18 



Several reports indicated ^hat soil organic matxer changes with 

 continuous and with intensive cropping systems ('^0, 98» HI, 114, 166). 

 The changes can be an increase or decrease depending on the crop species, 

 tillage level, and fertilizer level. For example, rotation of spinach 

 ( Spinacea oleracea L.) and cabbage with green manures such as alfalfa 

 ( Medicago sativa L. ) , timothy ( Trifolium pratense L. ) , red clover 

 ( Lolium multiflorum L.), and sweet clover ( Melilo^us indica L.) resulted 

 in higher carbon and !! in the soil than rotations with continuous 

 vegetables (40). Continuous cropping of corn for thjree consecutive 

 years followed by four seasons of cultivation wi-h cropping sequences 

 of corn-corn-cowpea, pigeon pea-corn, soybean-soybean, corn-soybean, 

 and cowpea-cowpea resulted in greater decline in organic matter than 

 the no-tillage plots (98j . The rate of decline was much higher under 

 co^rpea and soybean where smaller amounts of crop residues were produced 

 than with corn. Standifer and Ismail (15^) also found that organic 

 matter was lower in conventional tillage plots than in min.imum tillage 

 plots after four years of multiple cropping crimson clover ( Trifoliu,m 

 incarnat-'jm L.), sweet corn, and cowpea. Stevenson (15^; reported tha.t 

 rotations including legumes maintained higher organic matter contents 

 than continaous cropping with non-leguminous crops. 



A combination of m.oderate manuring and medi'jm rates of complete 

 fertilizer application is most effective in producing high yields of 

 vegetables without depleting soil fertility (111). In a continuous 

 corn-green manure crop rotation, Thompson and Robertson (160) found 

 that organic matter in the high fertilized corn plots was more than in 

 the unfertilized plots. In India, Havanagi and Mann (7I) reported that 



