Atributps químicos do solo e produtividade de soja em função de doses de calcário

Abstract

Soil acidity is a limiting agricultural production due to aluminum toxicity that limits plant growth and results in reduced efficiency of applied fertilizers. The elevation of soil pH with liming to around 6.0 and 6.5 favors the availability of nutrients in the soil. However, the superficial applications of limestone for correction of the acidity in depth are not efficient due to the slow mobility of the limestone in the soil profile, being restricted to short distances near the applied layer. Acidity in depth is a major obstacle to higher yields of crops in periods of water stress. In view of this, the objective of this work was to observe a possible neutralization front of soil acidity below the layer of incorporation of the corrective from the application of limestone doses through evaluation of soil chemical attributes and soybean crop productivity. For this, a field experiment was installed in a Ferralsol in the municipality of Santo Ângelo-RS, from January to June, 2018. The experimental design was a randomized complete block design with 7 treatments and 3 replicates. Treatments consisted of the following doses: 0; 8,3; 9,9; 11,4; 15; 21 and 29 t ha-1 of limestone 100% PRNT. The limestone used had PRNT of 59,1%. The lime was applied in an incorporated form in the layer 0-20 cm, with half of the dose previously applied to subsoiling and plowing and another half of the dose applied after the plowing followed by two gradations. Data were submitted to analysis of variance by SASM- Agri software and regression analysis in Sigma Plot software. The rainfall occurred during the period of the experiment was recorded and totaled 770 mm in the 5 months. The soil chemical attributes and the clay content in the 0-20 cm and 20-30 cm layers were analyzed, as well as the soybean crop yield. The neutralization of the active and potential acidity occurred efficiently in the 0-20 cm layer proportionally to the applied doses. There was a reduction of the clay content of the 0-20 cm layer caused by the dispersing action of the limestone. The soybean yield did not present a proportional response to the limestone doses and did not present a relation to the chemical attributes of the soil due to the condition of water satisfaction of the crop during its cycle. It was observed that there is a downward acidity neutralizing front in the soil profile that promoted changes in the chemical attributes of the 20-30 cm layer caused by the movement of ions from the dissolution of limestone (Ca 2+ ,Mg 2+ and HCO 3 - ) by percolation next to rainwater.