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May 2020 FINAL STUDY REPORT Bridger Materials Center Bridger, MT

Effect of Guar and Sunn Hemp Seeding Rate on Stand Count and Biomass Production in a Warm Season Cover Crop Mix – One Year Results

Mark Henning1, Joe Scianna2, Jim Jacobs3, and Monica Pokorny4

Figure 1. Guar (left), sunn hemp (right) in demonstration plantings at MTPMC, 2019. ABSTRACT

Soil health is a priority resource concern for the USDA-Natural Resources Conservation Service and cover crops are a useful tool for enhancing soil health. Limited information is available on individual species performance in multi-species cover crop mixes when planted in Montana. Species compatibility and establishment influence numerous conservation benefits, crop productivity and practice cost. This study investigated seeding rates of 2.5, 5.0, and 10 pounds per acre (lb./A) pure live seed (PLS) of two leguminous cover crops, guar ( tetragonoloba (L.) Taubert) and sunn hemp (Crotalaria juncea L.), when incorporated into a six-species warm season cover crop mix. Plots were evaluated for plant density ( per foot) and aboveground biomass production. The null hypotheses were that seeding rate would have no effect on plant

1-Mark Henning, Area Agronomist, USDA-NRCS, Miles City, MT. 2-Joseph Scianna, PMC Manager, USDA-NRCS, Bridger, MT 3-Jim Jacobs, Plant Materials Specialist (retired), Bozeman, MT. 4-Monica Pokorny, Plant Materials Specialist, Bozeman, MT density or aboveground biomass production for either species or on total above-ground biomass production of the cover crop mix. For guar plant density, there was no significant difference between the 2.5 and 5.0 lb./A rates but there was a significantly greater number of seedlings at the 10 lb./A rate than the 2.5 and 5.0 rates. Similarly, there was significantly greater aboveground biomass production of guar at the 10 lb./A rate than the 2.5 and 5.0 lb./A rates. For sunn hemp, there was no significant difference among seeding rates for plant density or aboveground biomass production. The seeding rate of guar and sunn hemp had no significant effect on the aboveground biomass production of the six-species warm season cover crop mix.

In Montana and Wyoming, one year of study results suggest both guar and sunn hemp do not warrant inclusion in cover crop mixes, as tested, if biomass production is a primary goal of the planting. If the goals of the cover crop planting are pollinator habitat enhancement, soil erosion prevention, or other conservation benefits, guar and sunn hemp may warrant consideration. Warm season cover crop mixes planted at lower seeding rates of warm season grasses may allow for more growth of sunn hemp and guar.

INTRODUCTION

Cover crop mixes in Montana and Wyoming are increasingly used as a tool for producers to improve soil health. Producers plant mixes for a variety of reasons including supplemental grazing, and soil compaction reduction. In Montana, mixes typically have five or more species and are often dominated by warm season species, as warm season crop types are often missing in crop rotations. While there are numerous choices of warm season grasses [millet (various genera), sorghum (Sorghum bicolor L. Moench), corn (Zea mays), sudangrass (Sorghum bicolor L. Moench), etc.], there are limited choices of warm season . Soybeans (Glycine max), cowpeas (Vigna unguiculata L.), and mung (Vigna radiata L.) are commonly used legumes. However, soybeans are not very drought tolerant, limiting their potential in dryland systems. Cowpeas and mung beans do not compete well with warm season grasses and nodulate poorly, if at all, in our environment. A study conducted in 2017 at the Bridger Plant Materials Center (MTPMC) showed that if mung or cowpea are included in a cover crop mix then 5 to 10 lb./A is an economical seeding rate (Henning and Kilian, 2017).

Guar and sunn hemp are warm season legumes that showed promise in irrigated demonstration plantings at the MTPMC in 2018. Guar is an annual and member of the pea family () primarily cultivated in semiarid parts of the world (USDA, NRCS, 2020). It is used in crop rotations and is valued as a green manure crop and for its nitrogen-fixing ability. Depending on production practices and environmental conditions, seed yields vary from 300 to 2,000 lb./A (Purdue University, 2020).

