A soybean trial using a sample of Dark-Red distrophic medium texture Latosol was carried out under greenhouse conditions at the Escola Superior de Agricultura 'Luiz de Queiroz' in Piracicaba, São Paulo, Brazil, from December 1993 to July 1994, to evalvate the effects of subsurface compaction and the application of gypsum on nitrogen and phosphorus levels of soybean shoots. A scheme in a bloc randonized desdign, with treatments arranged in a 4 x 4 factorial, with four replications, corresponding to the soil surface application of four levels of gypsum (0, 3.25; 6.50 and 9.75 t ha-1) mixed with 15 t ha-1 of Crotalaria dry matter and 2.5 t ha-1 of lime, at four compaction levels (soil densities of 1.32; 1.47; 1.62 2 1.77 kg dm-3), applied by means of a hydraulic press onto the soil of the central ring of a column formed by three stacked 15 cm diameter PVC rings. It was observed that doses of gypsum did not affect N content of soybean shoots when depth root growth occurred. When soil compaction restricted root growth to soil surface, N concentration in soybean shoots was higher when the estimated applied gypsum was 5 t ha-1, with decreasing values for greater amounts. In general, compaction in the presence of gypsum did not alter N levels in the aerial parts of soybean plants, but led to a linear reduction in the absence of gypsum. Both gypsum and high compaction levels increased the amount of P absorbed.
Soil degradation; bulk densities; root growth; nutrient absorption; mineral nutrition