Abstract
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.
Highlights
Throughout the last five decades, the agricultural sector in the high Andes of Ecuador has experienced political and social changes that have promoted a rapid expansion of agricultural and forestry land use
According to Buytaert et al [18] the soils in the northern part of the Paute watershed are classified as Histic Andosols (Regions 1 and 2), and as Dystric Histosols in the southern part of the watershed (Regions 3 and 4) because of lower soil Al and Fe content (Figure 1)
Land use (p = 0.016; Table 1) and region (p = 0.033; Table 1) effects were present for soil organic matter only, with stronger land use effect than region effect
Summary
Throughout the last five decades, the agricultural sector in the high Andes of Ecuador has experienced political and social changes that have promoted a rapid expansion of agricultural and forestry land use. On one hand, these changes have caused a reorientation of cultivation practices towards large-scale agri-businesses motivated by increased food exportation [1] [2]. The increase in land use without regard to soil nutrient replenishment by both large-scale farming enterprises and small to medium sized farmers has, in turn, led to the rapid decline of soil fertility and possibly to an irreversible transformation of native forests into farmlands, pastures or tree plantations [6]-[10]. Inorganic forms are readily fixed and adsorbed [16] due to the presence of amorphous sesquioxides of Fe and Al, and organometallic complexes in these soils [17] [18]
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