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Planting Date Affects Production and Quality of Grass Pea Forage

Grazinglands Research Laboratory, USDA-ARS, 7207 W. Cheyenne St., El Reno, OK 73036

^* Corresponding author (Srinivas.rao{at}ars.usda.gov).

The rising cost of commercial nitrogen fertilizers indicates that additional research is needed concerning agronomic practices required to integrate legumes into cereal-based cropping systems. This study examined how planting date affects the productivity of grass pea (Lathyrus sativus L.) in central Oklahoma. Experimental plots (3 by 20 m, n = 3) were disked and fertilized with 60 kg P₂O₅ ha^–1, and inoculum-treated (Rhizobium leguminosarum) seeds (‘AC-Greenfix’) were planted at 60 kg ha^–1 on 15 March, 1 April, and 15 April in 2004, 2005, and 2006. Biomass, N concentration, N accumulation per hectare, and in vitro digestible dry matter (IVDDM) of grass pea forage were determined on samples collected at 7 d of the year (DOY) after planting. Significant (P < 0.05) interactions occurred in response of biomass (DOY x year), N concentration, and IVDDM (DOY x year x planting date), and accumulated N (DOY x year; DOY x planting date). Peak biomass in 2004, 2005, and 2006 was 3900, 5800, and 3500 kg ha^–1, respectively. Maximum accumulated N related to years was 115 to 157 kg ha^–1 between DOY 165 and DOY 195. Peak N accumulation of 125 to 153 kg ha^–1 occurred between DOY 180 and DOY 210. Grass pea is flexible in response to spring planting dates, indicating that it can be sown as a green manure or forage crop during a 30-d period in the southern Great Plains and still maximize biomass and N accumulation.

Abbreviations: DM, dry matter • DOY, day of year • FRV, fertilizer replacement value • GDD, growing degree days • IVDDM, in vitro digestible dry matter • SGP, southern Great Plains

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Received for publication February 25, 2008.