Scoping study reviewing the potential and feasibility to predict PAWC for different crops

[摘要] Water is the major limiting factor for grain production from dryland agriculture and efficient use of it requires an understanding of the plant available water capacity (PAWC) of a soil. PAWC is defined as the difference between the drained upper limit (DUL) and the crop lower limit (CLL) for a particular soil type. This knowledge of PAWC helps inform grower and advisor decisions in relation to crop management and contributes to improving the quality of yield forecasts.Past investments by GRDC and CSIRO have helped deliver the APSoil database of over 1100 soil characterisations for PAWC for 26 crop and pasture species. Most of the characterisations are, however, for a single crop. This means that to use the information for other crops, growers and advisors need to estimate the missing CLL. This scoping study reviews current rules of thumb used by advisors to estimate CLLs for different crop and soil types and the scientific evidence that can support them. It also identifies the next step in developing a consistent framework and further testing of the rules of thumb.Most of the rules of thumb used by advisors relate to relative rooting depths of different crops, which is linked with crop duration. The effect of physical and/or chemical subsoil constraints (SSC) which limit the extent of crop roots to access water, resulting in a higher CLL and lower PAWC, is also captured to some extent. Quantitative differences in crop specific responses to these SCC are, however, less well understood. The advisors noted the rules of thumb were based on very limited data, with untested extrapolations across regions and soil types common.The scientific literature contains various data sets and observations which can serve to corroborate the rules of thumb, if not add some quantification. For example, knowledge of rooting depth of specific crops, 15 bar theoretical lower limit, varietal differences and management practice, and effect of subsoil constraints on root exploration. Tapping into this literature and (re)evaluating existing datasets will be used to help shape and test these rules and allow their integration into a generalised and more broadly applicable predictive methodology. The APSoil database itself is also a source of data. It contains at least 928 field measured characterisations of CLL*. This includes 51 with two crops, 18 with three crops, 12 with four, 20 with five and 4 with six. The majority of these are on vertosols situated in northern NSW and southern Queensland. In many of these the different crops were, however, characterised in different seasons, introducing an uncertainty around seasonal variability. It will hence be important to add further new multi-crop characterisations that are performed side-by-side, including on other soil types and other (sub)regions.

[发布日期] 2018-09-30 [发布机构] CSIRO

[学科分类] 地球科学(综合)