Description

Highland vegetable systems in the Manupali watershed, Mindanao, the Philippines are important to supplement the demand for fresh vegetables in lowland cities, but the sustainability of these systems is constrained by declining soil productivity. A farm survey, soil characterizations, field experiments, and erosion modeling were undertaken to characterize vegetable production systems and soils; to test erosion control measures; and to evaluate impact of crop rotation on soil erosion. Two vegetable systems were identified: the Higher External Nutrient and the Lower External Nutrient systems. The former system existed at relatively higher elevations and showed negative profit. Despite a gradient in the degree of soil development across the four geomorphic units, soils were surprisingly uniform in their morphological and physical properties. However, they differed in fertility characteristics. Upper layers of mountain pedons showed 1.7 to 2% oxalate extractable Al, 1.4 to 2.7% oxalate extractable Fe, > 90% P retention, 10.7 to 11.5 pH in NaF, and < 0.9 cm-3 bulk density, indicating more recent ash cappings on them. Effects of these properties on fertility were evidenced by a high phosphate sorption maxima (14208