Sunn hemp is also an annual legume and member of the Fabaceae family used as a cover crop for improving soil properties, reducing soil erosion, and recycling plant nutrients (USDA-NRCS, 2020). It can grow up to 9 feet tall under ideal conditions and has a well-developed root system with a strong taproot. Although a tropical or sub-tropical plant, it grows in the continental U.S. where it acts as a summer annual. It can produce over 5,000 pounds of biomass and 100 pounds of nitrogen per acre (Joy and Peterson, 2005). Although considered quite drought tolerant, 1 inch of moisture per week is recommended for optimum growth and production (Joy and Peterson, 2005). ‘Tropic Sun’ is a USDA-NRCS Hawaii Plant Materials Center and University of Hawaii Institute of Tropical Agriculture and Human Resources release considered non-toxic to poultry and livestock. 2 The objectives of this study were to determine if seeding rates effected guar and sunn hemp plant density, leguminous biomass production, and total warm season cover crop biomass production.

MATERIALS AND METHODS

The study was conducted at the USDA-NRCS Bridger Plant Materials Center in Bridger, MT (45º17’12.7”, 108º53’9.7”). Composite soil samples were collected on May 17, 2019, to quantify existing soil nutrient levels. Samples were sent to lab name for analysis (Table 1). The study was established on June 6, 2019, in a Haverson silty clay loam soil (Parker et al., 1975) in a clean tilled and leveled field to ensure good seed to soil contact and minimal weed competition. Plots were seeded 1.25 to 1.5 inches deep with a 4-row, precision cone planter (Kincaid Equipment Manufacturing®, Haven, KS) equipped with double disk furrow openers, depth bands, and double packer wheels. Each plot consisted of eight seeded rows with 14-inch between-row spacing. Plots were 25 feet long and 9.4 feet wide. The study design was a randomized complete block with four replications. Table 1. Soil test results, legume seeding rate study, USDA-NRCS, Bridger, MT. Sample Depth Sample Depth Sample Depth Soil Test 0 to 6 inches 6 to 24 inches 0 to 24 inches

Nitrate N 27 lb./A 57 lb./A 84 lb./A Phosphorus (Olsen) 5 ppm - - Potassium 215 ppm - - Sulfur 12 lb./A 42 lb./A - Carbonate (CCE) 1.6 % CCE - - Soluble Salts 0.28 dS/m 0.28 dS/m -

The first treatment compared the plant density of ‘Kinman’ guar and variety not stated (VNS) sunn hemp seeded at 2.5, 5, and 10 lb./A pure live seed (PLS) in a warm season cover crop mix (Table 2). The second treatment compared biomass production of warm season cover crop species seeded with either guar or sunn hemp. Four control plots were seeded to the warm season cover crop mix without the two test legumes. The experiment was maintained under dryland conditions; no supplemental irrigation was provided. Long-term average annual precipitation in the area is 10 to 11 inches.

Table 2. Warm season cover crop mix, USDA-NRCS, Bridger, MT. Percent Percent by Seeds per Seeding Percent by No. of Square Species Selection/Type Rate Full Rate Weight Seeds Foot --lb./A-- --%-- --%-- --%-- Sorghum X Sudan Sweet Forever 5 28 29 13 2 Grazing Corn BMR90 5 29 29 1 0.2 Pearl Millet Tifleaf III 3 27 18 34 5.5 Collards Impact Forage 1 17 8 25 4.0 Purple Top Turnip VNS1 1 25 6 24 3.9 Sunflower Black Oil Seed 2 33 12 2 0.37 1- VNS – variety not stated.

3 Plant density data of the legume species was collected on August 17, 2019. Aboveground biomass samples were collected on October 3, 2019. Sampling involved clipping all material 1 inch or more above the soil surface. Legume biomass was sampled f rom 15-feet of row from one of et ht wo center rows of each sub-plot. Warm season cover crop biomass swa collected from 5 feet of the same row sampled for the legumes. Biomass samples were dried separately by treatment and sub -plot at 50°C for 168 hours. Plant density counts and aboveground biomass were analyzed using analysis of variance (ANOVA). Tukey’s HSD separations were used when P<0.05.

RESULTS AND DISCUSSION

Guar plant density analysis indicates a significantly greater plant density (P=0.0055) when seeded at the 10 lb./A rate compared to 2.5 or 5.0 lb./A rates (Table 3). There was no significant difference in seeding rates for plant density of sunn hemp (P=0.059) (Table 4).

Table 3. Guar plant density by seeding rate, USDA-NRCS, Bridger, MT. Seeding Rate Plant Density --lb./A-- --plants/foot-- 2.5 0.47 B* 5.0 0.99 B 10.0 1.91 A *ANOVA means in columns followed by the same letters are not significantly different according to Tukey’s HSD at P<0.05.

