Study of nitrate movement in a sandy loam soil (Studie zur Nitratbewegung in einem sandigen Lehm)

摘要

A study was conducted in sandy loam soil at Kharagpur, West Bengal (India) in 1996-1997 to assess the influence of different rates of nitrogen (N) fertilization on nitrate leaching. The nitrogen source was urea and there were four N fertilization treatments (70, 80, 100 and 120 kg N/ha), each having three replications arranged in a randomized complete block design (RCBD). The soil was irrigated to a field capacity at 50% available soil moisture depletion regime throughout the season and leaching losses were calculated. A sand tank was used to study the movement of pH, EC, calcium content and NO_3-N in the leachate. pH, EC, calcium content was varied with respect to depth and time but due to the restriction of depth up to 105 cm, NO_3-N concentrationin the leachate remained constant up to 48 h of fertilizer application. A similar experiment was conducted in the field by collecting leachate up to a depth of 220 cm. Different doses of fertilizer application led to a build-up of NO_3-N in the soil andvadose zone. Field results showed that the amount of NO_3-N was positively correlated with soil depth up to 220 cm when fertilizer was applied in a single dose. This build-up acted as a reservoir, which could supply NO_3-N to percolating water, which inturn carried NO_3-N to the saturated zone. Statistical analysis was carried out with differential amounts of nitrogen and soil depth. Regression analysis was done to investigate the best fit of NO_3-N movement with passage of time in different soil layers. The current study showed that at the shallow ground water table conditions (where groundwater table lies immediately below the root zone depth) with sandy loam topsoil, the application rate of commonly used nitrogenous fertilizer (urea) should not exceed 80 kg N/ha.