Intensifying cropping systems in semi-arid environments to enhance soil health and profitability
PI: Paul DeLaune
Materials and methods
Three producers were identified in three counties: Archer, Wichita, and Wilbarger, in which research demonstration sites were ultimately placed. At time of selection, each site was cropped to winter wheat and had been under no-till production for at least 8 years. Soils as each consisted of Kamay silt loam (Archer); Winters loam (Wichita); Tipton loam (Wilbarger). These three sites complemented the university site located at the Texas A&M AgriLife Research and Extension Center at Vernon (Vernon site). The Vernon site consisted of Miles sandy loam soils. Each on-farm location had the following treatments: 1) continuous wheat with fallow summer; 2) wheat/canola rotation with fallow summer; and continuous wheat with 3) mixed species cover crop planted at 15 lb/ac and terminated at 55-70 days; 4) mixed species cover crop planted at 20 lb/ac and terminated at 55-70 days; 5) mixed species cover crop planted at 15 lb/ac and terminated at 75-90 days; 6) mixed species cover crop planted at 20 lb/ac and terminated at 75-90 days; 7) broadleaf mixed species cover crop planted at 20 lb/ac and terminated at 55-70 days; 8) guar; and 9) mungbeans. The Wilbarger and Wichita Country also have black-eyed cowpeas and the Archer and Wichita County sites have pigeon peas. The guar, mungbeans, cowpeas, and pigeon peas were planted as double crops. All of these treatments are evaluated at the Vernon site, with each treatment evaluated as a cover crop and a double crop. The mixed species cover crops include mungbeans, guar, cowpeas, forage sorghum, pearl millet, proso millet, foxtail millet, buckwheat, and sunflower. The broadleaf mix consisted of cowpeas, mungbeans, guar, buckwheat, and sunflower. At the Archer County site, a cool-season mixed species is planted followed the warm-season mixed cover crop and compared to forage production of wheat following the same summer treatments.
The low cover crop mix was planted at a rate of 15 lb/ac for the on-farm locations and consisted of: forage cowpea (3 lb/ac); mungbeans (3); guar (2); forage sorghum (1); pearl millet (2); proso millet (1); foxtail millet (1); buckwheat (1); and sunflower (1). The high cover crop mix was planted at a rate of 20 lb/ac consisting of: forage cowpea (3); mungbeans (3); guar (3); forage sorghum (2); pearl millet (3); proso millet (2); foxtail millet (2); buckwheat (1); and sunflower (1). These rates and mixes were similar to those used and recommended by local NRCS field office personnel, thus represented what a farmer may actually plant if using cost share programs through NRCS or using NRCS guidelines in general. The broadleaf cover crop mix was planted to allow in-season herbicide applications to control summer weedy grasses if needed. Sumer annual grasses were expressed as a concern by producers and the advisory panel prior to initiating the project. The broadleaf cover crop mix was planted at 20 lb/ac and consisted of: forage cowpea (10); mungbeans (4.5); guar (2.5); buckwheat (1.5); and sunflower (1.5). During the first year (2016), planting was delayed due to late wheat harvest as a result of heavy May precipitation. Thus, cover crops were planted in late June, at which time hot and dry conditions persisted. The Archer county location was planted in a small field that had been traditionally cropped to wheat, but had been abandoned for 2-3 years and was overgrown with summer weeds (pigweed, curly dock, horse weed). Thus, a great deal of time was taken to clean the field up prior to planting. The first planting at the Archer Co. location did not take place until July, which would not allow sufficient time for a double crop to mature. As a result, double crops were treated as a cover crops.
