Cover crop effects on the fate of N following soil application of swine manure

Cereal grain cover crops increase surface cover, anchor corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] residues, increase infiltration, reduce both rill and interrill erosion, scavenge excess nutrients from the soil, and are easily obtained and inexpensive compared to other cover crop options. The use of cereal grain cover crops in fields where manure application occurs should increase nitrogen (N) recovery and cycling for use in subsequent crops. The objectives of this study were to determine if a rye (Secale cereale L.) cover crop increases N retention after soil application of swine lagoon slurry. Experiments were conducted in a controlled environment chamber using plastic buckets as the experimental units. Three manure-N loading rates (no manure, low, high) were applied to soils with and without a rye cover crop. A partial N balance was determined from measurements of NO₃ leaching, N₂O and NH₃ emissions, cover crop N uptake, and NO₃ + NH₄ remaining in the soil. Cumulative nitrate load in the drainage water was less than 0.31 g m-² NO₃-N for rye treatments regardless of the manure rate, however in the fallow treatments, at the high manure rate NO₃ leaching losses were 6.28 and 3.77 g m-² NO₃-N, for experiments 1 and 2, respectively. Rye N uptake ranged from 2.95 g N m-² to 10.7 g N m-², and was related to manure rate. Rye had lower cumulative N₂O emission than the no rye treatment for the high manure treatment. Ammonia emissions were low for all treatments during both experiments, which was probably related to the rapid manure incorporation after application. Rye can increase N retention, reduce cumulative N₂O emissions, and reduce cumulative N load in drainage water when manure is applied to soils. Nitrogen balance calculations in the cover crop treatments accounted for less than the equivalent of 50% of the added manure N. We speculate that the living rye plants may have increased immobilization of N in the organic N pools.