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Vertical tillage impacts on water quality derived from rainfall simulations

Douglas R. Smith, Elizabeth A. Warnemuende-Pappas
Soil & tillage research 2015 v.153 pp. 155-160
Glycine max, Zea mays, agricultural runoff, agricultural watersheds, ammonium nitrogen, atrazine, conservation practices, conventional tillage, corn, crop rotation, herbicide residues, losses from soil, nitrate nitrogen, no-tillage, nonpoint source pollution, nutrients, phosphorus, pollution load, rainfall simulation, risk, sediment yield, sediments, soybeans, surface water, water quality
Increasing soluble phosphorus (SP) loads to Lake Erie occurring around the same time as the implementation of no-tillage in the watershed has led to speculation that this important conservation practice is a primary cause of the SP loading. Thus, conservationists are interested in finding management practices that will minimize stratification of P, which may be common in no-tillage systems, while also minimizing erosion losses that result from conventional tillage practices. As no-tillage was marketed as a practice to decrease sediment and total P (TP) loads, it is important to examine adoption of future conservation practices for their impact on multiple resource concerns. This study was conducted to determine if a shallow vertical tillage practice was sufficient to minimize P, N and atrazine loading from long-term no-tillage fields in a corn-soybean rotation, while maintaining minimal erosion. Rainfall simulations (average intensity of 53mmh−1) were performed on no-tillage and vertical tillage plots (5×1m) sufficient to produce 30min of runoff. Runoff was collected every 2.5min, and analyzed for sediment and nutrients (NH4–N, NO3–N, total Kjehldahl N (TKN), SP and TP). Runoff was delayed by 17min using vertical tillage; however, the steady-state rate of runoff was significantly greater from vertical tillage compared to no-tillage. There were no significant differences for N from runoff (NH4–N, NO3–N, or TKN). There was a trend of slightly higher SP loads from vertical tillage than no-tillage. Total P losses were correlated with sediment, and were observed to be higher from vertical tillage than no-tillage. The primary advantage that vertical tillage has with respect to nutrient losses is in delaying runoff initiation, however this effect could be nullified in subsequent runoff events. If P loading to surface waters is the primary concern, it would appear from the data presented in this study that vertical tillage may not be an appropriate practice, and in fact may impose greater risks due to greater erosion and associated TP losses.