The effects of nitrogen, irrigation and sowing date on growth and yield of lentils (Lens culinaris Medik.)

Effects of additional nitrogen (N), irrigation and sowing date on early growth, N nutrition, leaf growth and yield of Lens culinaris (lentils) were examined under glasshouse and field conditions. For Olympic and Titore lentils grown under glasshouse conditions, leaf area, and shoot and root fresh weight (f.wt) and dry weight (d.wt), when nodules were first visible, increased with increased applied nitrate (NO₃⁻) concentration to 5.0 mol m⁻³, then changed little with additional NO₃⁻ thereafter. Increases were substantial in all cases. For example, the increase in leaf area with additional NO₃⁻ (5.0 mol m⁻³) was > 100% for both cvs. Additional NO₃⁻ had a negative effect on nodule d.wt. Twenty one days after nodules were first visible, nodule d.wt decreased by 88% with additional NO₃⁻ (10 mol m⁻³). Nitrate reductase activity (NRA) and plant NO₃⁻ content of both cvs. were influenced by additional NO₃⁻. With the exception of NO₃⁻ content of leaves of Titore, NRA (µmol NO₂⁻ g⁻¹ f.wt h⁻¹) and NO₃⁻ content (µmol NO₃⁻ g⁻¹ d.wt) of all tissues of both cvs. increased with increased applied NO₃⁻ concentration from 0 to 10 mol m⁻³. For both cvs. supplied 1 or 10 mol m⁻³, NRA and NO₃⁻ content were substantially greater in root than stem or leaves and the greater proportion of total plant NRA and NO₃⁻ content were in the root. For cv. Olympic under glasshouse conditions, water stress de1ayed leaf appearance rates by 3-17 days for leaves 1-12 while N at all rates from 50 to 150 kg ha⁻¹ reduced the time taken for leaves to appear. Time to the onset of senescence of the early leaves was delayed with both water stress and low N level. Leaf appearance rates were linear. Rate of appearance was increased by full irrigation and 150 kg N ha⁻¹ when compared to 1/4 irrigation and 0 N. With full irrigation and 150 N, leaves appeared at the rate of one every 3.8 days compared to one every 5.8 days with 1/4 irrigation and 0 N. The field experiment was autumn and spring sown and used cv. Olympic only. There was no effect of irrigation on all parameters measured due to the unseasonally high rainfall recorded during November and December, 1991. However, both N application (calcium ammonium nitrate-28% N) and sowing date gave large increases in dry matter production (DM), seed yield and harvest index (HI). Maximum DM production increased from 680 to 794 to 1053 g m⁻² with increased additional N from 0 to 50 to 100 kg ha⁻¹. Maximum DM production was approximately 60% higher for the May sowing than for the September sowing. Seed yield showed a similar trend to DM production. For example, with increased applied N from 0 to 100 kg ha⁻¹, seed yield increased from 198 to 301 g m⁻². Seed yield was approximately 67% higher for the May sowing than for the September sowing. Effects of applied N and sowing date on DM production and seed yield were consistent with the effect these factors had on leaf area index (LAI) and photosynthetically active radiation (PAR) interception by the crop canopy. Plants supplied 100 kg N ha⁻¹ had LAI of 10.8 and intercepted 764 MJ m⁻² PAR while plants supplied 0 N had LAI of 5.5 and intercepted only 666 MJ m⁻² PAR. Thus, it was concluded that findings in the field and glasshouse were consistent as the N effect on early growth under glasshouse conditions were maintained in the field in the longer term. Hence, lentils may respond to applied N in the field especially in a wet and cold season. Although applied N reduced nodulation, increased yield may compensate for loss of N fixation.