Agriculture and Environmental Degradation in Baja California Peninsula:A Viewpoint
　

The United Graduate School of Agriculture Science,
Tottori University. Raul Lopez
  1. INTRODUCTION
    The rapid spread of desertification in dry environments is a problem of international dimension. Many ecosystems are being degraded, mainly due to over-exploitation of their natural resources. In Mexico, desertification occur particularly on fragile nature of the arid and semiarid regions of the northwest part of the country which account for 60% of total land surface. In Baja California Peninsula, soils are frequently poorly structured, pH is generally very high (8.5 to 9.5) and salt deposits and salinization are common phenomena. Prevailing winds are strong, unhampered by obstacles on the ground and erosion is common. These achieve a delicate natural equilibrium which requires little disturbance to cause inestability and imbalance leading to degradation. Here, the task of anti-desertification action would be to stabilize,reclaim or rehabilitate several thousands of hectares by appropriate methods.

  2. AGRICULTURE
    The Baja California peninsula has a very dry climate, where the average annual rainfall goes from less than 100 to 300 mm and mean temperatures range between 18 to 22℃. Rainfall is characterized by its irregularity and variability in both time and space.
    　Most soils in Baja Peninsula are Aridisols, low in organic matter and nitrogen. Levels of plant nutrients except nitrogen tend to be high (Table 1). These soils can be highly productive where irrigation water and necessary skills are available and temperature are favorable. In the JICA project developed in Guerrero Negro, B.C.S., higher yields of tomato, bell pepper, melon, onion, cabbage, cauliflower, brocoli, beet, have been reported by using drip irrigation and fertilizers applied together with the irrigation water (Table 2). In San Quintin and La Paz valley (Figure 1) due to economic pressures the most profitable crops are grown and the crops most adapted are planted. This results in much monoculture, where the same crop, mainly tomato and bell pepper is grown year to year unless diseases or insect pressures, necessitate a change. In Santo Domingo velley and in the south part of the peninsula, legume crops are used extensively , but the number adapted species is limited. Pasture species include some clovers and alfalfa,being the latter the most extensively grown forage legume.

  3. SOME PRDBLEMS TO FACE TO PREVENT DESERTlFICATION
    Salt-Affected Soils
    Risk of Salinity
    Recently, intensification of agriculture in Baja California Peninsula has occurred in only localized areas by means of the widespread use of commercial fertilizer. Here,the management and fertilizers recommendation for crop production are based largely on research conducted elsewhere under different environmental and soil conditions.
    Consequently, in some areas of Baja California, such as, San Quintin valley, Santo
    Domingo valley, and Vizcaino valley (Figure 1), the indiscriminate use of large amounts of chemical fertilizers and the overexploitation of groundwater have dramatically increased the surface affected by salinity. It is true that growing crops redistribute water in a landscape (by changing vegetation, water infiltration into the soil,and runoff), which in turn can aggravate the natural salinization of soil.

    Solutions to the Salinity Problem
    lt is necessary carry out a first attempt to describe salinity in Baja California peninsula in a standard way to provide a base line against which to compare future measurements of salinity. The aims of the assessment must be focused on:
    1) To estimate the current extent and severity of soil salinity
    2) To assess the risk that soil salinity levels will increase under current agricultural land use and management practices.

    Nevertheless, improving the management and use of salinized land requires an
    attitude shift on the part of policy makers, planners, and producers. Reducing the severity and extent of soil salinity is primarily a problem of water management. Good water managment involves both preventing water received in the recharge areas from percolating into groundwater, an maintaining the water table in the discharge area at a low, safe level. The most common approach to salinity management is to maintain a prescribed leaching requirement. However, this method is inadequate when irrigation water have substantial salt contents, such as, sodium, carbonates, and bicarbonates. In addition, usually in these soils surface drainage-ways are poorly developed, often causing closed outlets for leaching resulting in high water tables. Therefore, leaching is not a viable option to reclaim these saline soils. Hence, studies of halophytes that accumulate salt and tolerate very dry conditions must be considered. If the plant regrow, or can be seeded then this may be an option in removing salt from these Systems.

