Effects of sunflower on soil quality indicators and subsequent wheat yield

Sunflower (Helianthus annuus L) production has increased in the central Great Plains, but Little is known regarding how this crop will affect surface biomass production, various soil quality indicators, and subsequent winter wheat (Triticum aestivum L.) yields. We hypothesized that sunflower production was reducing soil quality relative to other summer crops because of the need for tillage to incorporate herbicide, thus reducing surface residue. Our objectives were to quantify on a Weld silt loam (fine, smectitic, mesic, Aridic Argiustolls) surface crop residue levels immediately after seeding wheat, subsequent wheat grain yield, soil organic carbon (SOC), particulate organic matter-carbon (POM-C), aggregate stability, and texture in 3- or 4-year rotation. A randomized complete block design with three replications was used to compare rotations both with and without sunflower. Our data showed 13% lower SOC content and 26% lower POM-C content at the 0- to 5-cm depth in rotations with sunflower versus those without. At the 5- to 15- cm depths, differences were not significant (P < 0.05). Crop residue by mass was 5 times lower and wheat yields 33% lower in rotations with sunflower, but no differences were measured for wind erodible aggregates or texture. Tillage to incorporate herbicides for sunflower and low amounts of residue after sunflower in the 3-year rotation contributed to reduced SOC and POM-C, decreased residue at wheat planting, and reduced wheat yield. If sunflower is to be included in the central Great Plains, efforts should be made to use no-till production practices and 4-year rotations with corn.