Growing fruit trees with rainwater harvesting in arid environments: the case of almond in Northwest Iran

Fruit trees are grown in arid environments under irrigation. In most of the dry environments, irrigation water is not available or is scarce during the growing season; therefore, irrigation may not be possible or feasible. Yet farmers continue to grow trees under this dry rainfed condition. Low precipitation and the occurrence of frequent drought spells stress trees and cause low yields or crop failure. Farmers, to avoid crop failure, supplement rainwater with costly irrigation water often transported to the sites by tankers. Through rainwater harvesting, precipitation is concentrated through runoff from larger catchments to the basins of trees to be stored in the root zone for using during the dry period. It is however important to evaluate the capacity of system and its design parameters to ensure sufficient and efficient water supply for individual trees over the drought periods. Field trials for almond orchards were conducted over 7 years in a dry area in Northwestern Iran with mean annual rainfall 250 mm. The objective is to evaluate the impact of a range of micro-catchment rainwater harvesting practices and soil amendments on the performance of two varieties of almond trees widely grown in the area. Treatments include catchment size and geometry, surface treatment, soil water absorbent and fermented manure. Results showed that a 49 m^2 compacted catchment is sufficient to generate enough runoff to supplement rainfall for each almond tree with no effect of catchment geometry. The addition of a super absorbent material to increase soil-water storage of the root zone did not outperform the use of fermented manure. Threshold rainfall for initiation of runoff ranged from 3.5 to 5.5 mm. In a 7 mm rainfall event and basin size of 49 m^2, the runoff coefficients ranged from 13.1, to 48.4 percent. At maturity, almond trees yielded 612 kg dry nuts/ha using water-harvesting system where no irrigation was needed. In this dryland environment, farmers can grow economical rainfed almond orchards with appropriate micro catchment rainwater harvesting system.