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The susceptibility of surface soil to drying when rainfall is scarce has prompted evaluation of deeper placement (20 cm) of fertilizers within the profile to where soil moisture is more likely to be stored. However, concerns arise regarding potential chemical challenges to P availability in the subsurface. This study examined differences in chemical conditions between the soil surface (0–10 cm) and subsurface (15–25 cm), and investigated the effect on the diffusion and extractability of banded P. Analysis of surface and subsurface samples from 15 sites revealed substantial differences in characteristics that influence P behavior between depths. The phosphorus buffering index (PBI) was largely explained by concentrations of amorphous Al and Fe (hydr)oxides and CaCO3. The measured diffusion distance of P from monoammonium phosphate (MAP) granules was found to be inversely related to PBI. Consequently, significant differences in diffusion distances were typically observed between soil layers characterized by marked PBI variations. The measured diffusion radii were used to calculate the mean P concentrations of surface-banded and deep-banded MAP in a field scenario, which were replicated in a 4-week laboratory incubation. The resulting lability of applied P was determined through isotopic exchange, and although significantly higher P recoveries were measured from the subsurface at two sites where large pH differences existed between depths, no significant differences were measured between depths at all other sites. Hence, the subsurface is not a more hostile zone for deep-placed P. [ABSTRACT FROM AUTHOR]

In semiarid sandy soil environments there is a dual challenge of carbon and nitrogen (N) limitation that needs to be managed to ensure timely supply of N to crops. Management of N inputs to soil using combinations of legume stubble addition and fertiliser N in cereal systems is essential to meet crop demand and maintain N in soil organic matter. The aim of this study was to assess soil mineral and biological N pools that influence N supply and N uptake of wheat at early growth stages. The recovery of [sup.15]N-labelled fertiliser by wheat was evaluated using a factorial combination of either wheat, lupin or no stubble incorporated with or without [sup.15]N fertiliser in a sandy soil system. Soil and plant samples were collected at sowing, tillering, first node and booting to monitor changes in N pools and [sup.15]N uptake by the wheat. Crop stubble incorporation one week before sowing increased biological N pools in the surface soil (0-10 cm). Early N immobilisation (sowing-tillering) in all the treatments without [sup.15]N fertiliser may have limited N availability for wheat uptake in the subsequent period (tillering-first node), when fertiliser N appeared critical to maximise N supply for plant requirements. Up to 38% of the [sup.15]N fertiliser applied at sowing was incorporated into the soil microbial biomass pool, so that fertiliser N was critical to relieve short-term inherent N limitations for both plant and microbial growth, and to supply the longer-term biological pools (microbial biomass) to support subsequent mineralisation potential. Reducing the energy limitation to the microbial pool through inputs of carbon from stubble was also critical to ensure fertiliser N supplied sufficient N to satisfy plant demand later in the growing period. These results have implications for management decisions on semiarid sandy soil systems that aim to synchronise N from inputs of legume stubbles and fertiliser with crop N demand during early growth stages of wheat. Keywords: growth stages, Kandosol, microbial biomass, mineralisation-immobilisation, nitrogen recovery efficiency, semiarid environments., Introduction Globally, maintaining supply of nitrogen (N) to low-input rainfed cereal crops is becoming increasingly challenging due to a decline in soil organic N reserves, particularly in semiarid agroecosystems where [...]

Sandy soils make up a substantial fraction of cropping land in low rainfall ( Additional keywords: crop nutrition, deep ripping, soil compaction, soil fertility, water repellency. Received 14 June 2019, accepted 19 January 2020, published online 26 February 2020, Introduction The low-medium rainfall zone (3 :1), making it one of the driest rain-fed grain cropping environments in the world. In addition, rainfall is erratic with a coefficient of variation [...]

Early growing season immobilisation affects post-tillering wheat nitrogen uptake from crop stubble and [sup.15]N fertiliser in a sandy soil Pilar Muschietti Piana, Therese Marie McBeath, Ann Marie McNeill, Pablo Ariel [...]

