Sulfur Source, Rate, and Methods of Application for Polyethylene-mulched Tomato

Tomato (Lycopersicon esculentum L.) was grown with polyethylene mulch and drip irrigation on a Millhopper fine sandy soil testing very high in P and low in organic matter during two seasons to evaluate the effect of S source, rate, and application methods on plant growth and yield of fruit.  Sulfur rate of 34 and 68 kg S.ha-1 were applied with  preplant (broadcast in the bed), drip (10 weekly drip application), and  by split applications (50% preplant and 50% drip).  In split applications, S sources evaluated were ammonium sulfate and ammonium thiosulfate.  Plant height was increased with S application from 0 to 68 kg S.ha-1 in both studies. However, response on plant dry weight only occurred in spring 1999. Total marketable yield was 17.9 tons.ha-1 with 0 kg S.ha-1 and was increased linearly to 48.1 tons.ha-1 with application of 68 kg S.ha-1 in Spring 1999, but no response to S was obtained in the Spring 1998 study. Measured variables were not affected by S source and methods of application.  Increasing S application from 0  to 68 kg S.ha-1 reduced leaf and plant tissue P concentration 14 and 12% at mid season, 26 and 25% at  late season sampling times, respectively.  S application of 68 kg S.ha-1 reduced soil pH approximately 0.3 unit at the end of the season in both studies.   Key  words:  drip irrigation, sulfur,  fertigation, Lycopersicon esculentu

Evaluation of a computer model to simulate water table response to subirrigation Avaliação de um modelo computacional para simular a resposta do lençol freático à subirrigação

The objective of this work was to evaluate the water flow computer model, WATABLE, using experimental field observations on water table management plots from a site located near Hastings, FL, USA. The experimental field had scale drainage systems with provisions for subirrigation with buried microirrigation and conventional seepage irrigation systems. Potato (Solanum tuberosum L.) growing seasons from years 1996 and 1997 were used to simulate the hydrology of the area. Water table levels, precipitation, irrigation and runoff volumes were continuously monitored. The model simulated the water movement from a buried microirrigation line source and the response of the water table to irrigation, precipitation, evapotranspiration, and deep percolation. The model was calibrated and verified by comparing simulated results with experimental field observations. The model performed very well in simulating seasonal runoff, irrigation volumes, and water table levels during crop growth. The two-dimensional model can be used to investigate different irrigation strategies involving water table management control. Applications of the model include optimization of the water table depth for each growth stage, and duration, frequency, and rate of irrigation.<br>O objetivo deste trabalho foi avaliar o modelo computacional WATABLE usando-se dados de campo obtidos em uma área experimental em manejo de lençol freático, localizada em Hastings, FL, EUA. Na área experimental, estavam instalados um sistema de drenagem e sistemas de irrigação por subsuperfície com irrigação localizada e por canais. Ciclos de cultivo de batata (Solanum tuberosum L.), nos anos de 1996 e 1997, foram usados para a simulação da hidrologia da área. Profundidades do lençol freático, chuvas, irrigação e escorrimento superficial foram monitorados constantemente. O modelo simulou o movimento da água a partir de uma linha de irrigação localizada enterrada, e a resposta do nível do lençol à irrigação, precipitação, evapotranspiração e percolação profunda. O modelo foi calibrado e avaliado comparando-se os resultados simulados com os dados de campo, obtendo-se um desempenho bastante satisfatório na simulação dos volumes de escorrimento superficial e de irrigação, e dos níveis do lençol freático durante o ciclo da cultura. O modelo pode ser usado para pesquisar diferentes estratégias no manejo da irrigação envolvendo manejo do lençol freático. Aplicações do modelo incluem a otimização da profundidade do lençol freático para cada estádio de desenvolvimento da cultura, e da duração, freqüência e quantidade de água para irrigação a ser aplicada