Efeito da fertirrega com azoto e potássio num olival sobre os teores de nitratos e de potássio do solo

Abstract

The use of drip irrigation systems allows the application of fertilizers through water providing the necessary nutrients to crops in times of greater consumption. In the case of the olive tree, it is increasingly common the use of this cultural technique, especially in young olive groves, but in most cases this fertilization is carried out empirically. In order to evaluate the effect of nitrogen and potassium applied by fertigation on yield, on foliar nutrient concentrations and on some soil parameters, a field experiment was established on an olive grove, cv. Cobrancosa, planted in 1990 in Safara, in the Portuguese region of Alentejo. Three levels of nitrogen (0, 50 and 100 kg ha-1 N) and potassium (0, 42 and 84 kg ha-1 K) were used, arranged into a factorial experiment with three replications. The trees were irrigated with a drip irrigation system. The management of irrigation was made using tensiometers, and all trees received the same amount of water. The nitrogen (UAN solution) was applied through fertigation from March to September and the potassium (potassium sulphate) from April to October. The present paper reports the results on nitrate and potassium concentrations at different soil depths (0-0.2 m, 0.2-0.4 m, 0.4-0.6 m and 0.6-0.8 m) in the first two years. Nitrogen fertilization caused an increase in soil N-NO3-concentration between 0.2 and 0.8 m depth. This effect was more pronounced in the samples taken in the two deeper layers and when it was applied the highest level of nitrogen (100 kg ha-1 N). For the potassium, the effect of potassium fertilization occurred on exchangeable potassium only in 0-0.2 m and 0.2-0.4 m depths, whereas the levels of extractable potassium did not suffer significant changes in four soil layers studied.