Nutrient and sediment losses in surface runoff can be high that may cause water pollution and can represent a significant portion of total farm costs in irrigated cropped field. A field study with cotton (Gossypium hirsutum, L.) was conducted in production farms to quantify soluble nutrients and sediments losses from surface runoff associated with crop management practices: Conventional system, irrigated (CTIR), Conservation system, irrigated (FTIR), Conventional, rainfed (CTRA), and Conservation, rainfed (FTRA). Lint yields and concentrations of NH₄-N, NO₃-N, NO₂-N, dissolved P, soil sediments, other water quality metrics in irrigation runoff water were measured in all management systems. Mean lint yields ranged from 792 to 1,774 kg ha^-1 and were not significantly affected by irrigation or conservation practice (P = 0.179 – 0.371). The intensity and chemical form of nutrient losses were primarily controlled by volume of water runoff and agronomic practice. Across all systems, average concentrations of N in the runoff were <4.6 mg L^-1 and dissolved P were <0.58 mg P L^-1 and were affected by amounts of runoff water. Average nutrient concentrations in surface runoff were significantly higher in Conservation systems than in Conventional system. Water pH, specific electrical conductivity, alkalinity and hardness were within the levels that characterize irrigation water and less likely to impair pollution in waterways. Soil sediment concentrations (SSC) and total suspended solids (TSS) ranged from 27 to 1,831 mg sediments L^-1 and 1.4 to 1,555 mg L^-1, respectively. Sediment losses were reduced by 43 to 59% in Conservation system compared to Conventional systems. On average, the levels of soluble nutrients measured during field outflow were relatively small and within the range of values observed in agricultural fields. Results of this study show continuous measurements of runoff water quality are needed to better assess multiple benefits of implementing conservation management practices in the region.

Richard Woodruff

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