All double crops and cover crops were planted with a no-till drill on 7.5 inch row spacing after wheat harvest each year. Cover crops were chemically terminated each year within the allotted days after planting time frame. Prior to termination, biomass was clipped from 3 ft2 quadrants and dried to determine biomass production. Double crops were harvested using a plot combine upon maturation. Winter wheat was planted across all plots after the last double crop was harvested at each location (typically guar). Bentley heat was planted at 60 lb/ac using a no-till drill on 7.5 inch row spacings. All plots were 12×40 ft and replicated four times, with the exception of the Wichita County location where treatments were replicated three times. At the Archer County location, a cool-season mixture was planted following summer mixtures to compare to wheat forage production. Thus, the low and high mix treatments were followed by either wheat or a cool-season mixture (rather than different termination dates for each mix as at other locations). Bentley wheat was planted at 75 lb/ac at the Archer county site, which resulted in a total planted seed population of approximately 956,000 seeds/ac. A cool-season mix was planted to supply the equivalent amount of seed per acre. The cool-season mix was planted at 63 lb/ac and consisted of: Triticale (16 lb/ac); black oats (14); barley (15); Austrian winter pea (13.75); hairy vetch (3); and radish (1.25).
Prior to wheat planting, soil samples were taken to to determine soil nutrient and microbial concentrations. Soil samples were sent to Ward Laboaratories for determination of microbial populations using phospholipid fatty acid analysis (PLFA). At the Wilbarger County location, aluminum access tubes were placed to a depth of 4.6 ft in three of four treatment replications. A neutron moisture meter was used to determine stored soil moisture bi-weekly at 8 inch increments through the year.
The Vernon site was established in summer 2015 within a field that had been in continuous no-till wheat production since 2001. Summer crops were established on 12×20 ft plots (four reps) using a no-till drill. Evaluated treatments for this study included: summer fallow; forage cowpeas; mung beans; cover mixture terminated 55-70 DAP; cover crop mixture terminated 75-90 DAP; and a cover crop mixture that was harvested as a hay crop. The cover crop mixture was planted at a rate of 25 lb/ac and consisted of forage cowpea (6.5 lb/ac); mung beans (5); guar (3.5); pearl millet (3); forage sorghum (5); and G. foxtail millet (2). Management of plots were similar to those stated for the on-farm locations. Soil moisture sensors were installed at depths of 4 and 8 inches in three of four treatment reps.
Research results and discussion
Archer County
The site at Archer County was an abandoned field that had been overgrown by weeds. After cleanup via shredding and spraying, cover crops were planted on July 15, 2016. Moisture conditions were not ideal at planting, followed by hot and dry conditions. Due to the late plant date, double crops were treated as cover crops in the first year. Even under dry conditions, the mixtures produced more than 1000 lb/ac biomass (Table 1). Larger seeded legumes did not germinate well and/or thrive. The pigeon peas provided to the project were found to have less than 10% germination after planting and a new source was identified in future years. During the first year, plots were harvested as forage, comparing winter wheat versus a cool-season mixture. While biomass was greater for the mixture compared to wheat at the first cutting in December, radishes and oats both had heavy winter kill and subsequent cuttings were lower for mixture than wheat. Overall, total season forage production was similar between wheat and a cool-season mixture and protein levels were similar as well. In addition, the cost of the mixture was about $40/ac, compared to $17.25/ac for wheat. Cover crop biomass production was about 100% higher in 2017 than 2016. There were no differences in biomass production between high and low seeding rates. Mung beans produced 651 lb/ac and guar produced 421 lb/ac, indicating capability as a viable double crop. Contracts for returned about $0.30/lb for mung beans and $0.16/lb for guar. However, a dry fall in 2017 resulted in subsequent impact on wheat yields. Wheat yields in 2018 were 19.9 bu/ac for the fallow system, compared to less than 10 bu/ac for double crops. Yields following the broadleaf mixture was 15 bu/ac, indicating that earlier termination of a cover crop or double crop may be critical for subsequent crop performance. Dry conditions persisted through the summer of 2018. Cover crop mixtures provided the greatest biomass production, compared to double crops than were converted to a cover crop due to lack of yield potential. During the final year, ryegrass heavily infested the plot area. As a result, wheat yields were not measured. However, canola in rotation with wheat yielded 32 bu/ac. As the canola was roundup ready, winter annual grassy weeds were easily controlled. There was little to no difference for measured soil parameters, including PLFA analysis.
