Soil Agricultural Potential in Four Common Andean Land Use Types in the Highlands of Southern Ecuador as Revealed by a Corn Bioassay

摘要

In the Andes, little is known about the relationships among current land uses and their effect on soil fertility. Corn (Zea mays L.) was used to evaluate soil quality for plant growth on soils of four land uses, along an expected gradient of fertility: native forests (Nf) > pastures (Pa) > Eucalyptus globulus Labill. plantations (Eg) > Pinus patula Schlecht. plantations (Pp). Corn was grown in soils taken from four different areas, for the four land uses in each. In a common garden, a randomized block design was used with four treatments: controls (C), ammonium nitrate (N), triple superphosphate (P), and combined N and P fertilizers (N + P). On soils from Nf, Pa and Eg, fertilization response was N + P > P > N > C;corn biomass (g/pot-1) averaged 4.5 in N + P, 3.3 in P, 1.8 in N, 1.7 in C;P content (mg/pot-1) averaged 12 in N + P, 11.9 in P, 2.3 in N, 2 in C. N + P enhanced growth the most. Mortality was high on Pp soils, growth weak, and fertilization response was P > N + P > C ≥ N;corn biomass (g/pot-1) was 0.9 in P, 0.5 in N + P, 0.8 in C, 0.4 in N;P content (mg/pot-1) was 4.4 in P, 2.3 in N + P, 1.8 in C, 1 in N. All soils had P, K, Ca and Mg deficiencies. Al toxicity possibly occurred only in Pp soils. All control soils had low fertility. Responses to N and P were high except for Pp. Pastures and plantations were once natural forests converted to agriculture, then to pastures as soil fertility declined. Plantations were likely established on poorest pastures;only pine grew on poorest soils. This land use endpoint has the lowest agricultural potential;other land uses have limitations in P, N, and potentially K.