Long-term effects of tillage on stratification and plant availability of phosphate and potassium in a loess chernozem

Within a long-term tillage trial first laid out in Bernburg, Saxony Anhalt, Germany in 1992, the effect of tillage practice on crop yield, depth distribution and plant availability of P and K, as well as plant nutrient uptake, were investigated. With demand-orientated nitrogen fertilization and pesticide application, yields in both ploughing and conservation tillage treatments were comparable. Extensive management led to a yield decline of 11% and 17% under ploughing and conservation tillage, respectively. Soil samples showed significant P and K stratification under conservation tillage. Calcium-acetate lactate (CAL) soluble P and K concentration in 0-15 cm soil depth increased by 24% and 118%, respectively, without significant decline in deeper soil layers. This led respectively to an increase of 18% and 62%, on average, of the top soil (0-30 cm). Effects on soil pH and lime distribution were negligible. Humus content, which can positively affect nutrient availability, increased from 2.5% to 3.0% in 0-15 cm. Penetration resistance and dry density of top soil were significantly higher under conservation tillage resulting in a large decline of air capacity. This may enhance diffusion and mobilize iron-bound phosphates, but can reduce root penetration, root respiration, and microbial activity. The main reason for the large K accumulation near the soil surface is the relocation of plant residues, which contain only small amounts of phosphorus, from deeper soil layers. Despite higher P and especially K availability according to soil tests. P and K uptake and removal by harvest were equal or even tended to be less, respectively. Under present conditions, nutrients enriched in the uppermost soil layer are used insufficiently. Hence, the need for adjustments of soil sampling and the calculation of fertilization demand for reduced tillage practices should be further investigated. (C) 2011 Elsevier B.V. All rights reserved.