The profitable management of soil constraints is imperative in the grain growing region of New South Wales and Queensland, Australia. This paper consolidates information regarding the management of sodicity, salinity and acidity relevant to this region and identifies key knowledge gaps. This work helps to identify areas important for future research, which will enhance the ability of growers to profitably manage constrained soils for grains production.

We needed a method for accurately sampling soil carbon (and nitrogen) in commercial fields. Variability in soil carbon occurred over a scale of about 1 m near the soil surface and 10 m at 1.5 m depth, requiring an excessive number of cores to achieve accuracy. The resources required for verifying changes in soil carbon might negate its present market value.

This paper presents a case study showing why the errors-in-both variables problem should be addressed when collating data for soil inventories, calibration datasets and monitoring. Here, soil organic carbon data from different sources were modelled by constructing maximum likelihood functional relationships; and compared to modelling with ordinary linear regression as is more often used to harmonize data.

The amelioration of saline-sodic soil is essential for increasing crop production and preserving the ecological environment. A pot experiment was conducted to investigate the effect of vinegar residue and silicon-potash fertiliser on two calcareous saline-sodic soils and the growth of oat plants. The combined use of vinegar residue and Si-K fertiliser was considered to be a wise method for ameliorating two calcareous saline-sodic soils.

Soil hydraulic parameters are a major source of uncertainty when modelling water movement and the fate of nitrogen, including nitrous oxide emissions (N₂O) in agricultural systems. We tested the sensitivity of the outputs from the APSIM model to variations in soil parameter data. The results indicate that this variability needs to be accounted for when such models are used for estimating N₂O emissions at the catchment or regional scale.

The physically uncomplexed organic matter, the free light fraction (<1.6 g cm^–3 density), is the labile fraction which builds up and turns over faster than the remaining soil organic matter. We measured free light fraction carbon and nitrogen in soil under leucaena–grass pasture. The free light fraction formed 20% of carbon and 14% of nitrogen over the 40-year-period considered. Thus, the free light fraction is a significant proportion of labile organic matter in pasture soils.

Addition of soil physical amendments (e.g. fine sand and wood chips) may improve salt leaching within a soil profile. This paper investigated the success of salt leaching in amended and non-amended soil profiles. This paper also assessed the applicability of HYDRUS-1D to simulate salt leaching and predict the success of the amendment strategy.

We evaluated the effect of cover crops in succession or rotation with onion crops, in different soil management systems, on the C and N contents and their fractions in soil aggregates and bulk soil. Treatments with plants from different botanical families, or greater diversity increased C and N contents and their fractions. The main changes found were due to management systems and combinations of soil cover crops for the particulate fractions, especially soil aggregates.

Labile organic carbon (C) can sensitively indicate the change in soil quality and is greatly influenced by organic residue input. We assessed the long-term effects of various rates of residue return on soil organic C fractions, and found that high amount of residue input was necessary to increase soil organic C and its fractions were differently regulated by the source of organic residue.