Water quality effects of cover crop implementation or tillage in a long-term no-till wheat system

Authors: Mubvumba, Partson; DELANE, PAUL - Texas A&M Agricultural Experiment Station

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2022
Publication Date: 10/12/2022
Citation: Mubvumba, P., Delane, P.B. 2022. Water quality effects of cover crop implementation or tillage in a long-term no-till wheat system. Soil & Tillage Research. 225. Article 105547. https://doi.org/10.1016/j.still.2022.105547.
DOI: https://doi.org/10.1016/j.still.2022.105547

Interpretive Summary: Agriculture anthropogenic nitrogen and phosphorus are major surface and subsurface water pollutants. Integrated agriculture systems are characterized by continuous cultivated monoculture combined with grazing. Grazing can increase soil compaction and subsequently decrease infiltration exposing soil to erosion. Texas A&M University and USDA Crop Production Systems Research Unit in Stoneville conducted a study to characterize soil water quality following cover crops under continuous wheat, grazing, tillage, and no-till practices. Treatments evaluated included 1) conventional tillage without a cover crop (CT); 2) no-till without a cover crop (NT); 3) no-till with a cover crop (NTC); and 4) no-till with a grazed cover crop (NTCG). Cover crops treatments NTCG and NTC significantly reduced amount of runoff compared to no cover crops. Converting 12-year-old NT to CT resulted in CT reducing infiltration and increasing runoff sediment and total P loads compared to NT with or without cover crops. Tilling the soil increased amount of P lost to the environment and had more deleterious effects compared to grazing. Cover crops improved water quality but increased SRP and DOC discharged into the environment.

Technical Abstract: Agricultural anthropogenic nitrogen (N) and phosphorus (P) continue to be major surface and subsurface water pollutants in developed countries. Integrated crop-livestock systems in the semi-arid Texas Rolling Plains are characterized by continuously cultivated monoculture combined with grazing. Improperly managed grazing can increase soil compaction, and subsequently, decrease infiltration, which leaves the soil exposed to erosion. Grazing is therefore of paramount importance to water quality. Cover crop (CC) use improves soil ecosystem services and functions. The objective of the current study was to characterize soil water quality following CC under continuous wheat (Triticum aestivum), grazing, tillage, and no-till practices under a typic Haplustepts, Rotan clay loam soil type. Treatments evaluated include 1) conventional tillage without a CC (CT); 2) no-till without a CC (NT); 3) no-till with a CC (NTC); and 4) no-till with a grazed CC (NTCG). Portable rainfall simulators were used to assess surface runoff water quantity and quality after CC implementation in a long-term no-till continuous wheat system. Cover crop treatments, both grazed and un-grazed, reduced the amount of runoff by 4–6 times compared to no CC treatments (NT and CT). Converting 12-year-old NT to CT reduced infiltration by at least 43 % and increased runoff by 58 % compared to long-term NT. Consequently, total solids load and concentration for CT were 4–14 times greater than all NT treatments (NT, NTC, NTCG). Conventional tillage (CT) also increased total P loads and concentrations by 2–11-fold compared to all NT treatments (p < 0.05). Rainfall events occurring within three weeks after CC termination resulted in about 6 times greater soluble reactive P (SRP) (except NTCG) and about 2–3 times greater dissolved organic C (DOC) concentrations from CC treatments than non-CC treatments, although this was not observed for subsequent runoff events. Tilling the soil had more deleterious effects compared to flash grazing CC. Adopting NT, either alone, or long-term in combination with CC (either flash grazed or un-grazed) are potentially sustainable viable practices in semiarid regions that can reduce environmental contamination.