Abstract
Sunn hemp (Crotalaria juncea L.) is recommended as a warm season cover crop in the Midwest due to its ability to produce high levels of biomass and fix atmospheric nitrogen. It can also be grown in biculture with other cover crops to enhance overall ecosystem services. Two field experiments were conducted over four growing seasons (2014 – 2017) in Wisconsin on a forest derived Fox silt loam (Fine-loamy, mixed, mesic Typic Hapludalfs) under organic certification to determine the effect of planting date on sunn hemp dry matter yield, N and C addition and to determine the effect of species ratio in a biculture with sorghum-sudan [Sorghum bicolor (L.) Moench] on the same output variables as well as seed cost and the related per unit cost of production. Planting dates significantly affected all biomass yield variables, which declined linearly from the initial date and appear related to growing degree accumulation. Regression analysis revealed a biomass yield decline of 1.3% per day (8.9% week-1) in relative yield, and 0.90 Mg day-1 (0.61 Mg week-1) in actual yield. In biculture, sunn hemp grown in a planting ratio of 50:50 with sorghum-sudan maximized N addition through nitrogen fixation and added N from dry matter, without a significant difference in the dry matter recorded. Analysis of seed cost data revealed that as the ratio of sunn hemp in the planting mixture decreased, the cost per hectare decreased. The cost of production per unit of DM, N, C and CO2 equivalent at this planting ratio were 7.08 $ Mg-1, 0.57 $ kg-1, 17.51 $ t-1 and 4.78 $ t-1 respectively. In pure culture, early planting dates (June 15th to July 15th) are recommended for sunn hemp, and in biculture, a planting ratio of 50:50 with sorghum-sudan could serve Midwestern producers well by reducing per unit cost of biomass production.
Highlights
Cover cropping is a conservation practice which protects soil while providing other benefits like weed suppression, nitrogen (N) fixation, increased soil organic matter (SOM) and improved soil health
Two field experiments were conducted over four growing seasons (2014 – 2017) in Wisconsin on a forest derived Fox silt loam (Fine-loamy, mixed, mesic Typic Hapludalfs) under organic certification to determine the effect of planting date on sunn hemp dry matter yield, N and C addition and to determine the effect of species ratio in a biculture with sorghum-sudan [Sorghum bicolor (L.) Moench] on the same output variables as well as seed cost and the related per unit cost of production
This study evaluated the effect of sole seeded sunn hemp, sorghum-sudan cv “Special Effort”, and biculture mixes of several compositional ratios on the same variables related to aboveground biomass yield as Experiment 1
Summary
Cover cropping is a conservation practice which protects soil while providing other benefits like weed suppression, nitrogen (N) fixation, increased soil organic matter (SOM) and improved soil health. Several cover crops are effective under Midwest conditions; their ability to produce high quantities of biomass (DM) in a relatively short time is severely limited (Esther & Stute, 2018). Creamer & Baldwin (2000) and Schomberg et al (2007) found that several legumes can be successfully grown as warm season cover crops to provide both biomass and nitrogen. A tropical legume, is a potential warm season cover crop for the Midwest. In the southern U.S large biomass yields are reported to be produced in a relatively short time (Price et al, 2012). Sunn hemp provides weed suppression due to rapid canopy development (Mosjidis & Wehtje, 2011) which could contribute to early soil protection compared to other species.
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