Weed Residues Research Articles

Allelopathic effect of common weeds on soybean growth and soybean-Bradyrhizobium symbiosis

Water extracts of shoot of common lambsquarters (Chenopodium album), yellow nutsedge (Cyperus esculentus) and sunflower (Helianthus annuus) at 1% level significantly reduced soybean seed germination. Soybean seedlings inoculated with broth culture of nodule bacterium were grown for 25 days in N-free nutrient solution amended with cold water extracts of weed residues at 1 and 2% levels. At both levels extracts from residues of all weeds except that of lambsquarters enhanced growth of soybean. Nodulation was generally stimulated by the extracts of five weeds at 1% level except that of lambsquarters. Extracts from lambsquarters at 2% level completely suppressed and at 1% level reduced nodulation by 60%. Extracts from green foxtail (Setaria viridis), Pennsylvania smartweed (Polygonium pensylvanicum) and sunflower at 2% level reduced and at 1% level enhanced nodulation. The residues of lambsquarters shoot incorporated with soil at 0.5 and 1% levels caused 85 and 96% reduction respectively in seed germination and those of Pennsylvania smartweed and sunflower at 1% reduced seed germination by 40–70% but not at 0.5% level. The residues of foxtail and smartweed at both levels enhanced growth and nodulation. Under similar conditions nutsedge at 1% level stimulated nodulation but not growth. The residues of lambsquarters at both levels were inhibitory to nodulation but stimulated growth at 0.5% level.

Nitrogen Cycling in Conventional and No-Tillage Agro-Ecosystems: Analysis of Pathways and Processes

(1) The nitrogen dynamics of conventional and no-tillage agro-ecosystems are compared. Sorghum/rye (1978-1979) cropping systems were followed in rotation by soybean/rye (1980-1981) systems. Measurements of ecological processes including crop and weed production, litter decomposition, insect consumption, along with solution chemistry of soil, precipitation, throughfall, and ground water provided the data base for modelling nitrogen cycling in the two tillage systems for four complete annual farming cycles (two sorghum/rye and two soybean/rye). (2) Summary budgets indicated that both similar and dissimilar nitrogen cycling processes were occurring in conventional and no-tillage agro-ecosystems. Differences between agro-ecosystems were not definitive but suggestive of a trend of increasing ecosystem divergence through time. (3) Nitrogen fluxes between several agro-ecosystem component pairs were increased by ploughing. Crop shoot to root ratios differed between tillage treatments, suggesting distinct nitrogen uptake and storage strategies. (4) As a consequence of leaving crop and weed residues on the soil surface, no-tillage soil maintained higher (t30, P < 0.05) organic nitrogen in the upper soil layer (0-10 cm) than conventionally tilled soil. (5) Grain yields for the 4-year period were insensitive to tillage practices except during a drought year (1981) when no-tillage systems yielded higher (t30, P < 0.01) than conventional tillage. (6) Arthropod species diversity and weed biomass were higher (t30, P < 0.05) on several occasions in no-tillage systems. (7) We conclude that soil tillage practices were important regulators of nitrogen flux between agro-ecosystem components and nitrogen storage capacity within them. The undisturbed soil and litter layers of no-tillage systems generate complex decomposition subsystems which mimic those found in natural terrestrial ecosystems. We speculate that biologically-mediated nitrogen-retention mechanisms develop and operate to a greater extent in no-tillage than in conventional tillage systems.

Allelopathic Effects of Annual Weed Residues on Growth and Nutrient Uptake of Corn and Soybeans1

