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Estimation of N credits from cover crops and increased N use efficiency by subsequent crops.

In July, 2016, an inter-seeding of 40 lbs cereal rye per acre and 5 lb forage radish per acre was conducted
near Rutland, ND utilizing the prototype interseeder described in Objective 1a. The plot area was seeded 23 June, when the corn was in V6 stage. The experiment was established as a randomized complete block design with 2
cover crop treatments (no cover crop and cover crop) and 3 replications. The dimensions of each
experimental unit were 60 feet wide and 60 feet long. This will enable us to add 6 N rate treatments (0,
40, 80, 120, 160, and 200 lb N/acre) in spring 2017, to make the study a split-plot with main plots cover crop history and sub-plots N rate, with 3 replications. Initial soil samples were taken in each experimental unit 23 June at the 0-6 inch and 6-24 inch depths for N, P, K, pH, organic matter, Zn, EC, and soil moisture. The rye and radish emerged 6 July, and the first plant sampling, sampling, weighing and N analysis of rye and radish separately. Cover crops were also sampled 8 and 28 September and 11 October. Follow-up soil samples were obtained on 8 and 28 September. Corn ears were harvested, 60 foot of row 15 from center of each experimental unit, shelled, and grain yield, moisture and test weight of grain were determined.
A cover crop study following winter wheat was established August 8 about two weeks following winter wheat harvest. The winter wheat volunteers were allowed to grow and the area was seeded to field pea in 30 inch rows, with the area between rows seeded to turnip and forage radish and flax. The field will be seeded to corn in 2017, so the turnip/radish area will act as a biological ‘strip-till’ to seed corn into. The study was established within the field as a randomized complete block design with 2 cover crop treatments (no cover crop and cover crop) and 3 replications. The dimensions of each experimental unit were 60 feet wide and 60 feet long. This will enable us to add 6 N rate treatments (0, 40, 80, 120, 160, and 200 lb N/acre) in spring 2017, to make the study a split-plot with main plots cover crop history and sub-plots N rate, with 3 replications. On 25 August, the cover crops were emerged and the no cover crop treatments were sprayed with 22oz/acre Roundup PowerMax with 22 oz/acre of 4 lb/gallon ammonium sulfate solution, at 10 gallon per acre using 30 psi pressure with a bicycle cart sprayer. Elimination of cover crop in these treatments was complete within 10 days. Soil samples were obtained at the 0-6 inch and 6-24 inch depths on 12 August, followed by soil samples for residual soil nitrate and soil moisture 28 September, 24 October, and 9 November.
Reduction in soil water content to 2 ft in depth was 2.89 inches due to cover crop, and the cover crop contained 142 lb N/acre in 5100 lb/acre dry-matter of the total of flax tops, winter wheat tops, radish/turnip tops field pea tops, and radish/turnip roots.
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