Effect of Nitrogen and Phosphorus Fertilization on Forage Yield and Quality of Annual Ryegrass in Southwest Texas, 1999
This study has generated three years of excellent ryegrass yield response data to N and P fertilization in southwest Texas. This information has been used extensively in developing newsletters, articles, and educational programs. The last phase of this work involved analyzing N and P soil test data from samples taken in the final year of the study to determine relationships to ryegrass yield. Data were available from four different P extraction methods for samples taken shortly after the last harvest of the third year. The levels of N and P applied annually were also included in the statistical models seeking to explain sources of variation in yield. The N by P interaction effect was very strong, forcing examination of each level of N and P individually.
Ryegrass yield was strongly related to P fertilization. Generally, the amount of P fertilizer applied explained 90 percent or more of the variation in ryegrass yield within each level of N fertilization. Soil P level across the four extraction methods was only weakly correlated with ryegrass yield. The failure of soil P to influence yield is probably related to the high P fixing capacity of the alkaline clay soil. Within each level of P fertilization, the amount of N applied explained 80 to 90 percent of the variation in yield. Soil test parameters did not significantly affect yield when examined within P application rates. TX-35F