Effect of residue management and fallow length on weeds and rice yield

Abstract

Reduced fallow length in slash‐and‐burn rice (Oryza sativa L.) production systems of northern Laos increased weed pressure, labour requirement and the need for soil and moisture conservation. On‐farm and on‐station studies and on‐farm surveys were used to evaluate the effect of residue management and cropping intensity on weed population, rice yield and nematode density. Residue loads were 2.3–4.4 t ha−1 after a rice crop and 9.5 t ha−1 after 1 year of fallow. Compared with farmers' traditional burning of crop and weed residues, mulching reduced rice yield by 43% in one out of four comparisons and increased weed biomass by 19–100%. Compared with continuous rice treatments (averaged over burning and mulching treatments), treatments with fallow or cowpea [Vigna unguiculata (L.) Walp.] in the previous year had 32% less herbaceous weed biomass, 90% fewer Ageratum conyzoides L. and over 99% fewer Meloidogyne graminicola Golden & Birchfield. Rice yield was negatively associated with A. conyzoides density (−0.62, P < 0.01) and M. graminicola number (−0.42, P < 0.05). Less striking effects of fallow period on A. conyzoides and M. graminicola, observed from on‐farm surveys, demonstrate the limitations of on‐farm studies because of undocumented effects of farmers' management decisions.

Planted legume fallows reduce weeds and increase soil N and P contents but not upland rice yields

“…Toward the end of the 5-year experiment, during the growing season of the last crop, Ageratum conyzoides density was higher in CR than in the other treatments (Table 5). This supports earlier observations that there is a shift in weed populations toward A. conyzoides as cropping systems intensify (Roder et al 1998a). There were no differences between the treatments in soil inorganic N content at cutting time in 2003 and 2005 (Table 6).…”

“…In 2002, fallow periods of only 2 or 3 years were common (Troesch 2003). Increased cropping intensity has resulted in reduced soil fertility and rice yields, and increased problems from weeds and pests in northern Laos (Roder et al 1997a(Roder et al , b, 1998aSaito et al 2006a). …”

Rice Root-Knot Nematode (Meloidogyne graminicola) an Emerging Problem

“…Burning of 15 cm deep rice hulls significantly reduce M. graminicola populations in the soil (Gergon et al, 2001). Compared with continuous rice treatments (averaged over burning and mulching treatments), treatments with fallow or cowpeas in the previous year had 32% less herbaceous weed biomass, 90% fewer A. conyzoides and over 99% fewer M. graminicola in field trials (Roder et al, 1998). In Philippines, rice based cropping sequences such as rice-mungbean, corncabbage rice, rice-tobacco-rice, ricewatermelon-rice, rice-cotton-rice, have been found effective in combating root-knot nematode menace in rice (Davide and Zorilla, 1983).…”

Allelopathy Studies in Weed Science in India——A Review

“…The exact figures concerning the percent loss of yield are not framed, nonetheless, it is determined by the intensity capacity of weed. Roder et al (1998) have reported that yield of rice is negatively associated with the density of Ageratum [37]. Ageratum due to its heavy infestation intensity ruined the croplands of farmers of the lower Shivalik ranges of the Himalayas due to which farmers even abandoned their fields.…”