Roger Armstrong

Chemical characteristics of phosphorus in alkaline soils from southern Australia

This study was performed to better understand the chemical behaviour of P in a variety of alkaline soils from southern Australia. To do so, surface soil samples of 47 alkaline cropping soils from Upper Eyre Peninsula in South Australia and from western Victoria were collected. The 22 soils collected from Eyre Peninsula were Calcarosols, and those from western Victoria were Vertosols, Alkaline Duplex soils, Sodosols, and Red Brown Calcareous soils. Parameters included total and amorphous Al and Fe, organic C, organic P, CaCO3 content, P sorption characteristics, phosphorus buffer capacity, calcium lactate (Ca-Lac) extractable P, bicarbonate-extractable (Colwell) P, water-extractable P, anion exchange membrane extractable P (AEM-P), and isotopically exchangeable P (labile P). Concentrations of micronutrients in the Calcarosols were relatively low, considered to be a function of low clay contents. Given very low background Cd concentrations in the soils, it was estimated from Cd measurements that the majority of total P in the soils was derived from previous fertiliser applications. Phosphorus buffer capacities (PBCs) were relatively high in the Calcarosols and moderately high in the other alkaline soils. P sorption behaviour in the Calcarosols was a direct function of CaCO3 content, although in the other alkaline soils, amorphous Al and Fe oxides were the principal determinants of the P sorption behaviour. Both Colwell and Ca-Lac extractants dissolved non-labile P in the highly calcareous soils, whereas AEM appeared to only remove surface-adsorbed P. In addition, Colwell P values were positively related to PBC and to the slope term in the Freundlich model (Kf) when Kf > 10. It is suggested that AEM-P may be a better predictor of P availability in highly calcareous soils compared with the other extractants.

Evaluating physicochemical constraints of Calcarosols on wheat yield in the Victorian southern Mallee

Soil salinity, sodicity, and high extractable boron (B) are thought to reduce wheat yields on alkaline soils of south-eastern Australia; however, little quantitative information on yield penalties to edaphic constraints is available. The relationships between wheat yield of a B-tolerant cultivar and soil physicochemical conditions in the Victorian Mallee were explored using ridge regression analysis, using natural variation in the field. Wheat yields in the survey ranged from 1.3 to 6.1 Mg/ha, with low yields attributed to inadequate soil water supply during pre-anthesis growth. Crop sequences, fallow–wheat, and pulse–wheat left greatest soil water prior to sowing of the wheat crop, and lucerne–wheat the least. A descriptive model explained 54% of variation in wheat yield, with rainfall around anthesis, available soil water in the 0.10–0.40 m layer, nitrate in the 0–0.10 m layer at sowing and salinity, and sodicity in the 0.60–1.00 m layers being important factors. Subsoil salinity (ECe) and sodicity (ESP) appear to be effective surrogates for estimating the likelihood of water extraction in the deep subsoil. The analyses suggest that subsoils need to have an ECe <8 dS/m and ESP < 19% for crops to make use of water deep in the profile. Although soluble B ranged from 2 to 52 mg/kg in the 0.60–1.00 m layer of the alkaline soils considered, B appeared to have little correlation with root growth, water extraction, or yield of wheat, which has been attributed to B-tolerance of the cultivar tested and/or the overbearing effect of high Na+ in these soils.

Interrelationships between edaphic factors potentially limiting cereal growth on alkaline soils in north-western Victoria

Calcarosols of the Victorian southern Mallee comprise subsoils that are typically saline, sodic, and have high concentrations of soluble boron (B), which have the potential to restrict growth of rain-fed grain crops. This paper reports relationships between various soil factors, from 150 soil profiles over a survey area of 3600 km 2 , to determine if field texture, pH1:5, electrical conductivity (ECe), and Na + could be used to estimate exchangeable sodium percentage (ESP) and B. Assessment of soil profiles across 5 layers to 1 m (n = 750) showed that exchangeable Na + correlated well with both ESP (r = 0.96) and B (r = 0.88). High correlation also existed between ESP and ECe (r = 0.71) and between B and pH1:5 (r = 0.70). Using linear and asymptotic regression functions, ESP overall was defined by: ESP = 1.47 + 2.68 × Na + (r 2 = 93.9) or ESP = 26.53 – 29.84 × 0.84 ECe (r 2 = 75.5). Boron was described by: B = –0.34 + 3.93 × Na + (r 2 = 76.7) or B = 3.2 × 10 –6 × 6.11 pH 1:5 (r 2 = 68.5). Inclusion of multiple explanatory variates, using stepwise multiple regression, did not account for more variation; hence, prediction using several variables simultaneously appeared unnecessary. Rapidly determined Na + , by ion-specific electrode, could also accurately predict sodicity: ESP = 1.31 + 0.03 × Na + (r 2 = 95.1). Soils with a pH1:5 <8.1 were shown to have B levels not potentially toxic to cereal growth. Soil texture also provided valuable estimation of B. Soils in the sand to clay loam texture range did not have levels of B toxic to cereal growth, unlike soils in the light to heavy clay range, which frequently had levels of B potentially toxic to cereal growth. SR ro a Jt et

