Soil conditions and farming practices affecting the yields and sustainability of maize (Zea mays L.) crops in the Texcoco River watershed, central Mexico

This is an ecological study of traditional maize-based agriculture in the Texcoco River watershed, concerned with changing environmental conditions, the adoption of modern agricultural technologies, and the impact of current farming practices on maize yields and soil fertility. Seventy-five maize fields were sampled in the middle, agricultural part of the watershed in the summer of 1997, and each farmer (n = 70) was interviewed about cultivation practices used. Site and soil variables measured at each field were slope, altitude, soil depth, and soil organic matter content (OM), pH, N, P, K, Mg, Ca, cation exchange capacity and texture. Crop management variables summarized from farmer interviews cover all aspects of crop production, from the schedule and timing of cultivation activities, to cropping patterns, fertilizer use, and the use of terraces and field borders. Soils in the area vary greatly in depth and are generally sandy, low in OM, and nutrient poor, particularly in N and P. Soil depth emerged as the biophysical factor most correlated with maize yields, perhaps because absolute amounts of available soil nutrients are lower in shallow soils. Topographical position in the watershed was also correlated with maize yields and soil fertility. Yields, OM, and concentrations of some nutrients are greater further up-slope in the study area. Farming practices are changing in the study area, as farmers are incorporating some "modern" practices into their traditional maize cultivation. Tractors and chemical fertilizers are widely used, and maize monocultures are replacing the traditional maize-beans-squash intercrop. Farming practices do not differ significantly between ecological units in the study area, and no clear relationships were observed between the different farming practices, and maize yields and soil fertility. This thesis also includes discussion of the approach taken to working with farmers in this study, and some historical, cultural and social background information that forms the context for traditional agriculture in the area.