Is Soil Water Stored for Tung (Aleurites Spp.) Growth Facilitated or Competed for by Intercropping, Crop Succession and Organic Manure in a Sandy-Loam Soil?

This study aimed to evaluate whether soil water is facilitated and secured for tung growth or is competed by cover crops in tung-based intercropping and crop succession system in sandy-loam soil in southern Brazil. Additional effect of poultry manure was also evaluated during the winter and summer periods of 2012/2013 and 2013/2014 growing seasons, using split plot in randomized complete block design and four replications. During the winter season, the treatments were control (tung only); tung + crambe (Crambe abyssinica H.) + NPK fertilizer; tung + crambe (Crambe abyssinica H.) + poultry manure; and tung + oats (Avena sativa) and vetch (Vicia sativa). During the summer season, peanut (Arachis hypogea L.), sunflower (Helianthus annuus) + NKP fertilizer; and sunflower (Helianthus annuus) + poultry manure was cultivated in sequence of the winter intercrops. Soybean (Glycine max) replaced sunflower during the second summer season. Intercropping increased the soil water content of the tung-based agroforestry systems during both winter and summer periods. The intercropped cover crops showed interspecific facilitation for water use by tung during the summer period, but no clear-cut trend for the winter cover crops. The additional organic manure enhanced soil water storage and increased the facilitation potential of the intercrops. Any of the intercrops (soybean, sunflower, or peanut) can be employed for conservation agriculture in agroforestry systems. However, further studies are required during the winter season for establishing the efficacy of the winter intercrops with a view to establishing their competition or facilitation potentials