The growth, yield and water use responses of lentils (Lens culinaris Medic.) to irrigation

In a field trial conducted at Lincoln, New Zealand, during 1984/85, the water relations and the growth and yield responses of lentils (Lens culinaris Medic.) to irrigation were investigated. The cultivars Titore and Olympic were sown in May (autumn) and September (spring) and were grown with or without irrigation in a stony sandy loam. The season was warmer and drier than normal. In May sown plants, irrigation increased the rate of green area development and its maximum value but did not greatly increase seed yield (average = 325 g/m²). Harvest index was unaffected by irrigation in Titore (47.8%) but decreased from 48.7% to 43.6% with irrigation in Olympic. Water use scarcely differed between the two cultivars (average = 430 mm) but was increased by irrigation from 385 mm to 485 mm. The water use efficiency (WUE) of dry matter (DM) production was similar for both cultivars and was unaffected by irrigation; it averaged 2.8 g/m²/mm. However, the WUE of seed yield (SY) was greater in Titore, at 0.84 g/m²/mm, than in Olympic, at 0.70 g/m²/mm. Also, unirrigated plants (0.82 g/m²/mm) had a higher WUE of SY than did irrigated plants (0.72 g/m²/mm). Irrigated Olympic plants extracted about 73% of the total amount of water held in the profile at field capacity compared with about 65% for all other plants. In September sown plants, green area expansion and dry matter accumulation were unaffected by irrigation but both were faster and reached a greater maximum in Olympic than in Titore. Titore’s seed yield of 183 g/m² was unaffected by irrigation but Olympic’s was depressed from 132 g/m² to 87 g/m². Harvest index responded to irrigation in the same way as seed yield, being a constant 45% in Titore but decreasing from 31% to 24% in Olympic. Total water use of the two cultivars was identical at 265 mm but increased from 230 mm to 300 mm with irrigation. WUE of OM production was higher in Olympic at 3.0 g/m²/mm than in Titore at 2.2 g/m²/mm. Unirrigated plants (3.0 g/m²/mm) had a higher WUE of OM production than irrigated ones (2.2 g/m²/mm). The WUE of SY was higher in Titore at 0.72 g/m²/mm than in Olympic at 0.43 g/m²/mm. Also, unirrigated plants (0.69 g/m²/mm) had a higher WUE of SY than irrigated ones (0.46 g/m²/mm). The proportion of water (present at field capacity) extracted from the profile (average = 47%) and its pattern of extraction was unaffected by cultivar or irrigation. Differences in the magnitude of variates between sowing dates were primarily due to differences in the amount of energy absorbed. The different responses to irrigation in the two sowings were due to the difference in the extent of water stress experienced by the plants. Water stress was severe for May sown unirrigated plants but was minimal in both irrigated and unirrigated September sown plants. However, September sown irrigated plants were severely waterlogged. Response differences between cultivars were due to differences in their tolerance of waterlogging and their tendency to lodge. Water was extracted from deeper in the profile, and to a greater degree, by May sown plants than by September sown plants. This was probably due to more extensive root growth by May sown plants.