Water deficiency is one of the most severe abiotic stresses in rainfed dry lands and limits crop productivity. Exogenous applications of salicylic acid (SA) have been applied to mitigate the adverse effects of water-deficit stresses, but the relative efficacy of different derivatives of SA in enhancing water-deficit tolerance along with the underlying physio-biochemical mechanism and yield of crops is not well documented. Field experiments were conducted to ascertain the relative efficacy of exogenous application of three plant bioregulators (PBRs) [SA, thiosalicylic acid and 5-sulfosalicylic acid (SSA)], each at three concentrations (0.5, 1.0 and 1.5 mM), on the growth, physio-biochemical characteristics and yield of cluster bean under rainfed conditions. Based on a 2-year field experiment, the application of PBRs enhanced yield (from 8 to 16%). The yield enhancement with the application of PBRs was associated with elevated water content (from 9 to 17%), membrane stability (from 12 to 18%) and antioxidant enzyme activity (from 12 to 33%) and reduced lipid peroxidation (from −15 to −34%) in leaves. The effects of PBRs were conditionally type and concentration dependent. The application of SSA at a rate of 1 mM was more effective in enhancing water-deficit tolerance and improving the yield of cluster bean under water shortage conditions. This study provides empirical evidence of the potential for the application of SA and its derivatives to enhance crop yields under drought conditions. The results have direct implications for sustainable crop production for similar regions of the world facing water deficits.

The relationships between the actual amount of spring-applied trifluralin detected in soil at seeding, initial injury to flax, and crop growth and yield were investigated in southern Manitoba over three growing seasons. As the amount of trifluralin in the soil increased, flax density and dry matter production decreased, such that at a soil concentration equivalent to 1 kg ai ha−1 trifluralin, the two were reduced by 40 and 49%, respectively. Recovery from early-season injury was characterized by enhanced crop growth rates (CGRs) and net assimilation rates (NARs) of surviving plants during the remainder of the growing season. Maximum recovery occurred in plots where trifluralin levels in the soil were between 0.8 and 1 kg ha−1 at seeding. During the interval between stem elongation and bud initiation, CGRs and NARs of flax in the trifluralin-treated plots exceeded those of flax in the untreated plots by up to 1.5 and 1.2 times, respectively. Additionally, the number of branches per plant increased linearly as trifluralin amounts in the soil increased. Flax seed yield was decreased by trifluralin as described by the equation: flax seed (% of untreated control) = 104.9 - 13.3[trifluralin detected (kg ha−1) at seeding]. Based on this equation, trifluralin levels in the soil of up to 0.7 kg ai ha−1 caused less than a 5% reduction in flax yield under weed-free conditions.

The relationship between trifluralin dosages detected in the soil at seeding, initial crop injury, and subsequent recovery of spring wheat during the growing season was investigated in field experiments in 1986 and 1987. As the amount of trifluralin in the soil increased, both crop density and dry matter production decreased such that at 1 kg/ha the two were reduced by 37 and 50%, respectively, early in the season. As the season progressed, crop growth rates (CGRs) of wheat in trifluralin-treated plots exceeded those of wheat in the untreated plots. Maximum CGRs occurred between Zadok's growth stages 30 and 45 where trifluralin levels in the soil were 0.3 to 0.5 kg ai/ha at seeding. Recovery from trifluralin injury was characterized by enhanced net assimilation rates of surviving plants, increased tillering and greater dry matter production per plant. Wheat seed yield was only weakly correlated with trifluralin levels in the soil at seeding. From a linear regression model it was determined that a 35% reduction in plant dry weight from the trifluralin injury at the beginning of tillering would result in no more than a 10% reduction in seed yield at final harvest.

A 2-yr study was conducted to determine the influence of early and late soybean [Glycine max (L.) Merr.] planting dates on the competitiveness of velvetleaf (Abutilon theophrasti Medic). Velvetleaf was planted at densities of one plant per 61 and 30 cm of row, and competition ranged from 4 weeks to full season. Soybean planting dates were mid-May and late-June. Velvetleaf emerging with soybeans in mid-May were twice as competitive as those emerging with soybeans planted in late-June. A density of one velvetleaf per 30 cm of row competing full season reduced soybean yields 27% for the early and only 14% for the late planting date. The competitive difference was due to the short-day photoperiodic response of velvetleaf. Although the early growth stages of soybeans are more competitive than those of velvetleaf, 10 weeks after emergence velvetleaf competition reduced soybean growth and development. Velvetleaf does not appear to be a potential major problem in Arkansas for soybeans planted in June due to its photoperiodic response and late season competitiveness. However, the weed could present problems for soybeans planted early, especially when an early maturing variety is used.