Efecto de la fertilizacion nitrogenada y fosfatada en las propiedades quimicas de un argiudol tipico

A field experiment established in 1988 was evaluated to examine the effect of nitrogen and phosphorus fertilizer on some chemical properties of a Typic Argiudoll. Soil samples were taken from plots fertilized continuously for eight years, under wheat-wheat rotation or every other year during the same period, under wheat-sunflower rotation. Fertilizer treatments were: control, 120 kg N ha^-1 as urea, 22 kg P ha^-1 as superphosphate, and 120 kg N ha^-1 plus 22 kg P ha^-1. In the continuously fertilized plots, organic matter, total nitrogen, exchangeable calcium, magnesium, potassium and sodium, cation-exchange capacity and micronutrients were not significantly affected by phosphorus or nitrogen fertilization; however, pH decreased by 0.39 units in the nitrogen treatment, showing the acidifying effects of nitrogen fertilizer. In plots fertilized every two years, the highest organic matter content was observed in the treatment with 120 kg N ha^-1; whereas total nitrogen, pH, exchangeable magnesium, potassium and sodium, cation-exchange capacity and micronutrients were unaffected by fertilization. Available phosphorus showed a significant response to phosphorus fertilization, because of residual phosphorus. Exchangeable acidity (KCI) was very low, (0.07-0.20 cmol((c)) kg^-1) in all treatments, according to soil characteristics. Total acidity, ranged from 9.28 to 11.38 cmol((c)) kg^-1 and was highly correlated with organic matter, suggesting that organic carbon was the major contributor to soil buffer capacity.