Mike Wong Ting Fook

Managing phosphorus (P) is a global priority for environmental water quality due to P lost from agricultural land through leaching, runoff and subsurface flow. In Western Australia (WA), following decades of P fertiliser application to crops and pastures in low rainfall regions, questions have been raised about this region’s contribution to environmental P loss. This study was conducted on the Fitzgerald River catchment in the south Western Australia (WA) with mixed cropping and grazing land uses and a mediterranean climate with low mean rainfall (~350 mm yr-1). Phosphorus forms were monitored continuously over a three-year period in five separate streams, each draining a defined sub-catchment. The P concentrations in streams consistently exceeded Australian and New Zealand Environment Conservation Council (ANZECC) trigger values throughout the monitoring period. Of the measured total P concentration, ~75% was dissolved P (DRP; <0.45 μm) and 80% of that fraction was in the filterable reactive form (FRP). These water quality measurements and other independent soil investigations at this site, suggest that transport of dissolved P rather than erosion of sediment-bound P was dominant in this environment. Based on extractable soil P (Colwell P) and the P buffering index (PBI), predicted concentrations of dissolved reactive P (DRP) in soil solution in topsoils (0-10 cm) across this catchment, generally exceeded ANZECC’s values of 0.07 mg PL-1. The level of exceedance was spatially variable. Streams draining areas with the lowest predicted DRP concentrations also had the lowest measured FRP concentrations. Elsewhere stream water FRP concentrations depended on both DRP concentration and the PBI of the land being drained. Our findings suggest that deployment of practices that physically filter runoff, for example riparian vegetation, would be ineffective in restricting P transport into stream in this environment. This conclusion is consistent with previous findings of the ineffectiveness of riparian buffers on coarse textured sandy soils in higher rainfall areas of south west WA (Weaver and Summers, 2014). A reduction in DRP losses without yield loss could be achieved by following evidence-based fertiliser advice from soil testing to limit losses of legacy P (Rowe et al., 2016).”

Controlled‐release fertilizers (CRFs) have the potential to deliver crop production and environmental benefits through better control of applied nitrogen (N) in cropping systems. Whereas N release from CRFs can be impacted by several factors, there has been a widely held view that soil water has little effect on N release from polymer‐coated CRFs. Past research has often studied the soil water effect as a function of soil water content. This limits the transferability of results. In this study we measured N release from a polymer‐coated urea (PCU) and a polymer‐sulfur–coated urea (PSCU) using undisturbed soil cores at set matric potentials. Soil matric potential had a significant effect on N release from PCU. Release at −1,000 kPa was delayed by up to 30 d compared with −10 kPa. Optical stereo microscopy clarified that this was linked to differences in the rate of water absorption. Theoretical considerations demonstrate that these relatively large differences could not be explained by the effect of soil matric potential on vapor flow. It is possible that soil matric potential interacted with the properties of the coating to change its permeability or the involvement of liquid flow. The effect of soil water on N release from PSCU was less clear. The magnitude of the soil water effect is, therefore, product‐specific and dependent on coating properties. The soil matric potential provided a consistent description of release patterns between soils with contrasting soil water retention characteristics. Soil water effects should hence be studied as a function of soil matric potential.

There is increasing interest in use of ‘alternative’ soil amendments in agriculture, but the wide range of resources and products available differ greatly in their potential to overcome soil constraints and improve nutrient use efficiency. The three main types of biological amendments can be categorised as biostimulants, organic amendments and microbial inoculants. Many have potential to influence biological, chemical and physical conditions of soil, but most are not well researched or easily used in agriculture. The main exception is legume inoculants, which are very well researched and contribute enormously to agricultural productivity when legumes are incorporated into farming systems. Biostimulants include amino acids, chitosan, seaweed extracts and humic substances. Organic amendments include manures, composts, compost derivatives and biochars. Microbial inoculants include specific bacterial inoculants for legumes, and less specialised rhizosphere bacteria, arbuscular mycorrhizal fungi, ectomycorrhizal fungi and a range of disease suppressing microorganisms. Some biological amendments applied to soil may be more effective when used in combinations rather than singly. Furthermore, those used over longer periods may have potential for cumulative effects not captured when used over shorter timeframes. Such differences in effectiveness would occur primarily where benefits involve microbial interactions with chemical and physical soil processes leading to slow transformations within the soil matrix that influence soil fertility and soil health. Similarly, addition of manures and composts may require several years for any quantifiable increase in soil organic C. Although considerable knowledge of the modes of action of many biological amendments is available, their performance under field conditions is usually less well understood. The wide variety of natural and manufactured products available in most cases precludes adequate peer-reviewed research to support claims about their effectiveness. This can lead to proliferation of unsubstantiated assertions of efficacy. This review highlights the lack of field-scale evidence of benefits for many biological amendments with potential to be used in agriculture. We propose complementary approaches of (i) laboratory- or glasshouse-scale research to understand modes of action, and (ii) targeted field-scale participatory research involving groups of farmers using on-farm trials as a forward pathway. Use of biological amendments to overcome soil constraints is expected to expand with intensification of agriculture and as a result of climate change. Therefore, information that enables farmers to discriminate among products that have different levels of effectiveness is necessary, and on-farm participatory research should contribute to addressing this need.

