Nodulation, growth and water use of chickpeas (Cicer arietinum L.)

The potential of chickpea as an alternative rotation crop in Canterbury has already been established. Experiments were therefore planned to investigate the effects of inoculation, additional nitrogen fertilizer and supplemental watering on its nodulation and growth and the suitability of sowing in either winter or spring. Three experiments were carried out using kabuli chickpeas; two on a Templeton silt loam soil in the field and one in the glasshouse. The first field trial was sown on two dates (3 July and 30 September), provided with four rates of nitrogen fertilizer (0, 15, 45 and 90 kg N/ha) and three rates of Rhizobium inoculant (zero, recommended rate and twice the recommended rate). Experiment two was carried out in the glasshouse with three levels of supplemental watering (1/3 field capacity, 2/3 field capacity and field capacity), two rates of nitrogen fertilizer (0 and 90 kg N/ha) and either inoculated with the recommended rate of Rhizobium inoculant or not inoculated. In the last field trial, the chickpea was inoculated and sown on three dates (9 July, 9 August and 14 September) with (90 kg N/ha) or without additional nitrogen fertilizer. Under both field and glasshouse conditions, nodulation response to Rhizobium inoculation was poor with the number of nodules initiated per plant rarely exceeding 10. Added fertilizer nitrogen reduced the number of nodules per plant by 50% in the early part of the 1992/93 season. In the glasshouse, the reduction in nodule number in the presence of additional nitrogen persisted throughout plant growth such that at 30, 45 and 60 DAS, nodule number per plant was reduced by 84, 59 and 53% respectively. Seed reserve mobilization was enhanced by both additional nitrogen and supplemental watering. The cotyledons of the fully watered plants weighed 50 and 77% less than those of the plants maintained at 1/3 field capacity at 30 and 45 DAS respectively. At 30 DAS the plants receiving additional nitrogen had cotyledons weighing 31 % less than those not provided with additional nitrogen. In the glasshouse added nitrogen reduced root dry weights from 0.16 g/plant to 0.13 g/plant at 30 DAS and from 0.23 g/plant to 0.19 g/plant at 45 DAS. However, it increased branch number and leaf number per plant by between 21 and 87% and 17 and 48% respectively between 30 and 60 DAS. Green area per plant was increased from 72.3 cm² to 93.3 cm² at 45 DAS and from 66.8 cm² to 110.7 cm² at 60 DAS and shoot dry weight from 0.92 g/plant to 1.30 g/plant at 60 DAS in the presence of additional nitrogen. For plants maintained at field capacity the increase in root dry weight was between 33 and 180%, that of leaf number between 18 and 74% and green area between 52 and 226%. Shoot percent nitrogen increased by 30% in the presence of additional nitrogen and by 32% when the plants were inoculated with the recommended rate of Rhizobium inoculum. Seed yield averaged 2.87 t/ha with a harvest index (HI) of 0.29. Harvest index was significantly (p<0.05) increased by Rhizobium inoculation from 0.26 to 0.31 at zero and double the recommended rate respectively. It was also increased significantly (p<0.0001) as sowing date was delayed from winter (0.25) to spring (0.33). Maximum dry matter yield declined as the sowing date was delayed from 11.2 t/ha when sown in July to 9.5 t/ha when sown in September. Added fertilizer nitrogen increased leaf area index (LAI) from 2.7 without additional nitrogen to 3.7 when 90 kg N/ha was provided and total intercepted photosynthetically active radiation (PAR) from 725 MJ PAR/m² to 760 MJ PAR/m² at 0 and 90 kg N/ha respectively. Total PAR intercepted declined as sowing date was delayed with the July sowing intercepting 20% more PAR (810 MJ PAR/m²) than the September sowing (675 MJ PAR/m²). Total dry matter accumulation was closely related to PAR intercepted throughout the growing season and on average 1.64 g of dry matter was produced for every MJ of PAR intercepted. This work suggests that farmers are unlikely to obtain a yield advantage with winter sowing of chickpeas but sowing about late September to early October will give maximum yields. Rhizobium inoculation is necessary to ensure nodulation, however more work is necessary to determine suitable methods of inoculation. Water stress will reduce chickpea growth and dry matter yield in the glasshouse, primarily due to a reduction in green area. Chickpea crops do not fix adequate nitrogen for their own use. However in the field there was little indication that added nitrogen benefited crop growth.