Influence of crop rotation, tillage, and management inputs on weed seed production

Approaches to crop production that successfully reduce weed seed production can benefit farming systems by reducing management inputs and costs. A 5-y r rotation study was conducted in order to determine the effects that inter actions between crop rotation, tillage, and amount of herbicide and fertili zer (management inputs) have on annual grass and broad-leaved weed seed pro duction and fecundity. There were 10 crop rotation and tillage system combi nations and three levels of management inputs (high, medium, and low). Gree n and yellow foxtail were the major weed species, and together they yielded between 76 and 93% of collected weed seeds. From 1990 to 1994, average gra ss weed seed productions were 7.3 by 10(3), 3.7 by 10(3), 6.1 by 10(3), and 5.7 by 10(3) seeds m(-2), whereas average broad-leaved weed seed productio ns were 0.4 by 10(3), 0.4 by 10(3), 1.4 by 10(3), and 0.4 by 10(3) seeds m( -2) in crop rotations using conventional tillage (moldboard plow), conserva tion tillage, no tillage, and ridge tillage, respectively Crop rotations us ing conventional or ridge tillage consistently produced more grass and broa d-leaved weed seeds, especially in low-input plots. There was little differ ence in weed seed production among input levels for crop rotations using co nservation tillage. Comparing rotations that began and ended with a corn cr op revealed that by increasing crop diversity within a rotation while simul taneously reducing the amount of tillage, significantly fewer grass and bro ad-leaved weed seeds were produced. Among the rotations, grass and broadlea ved weed fecundity were highly variable, but fecundity declined from 1990 t o 1994 within each rotation, with a concomitant increase in grass and broad -leaved weed density over the same period. Crop rotation in combination wit h reduced tillage is an effective way of limiting grass and broad-leaved we ed seed production, regardless of the level of management input applied.