Project : USDA ARS

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Research Project: Contributions of Climate, Soils, Species Diversity, and Management to Sustainable Crop, Grassland, and Livestock Production Systems

Location: Grassland Soil and Water Research Laboratory

2019 Annual Report

Objectives
Objective 1: Develop procedures and quantify soil health attributes and their impact on agronomic production. Subobjective 1A: Determine the seasonal changes in inherent soil carbon and nutrient cycling potentials (N and P) using the Soil Health Nutrient Tool under conventional and no-till with two different crop rotation systems incorporating legume-dominated cover crops. Subobjective 1B: Determine the effects of conventional and conservation tillage (strip till, no-till) on soil fertility, greenhouse gas emissions, soil microbial diversity, yield, grain, fiber quality, and fertilizer use efficiency (N and P) which contribute to soil health attributes. Objective 2: Quantify native and managed grassland response to biological and climate variability. Subobjective 2A: Document long-term effects of precipitation variation on trends in biomass yield and ecosystem services from grasslands of different species composition. Subobjective 2B: Assess the linkage between the weighted values of Leaf Dry Matter Content of grassland communities and temporal variability in aboveground productivity. Subobjective 2C: Manipulate grassland community composition and resource availability to test the contributions of plant species and functional traits to grassland productivity. Objective 3: Operate and maintain the Texas Gulf Coast LTAR network site using technologies and practices agreed upon by the LTAR leadership. Contribute to the LTAR working groups and common experiments as resources allow. Submit relevant data with appropriate metadata to the LTAR Information Ecosystem. Subobjective 3A: Implement the Texas Gulf Coast LTAR Common Experiment comparing the sustainability of traditional grazing systems and adaptively managed rotational grazing systems. Subobjective 3B: Develop and enhance infrastructure for data acquisition, storage, and transfer to meet LTAR and REE data acquisition and archiving standards.

Approach
Research will apply a Genetics x Environment x Management approach quantify nutrient losses from fertilizer, interannual variability in biomass production, and grazing impacts on traditionally managed agroecosystems common in the southern U.S. Great Plains and evaluate results from management actions designed to reduce negative impacts of fertilization, precipitation variability, and grazing.

Progress Report
Objective 1. We combined and converted fields 1 and 2 into a conventional-tilled- no-till alternating every 120 feet running east-west. The New Field 1 (10 reps) was planted to a cover crop mix. We have combined and converted fields 3, 4 and 5 (New Field 2) into a no-till, conventional till field at 120 foot reps. These were planted with wheat last fall. We collected four sets of soil samples (November, February, May, and August) from each field to look at the dynamic changes to the soil under the various treatments. We began collecting monthly samples starting in September 2018 to better understand the dynamic flow of carbon and nutrients in these systems. Since October 1, 2018 we have collected and analyzed 225 soil samples from the treatments. We also implemented a mixed species vs. single species cover crop trial under both till and no-till systems. We then planted sorghum into the no-till and con-till fields following the mixed vs. single species cover crop test and will continue the monthly analysis. We additionally initiated agronomic studies evaluating safflower, teff and cotton production adding economic value to Central Texas cropping systems. The 2018 cropping season safflower yields increased 25% over 2017, to 1000 kg seeds ha-1. The study was expanded to include trials examining variety and date of seeding. Field studies evaluating the effect of row spacing of cotton and potassium nutrition on lint yield and fiber quality were repeated in 2019. Potassium (K) deficiencies can reduce fiber quality and yield and can result in plants that are more susceptible to drought stress and disease. In both 2017-2018 cotton yields increased 30% under skip-row but there was no effect of K. Teff trials initiated in 2019 produced first cutting yields of forage biomass were greater than 2.5 t ha-1. Objective 2. We evaluated the influence of means and temporal variation in two community attributes, species diversity and species abundance-weighted values of specific leaf area (SLA; leaf area per unit of leaf dry weight), on the productivity response of perennial grassland communities to inter-annual change in precipitation. We calculated inter-annual variability in aboveground productivity of communities by dividing the standard deviation of community productivity over five years by mean productivity. Precipitation differed by as much as a factor of three among years. We additionally completed the eighth year of yield measurement in the long-term stands of native perennial grassland and switchgrass, and initiated supplemental sampling of yield and plant species composition on the two soils on which the stands are located, to determine the contribution of the two soils to total stand yield. Stand soil properties were mapped using ArcGIS to support future analyses of spatial variation in biomass yield. We completed establishment of an experiment testing the effects of water and nutrient limitation on competition between switchgrass, exotic invasive grasses, and winter annuals and perennial forbs. We continued supporting research on switchgrass genetics led by university collaborators. Objective 3. Fall 2018-Spring 2019 have been unusually wet. The cattle herd on the south ranch has remained static, and the rotational grazing herd increased in numbers due to plentiful forage going into summer 2019. Soil, manure, runoff water and forage analyses have occurred as expected. Oats were planted as a grazing crop on the south ranch and a mixture of oats, winter pea and vetch were planted as grazing cover on the rotational grazing north ranch. Additionally, oats and winter pea were planted in some of the permanent pastures for winter 2018/2019 grazing on the north ranch, due to poor growing conditions (drought) in spring through summer 2018.

