through the growing season on soybean K uptake, shoot and root growth, and seed yield; (2) relate K accumulation patterns to grain K, protein, and oil concentration at harvest; and (3) compare the 5-minute sodium tetraphenylboron test (NaTPB), which access slowly available K, to the standard soil-test K (STK) under field conditions across years. A supplemental split-pot greenhouse study was designed to determine the effect of synchronous and asynchronous availability of localized K and soil water content on soybean root proliferation, K uptake and shoot development. Soil, root and shoot samples were collected by development stages and seed yields were determined at maturity. Highest yields were related to greater number of pods plant-1. Inadequate K fertility early in the season reduced overall crop growth, but soil K fertility above the optimum increased the amount of K cycling in the plant-soil system without improving yield or seed K, oil, and protein concentration. Prediction of tissue K concentrations in response to STK was improved 22% by sampling the 0 to 5 instead of the 0 to 20 cm depth increment. The STK was preferred over the NaTPB test because the STK was a more stable test across different growing season conditions and more closely assessed plant K uptake. Congruent soil K depletion, root growth, and higher K and water availability in the surface (0 to 5 cm depth increment) compared to the subsurface (5 to 20 cm depth increment) illustrated that in intermittent rainfed systems K stratification caused by no-till might not be detrimental to soybean production. Greenhouse results supported field findings and showed that root proliferation occurred in areas of localized soil water availability which, in turn, enhanced K uptake.