Integrating Winter Cover Crops Did Not Change Cotton Lint Yield Responses to Nitrogen Fertilization in Sandy Soils

<p>Cover crop mixtures of legumes and non-legumes have multiple advantages compared to bare soil like reducing erosion by covering the soil, fixing nitrogen from the air and reducing nitrate leaching, adding organic matter to the soil, increasing soil biological activity and improving soil structure. The advantages and disadvantages of a winter-hardy vs. a freeze-killed cover crop (CC) mixture were studied on an organic farm in Raipoltenbach in Lower Austria (10.5 °C, 760 mm) with non-inverting soil cultivation since 2008. Effects on soil inorganic nitrogen contents and the yield of a following maize crop were assessed. On an orthic Luvisol with a silty clay to silty loam texture, two field experiments (FE1 and FE2) were laid out in a randomized complete block design in four replicates in two consecutive years. The winter-hardy CC mixture was “Landsberger Gemenge” consisting of winter vetch, crimson clover and Italian ryegrass. The freeze-killed CC mixture consisted of fodder pea, common vetch, chickling vetch, buckwheat, phacelia and fodder radish. The winter-hardy catch crop mixture was terminated with a rotary cultivator and the freeze-killed CC was worked into the soil with a chisel on 4 April 2017 / 19 April 2018. After chiseling the soil (only in FE1), maize, cv “Connexxion RZ 340”, was sown on 4 May 2017 / 7 May 2018. In both treatments, soil was harrowed once in May and hoed twice in June. Soil inorganic nitrogen (N<sub>in</sub>) was analysed in 0.0125 M CaCl<sub>2</sub> extracts. The winter-hardy CC had a biomass of 2.8 t ha<sup>-1</sup> on average when terminated in April, the freeze-killed CC reached on average 3.1 t ha<sup>-1</sup> in November. The N<sub>in</sub> values in 0-90 cm soil depth in spring (2017 FE1 / 2018 FE2) were almost doubled in the freeze-killed CC treatment compared to the winter-hardy CC treatment. The winter-hardy CC mixture in took up soil nitrogen until termination in April, thus reducing N<sub>in</sub> contents after winter and the risk of nitrate leaching during winter, saving nitrogen for the following main crop. An assessment in June (FE1) and May (FE2) showed no differences in the number of maize plants per m<sup>2</sup>. Maize grain dry matter yield was 7.8 t ha<sup>-1</sup> in FE1 and 7.0 t ha<sup>-1</sup> in FE2 on average and did not differ between treatments. Also maize nitrogen yield did not differ. Sowing maize without inverting soil cultivation was more difficult in the winter-hardy CC treatment than in the treatment where the CC mixture was freeze-killed. But mainly due to the effective CC termination with the rotary cultivator, weed density was not higher in this treatment (except for one assessment date in July 2018 in FE2). In our study, both freeze-killed and winter-hardy CC mixtures consisted of a legume-dominated legume-non-legume mixture. This resulted in a narrow C-to-N ratio (10 to 13) in the CC biomass as a basis for a swift N mineralization from the CC residues in both treatments. Accordingly, maize grain DM yield and maize grain N yield did not differ between the CC treatments.</p>