Table 4. Sunn hemp plant density by seeding rate, USDA-NRCS, Bridger, MT. Seeding Rate Plant Density --lb./A-- --plants/foot-- 2.5 0.09 5.0 0.16 10.0 0.18

There were no significant differences in sunn hemp aboveground biomass production among seeding rates (P=0.2808) (Table 5). Guar produced significantly more biomass at 10 lb./A seeding rate (P=0.0021) than the 2.5 or 5.0 lb./A rates, although guar biomass production was still low.

Table 5. Guar and sunn hemp aboveground biomass production by legume seeding rate, USDA-NRCS, Bridger, MT. Seeding Rate Guar Sunn Hemp --lb./A-- --lb./A-- --lb./A-- 2.5 1.7 B* 19.3 5.0 2.8 B 15.3 10.0 7.5 A 40.0 *ANOVA means in columns followed by the same letters are not significantly different according to Tukey’s HSD at P<0.05.

Increasing seeding rates of guar or sunn hemp in warm season cover crop mixes did not increase total biomass production (P=0.8103) and (P=0.7805), respectively (Table 6). Henning and Kilian, (2017) reported no increase in biomass production withr a simila warm season cover crop mix in a study at the P lant Materials Center in Bridger, MT that used different cowpea and mung bean seeding rates. 4 Table 6. Mean cover crop aboveground biomass production by legume seeding rate, USDA-NRCS, Bridger, MT. Seeding Rate Guar Sunn Hemp --lb./A-- --lb./A-- --lb./A-- 0 8,273 8,273 2.5 6,406 6,620 5.0 7,585 7,034 10.0 7,431 7,246

Field observations on August 21 showed very poor growth of guar and sunn hemp within the cover crop mix. Guar was generally 6 inches or less in height, and sunn hemp less than 20 inches (Figure 2). The overall height of the cover crop mix was over 4 feet (Figure 3).

Sunn hemp

Guar

Figure 2. Guar and sunn hemp in cover crop mix on August 21, 2019.

5 Figure 3. Cover crop mix on August 21, 2019.

CONCLUSIONS

The goal of this study was to determine if seeding rates effected guar and sunn hemp plant density, leguminous biomass production and total warm season cover crop biomass production. Based on the results, we reject the null hypotheses that seeding rate does not affect plant density or aboveground biomass production of guar. However, we accept the null hypothesis that seeding rate does not affect aboveground biomass production of the warm season cover crop mix tested. Additionally, we accept the null hypotheses that seeding rate does not affect the plant density of sunn hemp, the biomass production of sunn hemp or the biomass production of the warm season cover crop mix tested.

With little biomass production of guar or sunn hemp it is questionable whether these species should be used in Montana, specifically in mixes that have warm season grasses such as corn, sorghum- sudan and millet. A similar 2017 study at the MTPMC also resulted in low leguminous biomass production (Henning and Kilian 2017). Warm season cover crop mixes typically include highly competitive warm season grasses. The grasses likely scavenged the high amount of nitrogen available in the soil, 84 lb./A, enabling rapid growth of the grasses while reducing the growth and production of the legumes (Table 1). Guar and sunn hemp may be more suitable in a broadleaf only cover crop mix, or in a mix with lower rates of warm season grasses.

6 LITERATURE CITED

Henning, M. and R. Kilian. 2017. Impact of Legume Seed Rate in Cover Crop Mix on Legume Presence and Production. USDA-Natural Resources Conservation Service, Bridger Plant Materials Center, Bridger, MT. 10p. Accessed at https://www.nrcs.usda.gov/Internet/FSE_PLANTMATERIALS/publications/mtpmcsr13307.pdf

Joy, R. and J.S. Peterson. 2005. Plant Guide for Sunn Hemp (Crotalaria juncea L.). USDA-Natural Resources Conservation Service. Hoolehua, Hawai’i. 3p.

Parker, J., G. Decker, L. Gray, and O. Muller. 1975. Soil Survey of Carbon County Area, Montana, USDA, in cooperation with the Montana Agricultural Experiment Station. 137 p.

Purdue University. 2020. Alternative Field Crops Manual (https://hort.purdue.edu/newcrop/afcm/guar.html, 26 March 2020). Department of Horticulture and Landscape Architecture, 625 Agriculture Mall Dr., West Lafayette, IN 47907-2010 USA.

USDA, NRCS. 2020. The PLANTS Database (http://plants.usda.gov, 26 March 2020). National Plant Data Team, Greensboro, NC 27401-4901 USA.

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