An assessment of the guidelines in Victoria, Australia, for land application of biosolids based on plant-available nitrogen

Abstract

In the application of biosolids to land for agricultural purposes, the supply of plant-available nitrogen (PAN) should match the crop requirements. This ensures that the crop yield is maximised while minimising the environmental risk from over-application. In Victoria, the amount to be applied is usually calculated according to the State EPA guidelines using the nitrogen limited biosolids application rates (NLBAR). These guidelines specify the mineralisation rates to be used in the NLBAR calculation for different types of biosolids. However, these rates have not been validated for Victorian soils and agricultural production systems. To test the veracity of these rates, this study quantified the amount of PAN for two different biosolids (anaerobically digested biosolids, ANDB; and aerobically digested biosolids, ADB) added to two types of soils, a sandy loam at Lara and a clay loam at the Melton Recycled Water Plant, Surbiton Park, Melton. The PAN was calculated by determining the N fertiliser equivalence of the biosolids. To achieve this, two field calibration plots were prepared, one for the biosolids and one for urea as the N fertiliser. Biosolids were applied based on total N at six rates (0, 68, 136, 204, 340 and 510 kg N ha–1); urea was applied at six rates (0, 60, 120, 180, 240 and 280 kg N ha–1). Perennial ryegrass (Lolium perenne) was planted 1 day after the application of biosolids and harvested after 120 days. The calculated amount of mineralisable organic N in ANDB was estimated to be 41% and 39% when applied to the clay loam and sandy loam soils, respectively; for ADB, it was 12% and 9%, respectively. These values indicate that the organic N mineralisation rates provided in the EPA Victoria guidelines (15% for ANDB and 25% for ADB) might not always be applicable. Also of note is that the values obtained for the each of the biosolids appear to be independent of the soil type.

N Mineralisation from Bioresources Incubated at 12.5°C

“…Furthermore, the results of Rigby et al [20] indicated that applying biosolids at guideline rates in autumn and spring may produce mineral nitrogen in excess of plant requirements at those times of year and increase the potential for leaching and denitrification. Similar to assertions by Al-Dhumri et al [31] regarding the Victorian biosolids guidelines, Eldridge et al [33] also questioned the adequacy of the current New South Wales biosolids guidelines [34] for calculating application rates.…”

“…This assertion was based on their study that found up to 65% of total N was released as PAN in the first season after application of lime-amended biosolids to sandy soils in Western Australia. Al-Dhumri et al [31] also found that 39% of total N was mineralised 120 days after application of anaerobically digested biosolids to Sodosols in Victoria. However, the results of this incubation experiment contrast with the Tasmanian Biosolids Reuse guidelines that suggest only about 20% of total nitrogen in the product is released in the first twelve months following application [32].…”

Effectiveness of Five Biosolids as Nitrogen Sources to Produce Single and Cumulative Ryegrass Harvests in Two Australian Soils

“…Although mineral-N concentrations of 10-20 mg kg -1 in soils are usually enough for adequate ryegrass growth (Al-Dhumri et al, 2013;Antille et al, 2013), an appropriate comparison among different sources of a given nutrient requires the cover of the whole plant demand range for this nutrient (Barrow and Bolland, 1990;Bolland, 1997). Thus, aiming to investigate complete plant responses to biosolids-N application, rates of N applied to soils as biosolids ranged from null to 261.4 mg kg -1 .…”

“…Sewage sludge contains significant concentrations of organic matter, nitrogen, phosphorus and other elements that improve soil structure and fertility, stimulate microbial activity, enhance root penetration and increase crop yield (Al-Dhumri et al, 2013;Jorge-Mardomingo et al, 2013;Jeke et al, 2015). The idea of recovering organic matter and plant nutrients by applying sewage sludge to agricultural lands has been widespread as a disposal option, a cost-effective practice, and a way to close the nutrient loop in agriculture and remediated soils (Torri et al, 2014;Yoshida et al, 2015).…”

“…From the economic point of view, N-agronomic rates provide enough N to achieve near maximum yield and well-nourished plants (Al-Dhumri et al, 2013;Antille et al, 2013). As N-agronomic rates maximize crop yields and minimize risks of groundwater contamination (Winker et al, 2009;Al-Dhumri et al, 2013), a safer and more effective management of different kinds of biosolids in soils demands an evaluation of their capacity to promote plant growth at N-agronomic rates (Al-Dhumri et al, 2013;Jorge-Mardomingo et al, 2015).…”