Winter cover crops and conservation tillage can be used by southeastern Coastal Plain cotton (Gossypium hirsuturn L.) growers to meet soil erosion control requirements of the 1985 Food Security Act. Our objective was to determine whether these production practices influence cotton productivity and quality. The study was conducted on a Norfolk loamy sand soil (fine‐loamy, siliceous, thermic Typic Kandiudult) near Florence, SC, in 1991 and 1992. Treatments were winter annual cover crops, tillage, and timing of cover crop incorporation or desiccation before cotton planting. Cover crop treatments were crimson clover (Tnfoliurn incurnatum L.), hairy vetch (Viciu villosu Roth.), rye (Secufe cereufe L.), and winter fallow. Tillage systems were conventional (annual disking and bedding with in‐row subsoiling) and conservation (in‐row subsoiling only). Soil strength was measured during the spring in the fallow plots in both tillage systems. Incorporation (conventional tillage) or desiccation (conservation tillage) of the winter cover was done 5 or 15 d before cotton planting. Winter legume dry matter production was e1800 lb/acre per yr. Rye dry matter production was approximately 2200 lb/acre per year. Soil and crop variables studied were not affected by timing of the cover crop incorporation or desiccation. Soil strength was lower in the top 12 in. with conventional tillage. In conservation tillage, soil strength was the same both years. Conservation tillage had lower lint yield than conventional tillage by 267 lb/acre following clover and by 259 lb/acre following vetch [LSD(0.05) = 221 lb/acre]. Within winter cover treatments following fallow and rye, tillage systems did not differ in yield, but lint yield for conservation tillage following rye was 292 lb/acre greater than yield for that tillage system following fallow. Fiber properties were not greatly influenced by tillage system or winter cover, but micronaire was 0.1 units lower for cotton following rye than cotton following legumes. Including a rye winter cover crop may better insure successful conversion to conservation tillage cotton production systems on Coastal Plain soils.Research QuestionSurface residues are important in conservation tillage systems. After cotton harvest, there are few residues for soil protection or improvement. Using winter annual cover crops to increase surface residues in conservation tillage cotton production has been proposed. Our objectives were to evaluate two legume and one cereal species as cover crops for a cotton conservation tillage production system and to determine if soil strength increased with time for continuous conservation tillage cotton produced without cover crops.Literature SummarySuccessful conservation tillage production of sorghum and soybean in the humid southeastern USA was dependent on doublecropping winter and summer crops to provide large amounts of residues. Since doublecropping cotton is economically risky in much of the region, winter annual cover crops can provide residues for a conservation tillage system. Cotton yields following winter cover crops in conservation tillage systems are somewhat dependent on cover crop species. Conservation tillage cotton following a rye winter cover crop yielded higher than conservation tillage cotton following fallow and the same as conventional tillage cotton. Fiber property data for conservation tillage cotton following cover crops are needed.Study DescriptionA cotton conservation tillage system (in‐row subsoiling only) was compared with conventional tillage for 2 yr on a Norfolk loamy sand soil at Florence, SC.Experimental design: Main plots: Winter covers of rye, vetch, crimson clover, and fallow. Sub plots: Conservation and conventional tillage. Sub‐subplots: Winter covers desiccated or incorporated at 15 or 5 d before planting. Applied QuestionsWhich cover crops produced the most residue?Rye was superior to the legumes for biomass production both years of the study. It provided about 2200 lb/acre of residues each year. Crimson clover and vetch yielded 1600 lb/acre or less each year, with the clover being about the same as winter weeds in 1991.Did conservation tillage increase soil strength?Two years of conservation tillage did not influence soil strength. Soil strength of the surface 12 in. in conservation tillage during the second spring was about the same as for the first year.Did cover crops and tillage systems affect cotton yield and fiber properties?Fiber properties were not substantially affected by either winter cover or tillage. With conventional tillage, lint yield was the same for all winter cover treatments (Fig. ). With conservation tillage, cotton following rye had greater yield than cotton following the legumes and fallow winter covers. The results of this study suggest that when converting to a conservation tillage system for continuous cotton, using a rye winter cover crop may help production on these Coastal Plain soils.Influence of winter cover and tillage on cotton lint yield at Florence, SC. Bars with common letters are not different by LSD (P = 0.05).image

Grazing cover crops can improve land‐use efficiency and diversification, making agricultural enterprises more resilient to market fluctuations. We investigated how grazing intensity affects cover crop forage responses and cotton (Gossypium hirsutum L.) lint yield. Cover crops were a rye (Secale cereale L.)–oat (Avena sativa L.) mixture managed as follows: no grazing + 34 kg N ha–1 (NG34), no grazing + 90 kg N ha–1 (NG90), heavy grazing (HG), moderate grazing (MG), and light grazing (LG), compared with a no cover crop control. All grazed treatments received 90 kg N ha–1. Average postgrazing herbage mass (HM) for HG, MG, and LG was 520, 1,350, and 2,120 kg dry matter ha–1, respectively. Herbage accumulation (HA) rate was greater for LG than HG, with MG being intermediate. Forage crude protein (CP) and in vitro digestible organic matter (IVDOM) concentrations decreased as the season progressed and were usually greater for HG than MG and LG. Stubble residue before cover crop termination was greatest for NG34 and NG90 in 2018 and 2020, however, in 2019 NG90 had greater stubble residue before termination than NG34 (7540 vs. 6650 kg dry matter ha–1). Heavy grazing resulted in greater weed proportion (17 vs. 6.5%) and lesser soil cover (49 vs. 70%) than nongrazed cover crops. Cotton lint yield was low and unaffected by treatment, reaching a maximum of 520 kg ha–1 in 2019. Although lint yield was not affected by cover crop fertilization or grazing during 3 yr, HG reduced soil cover and increased weed presence.

