Overcoming soil water constraints to chickpea yield in rainfed environments of Western Australia and Bangladesh

Wendy Vance

Chickpea (Cicer arietinum L.) is a major cool-season grain legume mainly grown in subtropical environments with summer-dominant rainfall or temperate environments with winter-dominant rainfall. In these environments, represented by the High Barind Tract of Bangladesh (HBT) and south-west Western Australia (WA), respectively, chickpea relies on either stored residual soil water or within-season rainfall. Limited soil water can constrain chickpea growth in both environments, from establishment to pod-fill. This thesis examines agronomic means of alleviating these stresses. It particularly considers the effects of newly introduced mechanised row-sowing and minimum tillage techniques in the HBT on soil water relations. Plant population density (PPD) (modified through row spacing) and soil water content within the profile at sowing (modified through pre-season irrigation) were investigated in WA to determine how best to alleviate soil water stress. Additional profile soil water significantly improved crop yields through improved early biomass production, including increased ability of roots to extract water. Wider row spacing enhanced yield in a season of low rainfall, but when average rain fell during the season, pre-season irrigation did not alter the effect of row spacing on grain yield. This indicated that in-season rainfall was the main determinant of differential chickpea performance with row spacing. In pot experiments, chickpea emergence was optimal at gravimetric soil water content of 17 % and delayed when lower than 12 % or higher than 23 %. Soil strength impeded early root growth at >1 MPa, causing lateral roots to predominate. Seedling shoots tolerated high soil strength better than emerging radicles. In the HBT, with one-pass machine planting, soil water contents in the range 12 to 24 % did not limit emergence of chickpea in the HBT across a wide sowing window (22 November to 22 December). However, the optimum sowing date for suitable seedbed conditions and to avoid limiting weather conditions during later vegetative and reproductive growth was found to be between 30 November and 10 December. Mechanised one-pass row-sowing, permits earlier sowing than under traditional broadcast, full tillage techniques, when soil water contents are higher. In this study the tillage types which IV disturbed the soil most, created a better seed-bed under high soil water contents and thus had greater success in chickpea emergence. Where soil water content in the seed-bed was moderate to marginal, emergence was not different between zero, strip and line sowing with full rotary tillage, but was better than traditional broadcast with full rotary tillage. Further, chickpea grain yields were higher with mechanised row-sowing than with traditional broadcast with full rotary tillage. In the HBT, profile soil water content (0 to 50 cm depth) at podding was lower than wilting point, after this time chickpea accessed water from deeper in the soil profile. In some cases the extraction of soil water at depth later in the growing season was different between tillage treatments; these differences were attributed to differences in PPD. The investigation of PPD and profile soil water content provide insight into possible benefits to alteration in row spacing in the HBT, an environment with high initial soil water content in the profile and very little inseason rainfall. In such conditions wider row spacing may be of benefit as was the case in the WA trials under lower rainfall conditions.

Overcoming soil water constraints to chickpea yield in rainfed environments of Western Australia and Bangladesh

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