The measurement of soil organic carbon (OC) is important for assessing soil condition and improving land management systems, as OC has an important role in the physical, chemical, and biological fertility of soil. The OC contents of Calcarosols often appear high compared with other Australian soil types with similar fertility. This may indicate either systematic overestimation of OC in Calcarosols or the existence of a mechanism of OC stabilisation specific to carbonate-rich soils. This study compares three dry combustion techniques (dry combustion with correction for carbonate-C determined separately, dry combustion following sulfurous acid treatment, and dry combustion following treatment with hydrofluoric acid) and two wet oxidation techniques (Walkley Black and Heanes) for the measurement of soil OC content, to determine which method is best for Calcarosols. Nine calcareous and nine non-calcareous soils were analysed. Of the methods, dry combustion with carbonate-C correction and dry combustion following sulfurous acid pre-treatment were found to be unsuitable for highly calcareous soils. Dry combustion with carbonate-C correction was unsuccessful primarily due to incomplete conversion of carbonate to CO2 under the combustion conditions used. However, even if this problem could be overcome, the method would still not be suitable for highly calcareous soils since it would involve the measurement of a relatively small value (OC) as the difference of two much larger values (total C and carbonate-C). Sulfurous acid pre-treatment was unsuitable because it did not remove 100% of carbonate present. Although the remaining dry combustion technique (i.e. following hydrofluoric acid treatment) did not have such problems, it did give very different (and much lower) OC estimations than the two wet oxidation techniques for the highly calcareous soils. These results are consistent with carbonate minerals interacting with and stabilising a substantial quantity of soluble OC. This has implications for the way OC levels should be measured and interpreted in Calcarosols, in terms of both fertility and C stabilisation and sequestration. Additional keywords: calcareous, stabilisation, dry combustion, wet oxidation, Walkley Black, HF treatment., Introduction Calcarosols are defined under The Australian Soil Classification (Isbell 2002) as soils that are calcareous through the soil profile. They are widely distributed across south-eastern Australia, mostly in the [...]

Grazing systems are a major producer of food and fibre across the world. These systems often require the addition of fertiliser phosphorus (P) for maximum pasture growth, and it is now estimated that a four-fold increase in the use of P fertiliser in grasslands is needed to meet increased food demand by the year 2050. However, the recovery of P from fertiliser is often inefficient and global issues associated with P scarcity will continue to worsen. Knowledge on the uptake of fertiliser P by grasslands, including the effect of agronomic management, remains incomplete under field conditions. The aim of this study was to quantify the effects of soil P fertility (across three levels of soil P fertility), time of fertiliser application (at one level of soil P fertility), and placement of fertiliser (at one level of soil P fertility) on the growth and uptake of fertiliser P by clover pastures during a growing season. Subterranean clover ( Trifolium subterraneum L.) monocultures established at two field sites in Australia were used to test the growth response to, and recovery of: (i) early-season (autumn) additions of fertiliser P to the soil surface at three levels of soil P fertility; (ii) mid-season (late winter) additions of fertiliser P to the soil surface; and (iii) early-season additions of fertiliser P placed 6 cm below the soil surface. Fertiliser P was applied to the pastures as single superphosphate that was labelled with a 33 P radiotracer to supply ∼20 kg P ha −1 . Total herbage yield and recovery of fertiliser P by the clover pastures was generally highest when fertiliser P was applied to the soil surface early in the growing season and to soils maintained at the optimum level of soil P fertility for maximum pasture growth. An audit of the 33 P recovery of fertiliser P in the clover pasture revealed that up to 50% of the fertiliser P was recovered by the clover plant (shoots and roots), 5–15% remained in the fertiliser granule, and 20–25% was recovered in the 0–4 cm soil layer (largely as inorganic P) by the end of the growing season. We demonstrate that clover pastures are able to recover a relatively large proportion of surface applied fertiliser P during a growing season. Surface application is the simplest and most cost-effective strategy for management of fertiliser P in pastures. [ABSTRACT FROM AUTHOR]

