In water seeded rice, the field is continuously flooded.Water seeding takes advantage of that by establishing an early water covering to suppress weeds, but continuous flooding in water seeded rice culture encourages aquatic weeds, and when continuous flood is not maintained, it encourages semiaquatic weeds .Cover crops provide numerous environmental and weed suppression benefits. The physical and allelopathic effects caused by cover crops residue can be used to suppress the emergence of weed and reduce weed growth . Cover crop mixtures provide more effective weed suppression relative to monoculture cover crops because of complementarity function of cover crop species .Cover crop mixtures of cereals and legumes are expected to accumulate more biomass than single-species counterparts at similar seeding rates . The experiment site was planted with winter wheat and crimson clover as cover crop in fall 2015 . Above ground cover crop biomass were sampled in April, 2016. Each biomass samples were taken within one meter square area Figure 1.
Biomass of selected rice cultivars and weed biomass in respective rice cultivars.with six samples each from cover cropped Land and fallow land . Cover crop and weed species were separated from each samples and dried biomass of cover crop and weed species were measured . Cover crop was incorporated one month before rice sowing.In June 2016,vertical grow system fifteen rice cultivars were planted using randomized complete block design with four replications. Water seeded rice and flooding were used as method to control weeds. Seeds were put in the individual cloth bags for varieties and replications then soaked in the water overnight and kept in moisture for two days before planting . Soaked seeds were uniformly spread into each small plot.After third week of rice sowing, photographs of each rice plots was taken twice a week for visual scoring of plant stand rating and plot weed pressure of each rice plots and this process was continued till eighth week after rice sowing. Plant stand rating and plot weed pressure measured on each week was computed as average score for each rice cultivar.
Plant stand rating was measured at scale of 1 – 10 score,where 1 represents 10% plant stand and 10 represents 100% plant stand in a plot.Likewise, Plot weed pressure was measured at scale of 1 – 10 score, where 1 represents 10% plot weed pressure and 10 represents 100% weed pressure.Three rice varieties Jasmine 85, Rondo and Presidio were selected for rice biomass sampling 80 days after sowing. Biomass samples were taken from three quadrats each with 50 cm × 50 cm within rice plots. Dry biomass of rice and weed in respective rice plots were measured. Cover crops have higher impact on weed biomass . In this experiment, mixtures of crimson clover and winter wheat produced considerable reduction in weed biomass and increase in total biomass. Crimson clover as a leguminous cover crop provides more organic matter to soil and atmospherically fix Nitrogen to succeeding crop . Cover crops including crimson clover as mixture or monoculture can suppress weeds and improve yield, primarily due to biomass effects.
Likewise, legume cover crop provides weed suppression during active cover growth and just after cover crop termination . On the other hand, because of high C:N ratio in residues of cereal cover crops, the residue of winter wheat after termination can offer increased weed suppression for a relatively longer period of time as cover crop residues left on soil surface suppress weed emergence and growth due to reduced light transmittance and daily soil temperature enabling lower initial competition on following crop. This cover cropping trial is limited to study on effect of mixture of crimson clover and winter wheat on weed biomass during growing season and question about effects of this cover crop on weed suppression and crop yield in subsequent organic rice remain unanswered. However, mixture of crimson clover and winter wheat could be successfully be used as integrated weed control alternative in organic farms.The use of water seeding in this study to suppress weeds and produce economic yield for organic rice was not successful.