Plant Available Water Capacity its relationship to soil properties, landscape position and management decisions.

Transcription

1 Plant Available Water Capacity its relationship to soil properties, landscape position and management decisions. Mark Glover Research Projects Officer CSIRO Land and Water 2 September 216

2 Plant Available Water Capacity (PAWC) PAWC = total amount of water that each soil type can store and release to different crops. (a) 69mm= *3 45mm=.5-.35*3 3mm= *3 21mm=.47-.4*3 15mm= * Volumetric water content (mm/mm) (PAWC) PAW = volume of water stored within the soil available to the plant at a point in time. (b) Volumetric water content (mm/mm) (PAW) 18 PAWC= =18mm 18

3 Plant Available Water Capacity What is required for Volumetric Water Content? Soil Bulk Density = Dry Mass/Volume grams/cc or mm/mm Values typically range between 1 and 2 If know the bulk density we can simply multiply any gravimetric water content by the bulk density to obtain mm of water per mm of soil depth for that soil horizon. Note BD can vary considerably with depth. When we subtract the Crop lower limit from the drained upper limit and add the resultant down the profile we obtain a total PAWC for that profile. note Need to be mindful of rooting depth. Bulk Density often varies with depth and can have a significant impact on rooting capacity of crops for a variety of reasons. 3

4 Factors affecting PAWC Soil texture Soil structure Crop impacts Subsoil constraints Salinity Sodicity Acidity Alkalinity Nutrient toxicities and deficiencies High bulk density

5 Soils and landscapes: Example 1 Insitu/Aeolian Soils Soil properties are determined by parent material, profile development and position in the landscape Memagong 1 - ~28 mm Memagong 2 - ~15 mm Volumetric H2O (mm/mm) SAT 2 Chromosol rock outcrop Volumetric H2O (mm/mm) SAT 2 Kandosol Dermosol Volumetric H2O (mm/mm) Wombat 1 - ~14 mm Chromosol SAT 6 8 Canola 1 wheat Volumetric H2O (mm/mm) Wombat 2 - ~13 mm SAT break of slope depression Granodiorite Sodosol Verburg, Glover, et al 215 Research Update paper Wagga Wagga (17 Feb 215)

6 Example 2 Soils in a Floodplain Setting PAWC is determined by soil s development (pedogenesis) and position in the floodplain landscape Meander plain Back plain Butler, 1958

7 Soil-landscape mapping 683 Volumetric Water Content (mm/mm) Volumetric Water Content (mm/mm) wheat (PAWC: 141 mm) Nyngan-Narromine soil-landscape maps (unpublished) David Duncan, Brian Murphy, et al. 2 wheat (PAWC: 193 mm)

8 What does all this mean in relation to management decisions? Many practices already in place to improve PAWC stubble retention, control track farming, min till, green manuring. Lime and gypsum can as assist in soil water retention in appropriate soil types and landscape positions - where it proves economic to do so. Use the soil-landscape and PAWC relationships to plan variable rate cropping systems. PAW and crop modelling used to minimize risk to in-crop fertilizer decisions. Reductions in sowing rates are minimizing yield reduction or protein reduction with a dry season finish canopy management in line with PAWC of the soil. Opportunity cropping when moisture level allow summer varieties. More information APSOIL, APSIM links, Espade, Soilmapp, ASRIS, GRDC Measuring and Managing Soil Water in Australian Agriculture. 8

9 Questions for growers and advisors.. What am I missing??? What do you need to make better decisions based on PAWC, soil properties and landscape position? Thank you CSIRO Land and Water Mark Glover Research Projects Officer t e mark.glover@csiro.au w