Optimization of water potential and nutrient levels for Kentucky bluegrass – white clover mixture on acidic soils

In Appalachian grasslands, soil acidity and highly variable topography are the main factors negatively affecting the productivity. There was a need to develop a yield response function and determine nutritive value of grasslands. Soil factors such as water potential (WP), soil pH, nitrogen (N) and phosphorus (P) levels are highly variable across mountainous grasslands. A greenhouse study was conducted to study the effects of WP, soil pH, N, and P levels on the herbage production and nutrient concentration of Kentucky bluegrass (Poa pratensis L.) and white clover (Trifolium repens L.) mixed sward. Central composite rotatable design was used to conduct this pot study. The effects of two levels of WP and five levels each of pH, N, and P fertilizers were evaluated. WP, pH, N and P levels as their interactions WP x pH, WP x N, pH x N, and N x P explained a significant part of sward accumulation in our trial. The importance of the different factors in explaining herbage accumulation variations was, in decreasing order, WP > pH > WP x pH > WP x N > P > N > N x P > pH x N. Optimum conditions for the production of bluegrass and white clover crop system were predicted, from this pot experiment, as follows WP of -422 to -171 kPa, 5.5 to 6.1 soil pH, 50 to 68 N mg.kg-1, and 38 to 40 P mg.kg-1. Concentration (%) of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were determined in shoot tissue to understand the impact of the different factors on nutrient content of forage. WP and soil pH had shown significant influence on concentration of all elements. Effects of soil pH and N level had significant effect on N concentration in plant tissue. Plant P concentration was significantly influenced by interaction of P level with WP and soil pH. Yield response function of Kentucky bluegrass and white clover mixture from this case study should be evaluated in field trials to obtain practical significance. Effects of WP, soil pH, and N and P levels on herbage accumulation of grasslands and nutritive value should be understood to harmonize productivity across this undulating landscape.