Conservation management practices such as no-tillage and cover crops can decrease soil’s susceptibility to wind erosion, but adoption of these practices has been limited on the Texas High Plains (THP) where producers are concerned with cover crop water usage. The objective of this study was to evaluate the impact of no-tillage and cover crops on cotton (Gossypium hirsutum L.) lint yield and soil water content in a deficit irrigated cropping system. Soil water was observed bi-weekly in long-term, continuous cotton systems established in 1998 that included (1) conventional tillage, winter fallow, (2) no-tillage with rye (Secale cereale L.) cover, and (3) no-tillage with mixed species cover located in Lamesa, TX, USA. Results include observations from 2018–2020 (years 21–23 of the study period). The adoption of conservation practices did not significantly reduce cotton lint yield compared to conventionally tilled, winter fallow cotton. Soil water was initially depleted with cover crops but was greater throughout the growing season following cover crop termination. Throughout the soil profile, water depletion and recharge were more dynamic with conservation practices compared to the conventionally tilled control. There were no differences in cotton water use efficiency between treatments. Results from this study indicate cover crop water usage is likely not the cause of cotton lint yield decline in this deficit irrigated semi-arid production system.

The termination timing of cover crops varies by farm. This research was conducted to determine whether the timing of cover crop termination alters cotton growth and development. The effects of cover crop (crimson clover, cereal rye, oat, and a blend of cereal rye + crimson clover) and termination timing (targeted dates 01 February, 01 March, 01 April, and 01 May) on cotton emergence, plant height, nodes above white flower and yield was evaluated near Starkville, MS on a Leeper silty clay loam (fine, smectitic, nonacid, thermic Vertic Epiaquepts) in 2017 and 2018 and near Tribbett, MS on a Dundee silty clay loam (Fine-silty, mixed, active, thermic type Typic Endoqualfs) in 2017. Timing of cover crop termination had a transient effect on cotton emergence. Relative to terminating cover crops in March or April, terminating in February or May decreased cotton emergence at 7 days after planting (DAP) by up to 26%. However, by 14 DAP, cotton stand averaged 74,190 plants/ha and there was no effect of cover crop termination timing on emergence. There were modest interaction effects of cover crop and termination timing on cotton development including plant height, number of nodes, and nodes above white flower. Cotton lint yield did not differ due to cover crop species but increased up to 8% when cover crop termination was delayed from February until May. This research indicates that April and May are the optimal times to terminate a cover crop in a Mississippi cotton production system, provided there is a suitable environment for healthy cotton growth.

Core Ideas Cereal rye/crimson clover cover crop mixtures can be used for weed suppression and soil moisture conservation in cotton production.Cover crop management at cotton planting can influence cotton emergence, weed suppression, and soil moisture dynamics.Cotton emergence declined when cotton was planted directly into standing cover crop and without row cleaners engaged, but this reduction did not affect cotton lint yield.Soil temperature was reduced and soil moisture was increased by the presence of a cover crop mulch regardless of cover crop residue management strategy at cotton planting.Cover crop residue management did not affect cotton lint yield when herbicides were used, indicating that conventional producers have flexibility in terminating cover crops and residue management at cotton planting. Cover crop residue management can affect performance of the subsequent crop. This experiment was conducted in five environments in North Carolina from 2014 to 2016 to determine the effect of a cereal rye (Secale cereale)/crimson clover (Trifolium incarnatum) mulch on cotton (Gossypium hirsutum L.) emergence, soil temperature, soil moisture, weed suppression, and cotton yield under a conventional and organic weed control context. The cereal rye and crimson clover mixture was planted in mid‐October and terminated 1 wk prior to cotton planting using a roller‐crimper or herbicide application. Cover crop residue management included fertilized, rolled cover crop with row cleaners engaged at planting (Roll+F+RC), rolled cover crop with row cleaners engaged at planting (Roll+RC), rolled cover crop (Roll), standing cover crop with row cleaners engaged at planting (Stand+RC), and no cover crop (BARE). Weed treatments included with and without herbicides. Cover crop dry biomass ranged from 3820 to 6610 kg ha−1 across environments. Fertilizing the cover crop enhanced cover crop dry biomass production by 250 to 1860 kg ha−1. Cotton emergence declined when cotton was planted directly into standing cover crop and without row cleaners engaged. Soil temperature was reduced and soil moisture was increased by the presence of a cover crop. Cover crop residue management did not affect late‐season weed biomass at four of the five environments. Cover crop residue management did not affect cotton lint yield when herbicides were used, indicating that conventional producers have flexibility in terminating cover crops and residue management at cotton planting.

