27 Sep 2022
27 Sep 2022

Wetting and drying cycles, organic matter and gypsum play a key role in structure formation and stability of sodic Vertisols

Sara Niaz, J. Bernhard Wehr, Ram C. Dalal, Peter M. Kopittke, and Neal W. Menzies Sara Niaz et al.
  • The University of Queensland, School of Agriculture and Food Sciences, St. Lucia 4072, Queensland, Australia

Abstract. In the natural environment, soils undergo wetting and drying (WD) cycles due to precipitation and evapotranspiration. The WD cycles have a profound impact on soil physical, chemical, and biological properties and drive the development of structure in soils. Degraded soils are often lacking structure and the effect of organic amendments and WD cycles on structure formation of these soils is poorly understood. The aim of this study was to evaluate the role of biotic and abiotic factors on aggregate formation and stabilisation of sodic soils after the addition of gypsum and organic amendments (feedlot manure, chicken manure, lucerne pallets, and anionic poly acrylamide). Amended soils were incubated at 25 °C over four WD cycles, with assessment of soil microbial respiration, electrical conductivity, pH, sodium adsorption ratio (SAR), aggregate stability in water (ASWAT), aggregate size distribution, and mean weight diameter. Our results demonstrate that WD cycles can improve aggregate stability after the addition of amendments in sodic Vertisols, but this process depends on the type of organic amendment. Lucerne pellets resulted in highest soil microbial respiration, proportions of large macroaggregates, and mean weight diameter. In contrast, dispersion was significantly reduced when soils were treated with chicken manure, whilst PAM only had a transient effect on aggregate stability. When these organic amendments were applied together with gypsum, the stability of aggregates was further enhanced, and dispersion became negligible after the second WD cycle. The formation and stability of small macroaggregates was less dependent on the type of organic amendments and more dependent on WD cycles as the proportion of small macroaggregates also increased in control soils after four WD cycles, highlighting the role of WD cycles as one of the key factors that improves aggregation and stability of sodic Vertisols.

Sara Niaz et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-469', Manfred Sager, 02 Nov 2022
  • RC2: 'Comment on egusphere-2022-469', Anonymous Referee #2, 06 Nov 2022
  • RC3: 'Comment on egusphere-2022-469', Anonymous Referee #3, 08 Nov 2022
  • RC4: 'Comment on egusphere-2022-469', Anonymous Referee #4, 08 Nov 2022
  • RC5: 'Comment on egusphere-2022-469', Anonymous Referee #5, 08 Nov 2022
  • RC6: 'Comment on egusphere-2022-469', Anonymous Referee #6, 09 Nov 2022

Sara Niaz et al.


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Short summary
Sodic soil affect ~580 Mha in semi-arid and arid regions of the world. These soils have weak structure. This laboratory study evaluated treatments to overcome the weak aggregate structure in two sodic Vertisols, by applying organic amendments, gypsum and wetting drying cycles. We conclude that sodic soils need to be treated with gypsum to flocculate clay, and organic matter (lucerne or chicken manure) to form aggregates, whereas drying cycles form stable small macroaggregates.