Improved Cover Crop Options for the Cornbelt.
Iowa is consistently among the top two states in the nation in acres planted and overall yield of corn and soybeans. Iowa also ranks highly in soil erosion rates and nitrogen and phosphorus runoff. This is due in part to the lack of soil residue cover. Soil residue cover is especially lacking shortly after soybean harvest is completed. From post-harvest to spring planting the ground has no living plants, leaving soil susceptible to loss of nutrients through leaching and runoff, increased erosion especially during the early spring rains, decreased microbial activity, open ground for weeds to colonize, and decreased water infiltration rate. Cover crops should partially mitigate these effects, but less than 3% of all Iowa farmland were planted to cover crops in 2013. Of the 3% planted to cover crops the overwhelming majority was planted to winter rye. Most cover crop research being done in Iowa is devoted to winter rye and other cool season grasses. Results from my M.S. research will expand information on the use of other species as cover crops, and ultimately improve cover crop options for farmers. The research explores the use of sole crops, binary mixtures, and trinary mixtures of cool season grasses, crucifers, and legumes when drilled in a no-till planting system immediately after soybean harvest. The cover crops being explored are: Secale cereale (winter rye), Triticosecale (winter triticale), Brassica napus canola (Sitro and Claremore), Camelina sativa (Bison), Hordeum vulgare (spring barley), Avena sativa (spring oats), Brassica rapa (Purple Top Turnip), and Vicia villosa (hairy vetch). The resultant effects on soil moisture, soil carbon and nitrogen, weed populations, cover crop ground cover, and corn health and yield are being measured. The 2013-2014 study is replicated at two locations, south Ames and 11 miles southwest of Atlantic. The 2014-2015 study will be replicated at three locations, keeping the current two and adding one more site near Sutherland, IA. Graduate student, Seth Appelgate is leading this project.
The Influence of Bradyrhizobium on Nodulation, Nitrogen Fixation and Yield of Fungicide Treated Soybean, Cowpea and Lablab Seeds.
Land degradation and loss of soil fertility remain an important global concern because of the adverse effects on agricultural production, food security and the environment. Nitrogen is one of the most important nutrients to plants yet declining soil fertility causes limitations on its availability in crop production around the world. The lack of adequate nitrogen in most soils limits farmers’ goals of increasing yield per unit area and thus need for research on alternative nitrogen sources. In addition, more research is needed to develop a combination of fungicides and seed inoculation that will not negatively affect nodulation and yield. A field study was conducted for 2 years to determine the existence of interactions between fungicide and bradyrhizobium, ascertain the abundance and effectiveness of indigenous rhizobia in the soil and how they affect the potential for improving biological nitrogen fixation through inoculation. The research also determined what percentage of nodules formed on the roots were actually fixing nitrogen to the soil. The plants were uprooted at R4 just before pod filling. Results revealed that nitrogen fixation by nodules peaked and then rapidly decreases when pod filling begun. All treatments were not significantly different from each other. However, soybean plots that received both bradyrhizobia and fungicide had higher mean values of yield per hectare compared to other treatments. Soybean plots that received only fungicide but no rhizobia had the lowest mean yield. High yield in plots with no rhizobia would be an indication of presence of already existing competitive indigenous rhizobia strains in the soil. Soybeans were the most efficient at nitrogen fixation followed by CA46 cowpeas. Graduate student, Rosemary Bulyaba is leading this project.
Effects of Legume Leaf Utilization on Overall Grain and Leaf Production.
Legume leaf and grain utilization for human consumption, as well as forage, may be a source of nutritional and harvest versatility that is rare with most other commonly grown vegetables. However, little is known about the potential for leaf harvesting from these crops, the nutritional and health benefits to both humans and animals that accrue to the harvested leaf nutrients and consumption or how plant defoliation would affect overall plant biomass, grain yield and nutritional composition of the leaves. More and better information about these elements would aid production and harvesting decisions. The 2-year research study involved harvesting 25%, 50% and 75% of upper plant leaves at V6 (six trifoliate leaves) just before flowering to determine optimum leaf harvesting percentages that will not compromise grain and leaf yield. The results also determined the chemical and nutritional composition of harvested leaves and seed oil-protein concentrations. Soybean results showed significant differences between the different percentages of leaf harvesting. Plots in which 25% of the leaves were harvested from the plants had the highest yield per hectare. Thus harvesting of 2 leaves from soybean would be recommended. This is elaborate evidence of how leaves can be utilized as leafy vegetables or forage yet not have negative impact on yield but instead higher yield compared soybean plots where no leaves were harvested. The average amount of nitrogen and calcium in the leaves from all plots with different leaf harvesting percentages was found to be the same in the first year of the experiment. Graduate student, Rosemary Bulyaba is leading this project.