Accomplishments
1. Precipitation effects on grassland growth depend on plant species diversity and leaf traits. Plant growth or productivity varies in response to inter-annual variation in precipitation. Researchers in Temple, Texas, evaluated species diversity and one leaf trait, specific leaf area (SLA; leaf area per unit of leaf weight) as predictors of community productivity responses to inter-annual change in precipitation. Precipitation differed by up to a factor of three among years. Variation in productivity among years was lowest in communities with high values of SLA and low diversity. High SLA and low diversity were associated with the presence of temporally stable dominant species which stabilized grassland productivity by increasing community growth rates. These findings indicate that land managers can increase agroecosystem sustainability by selecting for temporally stable dominant species with high values of SLA, thereby increase the reliability with which grasslands yield productivity-related ecosystem services. This in turn will help mitigate negative effects of increased precipitation variability associated with climate change.

2. Carbon sequestration from intercropping switchgrass and hybrid poplar. Perennial herbaceous crops such as switchgrass are important sources of cellulosic biomass for the developing bioenergy industry. Removal of this biomass for energy may adversely affect the carbon (C) dynamics within soil. Assessments of how much C will be lost or sequestered into soil and the turnover rates of that C are needed to assist producers as well as policy makers in determining the long-term sustainability of biomass production. The natural 13C abundance of soils was used to calculate the quantity and turnover of C4-C in a switchgrass/poplar intercropping system. After four years of cropping soil organic C increased 16% in the 0-15 cm depth. On average 10% of soil organic C in the 0-15 cm depth was derived from switchgrass. The results show that intercropping switchgrass with hybrid poplar provides forest plantation landowners increased economic returns from biofuel production by improving water use and nutrient cycling. Intercropping also promotes additional ecosystem services including C sequestration. These benefits directly impact air, water, and soil quality, which are increasingly challenged by climate change.

3. Genetic basis of adaptation in switchgrass. Finding the specific genes that adapt plants to their environments is a central goal of plant biology, and critical to breeding improved crops for agricultural production. This study tested for specific genes (‘loci’) that underlie adaptation to the environment (‘local adaptation’) in switchgrass, an emerging biofuel crop and dominant tallgrass species. The study assessed genetic variation across 10 locations spread across a large regional gradient in the range of switchgrass from Texas to South Dakota, USA. This is one of the largest studies to date of genetic controls of plant adaptation to the environment. The study identified loci related to biomass yield and found that that most loci contributed to local adaptation at some sites but were neutral in their contribution to adaptation at others. Few loci caused negative effects. These findings are critical to scientists working on the bioenergy potential of switchgrass because they provide a substantially new framework for understanding how genes control yield in different climates. The findings will also benefit switchgrass breeders by highlighting geographic differences in the genetics of biomass yield, providing a potential basis for region-specific selection in new cultivar development.

U.S. DEPARTMENT OF AGRICULTURE

Grassland Soil and Water Research Laboratory: Temple, TX