Water, sediment, and metolachlor transport differences between wide- and narrow-row cotton production systems

Abstract

Planting cotton (Gossypium hirsutum [L.]) in narrow rather than wide rows could reduce erosion and off-site agrochemical transport, but this hypothesis needs to be evaluated under midsouth cropping conditions. Field studies were conducted near Stoneville, Mississippi, on a Dundee silty clay loam in 2006 and 2007 to evaluate sediment, water, and metolachlor (2-chloro-N-[2-ethyl-6-methylphenyl]-N-[2-methoxy-1-methylethyl] acetamide) loss in narrow (38 cm [15 in]) and wide-row (102 cm [40 in]) cotton. One day after a postemergence metolachlor application over four- to six-leaf stage cotton, 60 mm h⁻¹ (2.4 in hr⁻¹) of simulated rainfall was applied until 25 min of runoff was generated per plot. Sediment loss, regardless of year, was at least 38% lower from narrow-row than wide-row cotton. Depending on year, planting cotton on narrow rows either had no effect or reduced cumulative runoff by 25%, compared to the wide-row system. Cumulative metolachlor loss was 27% higher in narrow-row relative to wide-row cotton in 2006, but the trend was reversed in 2007. Our results indicate that nearly flat seedbeds in narrow-row systems can reduce sediment loss relative to wide-row cotton planted on slightly raised seedbeds. Moreover, planting cotton in narrow rows rather than wide rows may reduce the loss of metolachlor applied postemergence if cumulative runoff is reduced in the narrow-row system and factors governing mixing-zone pesticide concentrations are similar between row spacings, primarily canopy coverage, and antecedent soil moisture conditions.