Cover Crop Biomass Removal Rates to Optimize Livestock Production and Soil Health in No-Tillage Dryland Cropping Systems

An on-farm study was established in fall 2022 on a 20-ha producer field in Russell Co., KS (38° 42’ 2.2” N, 98° 37’ 58.3” W) located in the KSU Kanopolis Reservoir Big Creek Middle Smoky Hill River Watershed Restoration And Protection Strategies (WRAPS) Area to investigate the effects of CC biomass removal rates with cattle grazing on soil health parameters, grain crop yields, and system profitability in NT dryland cropping systems. Soil types at the study site are the Crete silt loam (72%) and Harney silt loam (28%), and long-term average (30-yr) annual precipitation is 660 mm. However, the study period coincided with a period of exceptional drought. If fact, a second site that was expected to be located at the Kansas State University HB Ranch in Trego Co., KS was abandoned due to severe drought in both years of this study (background information not presented). The study design at the Russell Co. site was a randomized complete block with three treatments and four replications. Treatments included ungrazed CCs, “talk-half-leave-half” (T-H-L-H, 50% biomass removal), and “graze-out” (G-O, 90% biomass removal).
In fall 2022, a three-species CC mixture of triticale, pea, and rapeseed was planted into wheat stubble about October 1 at 67, 17, and 2.2 kg ha^-1, respectively, using a NT drill. No fertilizers were applied. In spring 2023, treatments were established with ungrazed plots of about 0.6 ha and grazed plots of about 2 ha each replicated and randomized across the field (Fig. 1). Plots were grazed with yearlings beginning in the last week of April and moved plot-to-plot every 1 to 2 days across the eight grazed plots to achieve desired CC biomass removal rates based on visual assessment (Fig. 2). Plots were only grazed once because of declining apparent forage quality (increasing plant maturity) and limited regrowth because of dry conditions.

Figure 1. Temporary electric interior cross fencing was used to limit livestock grazed areas and moved regularly across the plots of the on-farm cover crop grazing intensity study in Russell Co., KS.

Figure 2. Cover crop residue remaining after grazing a graze-out (90% removal) plot (left) next two an ungrazed plot (right) divided by temporary electric interior cross fencing in the on-farm cover crop grazing intensity study in Russell Co., KS 

In May 2023, following the end of grazing but before CCs were chemically terminated, CC biomass was measured in all plots by hand-clipping, to the ground level, two areas of 0.56 m² per plot. Samples were dried at 50˚C for a minimum of 48 hrs in a forced-air oven and weighed to determine CC dry matter produced. Cover crops were chemically terminated in the third week of May, and the whole field was planted to grain sorghum with a NT planter approximately two weeks after termination or about the first week of June. Fertilizer applied to sorghum was based on the standard producer practice and kept consistent across treatments. Grain sorghum was harvested with a field scale combine equipped with a calibrated yield monitor about the last week of October. Plot level yield and moisture content data were extracted using QGIS 3.34 Prizren software, and yields were adjusted to 13.5% moisture content.
At the initiation of the study in fall 2022 before planting CCs, soil samples and water infiltration measurements were collected from the 0-5 and 5-15 cm soil depths for initial characterization of soil chemical and physical properties. Again, in spring 2023, soil samples and water infiltration measurements from ungrazed, T-H-L-H, and G-O plots were collected to determine the effects of biomass removal on soil chemical and physical properties. Soil bulk density (BD) was determined as mass of oven dry soil divided by volume of the core following oven-drying at 105°C for 48 hr. Penetration resistance (PR) was measured at 10 random points within each plot using a hand cone penetrometer (Eijkelkamp Co., Giesbeek, The Netherlands) and readings were divided by the area of the cone (1 cm²). Values of penetration resistance were adjusted to a field capacity gravimetric water content of 0.35 (g/g).
Additionally, 10 soil cores were randomly collected within each plot, divided into the 0-2 and 2-6 in. depths, and composited by depth. Samples were air-dried, crushed, and sieved to pass through a 2 mm stainless steel screen. The SOC and particulate organic matter (POM, <0.0531 mm) concentrations were determined by loss-on-ignition. Soil pH was determined potentiometrically by an electrode. Soil NO3-N concentrations in samples were determined with a segmented flow analyzer after extracting the soil with 2 M KCl. Available P was determined by the Mehlich-3 extraction method, and P concentration in the extract was measured using inductively coupled plasma-optical emission spectrometry (ICP-OES). Lastly, intact soils samples were carefully collected with a flat shovel and were allowed to air-dry and then gently passed through a 19-mm sieve. Subsamples of <8-mm diameter aggregates were obtained and used to estimate mean weight diameter (MWD) of water stable aggregates by the wet-sieving method. The remaining sample was used to estimate wind-erodible fraction (WEF) (<0.42 mm) by the dry-sieving method.

In spring 2024, a spring CC was planting at a similar seeding rate as in fall 2022 and plots were grazed a second time as described above. Biomass and soil samples were collected and analyzed similar to that described for spring 2023. Following CC termination, grain sorghum was planted and will be harvested in fall 2024. Analyses of CC biomass, grain yields, as well as soil chemical and physical properties were performed using the PROC GLIMMIX procedure in SAS ver. 9.4.