Interspecific competition and facilitation for nutrient in wheat and legumes intercrops Influence of Orchard Sod Mowing on Nutrient Competition between Citrussinensis and Stylosanthes gracilis and Mechanisms Difference in Root Architecture of Two Stylosanthes Cultivars and Their Competition for Phosphorus with Citrus Rootstock Seedling Difference in Root Architecture of Two Stylosanthes Cultivars and Their Competition for Phosphorus with Citrus Rootstock Seedling