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Growth responses of annual legumes on saline soils

J.S. Dunbabin and D.G. Murray

NSW AGriculture & Fisheries, P.O. Box 736, Deniliquin, NSW 2710

Annual pastures (predominately subterranean clover) are widely grown on clay soils throughout the Murray Valley in New South Wales. Much of the area sown to annual pastures overlies shallow watertables, with associated salinisation problems. On the more saline soils establishment and productivity are affected. The relative salt tolerance of a range of annual legumes is being determined on a newly landformed saline soil with a watertable less than 2m from the surface. Yield reductions are being correlated with soil salinity measurements.

Methods

The trial is located within a bordercheck bay on a newly landformed, saline Moulamein clay. The site (10 x 196m) was chosen after a salinity survey showing ECe values increasing from 6.03 to 18.20 dS/m in the top 60cm (average saturation percentage, 65%). Ninety plots (15m2) were established on 20 April, 1988. The experiment was a randomised block design with subterranean clover (cvv. Clare, Nuba, Trikkala), persian clover (cv. Kyambro), balansa clover (cv. Paradana), berseem clover (cv. Bigbee) and medics (cvv. Sapo, Sephi and Circle Valley). Each variety was replicated 10 times along the salinity gradient. The trial received 1 autumn and 2 spring irrigations of channel water plus good autumn rains. The plots were harvested twice. Tissue chloride levels were measured in cv. Bigbee.

Results and discussion

Table 1. Cumulative yields of annual legumes as a function of soil salinity (expressed as the mean electrical conductivity of the saturation extract of samples taken from each plot to 15cm at the first harvest; ECe).

Bigbee and Paradana were the most productiye species (Table 1). Paradana was the most salt tolerant, yielding over 1.5 times as much as Bigbee when soil salinities exceeded 3.0 dS/m (0-15cm). With two exceptions the yield responses to salinity fell on straight lines, differing in intercept and slope. Bigbee and Sapo both fitted a linear plateau model, with thresholds of 4.0 to 5.0 dS/m (0-15cm) respectively. Chloride levels in leaves of Bigbee taken before the second harvest ranged from 2.83 to 4.36% (g/100g), but showed no obvious trend with increasing soil salinity. The experiment is continuing in the 1989 irrigation season to verify these salinity responses.

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