Desempenho agronômico e alterações morfofisiológicas de hortaliças submetidas a sombreamento para o cultivo orgânico com faixas intercalares

Abstract

Shading effects on morphophisiological characteristics and performance under organic cultivation with sunnhemp (Crotalaria juncea L.) hedgerows were evaluated on rocket plant [Eruca sativa (Mill)], radish (Raphanus sativus L.) and butter head and crisp head lettuce (Lactuca sativa L.), cultivated in different seasons. The experiments were carried out in Seropédica municipality, Rio de Janeiro, Brazil, in the Integrated Agro ecological Production System (IAPS Agro ecological farm, km 47 ). In the first experiment, carried out on a Fragiudult soil, treatments consisted of plants under four shading levels (30%, 50% and 70% of reducing light and a control with plants kept at full sun), arranged in a complete randomized block design with four replications. Shading was obtained artificially by means of semicircular galvanized steel frames (low tunnel) covered with black screen (sombrite). Although rocket plant and spring and winter butter head lettuce showed increase of chlorophyll a and b content, height, leaf number and specific and total leaf area, caused by shading levels, dry and fresh matter values were not sufficiently increased to improve plant growth. In radish, plant morphophisiological changes induced by shading, promoted aerial dry and fresh matter growth production. However, those modifications did not compensate reductions in diameter, yield and dry and fresh matter production of roots. Summer and winter crisp head lettuce presented augmented aerial fresh matter production at shading levels up to 25% and 32%, respectively. Crisp head lettuce planted in summer presented increases in dry matter yield at shading levels up to 22%, denoting best conditions to adapt to sunlight restrictions. The second experiment was conducted on an Ultisol, series Itaguai. Four treatments were allocated in a complete randomized block design in a split-plot arrangement with four replications. Treatments consisted of vegetables cropped with or without sunnhemp hedgerows, and mulch with sunnhemp straw. Aerial dry and fresh matter production of rocket plant and root fresh matter production of radish were not influenced by sunnhemp hedgerows and by mulching. In radish, mulch contributed to reduction of plant number and root diameter and the highest dry matter yield was obtained in the presence of sunnhemp hedgerows and absence of mulching. Fresh matter production of butter head and crisp head lettuce was positively affected by mulching, while sunnhemp hedgerows improved dry matter yield of butter head lettuce and diminished dry matter production of crisp head lettuce.