Comparison of Weed Seedbanks in Different Rice Planting Systems

Machine-transplanted rice (Oryza sativa L.) (MTR), water directseeded rice (WDSR), and dry direct-seeded rice (DDSR) are three important alternatives to traditional manual transplantation of rice. Weed infestation is a pervasive problem in all rice planting systems. Th e weed seedbanks under diff erent rice planting systems have seldom been compared. Th us, we sampled weed seeds in fi elds employing MTR, WDSR, and DDSR consecutively for at least 5 yr in Wujin County, eastern China. Seeds of 26 companion weed species of rice, comprising 16 families, were observed. Most weed seeds, 82.5% in MTR, 75.3% in WDSR, and 81.7% in DDSR, were distributed in soil 0-to 10-cm deep. As soil depth increased, the seedbanks of total weeds, broadleaf weeds, grasses, and sedges all signifi cantly decreased under the diff erent rice planting systems, except for sedges under WDSR. Th e DDSR tended to maintain larger seedbanks of sedges and grasses, as well as some upland weeds, such as Digitaria sanguinalis (L.) Scop. and Eleusine indica Gaertn. Th e WDSR system contained the smallest weed seedbank overall but tended to have larger seedbanks of several weeds, such as Ammannia arenaria H. B. K. and Lindernia procumbens (Krock.) Philcox. Weedy rice and Cyperus diff ormis L. tended to maintain larger seedbanks in DSR fi elds. Th e MTR fi elds tended to have larger seedbanks of broadleaf weeds and some traditional rice weeds, with signifi cantly lower richness of weed species in the seedbank. Th erefore, to downsize the weed seedbank, WDSR or MTR should be employed rather than DDSR when possible. Moreover, the infl uences rotation of diff erent rice planting systems on the weed seedbank merit more studies.