Effect of fertilizer nitrogen and herbicides on the growth and nitrogen content of soybeans glycine max and cowpeas vigna unguiculata

Behran, S.; Sheibany, B.; Hojjati, S.M.; Maftoun, M.

Agronomy Journal 71(4): 533-538


ISSN/ISBN: 0002-1962
Accession: 005239109

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Little is known about herbicide-N fertilizer interaction with respect to the growth and N content of soybeans (G. max (L.) Merr.) and cowpeas (V. unguiculata). The effect of added N and trifluralin (.alpha.,.alpha.,.alpha.-trifluoro-2,6-dinitro-N, N-dipropyl-.rho.-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and diphenamid (N,N-dimethyl-2,2-diphenylacetamide) on the growth and N uptake by these 2 crops was evaluated. Soybeans and cowpeas were grown in greenhouse for 74 days in soil treated with various levels of N (0, 25 and 50 ppm) and herbicide (0, 1, 2 and 3 ppm). Leaf chlorophyll, dry matter yields, N concentration and N uptake were determined. All N-treated soybean and cowpea plants had greater chlorophyll content, produced more growth and contained higher N than untreated check. An increase in growth and N uptake suggests that symbiotic N fixation probably failed to supply all of N required for optimum growth. Application of 1 ppm trifluralin slightly increased growth and N content of cowpea and enhanced chlorophyll content, N concentration and root dry weights of soybean. Higher concentrations exhibited strong phytotoxic effects. Soybeans treated with 3 ppm of herbicide developed stunted and chlorotic leaves and had fewer nodules than untreated seedlings. Soil amended with nitralin and diphenamid reduced leaf chlorophyll, growth and N uptake of soybeans and cowpeas. Nitralin exhibited a stronger inhibitory effect in roots than tops and was slightly less phytotoxic than trifluralin. Diphenamid-treated plants developed chlorotic leaf margins, followed by necrosis at the leaf edge. N addition to trifluralin treatment only affected N content of soybeans significantly, whereas there was increased chlorophyll content, N concentration and top dry weights of cowpea. N applied to nitralin- and/or diphenamid-treated soybeans and cowpeas resulted in an increase in dry weight and N content of tops, probably due to better nutrient and water supply to plants.