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Long-Term Trends in Nitrous Oxide Emissions, Soil Nitrogen, and Crop Yields of Till and No-Till Cropping Systems

W.K. Kellogg Biological Station and Department of Crop and Soil Sciences, Michigan State University, Hickory Corners, MI 49060. A.S. Grandy, current address: Department of Geological Sciences, University of Colorado, Boulder, CO 80309-0399

View larger version (36K): [in a new window]   Fig. 1. (a) Gravimetric soil water content in till and no-till treatments between 1989 and 2002. Letters indicate the crop harvested in that year: c, corn; s, soybean; w, wheat. * Indicates statistically different responses within a year (P < 0.05) determined by slicing of the treatment by year interaction. (b) Difference between conventional till (Ct) and no-till (Nt) normalized by the overall mean soil water content for that year. Points greater than zero indicate a till response greater than a no-till response. Year means were significantly different (P < 0.05) and separated using Tukey's test. Linear regression analysis showed no trends in soil water concentration (P < 0.05) across all crops and years or for specific crops over time.

View larger version (24K): [in a new window]   Fig. 2. (a) Soil NO3– concentration in till and no-till treatments between 1989 and 2002. Letters indicate the crop harvested in that year: c, corn; s, soybean; w, wheat. * Indicates statistically different responses within a year (P < 0.05) determined by slicing of the treatment by year interaction. (b) Difference between conventional till (Ct) and no-till (Nt) normalized by the overall mean NO3– concentration for that year. Points greater than zero indicate a till response greater than a no-till response. Year means were significantly different (P < 0.05) and separated using Tukey's test. Linear regression analysis showed no trend in NO3– concentration (P < 0.05) over across all crops and years; NO3– concentrations in wheat significantly increased in till relative to no-till over time [normalized NO3– difference = –15 650 + 7.84 (year); r2 = 0.44; n = 3 yr]. Mean ± SE.

View larger version (25K): [in a new window]   Fig. 3. (a) Soil NH4+ concentrations in till and no-till treatments between 1989 and 2002. Letters indicate the crop harvested in that year: c, corn; s, soybean; w, wheat. * Indicates statistically different responses within a year (P < 0.05) determined by slicing of the treatment by year interaction. (b) Difference between conventional till (Ct) and no-till (Nt) normalized by the overall mean NH4+ concentration for that year. Points greater than zero indicate a till response greater than a no-till response. Year means were significantly different (P < 0.05) and separated using Tukey's test. Linear regression analysis showed no trends in soil NH4+ concentration (P < 0.05) across all crops and years or for specific crops over time.

View larger version (19K): [in a new window]   Fig. 4. (a) Soil N2O emissions in till and no-till treatments between 1991 and 2002 (no data available for 1995). Letters indicate the crop harvested in that year: c, corn; s, soybean; w, wheat. * Indicates statistically different responses within a year (P < 0.05) determined by slicing of the treatment by year interaction. (b) Difference between conventional till (Ct) and no-till (Nt) normalized by the overall mean N2O emissions for that year. Points greater than zero indicate a till response greater than a no-till response. There was no detectable difference between years based on a Tukey's test. Linear regression analysis showed no trend in N2O emissions (P < 0.05) across all crops and years; emissions from soybean significantly increased in till relative to no-till over time [normalized N2O difference = 31 210 – 15.7 (year); r2 = 0.48; n = 4 yr]. Mean ± SE.

View larger version (30K): [in a new window]   Fig. 5. (a) Crop yields in till and no-till treatments between 1989 and 2002. Letters indicate the crop harvested in that year: c, corn; s, soybean; w, wheat. * Indicates statistically different responses within a year (P < 0.05) determined by slicing of the treatment by year interaction. (b) Difference between conventional till (Ct) and no-till (Nt) normalized by the overall mean crop yield for that year. Points greater than zero indicate a till response greater than a no-till response. Year means were significantly different (P < 0.05) and separated using Tukey's test. Linear regression analysis showed no trend in crop yields (P < 0.05) across all crops and years; wheat yields significantly increased in till relative to no-till over time [normalized yield difference = –5980 + 3.00 (year); r2 = 0.40; n = 3 yr]. Mean ± SE.