Validation of the NUTMON model for the diagnosis of agricultural management: study on two family farms in Rio de Janeiro State. / Validação do modelo NUTMON para o diagnóstico do manejo agrícola: Estudo em duas propriedades familiares do Rio de Janeiro.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

This study had the following hypothesis: the agricultural production systems adopted by small farmers brings about nutrient negative balances to soil, which causes the loss of soil fertility and crop yield decline in the time span. The general objective of this study was to validate the NUTMON model of the Food and Agriculture Organization of the United Nations (FAO) for the conditions of Rio de Janeiro State, and to evaluate the sustainability of small farms based on nutrient balances. For the adjustment of the model it was necessary to establish the following specific objectives: a) to estimate the rate of soil loss in the agricultural farms, using the technique of Cesium-137 (137Cs); b) to quantify the rates of ammonia (NH3) volatilization in the studied properties using a static semi-opened collector (SALE), after its calibration with the 15N isotope; c) to estimate N losses by nitrate leaching using ceramic cups extractors of soil solution; and d) to accomplish nutrients balance in two small farms in Rio de Janeiro State. The small farms selected are located in two municipalities, in Bom Jardim, the central mountainous region and designated to agriculture, and the other in Itaperuna, the Northwest region with pasture and cattle production. The determination of 137Cs activity for the erosion loss study was accomplished at UEL (University of Londrina). For other evaluations, analyses were accomplished at Embrapa Agrobiologia, Seropédica, RJ. Considering all the studied areas, the results obtained by the use of the 137Cs technique showed rates of soil loss, equivalent to 43.6 and + 77.6 Mg ha-1 yr-1. Tests with the trapping system for ammonia volatilization (SALE) measurement showed that its use is of low cost and easy handling, allowing to recover 57% and 67% of the total N-NH3 volatilized in studies at field and greenhouse conditions, respectively. Thus, to estimate the actual rate of soil NH3 volatilization using the collector SALE at field conditions, it is necessary to use a factor of 1.75. The use of the SALE identified losses of N by ammonia volatilization of 5% and 47% of the applied urea in the farms located in Bom Jardim and Itaperuna, respectively. In Bom Jardim farm, the adjusted nutrients balance, with erosion measured by the technique of 137Cs and ammonia volatilization measured by the proposed trapping system, were +26.2, +67.2 and 20.3 kg ha-1 yr-1 for N, P and K, respectively; taking into account the main rotation crop (taro/taro/corn/fallow). In Itaperuna farm, the cultivated pasture presented an adjusted nutrient balance of +6.6, +0.71 and 64.0 kg ha-1 yr-1 for N, P and K, respectively. The hypothesis of the study was not confirmed, as the management adopted in the family farms was sustainable on the base of the soil nutrients balance, as long as erosion practices are optimized. There was no indication of environmental contamination due to fertilizers. Considering the location of the property in a mountainous area, the fallow system should serve as a sustainability model for other farmers. In Itaperuna, the management system adopted will not cause a decreasing of nutrients level in the soil in a short or medium time range. However, this fact is due to the application of high rates of nitrogen compensating the high rate of losses.

ASSUNTO(S)

ciencia do solo erosão hídrica hydric erosion esium-137 modelling. n losses. césio-137 perdas de n. modelagem

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