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ABSTRACT
Sources of organic nitrogen (N) for the southern Great Plains (SGP)-and methods of their use- need testing to find ways to counter the rising cost of N fertilizer. This study examined the function of the cool-season pulse grass pea (Lathyrus sativus L.) as a pre-plant N source for continuous, conventionally tilled winter wheat (Triticum aestivum L.). It was conducted in Oklahoma (35°40' N, 98°00' W) during 2004 to 2008, on three replicate blocks of four experimental plots (6 by 10 m). Inoculated grass pea (cv. AC-Greenfix) seed was sown during late summer fallow (mid August) in one randomly chosen plot per block (75 kg ha-1 seeding rate in 60-cm rows with 75% germination). Three additional plots per block mimicked traditional summer fallow with no (control), 40, or 80 kg inorganic N ha-1. All treatments were repeated on the same plots throughout the study. Samples were collected from grass pea plots at flowering over a range of 41 to 59 d after planting in different years and analyzed for N and digestibility. Aboveground (AG) biomass of grass pea was then shredded with a flail mower and incorporated before applying fertilizer treatments and sowing (100 kg ha-1) wheat (cv. Jagger) in 20-cm rows. Aboveground biomass of wheat was collected at three growth stages (elongation, flowering, and maturity) and analyzed for N. Biomass of grass pea contained enough N to meet the needs of wheat at planting (40 kg N ha-1) in only 2 yr. Total AG biomass and N content of wheat under grass pea was similar to the control at elongation and intermediate between no and 40 kg N ha-1 at maturity in 2 yr. Biomass and N content of wheat grain under grass pea were intermediate between no and 40 kg N ha-1 in the first 2 yr and similar to the control thereafter. Therefore, grass pea was marginally effective as a pre-plant N source for wheat for a limited period but may be more effective in sorghum-based rotations in the SGP.
Abbreviations: AG, aboveground; CS, compound symmetry; GDD, growing degree-days; IVDDM, in vitro digestible dry matter; LTA, long-term average; SGP, southern Great Plains.
Production of winter wheat (Triticum aestivum L.) is an important component of agriculture in the southern Great Plains...