Ali Reza Tavakoli - Associate Professor, Agricultural Engineering Research Institute. Agricultural Research, Education and Extension Organization, Tehran, Iran.
Theib Oweis - International Center for Agricultural research in the Dry Areas (ICARDA).
Ali Reza Sepaskhah - Professor of Water Engineering Department, School of Agriculture, Shiraz University, Shiraz, Iran.
Mehran Mahdavi Moghadam - Professor of Department of Irrigation and Drainage, College of Aburaihan, University of Tehran.
Yadollah Farayedi - Instructor of Dryland Agricultural Research Institute, Agricultural Research, Education and Extension Organization (AREEO).

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 ۷ years in a dry area in Northwestern Iran with mean annual rainfall ۲۵۰ 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 ۴۹ m۲ 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 ۳.۵ to ۵.۵ mm. In a ۷ mm rainfall event and basin size of ۴۹ m۲, the runoff coefficients ranged from ۱۳.۱, to ۴۸.۴ percent. At maturity, almond trees yielded ۶۱۲ 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.

Micro catchments, Rainwater harvesting, fruit trees, drylands