Responsiveness of wheat (Triticum aestivum) to liquid and granular phosphorus fertilisers in southern Australian soils

Recent field trials on alkaline soils in southern Australia showed significant grain yield responses to liquid compared with traditional granular forms of P fertiliser. However the advantages of liquid over granular P forms of fertiliser has not been consistent on all soil types. In order to better predict the soil types on which liquid P fertilisers are likely to have potential, a glasshouse trial was conducted to compare the responsiveness of wheat to both liquid and granular forms of P on a wide range of Australian soils. A granular P fertiliser (triple superphosphate) and 2 liquid fertilisers (phosphoric acid and ammonium polyphosphate) were compared at a rate equivalent to 12 kg P/ha in 29 soils representing many of the soil types used for grain production in Victoria and South Australia. Wheat biomass was enhanced by P application in 86% of the soils tested. In 62% of the P-responsive soils, wheat dry matter was significantly greater when liquid P fertilisers were used compared with the granular form. Chemical analysis of the soils tested showed that the better performance of liquid P forms was not correlated to total P concentration in soil, P buffer capacity, or P availability as measured by Colwell-P. However, there was a significant positive relationship between calcium carbonate (CaCO3) content of soil and wheat responsiveness to liquid P fertiliser.

Tillage system affects phosphorus form and depth distribution in three contrasting Victorian soils

Major changes in tillage practices have occurred over the past 2 decades across the diverse range of soil types and rainfall zones that characterise cropping systems in southern Australia. However, there has been little corresponding change in the management of nutrients, especially phosphorus (P). This study investigated the effects of tillage and crop rotations on the stratification and transformation of P in soil profiles from 3 tillage/rotation trials encompassing 3 agro-ecological zones of southern Australia. Soil samples were collected from field trials at Longerenong (Vertosol, average rainfall 420mm), Walpeup (Calcarosol, rainfall 325mm), and Rutherglen (Chromosol, rainfall 650mm) in Victoria. Soil samples from various depths were sequentially analysed for organic and inorganic P fractions. Phosphorus accumulated in the surface soil (0-0.1m) across all sites and tillage practices/rotations studied but the proportion of P in different chemical fractions varied markedly among soil types and tillage practice/rotation. In the sandy Calcarosol, a greater proportion of fertiliser P was transformed into labile (resin-P) forms, whereas it tended to accumulate in non-labile pools in the finer textured Vertosol and Chromosol. The effects of tillage and crop rotation were generally confined to the topsoil with P strongly stratified in the topsoil in direct-drill and zero-tillage treatments compared with conventional tillage. The implications for management of P fertilisers in Victorian cropping systems are discussed.

The rapid assessment of concentrations and solid phase associations of macro- and micronutrients in alkaline soils by mid-infrared diffuse reflectance spectroscopy

Chemical analysis is a crucial but often expensive and time consuming step in the characterisation of soils. Mid-infrared diffuse reflectance (MIR-DRIFT) spectroscopy coupled with partial least square (PLS) analysis was used to determine macro- and micronutrient concentrations of a range of alkaline soils from southern Australia. Solid phase associations of macro- and micronutrients were also investigated using the mineralogical information contained in the infrared spectra of soil samples. Results showed that MIR-PLS analysis is a powerful and rapid technique for the accurate prediction of more than 15 chemical properties from each soil sample spectrum. Correlation coefficients for MIR derived concentration versus laboratory determined values were greater than R2 = 0.80 for soil moisture, calcium carbonate concentration, total concentration of Mg, K, S, Fe, Al, Mn, Zn, Cu, and oxalate- extractable Al, Fe, Mn, and Si. In calcareous soils, sulfur was associated with carbonate and conversely Mg was more related to the clay concentration of soils. Micronutrients such as Fe, Zn, Mn, and Cu were positively associated with smectite/illite in the clay fraction and negatively with kaolinite. The potential use of these results in partitioning model to assess plant available micronutrients pools is discussed.

Does phosphorus stimulate the effect of elevated [CO2] on growth and symbiotic nitrogen fixation of grain and pasture legumes?

Abstract. The effect of elevated [CO2] (700 μmol/mol) and phosphorus (P) supply on the growth and symbiotic N2 fixation of chickpea (Cicer arietinum L.), field pea (Pisum sativum L.) and barrel medic (Medicago truncatula Gaertn.) were investigated in the glasshouse. The effect of elevated [CO2] on the growth and N2 fixation at various growth stages of the chickpea and field pea plants (grown on a Vertosol) were also examined. Elevated [CO2] generally increased the aboveground biomass of chickpea (by 18–64%), field pea (by 24–57%) and barrel medic (by 49–82%), but the effect was greater when P was non-limiting. Elevated [CO2] only stimulated grain yield of chickpea (by 70%) and field pea (by 21%) if P supply was adequate. Elevated [CO2] reduced the grain protein concentration of chickpea (by 17–18%) regardless of P input, but increased that of field pea (by 11%) when soil P was limiting but had no effect at adequate P. The percentage of shoot N derived from the atmosphere (%Ndfa) of the three legumes was unaffected by elevated [CO2] regardless of soil P supply. Elevated [CO2] increased the amount of N fixed by chickpea (by 20–86%), field pea (by 44–51%) and barrel medic (by 114–250%) under P fertilisation, but had no significant effect when soil P was deficient. These results suggest that the predictions of future climates on the potential contribution of legumes to maintaining soil N fertility will depend on the particular response of a species to soil P status.

