Evaluation of Soil Fertility Indices of Freshwater Irrigated Soils in Mexico Across Different Climatic Regions

Irrigation has different impacts on soils. The most studied negative impacts are related with salinity, sodicity or soil contamination because of poor irrigation water quality or rising water tables. It is assumed that with suitable water quality the impact of irrigation on soil is positive. However, there are publications showing that under certain conditions long-term freshwater irrigation may cause soil fertility deterioration. Therefore a hypothesis has appeared that some Mexican soils may also be degraded. The objective of our study was to compare some properties of agricultural soils irrigated for more than 30 years with freshwater with non-irrigated virgin soils in different climatic zones. The principle agricultural crops studied were corn and wheat. The impact of furrow and border strip irrigation on soils were positive under arid climatic conditions, but in semi-arid, semi-humid and humid conditions irrigation gradually caused deterioration of soil fertility because of annual leaching of organic matter and exchangeable calcium. Comparison of the same properties of rainfed agricultural soils for the same crops and virgin soil properties did not show significant differences. Thus, irrigation itself can induce changes in soil fertility. Therefore, in semi-arid, semi-humid and humid conditions of Mexico it is appropriate to reduce irrigation water losses. Under humid conditions it is recommended to increase runoff using surface drainage in irrigated and rainfed lands and to improve irrigation technologies. These measures can conserve soil fertility, improve efficiency of water and land resource use, reduce water consumption, increase agricultural productivity, profitability and sustainability over the long-term.