Spatial variability of sunn hemp under residual effect of nitrogen and water salinity/Variabilidade espacial de crotalaria juncea sob efeito residual de niveis de nitrogenio e salinidade da agua

This work had as objectives to use the Sunn Hemp (Crotalaria juncea L.) to evaluate the residual effect in the soil of levels of water salinity and nitrogen doses, and the occurrence of spatial dependence within the experimental area. In previous years, the experimental area received six consecutive trials, which tested different levels of nitrogen and water salinity on different crops. The same experimental design was applied to this trial, that is, a randomized block design with split-plots (5 x 3), corresponding to the residual effect of water salinity and nitrogen, and four replications. The variables determined were: the plant height on six dates after the sowing, and the dry mass of the shoot, root and the whole plant. The data were firstly subjected to the variance analysis of the residual effects and to the study of spatial variability through geostatistics. The variance analysis did not show significant residual effects of the levels of salinity and nitrogen doses in the soil on the height and dry mass of Sunn Hemp. It was observed a spatial dependence, from moderate to high, in all dates, for height and dry mass of Sunn Hemp. Keywords: green manuring, spatial dependence, geostatistics, sustainability. O trabalho teve como objetivo cultivar Crotalaria juncea L. para avaliar o efeito residual no solo de niveis de salinidade da agua e doses de nitrogenio e a existencia de dependencia espacial dentro da area experimental. Em anos anteriores, a area experimental recebeu seis experimentos consecutivos para testar niveis de nitrogenio e de salinidade da agua sobre diferentes culturas. O mesmo delineamento foi usado neste experimento, ou seja, blocos ao acaso com parcelas subdivididas 5 x 3, correspondentes ao efeito residual de salinidade da agua e nitrogenio, com quatro repeticoes. As variaveis estudadas foram: altura de plantas em seis datas apos semeadura e as massas secas de parte aerea, de raizes e total. Os resultados foram submetidos a analise de variAncia do efeito residual e ao estudo da variabilidade espacial por meio da geoestatistica. A analise da variAncia nao indicou efeito residual significativo dos niveis de salinidade e doses de nitrogenio no solo sobre as variaveis de crescimento e massa seca da crotalaria. Observou-se dependencia espacial de moderada a forte de todas as variaveis de crescimento e massa seca dentro da area experimental. Palavras-chave: adubacao verde, dependencia espacial, geoestatistica, sustentabilidade.