Large-Scale Dryland Cropping Systems

This study was conducted from 2008–2018 at the Kansas State University Southwest Research-Extension Center near Tribune, KS. The purpose of the study was to identify whether more intensive cropping systems can enhance and stabilize production in rainfed cropping systems to optimize economic crop production, more efficiently capture and utilize scarce precipitation, and maintain or enhance soil resources and environmental quality. The crop rotations evaluated were continuous grain sorghum (SS), wheat-fallow (WF), wheat-corn-fallow (WCF), wheat-sorghum-fallow (WSF), wheat-corn-sorghum-fallow (WCSF), and wheatsorghum-corn-fallow (WSCF). All rotations were grown using no-tillage practices except for WF, which was grown using reduced-tillage. The efficiency of precipitation capture was not greater with more intensive rotations. Length of rotation did not affect wheat yields. Corn and grain sorghum yields were about 50% greater when following wheat than when following corn or grain sorghum. Grain sorghum yields were about 50% greater than corn in similar rotations.


Introduction
The change from conventional tillage to no-tillage cropping systems has allowed for greater intensification of cropping in semi-arid regions. In the central High Plains, wheat-fallow (1 crop in 2 years) has been a popular cropping system for many decades. This system is being replaced by more intensive wheat-summer crop-fallow rotations (2 crops in 3 years). There has also been increased interest in further intensifying the cropping systems by growing 3 crops in 4 years or continuous cropping. This project evaluates several multi-crop rotations that are feasible for the region, along with alternative systems that are more intensive than 2-or 3-year rotations. The objectives were to 1) enhance and stabilize production of rainfed cropping systems using multiple crops and rotations, and using best management practices to optimize capture and utilization of precipitation for economic crop production; and 2) enhance adoption of alternative rainfed cropping systems that provide optimal profitability.

Experimental Procedures
The crop rotations are 2-year (wheat-fallow [WF]); 3-year (wheat-grain sorghum-fallow [WSF] and wheat-corn-fallow [WCF]); 4-year (wheat-corn-sorghum-fallow [WCSF], and wheat-sorghum-corn-fallow [WSCF]); and continuous sorghum [SS]. All rotations are grown using NT practices except for WF, which is grown using reduced-tillage (RT). All phases of each rotation are present each year. Plot size is a minimum of 100 × 450 ft. In most instances, grain yields were determined by harvesting the center 60 ft (by entire length) of each plot with a commercial combine and determining grain weight with a weigh-wagon or combine yield monitor. Soil water was measured in Kansas State University Agricultural Experiment Station and Cooperative Extension Service 12-inch increments to 96 inches near planting date and after harvest either gravimetrically (RT WF) or by neutron attenuation (NT plots).

Results and Discussion
Precipitation averaged 101% of normal (17.90 in.) across the 13-year study period and was near normal (+/-15%) in 8 out of 13 years with three wet years (>20% above normal), one dry year (2020), and one exceptionally dry year (42% of normal in 2012) ( Figure 1). Fallow accumulation, fallow efficiency, and profile available water at wheat planting was greater with WF than all other wheat rotations ( Table 1). The fallow efficiencies of the 3-and 4-year NT rotations were only about 60-70% of WF under RT. With more water available, crop water use was also greater with WF than with wheat in other rotations. There were no differences in wheat water use among the 3-and 4-year rotations.
Fallow accumulation prior to corn planting and profile available soil water at planting was greater following wheat (WCF or WCSF) than following grain sorghum (WSCF) ( Table 1). However, the fallow period following wheat was longer, resulting in low fallow efficiencies (~18%) following wheat and only 22% following sorghum. Similar to wheat, corn water use was greater with greater available soil water at planting. Grain sorghum responded similarly to corn, with greater fallow accumulation and soil water at planting (and greater crop water use) when following wheat than following corn or sorghum. Again, fallow efficiencies prior to grain sorghum were low (16-22%).
Wheat yields were near normal in 2020 with yields in the 24 to 39 bu/a range ( Figure 2). The effect of cropping systems was not consistent across years, with WF sometimes in the highest yielding group and sometimes in the lowest yielding group. Averaged across the 13 years, cropping system had little effect (4 bu/a or less) on wheat yields.
Grain sorghum yields were also near normal in 2020 with yields greater when following wheat (Figure 3). Sorghum following corn produced 30 bu/a less yield than following wheat, and continuous sorghum yields were similar to yields following corn. Average grain sorghum yields following wheat were approximately 50% greater than following corn or sorghum.
Similar to grain sorghum, corn yields in 2020 were generally similar to the long-term average (Figure 4). Corn yields following wheat in either the 3-or 4-year rotations were always greater than corn yields following grain sorghum, except in 2015 where corn yields following sorghum (wsCf) were greater than wCf. On average, corn yields following wheat were about 50% greater than following grain sorghum.
When examining grain yields across crops, the greatest yields were produced by grain sorghum following wheat (either wSf or wScf) of ~85 bu/a ( Figure 5). These yields were about 40% greater than corn following wheat (wCf or wCsf). Sorghum yields following wheat were about 50% greater than sorghum following corn or sorghum (wcSf or SS), while corn yields following wheat (wCf or wCsf) were also about 50% greater than following sorghum. Wheat-fallow rotation is reduced-tillage; all other rotations are no-tillage. Means within a column with the same letter for the same crop are not statistically different at P = 0.05. The capital letter in the rotation denotes the crop phase of the rotation.