Growth and Yield of Jojoba Plants in Native Stands Using Runoff‐Collecting Microcatchments 1

Water‐harvesting techniques were applied to a waterstressed native stand of jojoba ( Simmondsia chinensis (Link) Schneider) near Phoenix, Arizona, to evaluate this method of supplementing the normally scant rainfall for increasing seed yield and to gain insight into the comsumptive water requirements of the plant. Thirty small, indigenous, female bushes were selected and randomly divided into three treatments: T 0 , no water‐harvesting catchments; T 1 , cleared, smoothed, and rolled 20‐m 2 catchments; and T 2 , like T 1 , but with the catchment treated with a water‐repellant coating. Data collected were: rainfall, runoff, soil moisture, relative leaf water content, plant volume, and seed yield. The 4‐year average of precipitation plus runoff to plants during the critical growth‐yield period of October through June was: T 0 , 154 mm; T 1 , 435 mm; and T 2 , 876 mm. The plant volume increase averaged 43, 44 and 237% for T 0 , T 1 and T 2 , respectively. Seed yield in 1974, the first year, averaged 0.5, 8, and 23 g/plant for treatments T 0 , T 1 and T 2 , respectively. Frost injury destroyed the flowers in 1975 and 1976, but in 1977 yields increased to 27, 76, and 208 g/plant for the respective treatments. Maximum yield was 514 g/plant. These preliminary results on this slow‐growing shrub suggest that its consumptive water requirement exceeds 450 mm, and may be as great as 900 mm. Water harvesting is one way of supplying this required water,