GROWTH, YIELD AND NITROGEN CONTENT OF LENTIL (Lens culinaris Medic) AS AFFECTED BY NITROGEN AND DIQUAT APPLICATION

As an indeterminate crop, lentil continues its vegetative growth after flowering under favourable conditions of water and nitrogen (N). Such conditions may delay its maturity due to excessive growth. Furthermore, lentil is a leguminous crop; late season N2 fixation could prolong its growth and maturity. The objective of this research was to determine the role of N supply and diquat application in suppressing post-flowering growth and biomass. Two experiments were designed for two distinct soil zones of Saskatchewan during 2007 and 2008. In the first experiment, different combinations of nitrogen, phosphorus and inoculation were employed to determine their effect on growth, yield, biomass and N accumulation in lentil. In a second experiment, diquat was applied at two rates (lower than recommended) at two post-flowering stages (earlier than end-of-season desiccation) to control lentil growth. In both experiments, post-flowering vegetative growth was greater at Indian Head (IH) compared to Saskatoon (SKA). Regardless of the site features, greater N availability resulted in increased biomass production at both locations. The yield trend was, however, different. At IH, highest yield was obtained with 10 kg N ha-1 (lowest N applied), while at SKA, yield was not significantly affected by fertility treatments. The hypothesis that greater amounts of N application may reduce post-flowering biomass accumulation by curtailing N2 fixation is not supported by the data since biomass increased with increasing N application. In addition, both biomass and N accumulation after flowering were not affected significantly by the fertility treatments, showing that post-flowering physiology in lentils is governed more by N2 fixation instead of N application. The overall lack of response of lentil biomass and N accumulation after flowering to the individual fertility treatments suggested that source and availability of N does not change within plant. Instead, environmental conditions were more likely to influence portioning of biomass and N to seed through remobilization from vegetative parts in mid to late-season reproductive growth. Diquat application successfully suppressed biomass and plant growth at maturity. However, a reduction in biomass was obtained at the cost of yield loss at both sites. This loss in yield was great when diquat was applied at the earlier stage (one WAF) at half rate at both sites. Early application of diquat at low rate at IH reduced biomass by 25% compared to the control without significantly affecting yield. The same treatment, however, reduced biomass by 45% at SKA with huge yield loss. The results suggested low rate of diquat application at earlier crop growth stage to avoid yield loss in lentil