Impacts of conservation tillage on water quality and soil health characteristics under furrow irrigation
Date
2017
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Abstract
Furrow irrigation-induced sediment and nutrient loss continues to be a serious problem in the Western States of the US. Sediment and nutrients in runoff can eventually be discharged into streams and rivers impairing water quality, causing adverse effects on the environment and reducing soil productivity over time. Continuous intensive tillage along with excessive sediment and nutrient loss ultimately lead to the degradation of soil quality. We hypothesize that conservation tillage under furrow irrigation can reduce the sediment and nutrient losses in surface runoff as well as improve soil quality parameters. The objectives of this research are to compare two conservation tillage treatments, minimum tillage (MT) and strip tillage (ST), to a traditional conventional tillage (CT) system under furrow irrigation and understand the impacts of these practices on annual sediment and nutrient concentrations and loads from irrigation and storm events. We quantified total suspended solids (TSS), total Kejdahl nitrogen (TKN), nitrate (NO3), ammonium (NH4), total nitrogen in aqueous solution (TNa), total phosphorus (TP), dissolved reactive phosphorus (DRP), and total soluble phosphorus (TSP) loads from irrigation runoff over two growing seasons for the three treatments. Relative to CT, conservation tillage reduced TSS loads by 84% and 88% in 2015 and by 98% and 87% in 2016 for MT and ST, respectively. In 2015, TKN was reduced by 80% and 86% in MT and ST respectively when compared to CT. Total P was significantly higher in CT, with an 87% load reduction under MT and ST in 2015 and an 85% load reduction under MT in 2016. Total P concentration (mg L-1) correlated well with TSS concentrations (g L-1) (R2 = 0.72, P < 0.001). Total soluble P loads were significantly higher in the CT treatment when compared to the conservation treatments in the 2015 season. Reduced tillage and residue management in the conservation treatments improved irrigation flow parameters such as reduced runoff. The conservation treatments had a greater impact on sediment-bound than soluble nutrients largely due to surface residue reducing erosion in the furrows. Results show that reduced tillage and residue management are an effective best management practices (BMPs) in sediment and nutrient abatement in irrigation and storm runoff. Furrow irrigation is still practiced in 40% of all irrigated lands in Colorado and it is expected to continue across much of the State. Under furrow-irrigated systems, CT practices are common, but such practices can degrade soil quality. The project sought to examine the effects of conservation tillage on soil health at a production scale, understand relationships between soil parameters, and to evaluate the economic feasibility of conservation practices. Soil biological, physical, and chemical parameters were evaluated during the fifth and sixth years of a study (2015 and 2016) comparing two different management systems, MT and ST, verses CT (the control). Measurements included Active C (POXC), macrofauna diversity and abundance, aggregate stability, infiltration, and residue cover. POXC was significantly higher for MT when compared to CT and ST. Results from both years suggest that conservation treatments increased macrofauna abundance, especially earthworms, and diversity (richness) relative to the control. Aggregate stability was significantly higher in the conservation treatments for 2015, but not in 2016. Infiltration rates in the ST treatment was 18% higher when compared to CT. Residue cover was positively correlated with earthworm abundance while earthworm abundance was positively correlated with aggregated stability and infiltration. When comparing economic cost, and returns among systems, ST and MT treatments had a 39% and 32% greater net return when compared to CT plots. These preliminary results show potential for conservation tillage under furrow-irrigation to improve soil quality parameters as well as increasing net income.
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Subject
soil health
total phosphorus
water quality
soil quality
furrow irrigation
total suspend solids