Nitrogen application after plant growth regulator herbicide drift reduces soybean growth and yield

Abstract

The success of dicamba-tolerant soybean [Glycine max(L.) Merr.] has revived concerns about plant growth regulator (PGR) herbicide exposure to conventional soybean. In laboratory studies, soybean root nodulation is inhibited by excess auxin, which is the mechanism of action of PGR herbicides. Soybean exposed to PGRs in a field environment may have a similar response, and if nodulation is compromised, nitrogen (N) fixation may be reduced, with subsequent seed yield or protein content decreases. Many soybean–N studies report minimal impact to soybean yield. However, if soybeans show foliar PGR injury symptoms, could N application compensate for a potential nodulation inhibition response? This study examined the response of non–PGR tolerant soybean to N after exposure to low doses of 2,4-D and dicamba applied once (at soybean growth stages V1, V3, and early reproduction [R1 or R2]) or twice (V1 + V3 or V3 + R). N was either foliar or soil applied at early (∼5 d after PGR application) or late (10 d after PGR application) timings. Nodulation and plant growth were evaluated at R3, and grain yield and seed protein and oil content were quantified at maturity. Plant biomass and nodulation were reduced by 10% with some PGR treatments, and early foliar N application after PGR injury resulted in reduction up to 25%. N applications to non–PGR treated soybean did not increase yield. Soybean treated with PGR at V1 or V3, with or without N, had yields similar to control treatments. However, yield reductions of up to 20% were observed when PGRs were applied at V5 or R stages or when double PGR applications were followed by early foliar N application. Seed protein and oil content were not affected by PGR or N treatment.

Effect of Irrigation Regime and Fertilization on Recovery of Dicamba Injured Soybean

“…At 1 g•ae•ha −1 of dicamba applied at R1 alone and V3 + R1 to soybean, biomass was reduced as much as 25% when applied with foliar N7 days following the R1 dicamba application; biomass reduction was only 10% when treated with foliar N 20 days following the R1 application of dicamba [17]. For soybean not treated with N, biomass reduction averaged 20% [17]. Addition of N to dicamba injured soybean does not allow for dicamba recovery; however, weekly irrigation of dicamba injured soybean can result in appreciable soybean recovery in terms of injury level, height, and yield [18].…”

“…Following dicamba application and foliar-applied N, a significant decrease in yield was noted but not when soil-applied broadcast N was used [17]. At one location soybean nodulation was not affected while, at another location, nodulation was decreased by 35% for plants treated at V3 and R1 with dicamba [17]. At 1 g•ae•ha −1 of dicamba applied at R1 alone and V3 + R1 to soybean, biomass was reduced as much as 25% when applied with foliar N7 days following the R1 dicamba application; biomass reduction was only 10% when treated with foliar N 20 days following the R1 application of dicamba [17].…”

“…For example, soybean injury from synthetic auxins can reduce legume nodulation, decreasing N fixation, which may partially account for yield reduction [16]. Van de Stroet et al [17] determined that the application of foliar and broadcast N in addition to synthetic auxins applied at low rates impacted soybean rhizobia nodulation, therefore decreasing biomass. Following dicamba application and foliar-applied N, a significant decrease in yield was noted but not when soil-applied broadcast N was used [17].…”

“…Van de Stroet et al [17] determined that the application of foliar and broadcast N in addition to synthetic auxins applied at low rates impacted soybean rhizobia nodulation, therefore decreasing biomass. Following dicamba application and foliar-applied N, a significant decrease in yield was noted but not when soil-applied broadcast N was used [17]. At one location soybean nodulation was not affected while, at another location, nodulation was decreased by 35% for plants treated at V3 and R1 with dicamba [17].…”

Use of plant growth regulators to reduce 2-methyl-4-chlorophenoxy acetic acid-Na (MPCA-Na) damage in cotton

“…For a long time, herbicide damage has been an important limiting factor of crop yield, especially in relation to inactivated herbicides [9][10][11]. Field observations show that cotton is extremely sensitive to MCPA-Na.…”