Abstract. Sustainable no-till practices utilize cover crops to protect the soil surface and to improve soil properties. Proper cover crop management is the key for successful planting of the main crop directly into cover crop residue without interfering with planting operations. In the Southern United States, the recommended time to plant cash crops into desiccated residue cover is typically three weeks after cover crop termination when the termination rate exceeds 90%; this minimizes nutrient competition between cover and cash crops. The standard method to manage cover crops is mechanical termination utilizing rollers/crimpers. This technique flattens and crimp plants to expedite termination. Another method that has been used in agriculture is to injure (desiccate) plants utilizing an external heat source. An example of utilizing an external heat source has been used in vegetable production for weed control. However, there is a need to evaluate another heat source such as exhaust heat generated by internal combustion engines (which otherwise is completely wasted) for cover crop termination effectiveness. To achieve cover crop termination with exhaust heat, a prototype was invented on board a walk-behind tractor powered by a single cylinder gasoline engine from which exhaust heat was funneled from the exhaust manifold to a perforated steel rectangular tube maintaining 204°C against a flattened cover crop to damage plant tissue. The heat pusher was equipped with electric heater strips to provide supplemental heating. Three electric heater strips (front, middle, back relative to the direction of travel) were supplied with electrical energy by a generator powered by the tractor’s PTO and generated temperatures of 379°C to 421°C with a temperature transfer efficiency of 83% to 91%. The performance of the unit with and without supplemental heating was compared with standard mechanical roller/crimper. Results demonstrated that using the exhaust heat concept can be a viable option to terminate cover crops. The exhaust heat transferring channel could be better insulated to exceed the lower 23% temperature transfer efficiency achieved by the device. Cover crop termination data during three weeks of evaluation indicated that the heat-based system was as effective as a mechanical roller/crimper. Keywords: Cereal rye, Cover crop termination, Crimson clover, Exhaust heat, Flattening cover crops, Heat transfer, Heater, Plant termination.

Weed suppression in cover crop mixtures under contrasted levels of resource availability

Apart from improving the physical and chemical condition of arable soils, cover crops have the potential to boost and activate selected soil microbiota that could contribute to improved nutrient cycling and strengthened disease suppressiveness. However, a main crop can only benefit from cover crop-induced microbial shifts if these persist until the onset of the main growing season. Here, we map the persistence of microbiome changes by cover crops over time. We performed a field experiment on a sandy soil with ten different cover crop monocultures belonging to five plant families, one cover crop mixture and a fallow control. Cover crops were grown for 4.5 months under field conditions in 70-L bottomless containers in a random block design with eight replications. We studied the total (DNA-based) and the potentially active (RNA-based) microbial fractions at the onset of the main growing season, and just after the harvest of the main crop, potato (respectively 3.5 and 10 months after cover crop termination), through MiSeq sequencing. All cover crops tested induced shifts in the soil microbiome that lasted at least until the onset of the main growing season. Cover crop treatments gave rise to species and even cultivar-specific microbial footprints, and - although roughly the same trends were observed - DNA-based microbial shifts were not necessarily paralleled by similar changes at RNA level. We conclude that cover crops have the potential to act as handles to steer the soil microbiome in a way that is supportive of sustainable crop production.

