The effects of tillage systems and weed control methods on some physical and chemical properties in corn-wheat crop rotation

Despite the many benefits of tillage to crop establishment and production in the past, new herbicide and minimum-tillage management systems have drastically changed today's methods of crop production. Although tillage systems are used to increase soil porosity, they are a short-term solution that has negative consequences on surface soil structural stability, surface crop residue, and surface soil organic carbon, which are critical features that control water infiltration and subsequent water transmission and storage in soil. Physical and chemical properties of soil such as organic matter of soil is a key attribute of quality that affects water infiltration and soil aggregation. The use of conservation tillage along with the application of appropriate management methods such as conservation of residues, the use of proper rotation and weed control caused to stabilize the particles of soil, prevent the destruction of soil structure and increase soil organic matter. Therefore, changing the method of tillage systems from conventional to conservation, especially in crop rotation cycles, is inevitable. Our objectives were to summarize these findings and present additional information with particular emphasis on changes physical and chemical characteristics in different soil depths due to adoption of conservation tillage in corn-wheat crop rotation.

The present study was performed to investigate tillage systems (4 levels including ZT-ZT: Zero Tillage-Zero Tillage; ZT-CT: : Zero tillage-Conventional Tillage; CT-CT: Conventional Tillage-Conventional Tillage and CT-ZT: Conventional Tillage-Zero Tillage) and 4 levels of weed management (including W1: Control; W2: Post-emergence Nicosulfuron herbicide + hand weeded in cultivation of corn and post-emergence Metribuzin herbicide + hand weeded in cultivation of wheat; W3: Pre-emergence Atrazine + post-emergence Nicosulfuron herbicides in cultivation of corn and post-emergence Clodinafop + post-emergence Bromoxynil+MCPA herbicides in cultivation of wheat; W4: Wheat residues as a mulch + post-emergence Nicosulfuron herbicide in cultivation of corn and corn residues as a mulch + Metribuzin herbicide) on some physical and chemical properties of soil depths (D1: 0 -15 and D2: 15-30 cm) in corn-wheat rotation during the 2021-22 croping year in the farms of Shavur Agricultural Service Center of Shush city was implemented as a split-factorial in the form of a randomized complete block design with three replications and 96 samples.

The results showed that interaction of the studied treatments significant effects of the all studied traits except for soil pH. The minimum of soil bulk density was observed in conventional tillage-zero tillage × Wheat residues as a mulch + post-emergence Nicosulfuron herbicide in cultivation of corn and corn residues as a mulch + Metribuzin herbicide as weed management treatment × 0-10 cm soil depths treatment with an average of 1.390 g/cm3, also, the highest hydraulic conductivity of the soil was obtained in conventional tillage-conventional tillage × pre-emergence Atrazine + post-emergence Nicosulfuron herbicides in cultivation of corn and post-emergence Clodinafop + post-emergence Bromoxynil+MCPA herbicides in cultivation of wheat × 0-15 cm soil depths treatment (with an average of 0.994 cm/h). The highest amount of organic matter (with an average 0.771 percent) and phosphorus and potassium elements was achieved in zero tillage-zero tillage × wheat residues as a mulch + post-emergence Nicosulfuron herbicide in cultivation of corn and corn residues as a mulch + Metribuzin herbicide × 0-15 cm soil depths treatment (with averages of 13.96 and 234.7 mg/kg, respectively). Interaction effects results (tillage system × sampling depth) indicated that highest amount of total nitrogen was achieved in the zero tillage-zero tillage (ZT-ZT) on soil surface layer (0-15 cm sampling depth) with an average 122.0 kg / ha with an increase of 40.1% compared to the other treatment such as zero tillage-conventional tillage (ZT-CT), conventional tillage-conventional tillage (CT-CT) and conventional tillage-zero tillage (CT-ZT) and soil substrate (15-30 cm sampling depth, with an average of 0.87 kg/ha). In addition, the preservation of residues in the form of mulch and the use of post-emergence Nicosulfuron and Metribuzin herbicides led to maintaining the balance of soil pH in the corn-wheat rotation.

Steady-state soil chemical and physical properties was greater under zero tillage than under conventional tillage as a result of soil structural improvements associated with surface residue accumulation and lack of soil disturbance. In addition, our data indicate that conservation tillage along with the application of crops residues in corn-wheat crop rotation is a viable management strategy to improve soil quality in the warm, semiarid region of Khuzestan Province. This strategy could lead to high production, minimal negative environmental impacts, and a socially acceptable farming system. Therefore, the use of previous crop residues in tillage systems will have a positive effect on improving the physical and chemical properties of the soil.