Inefficiency of fertilizer phosphorus (P) use in grazing systems is often associated with the accumulation of inorganic and organic P in fertilized soil. However, the chemical nature of the accumulated organic P remains poorly understood. The aim of this study was to use solution 31P nuclear magnetic resonance (NMR) spectroscopy on sodium hydroxide-ethylenediaminetetraacetic acid (NaOH-EDTA) extracts to identify the chemical nature of organic P in soils from a medium-term (13 years) permanent pasture field experiment. This included an unfertilized pasture (P0), and treatments designed to maintain soil P fertility at near 'optimum' (P1) and 'supra-optimum' (P2) levels for pasture growth; pastures at all levels of soil P fertility were continuously grazed with either a moderate or high stocking rate (SR09 and SR18). Approximately 20% of the fertilizer P added to pastures was recovered as organic P in NaOH-EDTA extracts at the P1 level of soil P fertility in the 0-10 cm soil layer, and the majority (≈ 65%) of this was detected as the broad phosphomonoester signal. In addition, several specific forms of phosphomonoesters ( myo- and scyllo-inositol hexakisphosphate, α- and β-glycerophosphate, and RNA mononucleotides) and phosphodiesters were detected across all soils but at low concentrations. This study shows that phosphate fertilization of pastures primarily results in the accumulation of complex forms of phosphomonoesters rather than that of specific forms of recognizable biomolecules ( e.g., myo-inositol hexakisphosphate). [ABSTRACT FROM AUTHOR]

Background and aims: Single superphosphate (SSP) is a major source of phosphorus (P) used in grazing systems to improve pasture production. The aim of this experiment was to determine the fate of fertiliser P in clover pastures under field conditions. Methods: A procedure was developed to radiolabel SSP granules with a P radiotracer, which was then applied to the soil surface (equivalent to ~12 kg P ha) of a clover pasture. Recovery of fertiliser P was determined in clover shoots, fertiliser granules and soil fractions (surface layer: 0-4 cm and sub-surface layer: 4-8 cm). Results: The P diffusion patterns of the P-labelled SSP granules were not significantly different to those of commercial SSP granules ( P > 0.05). Recovery of fertiliser P in clover shoots was 30-35 %. A considerable proportion of the fertiliser P (~28 %) was recovered in the surface soil layer and was largely inorganic P. Conclusions: Recovery of fertiliser P by clover plants was up to 35 % in the year of application. Much of the fertiliser P in soil fractions was inorganic P, which highlights the importance of inorganic P forms and dynamics in soils under clover pasture on a single season timeframe at these sites. [ABSTRACT FROM AUTHOR]

Abstract: At physiological maturity, nutrients in crop residues can be released to the soil where they are incorporated into different labile and non-labile pools while the remainder is retained within the residue itself. The chemical speciation of phosphorus (P) in crop residues is an important determinant of the fate of this P. In this study, we used chemical fractionation and 31P nuclear magnetic resonance (NMR) spectroscopy, first separately and then together, to evaluate the P speciation of mature oat (Avena sativa) residue. Two water extracts (one employing shaking and the other sonication) and two acid extracts (0.2N perchloric acid and 10% trichloroacetic acid) of these residues contained similar concentrations of orthophosphate (molybdate-reactive P determined by colorimetry) as NaOH–EDTA extracts of whole plant material subsequently analysed by solution 31P NMR spectroscopy. However, solution 31P NMR analysis of the extracts and residues isolated during the water/acid extractions indicated that this similarity resulted from a fortuitous coincidence as the orthophosphate concentration in the water/acid extracts was increased by the hydrolysis of pyrophosphate and organic P forms while at the same time there was incomplete extraction of orthophosphate. Confirmation of this was the absence of pyrophosphate in both water and acid fractions (it was detected in the whole plant material) and the finding that speciation of organic P in the fractions differed from that in the whole plant material. Evidence for incomplete extraction of orthophosphate was the finding that most of the residual P in the crop residues following water/acid extractions was detected as orthophosphate using 31P NMR. Two methods for isolating and quantifying phospholipid P were also tested, based on solubility in ethanol:ether and ethanol:ether:chloroform. While these methods were selective and appeared to extract only phospholipid P, they did not extract all phospholipid P, as some was detected by NMR in the crop residue after extraction. These results highlight the need for careful interpretation of results from chemical fractionation, as separation can be compromised by incomplete recovery and side reactions. This study also highlights the benefits of employing a technique that can simultaneously detect multiple P species (solution 31P NMR) in combination with chemical fractionation. [Copyright &y& Elsevier]