Mobility, solubility and lability of fluid and granular forms of P fertiliser in calcareous and non-calcareous soils under laboratory conditions

Despite a long history of application of phosphorus fertilisers, P deficiency is still a major limitation to crop production on calcareous soils. Recent field research conducted in highly calcareous soils in southern Australia has demonstrated that both grain yield and P uptake of wheat (Triticum aestivum L.) is greater when fluid forms of P are used compared to granular forms. To improve our understanding of the mechanisms underlying this response to P in the field, we compared the lability, solubility and mobility of P applied as either a fluid (3 products) or granular (3 products) form to two calcareous and one alkaline non-calcareous soils in the laboratory. Over a five-week period, between 9.5 and 18 % of the P initially present in the fertiliser granules did not diffuse into the surrounding soil. The degree of granule dissolution was independent of the soil type. In contrast, P solubility, lability and diffusion were significantly greater when fluid products were applied to the calcareous soils, but not to the alkaline non-calcareous soil. These findings are discussed in relation to field trials results where fluid products outperformed granular fertilisers.

Response of lentil ( Lens culinaris ) germplasm to high concentrations of soil boron

For lentil production to expand further in Australia, adaptation to the less favourable soils of the low to medium rainfall zones is required. To improve adaptation to these regions, varieties are required with increased tolerance to soil constraints such as high concentrations of boron (B), salinity and sodicity. To evaluate the range of B tolerance in lentil germplasm, 310 lines were screened in soil with a high concentration of B and tolerance was assessed at the seedling stage. A wide range in response to high concentrations of soil B was observed in the germplasm tested. Current Australian varieties were generally very intolerant to high concentrations of soil B. High levels of B tolerance was identified in germplasm originating from Afghanistan and Ethiopia. A subsequent experiment comparing lentils with different levels of B tolerance found that tolerant accessions (ILL213A and ILL2024) produced greater above and below ground biomass than intolerant accessions. The tolerant accessions had no significant yield loss under a high B treatment (extractable B = 18.20 mg/kg) compared to the control treatment (extractable B = 1.55 mg/kg). The large improvement in B tolerance, at soil concentrations typical of those found in the target regions, suggests there is potential to improve the tolerance level of adapted varieties and expand lentil production areas to regions with higher concentrations of soil B.

Identifying fertiliser management strategies to maximise nitrogen and phosphorus acquisition by wheat in two contrasting soils from Victoria, Australia

Crop yield and profitability in the dryland production systems of southern Australia are directly affected by the application of nitrogen (N) and phosphorus (P) fertilisers. How efficiently a crop utilises applied fertiliser is affected by several factors that interact in a complex way, including: nutrient mobility, soil type and soil physicochemical and biological factors, season (including rainfall amount and distribution), and crop physiology. In addition, nutrient supply and crop demand need to synchronise both temporally and spatially if nutrient use efficiency is to be optimised. In this study, the mechanistic simulation model, ROOTMAP, was used to investigate and generate hypotheses about the implications of a range of fertiliser management strategies on the nutrient utilisation of wheat. A range of seasons and 2 commercially important soil types (a Wimmera Vertosol and a Mallee Sodosol) were considered. Simulation results showed a strong interaction between the timing and placement of N and P fertiliser, soil type, seasonal conditions, root growth, and nutrient uptake by wheat. This suggests that region-specific recommendations for fertiliser management may be superior to the ‘one size fits all’ approach typically adopted over the Wimmera/Mallee region. Fertiliser use efficiency differed between the 2 soil types, primarily because physicochemical subsoil constraints were present in the Sodosol, but not the Vertosol. These affected rooting depth, total root system size, and root distribution—notably root growth and hence foraging in the topsoil layer. The root growth response to fertiliser management strategies and seasonal rainfall was also reduced on the Sodosol compared with the Vertosol. Simulated fertiliser uptake was responsive to the placement strategy in a dry year characterised by small rainfall events, typical for the Wimmera and Mallee regions. Shallow placement (0.05 or 0.025 m) of N and P in the topsoil utilised topsoil moisture from these small rainfall events, improving crop N and P uptake. The degree of benefit differed between the 2 soil types, and placement of fertiliser was more effective than topdressing. The simulation approach used here provides a preliminary assessment of a range of fertiliser strategies for different soil type and seasonal conditions. However, because ROOTMAP does not provide direct predictions of grain yield response, simulation results need subsequent validation under field conditions before they can be used by growers.