Accurate data on the distribution of the various types of sodic soils in New South Wales are not available. However, general observations suggest that large areas are affected by structural instability as a result of sodicity, particularly on grey clays and red-brown earths of the Murray-Darling Basin. There is a strong need for new sodicity surveys because the production of crops and pasture often is well below potential on these lands. Exchangeable sodium data on their own do not adequately describe sodic soil behaviour, so information is also required about related factors such as electrical conductivity, exchangeable magnesium, clay mineralogy, pH, calcium carbonate content, degree of remoulding, and the frequency of continuous stable macropores. Critical limits for sodicity that are used by soil management advisory services need to be redefined. Considerable research into the reclamation and management of sodic soils has occurred in the irrigation areas and rainfed cropping districts of the Murray-Darling Basin in New South Wales. Mined and by-product gypsum, and to a lesser extent lime, have been shown to greatly improve the physical condition and profitability of production from soils with a dispersive surface. However, the responses to these treatments are less likely to be economical when sodicity is confined to the subsoil. Adequate supplies of gypsum and lime are available in New South Wales, but further research is required to determine economically optimal and environmentally acceptable rates and frequencies of application, particle sizes and chemical compositions for different farming systems that utilize the various types of sodic soil.
Irrigated cotton yields in the lower Macquarie Valley, New South Wales, declined within a decade of the inception of irrigation, particularly on grey clays. Degradation of subsoil structure was thought to be involved.Two adjacent sites, one used for irrigated cotton production since 1968 ('cultivated'), the other for native pasture and grazing ('uncultivated'), were compared. The soil at each site, a sodic grey cracking clay (Vertisol), was described and sampled for a range of physical and chemical analyses.In the cultivated soil there was increased surface sodicity, greater dispersion of soil aggregates at 0-0 -3 m, decreased organic carbon levels to 0 -3 m and increased subsoil compaction. Also, the cultivated soil was observed to have more massive structure, with fewer macropores, between 0 . 2 and 0 . 7 m than the uncultivated soil. Probable reasons for this degradation of chemical and physical fertility following 15 years of intensive irrigated farming are discussed.
Structural degradation of Vertisols depresses cotton lint yield by extending the period of waterlogging following irrigation or heavy rainfall. Break crops such as wheat and safflower are often grown without irrigation to improve the macroporosity of degraded Vertisols, by encouraging deep cracking, after several years of cotton production.Investigations were made into the effects of cultivated fallow, wheat and safflower on soil structure, and the growth of a subsequent cotton crop. The tests reported in this paper, done over a 12-day period following irrigation, were: soil water content and potential, core and clod bulk density, air-filled porosity, an index of macropore continuity using Rhodamine dye, and penetration resistance.The results, when compared with established limits of aeration and penetration resistance to cotton root growth, indicate that soil physical conditions at 0.25 m should have impeded root growth regardless of water content. However, cotton roots continued to extract water in this hostile soil environment; this favourable performance was attributed to the better conditions for root growth in the interaggregate fissures than those within aggregates.Apart from water content, all indicators of soil structure were able to differentiate consistently between the three crop treatments to a depth of 0.25 m. Below 0 . 8 m , the cropped plots, particularly safflower, had lower water contents than the fallow plots.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.