  4. Nitrogen Use Efficiency and the Risk of Groundwater Contamination
    The sparse vegetation in areas of Baja California result in soils in soils which are low in organic matter.Since the major storehouse form of nitrogen is soil organic matter,nitrogen is usually the major limiting plant nutrient.Therefore,the intensification of crop production in Baja California requires the use of nitrogen fertilizers.However,in these soils,the efficiency of nitrogen uptake may not exceed 30%,then loss of nitrogen fertilizer through deep percolation cause nitrogen contamination of groundwater.
    Indeed,ineficient use of nitrogen fertilizers in intensive agriculture production appeared to be responsible for increased NO3 levels in groundwater.Therefore,understanding the crop demand for untrients during its growing period is the main information needed to plan the application rates and timing of nitrogen that could prevent nitrate losses.
    Leaching of applied fertilizer nitrogen results in reduced efficiency of applied nitrogen by the target crop and is an agricultural and environmental problem.The intensification of crop production in areas of Baja California requires a judicious use of nitrogen fertilizers.In JICA project developed in Guerrero Negro has been evaluated the growth pattern and the removal of nutrients by sevaral crops.These studies revealed that higher yields of horticultural crops can be obtained by using drip irrigation and fertilizers applied together with the irrigation water.However,further nitrogen fertilization studies are necessary as part a program to develop optimal fertilizer recommendations in the Vizcaino Desert and other dry areas of Baja California.

  5. EROSION
    In spite of the low rainfall, Baja Peninsula have their share of climatic storms from September to December. Because these soils are low in organic matter and tend to be less granulatcd than humid soils, and cropping systems are adapted to moisture conservation, with resultant periods without cover, erosion by both wind and water tends to be severe. High-intensity rains and high wind velocities are common even in these areas. The planting of trees, such as Eucalyptus and Pines, to slow down wind velocities have been used. However, there are conflicting observations concerning the effects due to these windbreaks. Therefore, further research is necessary to evaluate another plant material of trees or shrubs that tolerate drought and very dry conditions.
    On the other hand, some legumes crops or halophytes must be evaluated as covers on bare or unprotected dry soil to prevent erosion by water.

  6. ORGANIC AGRICULTURE
    Environmental issues on the excessive use of chemical fertilizers and energy shortage in recent years led to the renewed interest in using organic agriculture.
    　Recently, organic agriculture has gained interest in Mexico. In Baja California Peninsula, organic agriculture has an important role in Los Cabos zone (south part) and San Quintin valley (north part), where several horticultural crops, such as tomato, bell pepper, onion, among others, are being grown under this system. Here composting seems to be desirable solution for organic waste management. Readly available wastes such as cattle manure and yard waste have been found to be suitable materials for composting. However, development of new management systems which will increase the quality of the products, decrease salt concentration, and improve the physical structure is needed. In addition, the chemical nature of the descomposition process and the evaluation of compost maturity are a difficult problem, since several parameters are required to provide a definite evaluation for the readness of the material for use in horticulture.
    On the other hand, the effect of organic matter addition to soil in relation to soil pH changes is not well understood and merits further investigations in these soils.

  7. CONCLUSIONS
     Although specific actions still needs to be quantified in terms of resource requeriments and clear priorities need to be defined to solve the problem in Baja California Peninsula areas most threatened by desertification process, the comments highlighted above only provide a general action framework. The complexity of the desertification problem makes it imperative to conduct multidisciplinary research aimed at evolving improved techniques for the management of these regions which would need the close cooperation of the international community. Mexican researchers felt that they need coordination, exchange of knowledge and experience, and preparation of working plans for implementation so that the failures and successes in each country can be communicated to others and help in reaching an optimum result.

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