Like many developing countries, the Philippines has a shortage of land resource information at sufficiently fine scales for effective land-use planning. The country is also short of capacity to acquire such information with a declining number of soil surveyors and limited capability and resourcing of soil analytical laboratories. Digital land resource mapping (DLRM) provides an opportunity to address these shortages. A project in the Cabulig watershed (220km2) of Northern Mindanao developed operational protocols by combining existing technologies to form a DLRM framework based on four 'pillars'.1)Statistically-based sampling strategy to ensure unbiased coverage of the range of landscape positions, and remove the need for expert judgement in sample site selection in the field.2)Simplified site protocols that concentrate on soil specimen collection rather than soil description and classification.3)Rapid soil analysis by mid-infrared (MIR) to estimate soil attributes for all layers at every site after developing local calibrations using conventional laboratory analysis.4)Statistical spatial prediction to map a range of soil attributes using piece-wise linear regression modelling with bootstrap aggregation. Overall, this framework can enable more efficient use of scarce pedological expertise and laboratory facilities by devolving many tasks to local, non-expert teams. An added benefit is that the local teams acquire soil literacy and can help with on-going interpretation and application of the survey results. We also discuss how we addressed some of the practical issues that arise with conducting soil survey in the context of a developing country and in a remote survey area with rugged terrain.

Purpose: Phosphorus (P) lost from agricultural land by erosion, runoff, throughflow and leaching is of major concern for water resource managers worldwide. Previous study on soils from cropping land of southwest Western Australia suggested P loss as dissolved unreactive P (DURP) via leaching, but the implications for processes and rates of P transport in soils are not known. Material and methods: Two contrasting soil profiles (sand and loam) from cropping land of southwest Western Australia were exposed to artificial rain in packed boxes and field runoff plots to examine P forms and fluxes in runoff, throughflow, leachate and soil solution after three P rates of application (equivalent to 0, 20 and 40. kg P/ha). Solutions were analyzed for total P (TP), dissolved reactive P (DRP) and total dissolved P (TDP). Particulate P (PP) and DURP were calculated by subtracting DRP from TP and TDP. Result and discussion: In the sand profile, about 90% or more of P losses via runoff and leachate were in DURP and PP forms, whereas DRP was a minor contributor. Phosphorus load in soil solution, throughflow, leachate and run-off increased with increasing P rate. The relatively higher affinity of soil for DRP compared to DURP might cause the latter to be more mobile through profile in association with colloidal compounds <. 0.2. μm. Higher PP concentration for loam soil via throughflow is exacerbated by dispersed clay, which could be an additional process influencing P mobility in loam and duplex soils. Conclusion: The DRP played a limited role in P transport compared to PP and DURP that both appeared to be associated with soil particles or soil colloids in runoff, throughflow, leachate and soil solution. Further characterization of the latter forms of P is needed so that management practices can be developed to minimize P losses.