AbstractAnnual weeds have shown allelopathic potential in recent years. Few studies clearly compare effects of weed residues on growth inhibition and nutrient uptake in corn (Zea maysL.) and soybeans [Glycine max(L.) Merr.]. Therefore, the residues (aboveground biomass) of common lambsquarters (Chenopodium albumL.), redroot pigweed (Amaranthus retroflexusL.), common ragweed (Ambrosia artemisifoliaL.), velvetleaf (Abutilon theophrastiMedic.), and yellow foxtail [Setaria glauca(L.) Beauv.] were evaluated for their allelopathic effects on growth and uptake of N, P, and K in corn and soybeans in controlled environments. Weed residues in silica sand produced more inhibitory effects than the mixture of soil (Typic Agriudoll) and sand. The growth inhibition was more (8 to 14%) when the residues were incorporated in all soils than when they were surface applied. All residues except common ragweed reduced corn (6 to 20%) and soybean (2 to 20%) dry matter production. The inhibition or stimulation of N, P, and K uptake in both crops was not consistent and depended on the residue source, residue placement, or soil texture. Addition of supplemental N and P to various residues provided no alleviating effect on crop growth. Addition of P markedly enhanced P uptake without affecting total dry weights of both test species when compared to the controls. Yellow foxtail and common ragweed residues increased K uptake (21 to 48%) in corn but not in soybeans. The weed residues demonstrated an allelopathic inhibition of growth independent of N and P nutrition, and suggest that the inhibitory effects are not related to nutrient uptake.

Growth analysis of corn and soybean response to allelopathic effects of weed residues at various temperatures and photosynthetic photon flux densities

The effects of redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setariaglauca (L.) Beauv.] residues on corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] were evaluated at various temperatures and photosynthetic photon flux densities (PPFD) in a Biotron. Mathematical growth analysis techniques were used for the evaluation. Redroot pigweed markedly reduced leaf area duration (LAD), leaf weight ratio (LWR), and total dry matter production in both crops. Yellow foxtail residue inhibited total dry matter production in corn and soybeans 20 and 30 days after planting (DAP). It also reduced growth rate (GR) and LAD in corn and biomass increment (Δ W) in soybeans. Biomass increment was more closely correlated to LAD than net assimilation rate (NAR) in soybeans, whereas in corn NAR contributed more to Δ W than LAD. The 30/20 ° C temperature with a PPFD of 380 μE/m(2)/sec produced a larger Δ W with a greater NAR and larger LAD in corn, resulting in maximum dry matter accumulation than 20/10 ° C and other levels of PPFD. Under similar conditions, soybeans showed little or no response to the changes. The results demonstrate the allelopathic effects of weed residues on growth and dry matter production, affecting LAD, LWR, and GR. The results also show that environmental temperature and PPFD may alter the allelopathic effects of weeds on crops. The possible interference with photosynthesis and the partitioning of biomass into leaf component relative to the total biomass produced by the plant may be the inhibitory effects of allelochemicals present in redroot pigweed and yellow foxtail residues.

Inoculum potential of Verticillium species in crop and weed residues overwintering in infested soil

Viable propagules ofVerticillium albo-atrum were recovered from roots and stems of naturally infected weeds and sunflower cultivars before or after burial in the field and from stems and roots of certain non-infested crops after burial in the field for seven months.Verticillium dahliae was recovered less frequently, then only from the roots ofSolanum nigrum (black nightshade).

Damage to cereals caused by decaying weed residues

AbstractPoor establishment and growth of a succeeding crop has on some isolated occasions been observed after glyphosate has been used to kill dense infestations of couch (quack) grass. It appears that damage is caused by toxins and pathogens from the decaying weed residues rather than by the herbicide or its metabolites.

Allelopathic effects of goldenrod and aster on young sugar maple

A series of field, greenhouse, and laboratory studies were undertaken to elucidate the role of allelopathy in old-field sugar maple stands. Old-field weed residue inhibited germination and growth of maple even in the absence of competing vegetation. Goldenrod and aster were important producers of water soluble compounds that inhibited germination, nutrient uptake, and growth. These allelopathic chemicals were most readily extracted from putrefied plant residues, but they appeared to be natural plant products rather than microbial breakdown products. The deleterious effects of goldenrod on nutrition and growth of maple were overcome by large additions of soluble phosphorus fertilizer.

Manufacture of algal chemicals. U. Production of alginates from brown marine algae

AbstractA process for the production from the brown seaweeds Laminaria digitata and Ascophyllum nodosum of calcium alginate of reasonably constant ‘grade’ (50‐100 centistokes) and composition (approx. 95% calcium alginate, 1·3% ‘weed residue’) has been developed on the 25‐1b. wet weed batch scale. Certain aspects of the process have been further examined on the large laboratory scale with particular reference to the initial water‐washing and acid‐leaching stages. Under the best conditions found yields of 85% and upwards have been obtained.