Ground Cover Supplement : GC Supplement - Subsoil constraints
GROUND COVER SUBSOIL CONSTRAINTS 8 PROJECT UPDATES What management options are available to growers? PROJECT: IMPROVING THE PROFITABILITY OF CROPPING ON HOSTILE SUBSOILS. ROGER ARMSTRONG AND COLLEAGUES SUBSOIL CONSTRAINTS TO crop growth occur naturally throughout large sections of the Australian grainbelt, but are especially prevalent in the neutral and alkaline soils that dominate cropping in Victoria and South Australia. Previous research has shown that they can significantly limit on-farm profitability by reducing grain yields and quality. The challenge for growers, advisers and scientists managing these soils is that subsoil constraints (SSC) is a general term that covers a wide range of factors, including primary salinity, boron toxicity and soil physi- cal constraints. The impact of SSC on crops can vary spatially (at the paddock and regional scale), across seasons and between different crops. Consequently, there will never be ‘a one size fits all’ solution for graingrowers. In some situations growers may be able to maximise yield potential (as determined by rainfall) by ameliorat- ing the subsoil. For many farmers, however, the magnitude of SSC and the cost of potential solutions may mean that cur- rently there is no viable amelioration strategy. The best option is to ‘live with the problem’ and adjust inputs such as fertilisers or limit the type of crop grown to bet- ter match the potential of the soil. Measuring the extent of subsoil constraints When making decisions about how to effectively man- age SSC, an understanding of the extent and impact of SSC on different crops is needed. A survey of farmer paddocks throughout the Wimmera and Mallee regions of Victoria and the Eyre and Yorke Peninsulas in SA is measuring a range of chemical and physical properties throughout the soil profile at 10 fixed points within a paddock. These measurements are then related to the growth and water use, at the same point, of successive crops grown since 2003. Information from this survey is being used to rank the relative importance of particular SSC throughout the region as well as to determine critical values for different soil properties. One important finding is that paddocks may not necessarily have consistently high- or low-yielding areas but that these may vary with crop type and season. solution was used to reduce the specific ion toxicity to a minimal level and find out the effects of osmotic pres- sure, irrespective of the type of salt. The major conclusion from this experiment (Figures 1 and 2) is that when the osmotic pressure of the soil solution is less than 700kPa there is a low rate of reduction in crop yield. However, for osmotic pressures greater than 700kPa the rate of crop yield reduction is severe. When the soil solution osmotic pressure is about 1000kPa, crop yield is reduced by 50 per cent. Eighty to 95 per cent of available soil water was not taken up by plants. When compared with calcium chloride, sodium chloride treatments were reducing the growth and dry matter production more. Given that chloride levels were the same, this indicates the harmful effects of sodium (Figure 2) more than those of chloride. It is becoming clear that in dryland cropping, fluctuat- ing soil moisture level during the season is an important factor when considering the effects of transient salinity on crops. Table 1 gives the percentage of available soil water not taken up by plants in different soil types due to osmotic effect. Table 1 also gives the moisture content in the field soil below which osmotic pressure is more than 1000kPa for a given EC1:5 measured in the lab. The available soil water range for each soil type, under non- saline conditions, was calculated from the laboratory- measured field capacity and wilting point values. Dr Pichu Rengasamy is a senior research fellow in soil and land systems at the University of Adelaide. GRDC Research Code UA00023 More information: Dr Pichu Rengasamy, 08 8303 7418, firstname.lastname@example.org 100 90 80 70 60 50 40 30 20 100 0 10 20 30 40 50 60 70 FIGURE 2 DRY MATTER PRODUCTION OF WHEAT (KRICHAUFF) AS A PERCENTAGE OF CONTROL IN RELATION TO EC OF THE SOIL SOLUTION IN THE POTS EC of pot solution (dS/m) Osmotic pressure (kPa) 1000 1500 Hoagland nutrient solution calcium chloride sodium sulphate sodium chloride Dry matter production % FIGURE 1 GROWTH OF WHEAT PLANTS TREATED WITH HOAGLAND NUTRIENT SOLUTIONS OF VARYING SALINITY EC SOIL POT SOL. EC=4dS/m EC SOIL POT SOL. EC=9dS/m EC SOIL POT SOL. EC=20dS/m EC SOIL POT SOL. EC=33dS/m EC SOIL POT SOL. EC=44dS/m EC SOIL POT SOL. EC=64dS/m EC values of soil solution in the pots were calculated from EC1:5 and the gravimetric water content of the pot soil. An EC >27.7dS/m indicates an osmotic pressure >1000kPa.
GC Supplement - Pastures
GC Supplement - Farm safety