Purpose: Policy changes to reduce the transport of phosphorus (P) from agricultural land have triggered research in many parts of the world to improve understanding of processes controlling P mobility so that P management practices can be designed to limit losses to waterways. Previous studies on soils from cropping land in the Mediterranean-type climate of south-west Western Australia suggested that dissolved unreactive P (DURP) comprises a large proportion of extractable soil P, but the implications of these findings for P mobility in soil solution were not examined. Materials and methods: Intact columns of three contrasting soil profiles (sand, loam, loamy sand) from cropping land of the south coast region of Western Australia were leached to examine P forms in leachate (bottom of 20 cm columns) and extracted soil solution (5, 10 and 15 cm depths) after application of three P rates (0, 20 and 40 kg P/ha). Leachate and soil solutions were analyzed for total dissolved P (TDP0.45 μm and 0.2 μm) and dissolved reactive P (DRP0.45 μm and 0.2 μm). Dissolved unreactive P (DURP0.45 μm and 0.2 μm) was calculated by difference. Results and discussion: Initial high P concentrations in leachate were followed by a sharp decrease with successive leaching events at high P rates (sand > loamy sand > loam), suggesting that macropore flow dominated in early leaching followed by matrix flow which favours P sorption by soil. The major fraction of P in leachate and soil solution even after the application of KH2PO4-P was DURP. The leachate (0.45 μm pores) and soil solution (0.2 μm pores) both had similar predominance of DURP fraction, although the proportion of DURP0.2 μm in soil solution was less than in leachate. The difference suggests that a significant proportion of the DURP fraction was fine colloidal material in 0.2–0.45 um size class, but its composition remains unknown. Conclusions: The predominance of DURP in leachate and soil solution was the most striking finding of relevance to P mobilization on intact columns of sand, loamy sand and loam soils. Phosphorus sorbed on the surfaces of the colloidal particles and occluded P within the colloids may account for some of the calculated DURP fraction. Determination of the composition of DURP in soil solution collected might provide useful insights for P mobility since this more effectively excluded particulate P than the <0.45 μm filtrate used for leachate analysis.

The aim of this work was to develop a risk map for boron (B) deficiency in the grain cropping regions of Western Australia (WA), whilst avoiding the high costs associated with direct B measurements for an area as vast as the south-west of WA. The study firstly determined relationships between 0.01 m CaCl2-extractable soil B levels and readily available data on soil properties and parent materials for Reference Soils of south-west Australia and secondly assembled direct evidence of B deficiency risk from surveys of farmers’ crops and soils and from glasshouse experiments. Across 73 Reference Soils, there was a positive relationship between 0.01 m CaCl2-extractable soil B levels and clay (r 2 = 0.50) and pH (r 2 = 0.43) in the surface horizon. Soils containing <0.5 mg B/kg generally had <5% clay and pH CaCl2 <5.5. Plant and soil analysis surveys in farmers’ fields revealed 10–20% of fields had B levels below tentative critical levels. In a glasshouse experiment, B response in oilseed rape was obtained in 4 sandy acid soils, all developed on sandstone parent materials. From this prior evidence of B deficiency, spatial data layers for surface soil pH, subsurface pH, surface clay level, and geology in south-western Australia were weighted and combined using the Dempster-Shafer weight of evidence model to map B-deficiency risk. The weightings of evidence layers were revised to increase the correspondence between predicted areas of high risk and field areas with measured low B or B deficiency from a validation dataset. The model helps overcome the high cost associated with direct B measurements for risk mapping. A similar approach may have value for mapping risk of other deficiencies of relevance to agriculture.

The incidence of potassium (K) deficiency is increasing in crops, pastures, and forestry in south-western Australia. Although soil K can be measured using soil sampling and analysis, γ-ray spectrometry offers a potentially cheaper and spatially more precise alternative. This could be particularly useful in precision agriculture, where inputs are applied according to need rather than by general prescription. In a study of topsoils near Jerramungup, Western Australia, strong relationships (r2 = 0·9) were found between on-ground counts of γ-rays derived from 40K (γ-K) and both total K and plant-available K. The success of γ-ray spectrometry in predicting available K relied on a strong relationship (r2 = 0·9) between total K and available K which may not hold in all areas. Although the relationship between γ-K and available K held over the range of 36–1012 mg/kg, crop response to K fertilisers is only expected when the available K content is <100 mg/kg. Estimates of available K from γ-K were unreliable at this lower end of the regression curve. Separate analysis with a subset of the data with available K <100 mg/kg showed a poor relationship between γ-K and available K (r2 = 0·05; d.f. 11). The usefulness of γ-ray spectrometry may therefore be restricted to defining areas where response to fertiliser K may occur, and where further soil sampling and analysis are required to predict the fertiliser requirement. Strong relationships (r2 = 0·9) were also found between γ-K and a range of other soil attributes, including clay, silt, and organic carbon content. These relationships depended on the locally strong relationship between total K and these soil attributes. Since such relationships do not hold everywhere, the utility of γ-ray spectrometry will likewise be limited. Site-specific calibrations are required if γ-ray spectrometry is to be used for soil property mapping.