Weed Seedbank and Weed Biomass Dynamics in a Long-Term Organic Vegetable Cropping Systems Experiment

Abstract

Most previous research on changes in weed abundance and community composition in cropping systems has focused on field crops. The study presented here examined changes in the weed seedbank and aboveground biomass in four organic vegetable cropping systems over a 10-yr period. The systems included an Intensive system with six crops per 4-yr rotation, an Intermediate system with one cash crop per year, a Bio-extensive system with alternating cash crop and tilled fallow years plus prevention of seed rain, and a Ridge-tillage system with one cash crop per year. Systems also differed in the types and number of cover crops between cash crops. During the course of the experiment, the weed community shifted from one dominated by summer annual broadleaf species that reproduce at the end of their lives to a community dominated by summer and winter annuals that mature rapidly. This shift in community composition can be attributed to the change in land use from conventionally managed corn (Zea maysL.) and alfalfa (Medicago sativaL.) to organic vegetable production. In particular, crop rotations with diverse preplantings and postharvest tillage dates interrupted the life cycle of common lambsquarters (Chenopodium albumL.) and pigweed species (Amaranthusspp.: mostly Powell amaranth [Amaranthus powelliiS. Watson], with small numbers of redroot pigweed [Amaranthus retroflexusL.] and smooth pigweed [Amaranthus hybridusL.]), while favoring a diverse assemblage of quickly maturing species. The study thus demonstrates that an appropriate crop rotation can control the seedbank of weeds likeC. albumthat potentially persist well in the soil. The Ridge-tillage system greatly reduced the frequency and depth of tillage relative to other systems while effectively suppressing perennial weeds. The early-reproducing annuals, however, became more abundant in the Ridge-tillage system than in the other systems, primarily due to escapes along the edge of the scraped ridges. The tilled fallow periods coupled with prevention of seed rain in the Bio-extensive system substantially reduced weed abundance through time and relative to the other systems.

Impact of Tillage and Crop Residue Management on the Weed Community and Wheat Yield in a Wheat–Maize Double Cropping System

“…Agronomic practices can affect the weed flora and species composition of the weed community and soil seed bank in arable fields [7]. Crop rotation [8,9], fertilization [10][11][12][13], tillage [14][15][16], and crop residue retention [17][18][19] are effective measures to control weeds. No-till has been widely accepted in recent decades for many environmental benefits, such as reducing run-off, improving nutrient cycling, reducing soil degradation, decreasing water and soil pollution, and enhancing the activities of soil biota [20].…”

Improving Weed Management Based on the Timing of Emergence Peaks: A Case Study of Problematic Weeds in Northeast USA

“…Conversely, fields may have weed communities dominated by species with similar phenology, reflecting the history of management (Ryan et al, 2010). For example, an organic vegetable rotation and a conventional corn and alfalfa rotation resulted in two different weed communities with very different phenology (Mohler et al, 2018). Likewise, corn and soybean are more conducive to summer annual broadleaf weed emergence than wheat and alfalfa (Goplen et al, 2017).…”

Weed species and traits associated with organic grain crop rotations in the mid-Atlantic region

“…Although the FSP experiment included only agronomic crops, rotations including short-season vegetable crops have been shown to impose even more restrictive filters by imposing tillage at various intervals throughout the growing season. This interrupts the life cycle of summer annual species requiring a full season for reproduction in favor of generalist species with more flexible emergence and early reproductive traits (Mohler et al 2018). There is currently a need for greater vegetable and lower commodity crop production to meet world dietary requirements (KC et al 2018) and the proximity of population centers to agricultural production fields in the mid-Atlantic area would facilitate delivery of more nutritionally balanced products.…”

“…Fried et al (2008) suggest that a complex rotation with a complex array of crop perations would aid weed control by dampening populations of dominant noxious species and would be more favorable to species adapted to a range of cropping conditions, resulting in weed communities rich in generalist species. Mohler et al (2018) showed that vegetable crop rotations that employ multiple, appropriately timed tillage operations deplete the seedbanks of weed species having full-season reproductive requirements in favor of species with shorter reproductive cycles.…”