LEGUMES AXD GRASSES 



21 



Zook and Weakley (86) reported 

 on crop-rotation and tillage experi- 

 ments at North Platte for 1907-34 

 (table 12). Annual precipitation 

 averaged 18.9 inches. 



Their data on responses of winter 

 wheat immediately after green- 

 manure fallow and ordinary fallow 

 and 3 years afterward are presented 

 (table 13). 



They found that yields of winter 

 wheat immediately after green- 

 manure fallow averaged lower than 

 those after ordinary fallow. Rye 

 and peas for green-manure fallow 

 were plowed in May and June, 

 respectively, and the land was 

 fallowed the rest of the year. 

 Ordinary fallow was tilled as soon 

 as spring weed growth started. 

 Part of the moisture used to produce 

 the green-manure crops was stored 

 in the clean fallow. This addi- 

 tional moisture accounted for the 

 higher wheat yields after fallow 

 than after the green-manure crops. 

 The greater yield after rye com- 

 pared with peas was owing to more 

 moisture being conserved by the 

 earlier plowing date for rye. 



However, 3 years later, they 

 found that winter wheat yields after 

 green manures were slightly higher 

 than those after ordinary fallow. 

 Moisture differences had been equal- 

 ized by the intervening crops. 

 Differences in favor of green ma- 

 nures were greatest when the yields 

 were highest. 



Another experiment by Zook and 

 Weakley (86) showed the effects of 

 green manuring on yields of winter 

 wheat grain and straw. For 10 

 years one plot was clean fallowed 

 and a second plot was seeded to rye 

 each year and plowed under for 

 green manure. Winter wheat was 

 grown continuously on these plots 

 for the following 12 years. The 

 average yield of straw was 44 per- 

 cent higher on the green-manure 

 plot than on the fallowed plot. 

 Average yields of grain were the 

 same. Increased grain yields on the 

 green-manure plot in years of 

 favorable moisture were offset by 

 decreased yields in dry years when 

 the stimulated early growth of 

 straw on the green-manured soil 

 exhausted soil moisture before the 



Table 13. — Average yields of winter wheat immediately after and S years 

 after ordinary fallow and green-manure fallow, North Platte, Nebr., 

 1912-34 l 





Average yield, per acre, of winter wheat 

 for — 



Cropping treatment 



1912-34 



8 high- 

 yielding 

 years 



8 low- 

 yielding 

 years 



Immediately after: 

 Ordinary fallow 



Bushels 



29. 1 

 27.9 



25.8 



16.4 

 17.7 

 17.4 



Bushels 



Bushels 



Rve green-manure fallow 







Pea green-manure fallow 







3 years after: 



Ordinary fallow 



31.5 

 34.3 

 36.3 



13.0 



Rve green-manure fallow. 



13.9 



Pea green-manure fallow _ 



10.8 







Data from Zook and Weakley (86) . 



