Cowpea As a Cover Crop and Nitrogen Source in a Double Cropping System with Forage Rye.

Cowpea (Vigna unguiculata [L.] Walp) is a legume commonly grown in the southeast as a fresh vegetable, wildlife browse or seed crop.  In East Texas the use of cowpea as a green manure has potential to provide N to a cool season forage crop. The objective of this study was to evaluate cowpea cultivar as a green manure crop in a double cropping system to supply N forage rye (Secale cereale L.). The 2-year study was conducted at the Texas A&M AgriLife Research and Extension Center at Overton, Tx on a Darco soil during 2014 - 2016. Summer cover crop treatments included an early maturing cowpea ‘Combine’, a late maturing cowpea ‘Iron and Clay’ and fallow for a control in a 6x12m plot. Four N rates (0, 34, 67, 101 kg ha^-1) were applied in a factorial arrangement in a split plot design. Cowpea biomass incorporated as green manure was 2319 kg ha ^-1 and 2393 kg ha ^-1 for Iron and Clay and Combine, respectively. Cool season forage ‘Elbon’ rye was grown in 2015 and ‘Maton’ rye in 2016. Rye was harvested with a mechanical harvester and dry matter yield (DMY) was calculated. Data were analyzed using PROC MIXED and PROC REG in SAS. The summer green manure crop of cowpea was not influential as a N source on forage DMY after two years of cropping. Soil N data were analyzed and there were no statistical (P ≥ 0.40) differences between treatments of cowpea or N rate. A positive linear relationship (r² = 0.79) was consistent for N rate and DMY. Darco is a deep sandy soil and more time is needed to impact the organic matter content. This cropping system would benefit the soil in a long term production setting where measurements taken after short term application will not have desirable results.