Ground Cover Supplement : GC Supplement - Soil constraints
4 Non-wetting soils Dry seeding puts time pressure on moisture Drier autumns and the increasing adoption of dry seeding have led to a perceived increase in water repellency across Western Australian cropping systems By Dr Margaret Roper A perceived increase in the occurrence of non-wetting soils in Western Australia is likely the result of: ¢ drier autumns with less frequent and smaller rainfall events at the break of the season resulting in less opportunity for the repellent soil to wet up; ¢ increased concentration of organic matter (the source of water repellence) at the soil surface from minimum tillage; ¢ higher frequency of dry and early seeding; and ¢ widespread use of narrow knife-points, which can cause water-repellent topsoil to flow into the furrow and surround seed and fertiliser. Water repellence increases with increasing organic carbon content, particularly on sandy soils where the surface area of soil particles is low. Water repellence can be particularly severe in Mediterranean climates as new waxes become fused onto sand surfaces during hot and dry conditions over summer. Drier autumns and larger cropping programs in WA over the past couple of decades have led to a steady increase in dry sowing, with about 40 per cent of growers in low-rainfall areas and 20 to 25 per cent in higher-rainfall areas sowing a proportion of their wheat crop dry each year. However, despite its growing popularity the practice remains problematic, with many growers reporting that soil in dry-seeded rows remains dry while soil in the untilled inter-row wets up. CSIRO research shows disturbance (tillage) of dry non-wetting soils results in much slower water penetration than the same soils left undisturbed (Figure 1). Disturbing dry non-wetting soils can lead to up to two-fold increases in repellence -- as measured by the molarity of ethanol droplet (MED) method -- (Figure 2). Figure 3 illustrates the impact on crop emergence from seeding dry water-repellent soil. Canola emergence was severely impaired when the non-wetting soil was seeded dry (shown on right side of photo). However, when the same soil was sown 12 hours later after 25 millimetres of rain, crop emergence significantly improved (shown on left side of photo). SOURCE: CSIRO The water droplet on the ‘dry disturbed’ soil still remained on the soil after 40 seconds, while the water droplet on the undisturbed soil entered the soil shortly after 12 seconds. FIGURE 1 Time course of water drop infiltration into dry water-repellent soil that has been disturbed dry compared with the same soil left undisturbed. Undisturbed Disturbed dry 6 seconds 12 seconds 40 seconds SOURCE: MARGARET ROPER, CSIRO FIGURE 2 Water repellence level of compacted and non-compacted water-repellent soil either disturbed dry or left undisturbed. Not compacted Disturbed dry Undisturbed dry Compacted Not compacted Compacted Water repellency (MED, dried at 50ºC) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 3.3 3.3 1.5 1.6 The capacity for dry seeding is an important part of modern farming systems. However, further investigation is needed to fully understand the mechanisms at play in tillage of dry, water-repellent soil so mitigation strategies can be developed. □ GRDC Research Codes CSP00139, DAW00244, DAW00204 More information: Dr Margaret Roper, CSIRO Agriculture Flagship, 08 9333 6668, firstname.lastname@example.org; Dr Phil Ward, CSIRO Agriculture Flagship, 08 9333 6616, email@example.com; Dr Stephen Davies, DAFWA, 0408 439 497, firstname.lastname@example.org THE CAPACITY FOR DRY SEEDING IS AN IMPORTANT PART OF MODERN FARMING SYSTEMS. HOWEVER, FURTHER INVESTIGATION IS NEEDED TO FULLY UNDERSTAND THE MECHANISMS AT PLAY IN TILLAGE OF DRY, WATER-REPELLENT SOIL SO MITIGATION STRATEGIES CAN BE DEVELOPED.
GC Supplement - Foliar fungal diseases of pulses
GC Supplement - Grain storage 2015