TIMING THE REMOVAL OF WINTER PEAS INTERCROPPED WITH WINTER WHEAT TO OPTIMIZE AVAILABLE SOIL NITROGEN AND MOISTURE IN A DRYLAND SMALL GRAIN SYSTEM. K. A. Borrelli*, I. C. Burke, R. T. Koenig, D. R. Huggins, S. H. Hulbert; Washington State University, Pullman, WA (327)
Crop diversification is a common practice among growers interested in organic and sustainable farming practices. Wheat growers could benefit from intercropping a legume as a source of biological nitrogen (N) with the wheat if competition for other resources is not a concern. The main objective of this experiment was to determine the optimal time to mechanically remove winter pea (Pisum sativum L. cv. ‘Granger’) intercropped with winter wheat (Triticum aestivum L. cv. ‘Brundage’) to provide the greatest amount of fixed N and perhaps other benefits to the wheat crop while reducing soil moisture stress. Winter wheat and winter pea were seeded simultaneously using a 2.2 m wide double disk no-till drill on October 16, 2009 in Pullman, WA. The experiment was arranged in a 2-factor strip plot design with four replications and two controls, winter wheat alone and winter pea alone. Four removal times were determined based on percent cover of the intercrop (time 1 is 25% row canopy cover; time 2 is 50% row canopy cover; time 3 is 75% row canopy cover, time 4 is 100 % row canopy cover; and time 5 is harvest). Before removing the crop, a subsample of each crop was taken from 3 randomly selected, 25 cm lengths in the last 3 m of each treatment plot. Samples of aboveground biomass from wheat and pea were collected again from previously swept plots at each new treatment time. Soil samples were collected to a depth of 0 to 60 cm at each treatment time for treatment plots, non-intercropped controls and previously swept plots, and for all plots at harvest to a depth of 0 to152 cm. Soil samples were analyzed for gravimetric water content and inorganic N. Increasing duration of the intercrop did not affect wheat or pea growth. Soil moisture was lowest for both pea and wheat removed at 50% cover and no difference was observed in soil moisture over the other sampling times or the control. Soil N was higher in plots with peas as the main crop compared to plots with wheat as the main crop, suggesting that peas left more residual N than wheat. However, no difference was found between the treatments when wheat was removed. Higher soil N than the other treatments was observed when peas were removed at 75% cover. Results indicate that competition for soil water and N may not affect wheat growth when intercropped with a legume.