4 6 



NUTRIENTS APPLIED 



U. S. DEPARTMENT OF AGRICULTURE 



NEG. 59 (3)-2651 AGRICULTURAL RESEARCH SERVICE 



Figure 2. Model of yield response curve. 



operations (table 2). Production of hay per acre increased until 240 pounds 

 of nitrogen had been applied. The larger amounts applied - 320 and 640 

 pounds - did not actually increase production of hay per acre, but the crude 

 protein content of the hay increased at these higher rates of nitrogen. Uti- 

 lizing the research work of Spillman 3/ and others, a curve was fitted to 

 the yield data relative to production responses to nitrogen. The estimated 

 values obtained are included in table 2 under the column headed "Calculated 

 yield. " 



The equation used in determining the calculated yield is based on a large 

 number of experiments, and in conjunction with the data obtained by Willhite 

 and Rouse, it gives a better idea of expected yields from varying nitrogen 

 applications than does the arithmetic average of the original data. For this 

 reason, the calculated yields rather than the actual averages are used in 

 later discussions. 



While calculated or averaged yields give one a better idea as to what one 

 can expect on an average, they do not necessarily reflect what one will obtain 

 on any specific meadow or in a particular year. Figure 3 approximates the 

 individual ranch production response curves to nitrogen applications that are 

 found in table 2. It is evident from these production response curves that 

 there is no one most profitable nitrogen application rate applicable to all 7 

 ranches. 



3/ Spillman, W. J. Use of the nJxponential Yield Curve in Fertilizer 

 Experiments. U. S. Dept. Agr. Tech. Bui. 348, 67 pp. 1933. 



