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

2018 Nitrogen credits from cover crops to following crop

The study this year had three N-requiring crops following cover crop and no cover crop treatments.

Spring wheat (Triticum aestivum L.) at Gardner, ND, following soybean (oat (Avena sativa L.) and radish with camelina, with camelina growing into the spring. Estimated N uptake based on poor stand (about 4 plants m^-2) was 22 kg ha^-1. Corn at Gardner following spring wheat with oat and radish with camelina, with camelina growing into the spring. Estimated N uptake by camelina (oat and radish growth fall 2017 was negligible) was 22 kg ha^-1.

Corn at Rutland following bio strip-till after spring wheat with faba bean (Vicia faba Roth), flax (Linum usitatissimum L.), volunteer spring wheat, forage radish. Nitrogen tied up in cover crop residue from the fall 2017, sampled 9 October 2018 was 78 kg N ha^-1.

As in 2017, the N in the cover crops is not recycled as expected from the C/N ratios of the residues.

Work is proceeding to determine where the N is going, since 2017 and 2018 were not years where excessive rain would result in N losses.

Legume cover crops slightly increased corn yield with different nitrogen rates in the northern Great Plains.

Corn and wheat are major crops in the northern Great Plains. Conventional management has reduced winter soil coverage, impacting negatively on soil health. In this scenario, soil has been exposed to water and wind erosion which decreases soil productivity. On top of that, high levels of residual deep nitrogen, after cereal production, are easily lost by leaching, resulting in a negative economic and environmental impact in this cropping system. Cover crops and no-tillage provides soil coverage, preventing soil erosion, and reducing NO₃-N leaching. This experiment was conducted at two locations, Prosper and Hickson, ND, in 2017. The experimental design used was a RCBD with four replicates. The cover crops on study were forage pea (Pisum sativum L.), faba bean, winter camelina and a check plot (without cover crop) which were established into spring wheat stubble in August 2017. Biomass production and nitrogen accumulation on tissue averaged across locations was 1.92 Mg ha^-1 and 88 kg ha^-1, respectively with no significant differences between treatments. Soil NO₃-N, in late fall, was lower in winter camelina plots (36.0 kg ha^-1) in comparison with the rest of treatments (44.6 kg ha^-1), but there were not significant differences in the spring. Soil green coverage provides important protection against wind soil erosion. Plots with cover crops had 60% of green coverage while in check plots was 16.3% (volunteer wheat regrowth), leaving the soil with lack of coverage.

In May 2018, corn was planted in a RCB design with a split-plot arrangement, where the main plot was cover crops (from the previous year) and the sub-plot was nitrogen rates (0, 40, 80, and 160 kg N ha^-1). Winter camelina, as a winter hardy cover crop, was actively growing during spring, using soil resources and water, and because of this, gravimetric water content (0-15 cm depth) was significantly lower in winter camelina plots (17.9%) than the rest of treatments (24.1%). In addition to that, spring 2018 was dry and corn growth was more affected in early stages in the winter camelina plots. This was observed also with NDVI measurements in mid-June, where winter camelina plots were significantly lower (0.76 NDVI index) in comparison with the rest of the treatments (0.77 NDVI index) correlating less development and growth in corn plants, because of the lack of water into the winter camelina plots. Corn yield was also affected by winter camelina treatments. In Hickson, winter camelina plots showed significantly lower corn yield (10.3 Mg ha^-1) than corn planted in previous year faba bean (12.2 Mg ha^-1), forage pea (12.0 Mg ha^-1) and check (12.3 Mg ha^-1) plots. A similar situation was observed at Prosper, where winter camelina (11.1 Mg ha^-1) showed lower yields than faba bean (12.6 Mg ha^-1), forage pea (13.2 Mg ha^-1) and check (12.0 Mg ha^-1). However, in this location the differences were not significant. In the combined analysis across two locations, there were not significant differences in the cover crop, nitrogen rates or the interaction between them. Thus there is no evidence of decreased corn yield with the legume cover crops. In fact, legume cover crops increased the yield slightly in all the N rates in this study (not significant).

2017

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.