ChileanJAR

A spatial analysis of the available N in a potato crop (Solanum tuberosum L.) cv. Spunta is necessary in order to make a diagnosis of the local fertilization practice and to provide evidence on a potential environmental risk problem from nitrate wash. For this purpose a sampling scheme was designed during the 2000 season that consisted of a rectangular grid of 3 x 10 stations. Samples were taken on two dates (21/3 and 14/04) and at two depths (0-20 and 20-40 cm). The soil water content on both dates resulted to be high and hardly variable (coefficient of variation (CV < 7%) due to the samplings being carried out after similar rainfall events in quantity and distribution. The spatial variability of the N-NO₃^- (CV > 52%) was much higher than the soil water content on both dates. A localized comparison of the available N showed that in the superficial stratum the content of N-NO₃^- of all the area was always superior to 7.5 mg kg^-1, considered the minimal availability for an optimum growth of the tubers. Between 20 and 40 cm, on the other hand, the content of N was smaller on both dates, and the quantity of N of the latter was below 7.5 mg kg^-1 in 31% of the area. This vertical distribution of the N-NO₃^-, with greater content on the surface, does not guarantee a uniform consumption of N between 0 and 40 cm. At the same time, the greater accumulation of N-NO₃^- between 0 and 20 cm demonstrated that leaching did not occur in the profile.