Evaluation of Deficit Irrigation of Blackeye Cowpeas Under Variable Plant Densities.

Blackeye cowpeas are the main dry bean type grown in the southern portion of California’s  San Joaquin Valley. All of the acreage is produced under furrow irrigation. The cost and, in some years the availability of water, are issues facing growers. Two trials, conducted in 2009, evaluated the impact of different irrigation regimes on the yield and quality of two blackeye varieties, CB 46 and CB 50, planted at three populations.  One trial was at the University of California Kearney Research and Education Center and the other at the U.C. Shafter Research and Education Center. The irrigation regimes included the conventional treatment with irrigation every 7 to 10 days, alternate furrow treatment with irrigation timing the same as the conventional treatment but with water only in every other furrow, and the extended treatment which was irrigated in every furrow at 14 to 20 day intervals.  The experimental design was a split-split plot in both locations with irrigation as the main treatment, variety as the first split and three plant populations as the split on variety. Soil moisture was monitored in one location with soil moisture blocks and in the other trial with a neutron probe. The center rows of each plot were cut and allowed to dry before threshing.   Yields in the alternate and extended treatments were significantly reduced compared to the conventional treatment. Bean size was also reduced in the alternate and extended treatments compared to the conventional treatment. There were no significant differences in yield between the two varieties but CB50 had larger beans.  The highest plant population, approximately 6 plants per foot, produced significantly higher yields in all three irrigation regimes at the Shafter location compared to the 4 and 6 inch spacing.  In the Kearney location, there was an interaction between irrigation treatment, varieties and plant populations