*3.2. Soil Nitrate in the Fall and Spring*

In the late fall, soil nitrate levels were nearly identical in CC (2.0 mg kg−1) and NC (2.0 mg kg−1) plots (Table 3). Soil nitrate was significantly higher in the SH plots (3.3 mg kg−1), while SH + CC plots had intermediate soil nitrate (2.8 mg kg−1) (Table 3). As expected, spring soil nitrate was substantially higher overall compared to fall soil nitrate and ranged from 5.9 to 7.2 mg kg−1, depending on cover crop treatments. However, soil nitrate in spring was highly variable and the differences between treatments were not significant (Table 3).

## *3.3. Barley Seeding Rate Impact on Stand Establishment, Winter Survival, and Growth of Barley*

Barley seedling populations increased with increased seeding rate (Table 4). There was a significant quadratic regression describing this relationship (Seedling Population = − 0.0105x2 + 8.1424x − 1211), showing that there was a leveling off of barley population between 350 and 400 seeds m−1. This suggests that higher seeding rates do not increase barley populations towards the higher end of this range (Figure 4). Higher seeding rates also significantly improved seedlings' winter survival (Winter Survival = 0.0313x + 86.25) but the difference was small and all seeding rate levels had better than 95 percent winter survival (Figure 5).

**Figure 1.** Mean aboveground cover crop biomass (t ha−1) as a function of cover crop treatment. Means followed by the same letter are not significantly different from each other according to Bonferroni adjusted *t*-tests at *p* ≤ 0.05.

**Figure 2.** Cover crop biomass nitrogen content (g kg<sup>−</sup>1) as a function of cover crop treatment. Means followed by the same letter are not significantly different from each other according to Bonferroni adjusted *t*-tests at *p* ≤ 0.05.

**Figure 3.** Mean aboveground cover crop nitrogen (kg ha−1) as a function of cover crop treatment. Means followed by the same letter are not significantly different from each other according to Bonferroni adjusted *t*-tests at *p* ≤ 0.05.

**Table 3.** Mean fall and spring soil nitrate following different cover crops in South Deerfield MA in 2014–2015 and 2015–2016.


Note. \*\*, *p* ≤ 0.01; ns, non-significant according to non-parametric permutation tests. For significant effects, all pairwise comparisons were made using Bonferroni adjusted *t*-tests. Means followed by the same letter are not significantly different from each other (*p* ≤ 0.05).

**Table 4.** Mean barley establishment, winter survival, and growth metrics at different barley seeding rates in South Deerfield MA in 2014–2015 and 2015–2016.


Note. \*\*, *p* ≤ 0.01; \*\*\*, *p* ≤ 0.001; ns, non-significant according to non-parametric permutation tests. For significant effects, all pairwise comparisons were made using Bonferroni adjusted *t*-tests. Means followed by the same letter are not significantly different from each other (*p* ≤ 0.05). Barley seeding rate was also evaluated as a.continuous effect using orthogonal polynomial regression.

**Figure 4.** Mean seedling population (plants m<sup>−</sup>1) as a function of barley seeding rate. Means followed by the same letter are not significantly different from each other according to Bonferroni adjusted *t*-tests at *p* ≤ 0.05.

**Figure 5.** Mean winter survival (%) as a function of barley seeding rate. Means followed by the same letter are not significantly different from each other according to Bonferroni adjusted *t*-tests at *p* ≤ 0.05.

Seeding rate did not have a significant impact on late vegetative and reproductive growth (Table 4). Seeding rate showed no influence on heading date or height of the barley plants, the severity of foliar disease, or the prevalence of crop lodging. All plots reached 50 percent heading within two days of each other and height averaged 55 cm across the experiment. Forty-nine percent of the leaves were affected by foliar disease and eleven percent of barley lodged before harvest across all treatments.
