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Distribution of Legumes along Gradients of Slope and Soil Electrical Conductivity in Pastures

Dep. of Agron., Iowa State Univ., Ames, IA 50011-1010

View larger version (12K): [in a new window]   Fig. 1. Stocking system (continuous, rotational, and nongrazed) effects on the relationship between the percentage of cover consisting of legumes and slope (%) in pastures at Rhodes, IA. The range of slope was divided into six classes within each of the four pasture replicates. Legume cover was averaged within each slope class of the four plots of each stocking system. Some slope classes were not represented within all four plots of each stocking system (n 24). Points and bars represent the mean ± standard error.

View larger version (30K): [in a new window]   Fig. 2. Nonlinear relationship between the percentage of legume cover and apparent soil electrical conductivity (ECa) standardized within pastures at Rhodes, IA. Soil ECa was measured on 28 July 2000 and 2 Aug. 2001 and standardized by year. Standardization involved dividing the range of absolute soil ECa values within each pasture replicate (n = 4) into 10 classes and ranking these from 0 to 9. Legume cover was averaged within each ECa class of the four plots of each stocking system. Some ECa classes were not represented within all four plots of each stocking system (n 40). Points and bars represent the mean ± standard error. Before fitting the nonlinear response curve, the legume cover data were log-transformed. Additional outliers, represented as points, within the rotational stocking system of year 2001, were removed before analysis.

View larger version (29K): [in a new window]   Fig. 3. Negative relationship between the percentage cover of smooth brome (Bromus inermis Leyss.) and apparent soil electrical conductivity (ECa) standardized within pastures at Rhodes, IA. Soil ECa was measured on 28 July 2000 and 2 Aug. 2001 and standardized by year. Standardization involved dividing the range of absolute soil ECa values within each pasture replicate (n = 4) into 10 classes and ranking these from 0 to 9. Smooth brome cover was averaged within each ECa class of four plots of each stocking system. Some ECa classes were not represented within all four plots of each stocking system (n 40). Points and bars represent the mean ± standard error.

View larger version (31K): [in a new window]   Fig. 4. Positive relationship between the percentage cover of reed canarygrass (Phalaris arundinacea L.) and apparent soil conductivity (ECa) standardized within pastures at Rhodes, IA. Soil ECa was measured on 28 July 2000 and 2 Aug. 2001 and standardized by year. Standardization involved dividing the range of absolute soil ECa values within each pasture replicate (n = 4) into 10 classes and ranking these from 0 to 9. Reed canarygrass cover was averaged within each ECa class of four plots of each stocking system. Some ECa classes were not represented within all four plots of each stocking system (n 40). Points and bars represent the mean ± standard error.