Table 1. Cover crop and double crop biomass and/or grain production in Archer County, TX.
| Treatment | 2016 Biomass lb/ac | 2017 Biomass lb/ac | 2018 Biomass (lb/ac) |
| Low Mixture – Winter Wheat | 1420 | 3225 | 1632 |
| Low Mixture – Winter Mix | 1036 | 2497 | 845 |
| High Mixture – Winter Wheat | 1328 | 2920 | 1236 |
| High Mixture- Winter Mix | 1027 | 2461 | 1542 |
| Broadleaf Mix | 862 | 2495 | 615 |
| Pigeon Pea | 57 | 370* | 296* |
| Mung Bean | 287 | 651* | 435* |
| Guar | 98 | 421* | 175* |
| *Designates grain yield as double crop. |
Wichita County
During the first year of the project, legume summer crops were greatly affected by hot and dry conditions after planting in late June. Cover crop mixture biomass production ranged from 655-1353 lb/ac. Between drought and wildlife damage, no double crops were produced. There were no statistical differences among wheat yields for the duration of the project. Double crops were not harvested at this site due to extensive wildlife damage throughout the project, which also included damage to the wheat and canola cash crops. A native plot was added to the Wichita County site, which comprised of allowing the native annual weedy summer biomass grow throughout the summer without any mechanical or chemical control. In 2018, the native treatment produced numerically higher herbage mass than all other treatments with the exception of the late terminated cover crop mixture. There was no consistent trend in biomass production between early and late termination dates or seeding rates.
Table 2. Cover crop and double crop biomass and/or grain production in Wichita County, TX.
| Treat- ment | 2016 Biomass (lb/ac) | 2017 Biomass (lb/ac) | 2018 Biomass (lb/ac) | 2017 Wheat Yield (bu/ac) | 2018 Wheat Yield (bu/ac) | 2019 Wheat Yield (bu/ac) |
| Low Mixture – Early Termination | 655 | 613 | 408 | 15.1 | 9.5 | 44.9 |
| High Mixture – Early Termination | 1328 | 2217 | 581 | 13.6 | 26.5 | 55.3 |
| Low Mixture – Late Termination | 1353 | 934 | 912 | 8.3 | 12.2 | 37.1 |
| High Mixture- Late Termination | 1005 | 718 | 1102 | 10.8 | 24.6 | 37.6 |
| Broadleaf Mix | 569 | 270 | 210 | 14.1 | 12.9 | 51.0 |
| Cowpea | 0 | WD | 683 | 14.0 | 25.4 | 45.4 |
| Mung Bean | 27 | WD | 8.2 | 11.9 | 48.3 | |
| Guar | 21 | WD | 182 | 15.5 | 16.2 | 48.9 |
| Pigeon Pea | 0 | WD | 478 | 11.0 | 20.5 | 51.2 |
| Native | – | 568 | 1002 | 10.7 | 25.2 | 49.3 |
| Fallow | – | – | – | 13.5 | 19.9 | 49.4 |
| Canola/Wheat | – | – | – | 0* | 22.1 | 9.8* |
| WD = Wildlife damage | *Canola yields |
Wilbarger County
The Wilbarger County location was the most production location in terms of herbage mass production during the first two years among on-farm locations. In 2016, terminating cover crops at a later date resulted in much greater biomass production than early terminated cover crops. In addition, there was little difference in cover crop biomass production among varying seeding rates. These observations were due to above normal August and September rainfall events. In the drier 2017 fall, there was little to no difference in biomass production between early and later termination dates. Due to extensive drought conditions, cover crop biomass was less than 400 lb/ac across treatments in 2018. Cowpeas and mung beans production was very good in 2016; however, damage (wildlife and bovine) just prior to harvest decimated grain production. Hence, plots were treated as cover crops. In 2017, grain production was 764 for mung beans, 594 for black-eyed cowpeas, and 248 lbs/ac for guar. Wheat yields did not significantly vary among treatments within each year. It should be noted that wheat stands were extremely poor due to drought conditions in fall 2017. As a result, no wheat was harvested in spring 2018. Wheat failure was consistent across treatments, both fallow and summer cover crop/double crop treatments. Hence, income for the season would have been greatest for the cowpea and mung bean systems due to production of summer grain. However, at this time crop insurance is not available to dryland wheat farmers if a summer double crop is planted, although wheat is insurable if a cover crop is terminated in a timely fashion. Short-season crops such as mung beans or cowpeas could be a viable option to producers. Each of the varieties tested were 60 day crops, which allow an extended recovery time compared to guar or full-season cover crops (120 day crops).
