Claying and deep ripping can increase crop yields and profits on water repellent sands with marginal fertility in southern Western Australia

Abstract

Sandplain soils on the south coast of Western Australia have multiple limitations to crop production that include water repellence, low water and nutrient retention, subsoil acidity, and high soil strength. Crops on sandplain soils achieve, on average, almost 85% of their rainfall-limited yield potential; however, where there are multiple limitations the corresponding value is often <50% in any given year. Previous research has shown the value of applying clay-rich subsoil ('claying') to ameliorate water repellent soils and improve nutrient retention. Other studies have shown that deep ripping is effective in reducing compaction in sandplain soils. This paper quantifies the effects of 5 subsoil clay rates (0, 50, 100, 200, and 300 t/ha), with and without deep ripping to 0.5m, on soil properties, crop growth, and profitability in a replicated field experiment.Crop yields were increased by 0.3-0.6 t/ha as result of added clay. The clay content of the surface soil required to alleviate water repellence and achieve the highest yield increases was 3-6% in soils with~1% organic carbon. Longer term effects of claying included increased soil organic carbon by 0.2%, pH by 0.6 units, potassium by 47 mg/kg, soil strength by 250 kPa, and cation exchange capacity by 1.3 cmol c /kg to a depth of 0.1 m. However, changes in plant-available water (mm/m) were inconsistent between the clay treatments. Deep ripping to 0.5 m increased crop yields by 0.1-0.5 t/ha. These crop yield responses were still evident 3 years after the ripping treatment had been applied. Soil strength measurements indicate that re-compaction of the ripped treatments had occurred to a depth of 0.2 m in the second year following ripping. Crop responses to claying and deep ripping were additive. Claying and deep ripping, while almost doubling yields, achieved only 50-70% of the rainfall-limited yield potential on these marginally fertile soils. The highest clay rates (>3-6%) had cumulative discounted cash returns $AU100-200/ha higher than the unclayed 'control' treatment and $300/ha higher than the lowest clay rates. For most of the clay treatments, deep ripping increased discounted returns between 2005 and 2007 by $80-120/ha.

Management options for water-repellent soils in Australian dryland agriculture

“…Application of clay to waterrepellent sands increases the surface area of the soil and masks the waxy surfaces of the repellent sand particles (Ward and Oades 1993). An increase in clay content to 3-6% will alleviate repellency in most sandy soils (Cann 2000;Hall et al 2010), but additions of just 1-2% clay can reduce repellency (Ward and Oades 1993;McKissock et al 2000). However, not all clays are the same.…”

“…Because water-repellent soils wet up unevenly, crop and pasture seeds sown into them germinate at different times, resulting in patchy and delayed emergence, poor crop establishment and reduced grain yields (Blackwell et al 1994a;Abadi Ghadim 2000;Hall et al 2010). In Australian farming systems, water repellency is suggested to cause an annual average loss of 40% in crop production (Blackwell et al 1994a;Abadi Ghadim 2000), but solid estimates are not available.…”

“…Sodium (Na + )-dominated kaolinitic clays have been observed to be the most effective in reducing repellency, with less benefit from other clays such as smectite (Ward and Oades 1993;McKissock et al 2000;Hall 2009), whereas Ca 2+ -dominated montmorillonite clay appears to have little or no benefit (Ward and Oades 1993;Dlapa et al 2004). Benefits of application of clay to water-repellent soils include increased productivity due to more even wetting of the soil, even germination of weeds, increased water retention, increased cation exchange capacity and nutrient retention, improved soil stability, and increased soil organic carbon (Cann 2000;Carter and Hetherington 2006;Hall et al 2010) and microbial biomass (M. M. Roper, unpubl. data).…”

Biochar and Compost Increase Crop Yields but the Effect is Short Term on Sandplain Soils of Western Australia

“…Currently, clay is applied commercially to these sands to ameliorate water repellence. Added clay has been shown to increase nutrient retention in sands through increased CEC and organic C (Hall et al, 2010) and reduced leaching of nutrients including ammonium, nitrate (Dempster et al, 2012) D. J. M. HALL and R. W. BELL and P (Mokhtari et al, 2014).…”

“…The cation exchange capacity ( CEC) of topsoils commonly ranges from 2 to 4 cmol+ kg-1 . Together, soil organic carbon (C) and clay explain more than 80% of the variation in CEC in sandplain topsoils (Hall et al, 2010) even though they represent less than 4% of the soil mass. The issues associated with poor nutrient retention are not just limited to the south coast of Western Australia .. More than 70% of the wheatbelt soils in Western Australia have very low ( < 5 c1nol+ kg-1 ) CEC and approximately 50% of the wheat-growing soils within the states of South Australia and Victoria also have low to very low CEC.…”