Effects of spring top-dressing phosphorus on winter wheat (Triticum aestivum L.)

Three repetitions of fifteen treatments were laid out on a cooperator's winter wheat field in spring, following the fall planting.The cooperator was asked to drill in P fertilizer at seeding in the fall and to manage the planting as he normally would After the plots were laid out, plant and soil samples were taken and the fertilizer was spread.Soil temperatures, precipitation, and evaporation measurements were made throughout the growing season.Eighty-one sites were considered, 40 from the 1970 and 41 from the 1971 growing seasons.For both years the top-dressing resulted in an overall increase in yield of 2.1 bushels/acre and an overall decrease in protein percentage of 0.05%.Of the sites 69.1% showed an average yield increase of 3.6 bushels/acre; 4.9% showed no change; and 26.5% showed an average decrease of 1.5 bushels/acre.Of the sites 30.9% showed an average increase in percent protein of 0.48%; 25.9% showed no change; and 43.2% showed an average decrease of 0.45%.Simple correlations were run on change of yield and of percent protein versus percent P in the plant tissue collected at growth stage 2 to 3 (Peekes' stage), ppm P (0-6") im the soil, ppm P (6"-12") in the soil, and ppm P (0-12") in the soil.For the combined data of 1970 and 1971 the highest correlation was found between change of grain yield versus ppm P (0-6") in the soil (r = -0.256).The lowest correlation was found between change of percent protein versus ppm P (6"-12") in the soil (r = +0.070)Of all 24 correlations only two were found to be significant, change of grain yield versus ppm P (6"-12") in the soil, 1971 (r = -0.470),and change of grain protein percentage versus % P in plant tissue at Feekes stage 3, 1970 (r = -0.469)._______ppm P (6"-12") An expression, ppm p (0-6") -ppm P (6"-12"), increased the significance of the 1971 data to the 2% level; unfortunately it was poorly correlated with the 1970 data and the combined data had an insignificant r value.Because the expression was only qualitative, it was proposed that it should be multiplied by the ppm P (0-12") in the soil in order to make it quantitative.This new expresssion increased the r value of the 1971 data to 0.622, more than highly significant, and also increased the 1970 correlation.For both years combined the correlation was significant at the 3% level.Another significant correlation was found between percent P in the plant tissue at the two leaf stage versus the ppm P (0-6") in the soil.In presenting this thesis in partial fulfillment of the requirements for an advanced degree at Montana State University, I agree that the Library shall make it freely available for inspection.