As seen in the figure below, soil water content was measured through the project (Figure 2). Data are shown for the first two years. The final year is not shown due to extended drought and no plant growth. The red line in the figure denotes time of wheat planting each year. In late August 2016, shortly after the broadleaf and early termination cover crop mixture was terminated, the yet to be terminated cover crops (late treatments) has lower stored water content. As dates moved closer to wheat planting, stored soil moisture was lower in double crop treatments. However, these deficits were not statistically different and stored soil moisture was similar among all treatments entering winter dormancy. While the canola crop failed in 2017, marestail dominated the plots. As glyphosate is mostly ineffective for marestail control, roundup ready canola provided little benefit. As a result, lack of weed control in this treatment led to significantly lower stored soil moisture in June 2017. Water use by weeds were greater than that of wheat, hence weed control is also an important consideration for water conservation. The dry fall of 2017 led to lack of recharge of stored soil moisture deficits created by summer crops. However, earlier terminated cover crops and short-season double crop mung bean generally had higher stored soil moisture than other treatments. As stated earlier, failure of wheat establishment was consistent across all plots due to conditions resulting in the upper soil layer. At this location, in-season precipitation was the critical determining factor for wheat production. Soil nitrate levels were not negatively affected by cover crop or double crop options compared to the wheat fallow system (Figure 1). Although summer crops performed poorly in 2018, the impact of lasting residue as affected by termination timing could be observed. Residue buildup and persistence was visually evident in summer 2018 between early terminated and later terminated cover crops. In order of remaining residue on the soil surface in August 2018, late terminated mixture>early terminated mixture>broadleaf mixture. The broadleaf mixture was quickly degraded due to the high legume component and low C:N ratios.
Table 3. Cover crop and double crop biomass and/or grain production in Wilbarger County, TX.
| Treatment | 2016 Biomass lb/ac | 2017 Biomass (lb/ac) | 2018 Biomass (lb/ac) | 2017 Wheat Yield (bu/ac) | 2018 Wheat Yield (bu/ac) | 2019 Wheat Yield (bu/ac) |
| Low Mixture – Early Termination | 2326 | 2458 | 396 | 17 | – | 65.4 |
| High Mixture – Early Termination | 2842 | 2228 | 234 | 15.8 | – | 49.6 |
| Low Mixture – Late Termination | 5943 | 1809 | 228 | 16.0 | – | 63.2 |
| High Mixture- Late Termination | 5216 | 1833 | 254 | 17.4 | – | 63.8 |
| Broadleaf Mix | 3310 | 1992 | 354 | 18.3 | – | 53.9 |
| Cowpea | 1498 | 591* | 399 | 16.0 | – | 62.8 |
| Mung Bean | 1051 | 764* | 237 | 13.9 | – | 69.5 |
| Guar | – | 248* | 298 | 14.8 | – | 55.2 |
| Fallow | 20.3 | – | 58.0 | |||
| *Double crop grain yield |
Figure 1. Soil nitrate as affected by cover crop, cover crop termination timing, and double crops in Wilbarger County, TX.
Figure 2. Soil water content as affected by cover crops and double crops in Wilbarger County, TX
Vernon
The site at Vernon had irrigation capabilities, and up to one inch of water was applied to the system during a growing season. Specifically, irrigation was applied at cover crop planting and/or wheat planting to ensure stand establishment in 2016 and 2017. Thereafter, no irrigation was applied. Similar trends in biomass production were observed for early and late termination dates as the on-farm locations, with only one of three years indicating an advantage of a longer growing season on cover crop biomass production. Wheat yields were not different following various termination dates of cover crops and or cover crops vs double crops. In general, wheat yields were variable within treatments, which resulted in no significant differences among treatments. The focus of the Vernon site was the impact on soil properties if sufficient biomass was produced each year. These plots were initiated in summer 2015, thus an additional year of growth had been obtained compared to on-farm locations.
