Effects of Seven Herbicides on N2(C2H2) Fixation by Soybeans

Abstract

Greenhouse and laboratory investigations using four soils were conducted to determine the influence of seven herbicides on symbiotic nitrogen (N2) fixation by soybeans [Glycine max(L.) Merr. ‘Davis’]. Soils were treated with recommended rates of herbicides immediately after planting. After 8 to 10 weeks the nodulated root systems were assayed for nitrogenase activity using the acetylene (C2H2) to ethylene (C2H4) reduction technique, and total numbers and dry weights of nodules were determined. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] (0.3 kg/ha) decreased nodule dry weight and C2H4production per plant per hour in a Convent sandy loam. Alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide] (2.2 kg/ha) and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] (0.6 kg/ha) also decreased C2H4production per plant per hour in a Convent sandy loam, while metribuzin (0.6 kg/ha) increased C2H4production per plant per hour and per milligram of nodule dry weight in a Mhoon silt loam. Prometryn (1.7 kg/ha) increased production of C2H4per plant per hour in a Moreland silt loam. None of the herbicides affected C2H4production, nodule number, or nodule dry weight in a Commerce silt loam.