Single species cover crops and cover crop mixtures, especially legumes, can protect the soil surface and increase soil organic matter in a no-till system. Cotton producers who focus on soil health are interested in maximizing their economic return by minimizing production cost while maintaining yield. Producers can accomplish this by manipulating cotton seeding rates. From 2017 to 2020 field experiments were run in central Alabama to evaluate the effects of cover crop species (cereal rye [Secale cereale L.], crimson clover [Trifolium incarnatum L.], and cereal rye + crimson clover) and cotton seeding rates (54,116, 108,232, and 180,387 seeds ha-1) on no-till cotton production. During the experiments, biomass for cereal rye and crimson clover was similar (5,540 kg ha-1) but was lower compared to their mixture (6,469 kg ha-1). Seed cotton yield in 2018 and 2020 was similar, averaging 4,597 kg ha-1. In 2019 the yield was substantially reduced to 2,068 kg ha-1 due to severe drought. Profit in 2019 was $1,484 ha-1 compared to higher average profit of $6,209 ha-1 in 2018 and 2020. Yield and profitability were greater using the medium or high seeding rate during the 2018 and 2019 seasons. However, under severe drought conditions (2019 season) the low cotton seeding rate was similar in yield and profitability as the medium and high seeding rates. Overall, yield and profits were influenced by cotton seeding rate and weather and not by cover crop type.

Management constraints in reduced tillage organic vegetable production may be alleviated by combining strip tillage (ST) with overwintering cereal–legume cover crop mixtures. Field studies in Michigan and New York over 6 site‐years evaluated the effects of preceding cover crops, including cereal rye (R; Secale cereale L.), hairy vetch (V; Vicia villosa Roth) and crimson clover (CC; Trifolium incarnatum), on N availability, weed management, and yields in ST organic cabbage (Brassica oleracea L. var. capitata). Cover crop treatments included R–legume mixtures (RV and RCC) planted under two spatial arrangements, standard full‐width mixed [‐M] vs. segregated strips [‐S] (legumes planted in‐row and R between‐row), and R and V monocultures. Cover crop aboveground biomass (5–10 Mg ha–1) and N content (>90 kg N ha–1) were not different among RV and RCC but the C/N of RCC was 58% greater than RV. Cabbage yields after RCC‐M were lower than RV‐M in five of six cases with yield reductions ranging from 22 to 41%. Spatial arrangement had no effect on cabbage yield after RV but improved yields after RCC from 23 to 39% in one, relatively dry, site‐year. Without N fertilizer, yields after RV and V were equivalent to or greater than R‐S with 134 kg N ha–1 in seven of nine and four of four cases, respectively. Legume species and spatial arrangement had little or no impact on the efficacy of in‐row mechanical cultivation, hand‐weeding time or weed biomass. Overall, N supplied from V and RV mixtures was an important driver of ST organic cabbage yields across different soil types and weather conditions.

Core Ideas Use of N‐fertilizers decreased AMF populations and P, Ca, and Mg concentrations. Conservation tillage and cover crops increased C, N, and S cycling enzymes. Grass and brassica cover crops increased microbial populations compared to legumes. Agricultural production in the US Mid‐South has relied on frequent tillage and synthetic fertilizers decreasing soil health and system sustainability. Conservation tillage and cover crops can fill a vital role in reducing soil erosion while improving ecosystem functions. Seven cover crop blocks, including four legumes (berseem clover [ Trifolium alexandrinum ], crimson clover [ Trifolium incarnatum L.], winter pea [ Pisium sativum L.], and hairy vetch [ Vicia villosa Roth], three grass & brassica (cereal rye [ Secale cereale ], forage radish [ Raphanus sativus var. longipinnatus ], and a cereal rye–forage radish mix), and one fallow control were established in northeast Louisiana to examine the influence of cover crop and urea fertilizer application rates (0, 235, 268, 302 kg N ha −1 ) on corn production and soil health under conservation tillage. Soil health indicators were measured each year following corn harvest and cover crop termination. The combination of cover crops and conservation tillage increased C and N enzyme activity over the 2 yr while arylsulfatase increased in the spring following cover crop termination only. Relative abundance of saprophytic fungi tended to be higher in legume plots compared to grass & brassica treatments. Overall, the application of N fertilizer at rates of 235 kg N ha −1 or higher decreased populations of AMF and concentrations of P, K, Ca, and Mg, but increased populations of Gram‐positive bacteria. The use of grass & brassica cover crops promoted K, S, Ca, and Mg availability, and supported greater abundance of total FAMEs and all FAME biomarkers except for saprophytic fungi.