Table 4.
| Treat-ment | 2016 Biomass lb/ac | 2017 Biomass (lb/ac) | 2018 Biomass (lb/ac) | 2017 Wheat Yield (bu/ac) | 2018 Wheat Yield (bu/ac) | 2019 Wheat Yield (bu/ac) |
| Mixture – Early Termination | 5902 | 4527 | 4863 | 28.7 | 13.9 | 29.2 |
| Mixture – Late Termination | 6126 | 7693 | 3683 | 27.0 | 11.8 | 52.2 |
| Mixture – Hay | 6910 | 6988 | 5416 | 23.9 | 13.3 | 50.3 |
| Cowpea Double Crop | 259* | 106* | 516* | 30.2 | 5.5 | 41.8 |
| Cowpea Cover Crop | 5307 | 6020 | 3386 | 26.6 | 8.4 | 39.5 |
| Mung Bean Double Crop | 155* | 931* | 321* | 20.2 | 8.0 | 54.0 |
| Mung Bean Cover Crop | 3604 | 5137 | 3333 | 21.9 | 10.3 | 28.5 |
| Fallow | – | – | – | 20.5 | 10.7 | 47.4 |
| * Grain Yield |
As observed at the Wilbarger County location, stored soil water content was affected by treatment (Figure 2). Cover crops and double crops use stored soil water during peak growth periods. However, stored soil water content was similar among all treatments at wheat planting. In some cases, soil water content was higher due to cover crop or double crop treatments after wheat emergence. Cornell sprinkle infiltrometers were used at this location, but did not show significant differences among treatments during the spring. However, trends showed improved infiltration over the summer fallow treatment, particularly for the mixed species cover crops and the mung bean cover crop. The lasting residue of the grasses within the mixture may prove beneficial in water capture and infiltration in the long-term.
Figure 3. Stored soil water as affected by cover crop termination timing and double crops at Vernon, TX 2018.
Figure 4. Infiltration rates during wheat reproduction growth period as affected by cover crop and double crop treatment at Vernon, TX.
Increase awareness of soil health also increased the awareness of soil biological function and activity in the soil. As a result, laboratories focusing on microbial analysis are more common. Phospholipid fatty lipd analysis is an analysis offered by laboratories focusing on soil health. While costs are higher than traditional testing, demand for such testing justify the costs. The below table shows total PLFA, total bacteria, total fungi, and total arbuscular mycorrhizal fungi (AMF). Results varied by date and within microbial community. Significant differences were observed for the August 2018 date for total PLFA and total bacteria biomass, and for the Non 2018 date for total fungi and AMF. Numerically, the summer fallow treatment resulted in the lowest total PLFA, bacteria, and AMF for each of the above dates. The mixed species cover crops, cowpea cover crops and double crops, and mung bean cover crop and double crop had higher total PLFA and bacteria than the summer fallow treatment. Only the hayed mixed treatment did not differ from the summer fallow treatment.
Table 4. Effect of treatment on select soil microbial biomass as determined by phospholipid fatty acid analysis at all sampling dates. Lower case letters indicate significant differences (p<0.05) at the corresponding sampling date. All biomass values are reported on a ng g-1 basis.
The below figure demonstrates the impact of cover crops versus double crops on microbial parameters and active carbon. When observing the data based upon same species grouping, the double crop tended to have numerically higher values than the cover crop. For example, a double crop cowpea had higher values than a cover crop cowpea or a early terminated cover crop had lower values than a late terminated cover crop. Hence, active root/plant growth could lead to greater microbial activity and biomass and higher active carbon pools.
TEXAS A&M AGRILIFE ROLLING PLAINS AGRONOMY PROGRAM 
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