Mixing trees and crops increases land and water use efficiencies in a semi-arid area

Sustainable increases in food production in semi-arid regions require efficient use of land and water resources. Agroforestry is the practice of combining tree and crop cultivation on a land parcel and may increase both land productivity and water use efficiency. We conducted two years of field experiments in the semi-arid Khorchin region in Liaoning, China, to determine to which extent land and water use efficiencies were affected by mixing apricot (Prunus armeniaca) trees with annual crops: peanut (Arachis hypogaea), millet (Pennisetum italica) or sweet potato (Ipomoea batatas). Apricot yields were not significantly affected in the agroforestry, compared to the sole stand, but yields of the annual crops were lower when grown under trees than as sole crops, with relative crop yields of 0.46 for millet and 0.35 for both peanut and sweet potato in the agroforestry. Crop rows near tree rows had lower yields than crop rows further away from trees. Land equivalent ratios (LER) were 1.34, 1.44 and 1.33 in mixed systems with peanut, millet and sweet potato, respectively. Mixing crops and trees did not increase water extraction from the top 100 (2012) or 200 cm (2013) soil profile comparing to sole tree. Thus, with increased crop output and similar apricot yield, the water use efficiency was improved in the mixed system. Water use efficiency of the mixed system was characterized with the water equivalent ratio (WER). This index, analogous to LER, expresses the relative yield total per unit of water in the mixed system compared to the sole crops. WERs were 1.39, 1.51, and 1.34 in agroforestry systems with peanut, millet and sweet potato, respectively. We conclude that apricot-based agroforestry improves the productivity and water use efficiency of rain-fed agriculture in this semi-arid area, especially when a drought adapted crop such as millet is used.