Since the crucial issues in the three regions of SHMP are lack of sufficient food and soil conservation, the principal objective of the SHMP research unit is the design and generation of sustainable alternative technologies for the "milpa" system, assuming a permanent agricultural system as opposed to the current shifting system (Cortés et al., 2001).
Sustainable farming systems conserve and protect the essential agroecosystem resource base including soils, water, and genetic diversity; provide enough quality food and fiber to meet present and future requirements; optimize crop output; and are profitable enough to provide farmers with adequate living standards to support viable rural communities (Merwin and Pritts, 1993).
The design and generation of alternative technologies gives priority to terrestrial C sequestration, soil and water conservation, staple crop production, land and labor productivity, sufficient and distributed net income throughout the year, efficient land use, employment opportunity, and opportunity costs of land and water use. Since staple crops are in crisis in Mexico, an alternative technology for the milpa system for small farmers, such as those who live in the Cuicateca, Mazateca, and Mixe communities, based on maize and beans only, would not be able to achieve both SHMP objectives and farmer expectations.
Field research conducted in the Puebla Valley indicates that a rural family producing maize on 4 ha of land typically yields 5 and 7 Mt ha-1 of grain and corn stalk fodder. This is equivalent to a net income well below the minimum poverty-level wage of US $4.00 per day (Turrent and Cortés, 2002). Thus, an alternative technology for small farmers must include an economic alternative to support continued production of staple crops, and to enhance rural development.
Other studies in the same Puebla Valley show that intercropped maize with deciduous fruit trees is a farming system that will significantly increase family net income derived from cropping maize only. Fruit trees such as peaches, apricots, apples, pears, and other deciduous species represent cash crops, while annual crops guarantee family food security. This system, called "milpa intercropped in fruit trees" (MIFT), is being developed by an interdisciplinary research group of the Colegio de Postgraduados and Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias.
The MIFT system takes advantage of complementary relationships between fruit trees and maize and bean annual crops regarding the integral use of soil, water, sunlight, and family labor. Maize and beans can be rotated annually, and can take advantage of agronomic interactions by cropping them in alternate and microrotating strips (Turrent and Cortés, 2002). Thus, the MIFT system consists of integrated maize and bean crops in alternate strips of two rows for each species, intercropped between rows of fruit trees that are trained in Tatura trellis systems as shown in Figure 23.2.
Tree spacing is 1 to 2 m in rows, with 14.4 m between rows on level soils or on moderate slopes. For this model, each species occupies one-third of the land in the parcel, in strips of 4.8 and 1.6 m width for fruit trees and maize and beans, respectively. Fruit trees are planted in the middle of the strip, and maize and beans in six alternate strips of two rows spaced at 0.8 m on both sides of tree rows.
This model under rainfed conditions has yielded 6 Mt of fresh peaches, 2.5 Mt of corn, and 0.5 Mt of beans per hectare per year. This means that compared to monocropping systems, peach trees and maize yields are at 50%, and beans at 33%. The global land equivalent ratio (LER) for this system is greater than 1. Labor demand is distributed during the year according to species being cropped, and its accumulated demand is up to five times greater than that required for monocropped maize. Incomes derived selling several harvests over the course of a year can be 400% or more than those derived from staple crops. The peach, corn, and bean yields discussed above have a per hectare gross value equal to US $4800, US $375, and US $200, respectively. This gross income, which amounts to US $5375 per hectare, contrasts sharply with the US $1100 gross value of 5 Mt of corn plus 440 straw bales obtained when producing maize alone on the same land parcel. Thus, staple crops, such as maize and beans, when
produced using the MIFT system are less sensitive to low prices in global markets. Incomes generated by selling staple crops are relatively secondary to ensure a healthy local economy for small farming units, as compared with income derived from fruit sales.
Field research, conducted in the semihumid tropics of Mexico, has shown that terraces formed by planting Glyri-cidia sepium as living walls in contour rows effectively increase rain water infiltration, and diminish soil erosion to acceptable ranges for sustainable production of maize under hillside conditions (Turrent et al., 1995; Turrent and Moreno, 1998). This is possible because Glyricidia sepium are planted close together in the row, which forms a living wall that supports the runoff filter composed of whole corn stalks. These are placed horizontally along and on the upper side of tree rows immediately after the harvest of maize as illustrated in Figure 23.3. This technology, however, has a major drawback. In contrast to fruit trees, Glyricidia sepium uses land, but has no economic value. Small farmers would be unlikely to adopt it for soil erosion control.
Experiences described above can lead to the design and generation of alternative technologies in the SHMP. Research that is currently being conducted on alternative farming systems integrate the principles of living-wall terrace technology with the MIFT system practiced under level soil conditions to develop a MIFT system for hillside agriculture.
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