Cover Crop Management Influences Soybean Production.
Iowa often has extreme weather events in the spring, a time when few fields in the state have a living cover, leading to nutrient and erosion issues. These intense rain events also lead to excess soil moisture and runoff. While cover crops help address these issues and more there has been little adoption of cover crops in Iowa (less than 1% of farmed acres). A commonly cited worry is that cover crops aren't worth the money that a farmer must invest. To offset costs, some farmers use their cover crops for haying or grazing, but a major constraint is access to federal crop insurance for main crops. To address this, an experiment was designed to determine whether the USDA RMA cover crop haying and grazing guideline date (May 10) had an influence on soybean grain yields in Iowa. A replicated plot study was conducted near Ames, Iowa during the 2012-2013 and 2013-2014 growing seasons to investigate the effects of cover crop species, termination date and residue removal on subsequent soybean grain yield. Cover crop entries included Secale cereale ‘Spooner’, Brassica napus ‘Sitro’, Camelina sativa ‘Bison’, B. rapa ‘Purple Top’, and a no-cover crop control. The first year of the study found the only factor with a statistically significant effect on yield was aboveground biomass removal. Plots with biomass removed yielded 3818 kg/ha compared to 3668 kg/ha where biomass was left in place. Cover crop species also had a significant effect on weed pressure and accumulated biomass, carbon and nitrogen. Removal and use of aboveground biomass could serve as a powerful argument to help increase farmer adoption of cover crops. Graduate student, Timothy Sklenar is leading this project.
Practical methods to alleviate constraints limiting common bean
(Phaseolus vulgaris L.) production in Masaka, Uganda
There are many constraints limiting common bean production in Masaka District, Uganda. Bean yields typically range from 1000 to 3000 kg ha-1 in high-input monoculture crops (Graham & Ranalli, 1997); however, beans grown in Uganda use low-input systems and are usually intercropped with maize, cassava, cotton, banana, coffee, or groundnuts; therefore the yields range from only 900 to 1700 kg ha-1, which is far below the potential production of 4000 kg ha-1 (Ronner & Giller, 2012). Sole cropping bean systems usually achieve the highest yields, especially when utilizing cultivars that express an indeterminate growth habit and small seeds (Graham & Ranalli, 1997). According to local seed companies, planting in 50 cm wide rows with seeds planted every 10 cm is the recommended planting method which results in an optimum planting density of 20 plants m 2, but many farmers continue to scatter plant and at a low density of only 10 plants m 2. Land degradation and nutrient depletion is another issue farmers are facing and this is a result of continuous cultivation and low use of external inputs, which has led to a decrease in crop yields (Ronner & Giller, 2012). Infertile soils are particularly problematic in the Lake Victoria Crescent, which include 21 districts of Central Uganda, including the district of Masaka (Ronner & Giller, 2012). Soils here are often acidic and produce low crop yields (Wortmann, Kirkby, Eledu, & Allen, 1998). The production constraints to common bean production are complex and are frequently inter-linked and occur simultaneously, however, our experiments will determine if the alleviation of the top 4-6 most limiting constraints to common bean production can significantly increase bean yields. Furthermore, a system alleviating nearly all production constraints will be tested and compared against the conventional bean production system and the system alleviating the top 4-6 most limiting production constraints. This study will help farmers understand the importance of soil fertility and improved production and management practices on common bean yields. Lance Goettsch is the lead on research comparing three production systems, each with four bean varieties, on degraded red soil (Limyufumyufu) and black soil (Liddugavu) in Masaka, Uganda. His research is part of a larger project, “Farmer Decision Making Strategies for Improved Soil Fertility Management in Maize-Bean Production Systems”, Mazur et al., with funding from USAID Legume Innovation Lab and Borlaug Foundation.