Driving crop yield, soil organic C pools, and soil biodiversity with selected winter cover crops under no-till

Cover crops are widely used to increase the quantity of organic carbon (C) returned to the soil between cash crops. Roots play an important role in increasing soil organic carbon (SOC) levels, but the root traits that impact SOC likely vary widely among cover crop species and this variation has yet to be characterized. Recently, cover crop mixtures have expanded in popularity as a way to increase the diversity of cover crop benefits. We tested the quantity, quality and spatial distribution of roots in three monocultures and one mixture to increase our understanding of root trait variation among species, and how that variation impacts mixture design. Root cores were taken from in-row and between-row locations to a depth of 40 cm from cover crops planted after winter wheat during the 2016–2017 growing season. These samples were taken from a larger maize–soybean–winter wheat organic grain rotation experiment (2012–2018) located in central Pennsylvania, USA. Cover crop treatments included monocultures of triticale (X Triticosecale Wittmack cv. ‘Trical 815’), canola (Brassica napus L. cv. ‘Wichita’), crimson clover (Trifolium incarnatum L. cv. ‘Dixie’) and a five species mixture dominated by those three species. Additionally, cumulative carbon (C) inputs were assessed for the entire rotation to determine cover crop and cash crop root C contributions. Root biomass C vertical and horizontal distribution, root-to-shoot (R:S) ratio, and root carbon-to-nitrogen (C:N) ratio differed among cover crop treatments. Triticale produced more root biomass in the between-row space at all depth intervals compared to other cover crop treatments. The five species mixture had more total 0–5 cm and between-row 0–5 cm root biomass than crimson clover in spring 2017. Cover crop and cash crop roots increased cumulative C estimates by between 37% (crimson clover) and 46% (triticale) compared to shoot C alone. Cover crop root trait information can inform the belowground benefits from combining different species into cover crop mixtures. Crimson clover produced less root biomass, surface root biomass and between-row root biomass than other cover crop treatments. Therefore, combining crimson clover with grass and certain brassica species can improve total root biomass production, and root distribution compared to crimson clover monocultures, whereas reducing the C:N ratio of roots compared to grass species monocultures. The five species mixture led to greater cumulative carbon inputs compared to monoculture treatments, which was due to greater cover crop biomass C and its influence on the following corn crop's biomass C.

Core Ideas Soil organic C was two times greater with a no‐tillage rye cover crop system compared with conventional tillage (winter fallow) 17 yr after imposing treatments. A greater rate of C gain was observed with a no‐tillage mixed species cover crop system than with a rye cover crop in a 3‐yr period. Cotton lint yield and gross margins were less with a no‐tillage rye cover crop system than conventional tillage. Differences of lint yield and gross margins did not exist between the conventional tillage and no‐tillage mixed species cover crop treatments. Conservation tillage coupled with winter cover crops may reduce wind erosion in the North America Great Plains. Although farmers recognize the benefits of conservation practices, their decision to use cover crops is often based on the farm’s operating budget. In semiarid ecoregions dependent on irrigation for cotton (Gossypium hirsutum L.) production and limited groundwater resources, cover crops using stored soil moisture is a major concern. The objective of this research was to quantify the long‐term impacts of conservation tillage and cover crop use on C storage, cotton lint yield, and economic returns in monoculture cotton production. Conservation tillage and rye cover were implemented in 1998 and a mixed species cover of rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), radish (Raphanus sativus L.), and winter pea (Pisum sativum L.) was seeded in 2014 into half of the rye cover crop plots. Soil organic C in the top 15‐cm soil depth was increased by combining conservation tillage with winter cover crops. Cotton lint yield was less with no‐tillage and the rye cover when compared with conventional tillage in 2 of 3 yr. As a result, cotton lint revenue and gross margins of conservation tillage were on average less than conventional tillage.