Establishment of Permissible Levels of Residue Removal for Corn, Wheat, and Sorghum Fields as Biofuel Feedstocks
Field and laboratory activities were successfully executed in 2012. As explained in the 2011 report, six representative on-farm research sites under no-till management were chosen in western KS in summer 2011. Wheat straw was removed at five different levels (0, 25, 50, 75, or 100%) in a randomized complete block design with four replications at each site. All research plots were 30 m by 30 m in size for a total of 120 plots. Soil samples were collected from each plot in April 2012 and again in October 2012 to assess soil properties and soil C and N. We focused more on wind erosion risks during 2012 due to the prolonged drought conditions. Crop residue removal reduced soil dry aggregate size and aggregate stability, indicating that residue removal increased the soil’s susceptibility to wind erosion. Due to the drought, crop yield was very low in 2012. Among three crops (wheat, corn, and sorghum), wheat seemed to be the least affected by residue removal. Both sorghum and corn yield decreased with residue removal rates above 75%. Overall, crop residue removal above 75% may cause soil degradation and reduce crop yields in the short term in semiarid regions.
The main objectives of this project were to determine impacts of corn, wheat, and sorghum residue removal from no-till crop rotations on wind erosion, soil properties, and crop yields under rain-fed conditions in western Kansas and to establish the preliminary threshold levels of residue removal for representative no-till soils in the region.
During 2012, we focused on the following objectives:
1. 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.
2. Determine the effects of residue removal on grain yield for each site.
3. Establish the preliminary permissible levels of crop residue removal for different crops under different soil types based on residue removal effects on soil properties and crop yield in western Kansas.
- Figure 1. Map of Kansas showing the location of the six on-farm sites near Colby, Hays, and Garden City in western KS.
In spring 2012 and fall 2012, soil samples were collected from all six on-farm sites (Fig. 1; Table 1). In early June, wheat was harvested at La Crosse and Rush Center (Fig. 2). In early September, corn and sorghum were harvested. After the wheat, corn, and sorghum harvest, treatments were imposed again. Similar to 2011, a forage harvester was used to establish the treatments. The cropping systems in 2011 and 2012 were wheat-wheat-fallow at Rush Center, wheat-wheat-sorghum at La Crosse, wheat-fallow-corn at Colby, wheat-fallow-corn at Norcatur, wheat-fallow-wheat at Garden City, and wheat-fallow-sorghum at Scott City, respectively.
Wind Erodible Fraction
Soil samples for wind erosion test were collected from all the plots and sites twice in 2012. At each time, about 2 kg of surface soil (0-5 cm depth) was collected from each plot. Pin meter was used to study soil surface roughness. Samples were oven-dried at 56? for 72 hours. Dry aggregate size distribution and aggregate strength were determined using rotary sieve. Wind erodible fraction, which is the proportion of soil particles with diameter less than 0.84 mm, was computed. Figure 3 shows the results of the wind erodible fraction under different crop residue removal levels in fall 2011 and spring 2012 at each site. To observe the effects of freeze-thaw cycles, data from both fall 2011 and spring 2012 are shown in Fig. 3.
In general, wind erodible fraction increased with increasing crop residue removal levels in spring 2012. Residue removal at rates above 75% increased wind erodible fraction. In fall 2011, two out of the six sites showed significant differences in wind erodible fraction. However, in 2012 spring, five out of the six sites showed significant differences, indicating that residue removal effects were greater in spring 2012 due to longer duration of the experiments (Fig. 3).
The freeze-thaw period during the winter may have also accelerated the soil’ susceptibility to wind erosion in spring time. In the study region, wind erosion is high during winter and early spring when winds are strong and there is limited soil surface cover.
In fall 2011 (four months after experiment establishment), soil aggregate stability did not differ among residue removal treatments at any site, but in spring 2012 (eight months after experiment establishment), aggregate stability showed a decreasing trend with increasing residue removal rates at five sites. Removal rates above 75% appeared to have the largest adverse effects on dry aggregate stability. The greater the soil aggregate stability, the less susceptible the soil is to wind erosion. Aggregates with low stability tend to rapidly break into smaller aggregates. Plots with little or no residue cover develop crusts, which may temporarily reduce wind erosion. However, crusts can reduce seed germination and reduce plant growth.
Total C and N Concentration
Soil samples for total C and N were collected in spring 2012. The effect of residue removal on total C and N was not significant in five out of the six sites. The total C content, however, decreased significantly at the site near Rush Center with 100% residue removal. There were no significant differences in total N concentration among treatments at any site. Results show that effects of residue removal on soil C and N may not be measurable in the short term.
In 2012, two sites (La Crosse and Rush Center) were planted to wheat (Fig. 4). At these two sites, there were no significant differences in wheat yield among residue removal treatments. Similarly, two sites (La Crosse and Scott City) were planted to sorghum in 2012. The site at La Crosse was double cropped. Due to the extreme dry weather in 2012, there was no grain production at both sites. However, sorghum residue production decreased with an increase in residue removal rate, particularly at the Scott City site (Fig. 4). The biomass yield under 100% removal plots at Scott City was practically zero.
Corn was planted at the sites near Colby and Norcatur in 2012. The biomass and grain yield are shown in Fig. 4. At Colby, both grain yield and biomass decreased with increasing residue removal rates. Residue removal rates above 75% had significant negative impacts on corn yield. At the site near Norcatur, residue removal effects were also significant. The effect of residue removal on crop yield depended on cropping system. Residue removal appeared to affect sorghum and corn more than it did wheat.
- Table 1. Soil and crop management information for each on-farm site.
- Figure 3. Wind erodible fraction under different crop residue removal levels at all sites for both fall 2011 and spring 2012.
- Fig. 4. Crop yield for the study sites in 2012.
- Fig. 2. Wheat with and without straw removal in western KS (Photos taken in early spring 2012).
Impacts and Contributions/Outcomes
Impacts of crop residue removal on wind erosion and crop yields were significant in this region. Residue removal increased soil’s susceptibility to wind erosion. Residue removal also reduced crop yields by reducing soil water content. The effects of residue removal on crop yields were especially large during the drought (2012). However, crop residue removal had no significant effects on total C and N concentrations in 2012. Corn and sorghum are more negatively affected by residue removal compared with wheat. Based on the results from 2011 and 2012, a preliminary threshold of crop residue removal for biofuel production can be established. Residue removal above 75% can have adverse effects on crop yields and wind erosion.
These significant and rapid effects of crop residue removal were reported in the following outreach opportunities in 2012:
1. The 2012 ASA, CSSA, and SSSA Annual Meetings in Cincinnati, OH. Audience: mostly researchers.
2. Fall Field Day in Hays. August, 2012. Audience: producers, extension agents, crop consultants, and researchers (about 100 people).
3. Seminar at the Agronomy and Horticulture Department, University of Nebraska-Lincoln.
Yuxin He, a graduate student, has been helping with the execution of this project. His graduate assistantship was funded through this project till June 2011. The title of this thesis is “On-farm assessment of crop residue removal impacts on soil and environment in western Kansas”.
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