ARS | Publication request: Nitrogen and Winter Cover Crop Effects on Spring and Summer Nutrient Uptake

Submitted to: Grass and Forage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 23, 2011
Publication Date: September 1, 2011
Citation: Read, J.J., Brink, G.E., McLaughlin, M.R., Sistani, K.R. 2011. Nitrogen and winter cover crop effects on spring and summer nutrient uptake. Grass and Forage Science. 66:381-390.

Interpretive Summary: To avoid adversely affecting the environment, manure nutrients must be applied to soil at rates utilized by plants. Annual ryegrass, berseem clover and cereal rye are annual forages commonly grown as winter cover crops in the southeastern USA. The harvested hay captures soil manure nutrients, which, if not utilized, could cause pollution of surface water or aquifer. A team of scientists conducted a two-year study to test the hypothesis that despite repeated applications of swine–lagoon effluent to bermudagrass in summer (April–September), N availability limits growth and uptake of other nutrients in these cover crops. Crop response to spring N fertilization of 0, 45, 90, and 134 lbs/acre was compared to a bermudagrass-winter fallow system. The relative yield, defined as yield at a given N rate divided by the maximum yield, varied from 77 to 98%, suggesting N nutrition was not strongly limiting, even at the lowest fertilization rate. Although forage yield was not impacted by N fertilization, N concentration and uptake were, particularly in annual ryegrass and cereal rye. In 2000, a year with below normal rainfall, cover crop uptake of N and P increased linearly as more inorganic N was applied, without a significant difference between cover crops. Increased nutrient uptake was mainly due to higher nutrient concentration, rather than higher biomass. The findings suggest N fertilization in spring would probably not improve forage yield of fall-overseeded winter annuals in soil that already receives 230-476 lbs N/acre in swine-effluent. This data will provide information to support more accurate N management in double-cropped forage systems, which provide environmental and economic advantages to producers who regularly utilize manure as fertilizer.

Technical Abstract: Fertilization of bermudagrass [Cynodon dactylon (L.) Pers.] with swine-lagoon effluent in summer, April to September, does not match the period of productivity of the winter annual cover crops, annual ryegrass (Lolium multiflorum L.), cereal rye (Secale cereale), and berseem clover (Trifolium alexandrinum L). This study determined crop responses of dry matter (DM) yield and uptake of N and P to spring N fertilization rates of 0, 50, 100, and 150 kg/ha. The effect of inorganic N and cover crop was analyzed based on a single harvest in May and two summer harvests. Bermudagrass was responsive to N rate in 2000 when considerably less effluent was applied, as compared to 2001 (258 vs. 533 kg N/ha). Relative cover crop yield, defined as DM yield at a given N rate divided by the maximum observed DM yield, varied from 77 to 98%, suggesting N nutrition was not strongly limiting, even at the lowest fertilization rate. In 2000, ryegrass N concentration increased linearly across N rates from 10.2 to 20.6 g/kg; whereas, the relationship was not significant in rye and berseem clover. Cover crop N uptake increased linearly as more N was applied, and the crop effect was significant (P < 0.05) in 2000. Per unit of additional inorganic N applied, cover crop uptake of N and P increased by approximately 0.27–0.41 kg/ha and 0.03–0.01 kg/ha, respectively. Increased uptake of N and P was mainly due to higher nutrient concentration and not higher biomass. Bermudagrass-annual ryegrass was the most productive double-cropping system.