10 



CONSERVATION RESEARCH REPORT 5, U.S. DEPT. OF AGRICULTURE 



Table 5. — Effect of residual nitrogen and previous moisture levels on yield of hybrid grain sorghum inl960 



Yield Data 



Fertilizer treatment 1 



Yields at moisture treatment 2 of — 



Average 

 for all 



moisture 

 levels 



No. 



Nitrogen 



P 2 0, 



2^6 



M, 



M, 



M, 



M 4 



M. 



M B 



Fi- 



F 2 - 

 F 3 - 

 F 4 - 

 F 5 - 

 F,- 



Lb. /acre 

 240 

 

 60 

 120 

 240 

 240 



Lb. I acre 

 

 30 

 30 

 30 

 30 

 60 



Lb. I acre 

 6,486 

 5,220 

 6,519 

 6, 767 

 7,386 

 7,654 



Lb. I acre 

 6,878 

 4,026 

 5, 031 

 5, 174 

 6,584 

 7,047 



Lb. /acre 

 6,825 

 3, 354 

 3,967 

 4,940 

 7,478 

 7,360 



Lb. /acre 

 6,480 

 3,276 

 4,006 

 4, 561 

 6,741 

 5,938 



Lb. /acre 

 6, 506 

 3, 132 

 3,576 

 4,372 

 6,297 

 6,584 



Lb. /acre 

 6, 591 

 3,622 

 4, 144 

 4,633 

 7,393 

 6,055 



Lb. /acre 

 6,628 

 3,772 

 4,541 

 5,075 

 6,980 

 6,773 



Average. 



6,672 



5,790 



5,654 



5, 167 



5,078 



5,406 



5,628 



Analysis of Variance 



Component 



Moisture (M) 

 Error (a)-_ 



Fertilizer (F) . 



M X F 



Error (b)__ 

 Total- 



Mean squares 3 



8, 070, 671** 

 469, 260 

 43, 551, 814** 



1, 039, 166** 

 329, 169 



1 Applied in 1956, 1958, 1959. 



2 1956, 1957, 1958, 1959; adequate moisture supply in 1960. 



3 **= Significant at the 1-percent level. 



The results of this study illustrated the primary 

 interaction between nitrogen and soil moisture 

 levels; i.e., when available soil moisture limited 

 production, applied nitrogen requirements were 

 reduced, and when soil moisture was not the 

 limiting factor, applied nitrogen requirements 

 were greater to obtain good yields. Also, when 

 sufficient water was applied for average yields of 

 about 7,000 lb. /acre, the production without nitro- 

 gen fertilizer decreased the second year this soil 

 was irrigated and continued to decrease as the 

 reserve of available N was depleted. 



In 1960, the experimental site was irrigated 

 uniformly to evaluate the effects of residual nitro- 

 gen and previous moisture levels on yield (table 

 5). The 1960 yields on the F 2 , F 4 , and F s treat- 

 ments were inversely related to amount of irriga- 

 tion water and directly related to the amount of 

 nitrogen applied during the previous 4 years. 

 No significant yield response to phosphorus 

 occurred. 



Yield of grain sorghum was not materially 

 affected by soil moisture level if the average 

 available soil moisture in the 0- to 4-foot depth 

 just prior to irrigations was more than 30 percent. 

 Yields from the F 5 fertilizer treatment (and F 4 

 if the yield on the F 4 was not more than 2 or 3 

 percent less than the F 5 yield) on the M 3 , M 4 , and 

 M s moisture levels were used to evaluate this 



effect (fig. 4). The curve in figure 4 was fitted 

 by eye. Yields were greatly reduced when the 

 average available soil moisture level was less than 

 25 percent before irrigations. A similar pattern 

 of reduction in yield as influenced by the soil 

 moisture level reached prior to irrigation was 

 observed by Musick, Grimes, and Herron on 

 Richfield soil at Garden City, Kans. {12). 



8,000 

























i 



• 



• 



i 



• 



i 



• 



• • 







6,000 





* 



X 



/ 



















• 



• 













4,000 



s 



1 



/• 



• / 

















- 















1 





20 40 60 



AVAILABLE SOIL MOISTURE (PERCENT) 



80 



Figure 4. — Available soil moisture in the 0- to 4-foot depth 

 prior to irrigations can be depleted to an average of 30 

 to 40 percent before yields are materially reduced. 



