Establishment of Permissible Levels of Residue Removal for Corn, Wheat, and Sorghum Fields as Biofuel Feedstocks
This first year of this project was successfully completed. A total of six representative on-farm sites has been established in western Kansas. At each on-farm site, crop residue was removed at five different levels (0, 25, 50, 75, and 100%) after wheat harvest in a randomized complete block design with four replicates. The size of each treatment plot is 30 by 30 ft. Baseline data including soil texture, soil fertility, and soil aggregate stability were determined.
Samples for soil wind erodibility parameters were collected from each on-farm site in October, 2011 to assess residue removal effects on wind erosion. Results showed crop residue removal increased wind erodible fraction and reduced dry aggregate size distribution four months after residue removal in most sites. Soil aggregate strength and soil surface roughness are being measured. Greenhouse gas emissions (CO2, CH4, and N2O) are being measured at the research site in Hays, KS. In addition, crop yields and soil properties are being monitored across three existing plot-scale studies of crop residue removal at Hays, Garden City, and Colby, KS established in 2009.
In 2012, impacts of crop residue removal on crop yields, soil temperature, soil water content, bulk density, infiltration rate, soil-moisture retention, aggregate stability, total C and N content, and nutrient pools will be determined.
During 2011, we focused on the following objectives:
1. Establish six representative on-farm research sites for assessing effects of crop removal on crop production, soil quality, soil organic carbon storage, and other parameters.
2. Monitor changes in soil wind erodibility parameters for the six on-farm sites including wind erodible fraction, dry aggregate size distribution, and soil aggregate strength.
3. Monitor changes in crop yields and soil quality indicators including physical, biological, and chemical properties under three existing research plot-scale experiments of crop residue removal at Hays, Garden City, and Colby, KS.
4. Assess soil organic C pools and greenhouse gas emissions for the residue removal experiment in Hays, KS.
In summer 2011, six representative on-farm fields were identified near Hays, Garden City, and Colby, KS. Plots with different levels of crop residue removal were established within each farmer’s field. These field sites will complement the existing plot-scale studies at the Kansas State University (KSU)-Research and Extension Centers in Hays, Garden City, and Colby, KS. Locations of the six on-farm sites are shown in Figure 1.
On-farm fields managed under long-term no-till conditions were identified. All the fields were under winter wheat. After wheat harvest in summer 2011, wheat straw was cut at five different heights with a forage harvester, representing 0, 25, 50, 75, and 100% straw removal rates. The five straw removal treatments were established in a completely randomized block design with four replications. Therefore, a total of 120 plots were established. Plots were demarcated with marking flags at each corner and a GPS unit was used to record the geographic location of each plot. Figure 2 shows two on-farm sites. Additional information on the six on-farm sites is shown in Table 1.
For the collection of baseline data, soil was sampled from each replicate at three soils depths (0-5. 5-10, and 10-20 cm) after plot establishment. Total N and total C concentration were analyzed by dry combustion at the KSU-Soil Testing Lab, Manhattan, KS. Soil wet aggregate stability was also determined by the wet sieving method for each site in the Soils Lab at the Research Center in Hays, KS. Soil particle-size distribution was determined using the hydrometer method.
In October 2011 (four months after field experiment establishment), soil samples for the 0- to 5-cm soil depth were collected from each on-farm site for the determination of soil wind erodibility parameters (wind erodible fraction, dry aggregate size, and aggregate strength). A total of 120 samples (20 plots per site × 6 sites) were collected. In addition, pin meter method was used to assess soil surface roughness in each plot. About 2 kg of soil were collected from each plot. Samples were oven-dried at 56 ? for 72 hours. Dry aggregate size distribution by rotary sieve and aggregate strength by crushing device were determined at the USDA-ARS Wind Erosion Unit Lab in Manhattan, KS. Wind erodible fraction, which is the proportion of soil particles with diameter less than 0.84 mm, was computed. Table 2 shows the results of wind erodible fraction under the different crop residue removal levels at each on-farm site.
Results indicated that excessive crop residue removal had rapid effects on soil properties that affect soil’s susceptibility to wind erosion. Wind erodible fraction increased with the increasing crop residue removal rates in four sites (Table 2). Since the soil samples were collected only four months after on-farm site establishment, impacts of crop residue removal on wind erosion parameters were immediate. In spring 2012, soil samples for wind erosion will be collected again. Also, water infiltration, water retention curve and soil aggregate stability (wet), grain and biomass yields will be measured in 2012. Data from on soil properties will be used for modeling wind erosion in 2012.
To complement data from the farmer’s fields, changes in crop yields and soil quality indicators including physical, biological, and chemical properties were also monitored under the three existing research plot-scale experiments of crop residue removal at Hays, Garden City, and Colby, KS. Soil gas samples are being collected using the closed soil chamber method for the measurement of fluxes of CO2, CH4, and N2O by gas chromatography. The soil gas sampling is being done at the research site in Hays, KS (Figure 3). Soil chambers were installed in December 2011. They will remain in place throughout the study period except during harvesting and planting. Air samples (about 25 ml) of the chamber headspace gas are collected at 0, 60, and 120 min. between 11:00 and 15:00 h and stored in pre-evacuated and rubber-sealed vials. These vials are sent to the laboratory for analysis of the three gases by gas chromatography. Soil water content and temperature are measured at the time of gas sampling.
Impacts and Contributions/Outcomes
Impacts of crop residue removal on soil wind erodibility were rapid. Data on wind erodible fraction showed a negative effect of high rates of residue removal on soil dry aggregate stability shortly after residue removal from farmer’s fields. In addition, data from the existing plot-scale sites at the KSU-research centers in Hays, Colby, and Garden City showed that high rates (above 75%) of wheat and sorghum residue removal reduced soil organic carbon concentration and degraded soil structure in the short term. Residue removal also reduced crop yields by reducing soil water content. The effects of residue removal were especially large in dry years (2011).
These significant and rapid effects of crop residue removal were reported in the following outreach opportunities in 2011:
1. The ASA, CSSA, and SSSA Annual Meetings in San Antonio, TX. Audience: mostly researchers.
2. Northwest Agronomy Update in Hays. December, 2011. Audience: County extension agents and crop consultants.
3. Fall Field Day in Hays. August, 2011. Audience: producers, extension agents, crop consultants, and researchers (about 100 people).
4. Radio interview with Erick Atkinson for KSU Agriculture Today.
Yuxin He, a graduate student, has been helping with the execution of this project. His graduate assistantship is funded through this project. The title of this thesis is “On-farm assessment of crop residue removal impacts on soil and environment in western Kansas”.
In 2012, crop production, wind erosion parameters, soil water content, soil carbon storage, soil quality, and other parameters will be further documented for all sites.
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