Excessive nitrogen (N) fertilizer application does not increase rice grain yield and N retention in soils but may lead to higher soil N uptake by plants due to added N interaction (ANI). This study hypothesizes that large doses of fertilizer-N increase native soil N uptake by rice plants and reduce soil N balance. We conducted field experiments in two locations in Myanmar for four consecutive rice cropping seasons to determine grain yield, the source of N in plants, and net soil N balance in sandy loam soils to which 0, 30, 77.6, and 160 kg urea-N ha−1 was applied. We used 15N-labeled urea to determine the source of N in plants, ANI and soil N balance. Although rice yield increased with increased N input in the dry seasons, there was minimal yield benefit from N rates above 30 kg ha−1 in wet seasons. Fertilizer-N contributed only 30% of the total plant N, seldom exceeding 40%. Nitrogen rates over 30 kg ha−1 significantly increased soil N uptake in plants (p < 0.05), demonstrating a clear ANI effect of higher N rates. Soil N withdrawal by plants and ANI were the highest in the treatment receiving 160 kg N ha−1, but the fertilizer-N retention in the soil was not enough to compensate for the increased soil N withdrawal, leading to more negative net soil N balance. We demonstrate that excessive N input increases soil N uptake by rice plants, and this combined with low retention of fertilizer-N in sandy paddy soils, leads to more negative soil N balance.

Nitrogen (N) recoveries in rice paddies have barely exceeded 60%, despite the implementation of several management strategies, amounting to significant N being lost to the environment. We conducted field experi-ments for three consecutive rice growing seasons at two locations in Myanmar to investigate the performance of urea-briquette deep placement (UDP) against variable rates of surface broadcast urea for improving N recovery and yields in rice paddies. The experiment consisted of a control (N0), 77.6 kg N ha-1 as UDP, and surface broadcast urea at 77.6 kg N ha-1 (N78), 100 kg N ha-1 (N100) and 160 kg N ha-1 (N160). Surface broadcast urea was applied in two equal splits at 10 days after transplanting (10 DAT) and at panicle initiation (PI) stage. Urea briquettes (2.7 g) were deep placed (75 mm) in the middle of four rice hills between alternate rows as a single dose at 10 DAT. Microplots receiving 15N labeled urea were installed in each treatment plot (except N100) to trace the fate of the applied N. Nitrogen input almost always produced higher grain yields (p < 0.05) compared to the control. Rice grain yield in the UDP treatment was similar or higher than in the N78, N100 and N160 treatments. Crop dry biomass yield in the UDP treatment was mostly higher (p < 0.05) than in the N78 and always similar to the N160 treatment. Higher crop (47-61%) and soil (24-40%) recovery of 15N was observed in the UDP treatment than in the N78 and N160 treatments, leading to total recoveries of 77-95%. The N78 treatment had crop recoveries of 30-37% and total recoveries of 41-60% and the N160 treatment had crop recoveries of 29-39% and total recoveries of 40-54%. The rice plants in the UDP treatment relied less on native soil N, indicating that the UDP practice can minimize soil N depletion. Our results show that UDP has substantial advantages over surface broadcasting in terms of N fertilizer recovery and may provide environmental benefits.

Sugarcane (Saccharum spp.) farming systems globally have largely transitioned away from burning the crop prior to harvest. Harvesting the sugarcane crop 'green' results in large volumes of biomass residues being left on the soil. Despite this, there is little evidence for increased soil organic carbon stocks. We investigated the role of surface application or incorporation (0-200 mm soil layer) of harvest residues (15 t dry weight residues ha(-1)) and its biochar (5.4 t ha(-1) based on the quantity of resource recovered after pyrolysis) on the priming of native soil organic carbon (SOC), the mineralisation of the organic amendments and the source of crop nitrogen (N) uptake (soil, organic amendment or urea). All treatments received urea at 180 kg N ha(-1). To achieve the separation of C and N sources, dual C-13 and N-15-enriched sugarcane residues and corresponding biochar (350 degrees C) were used in an 84-d controlled environment study. A three-pool isotope mixing model, utilising two levels of C-13 enrichment in residue (16.6 parts per thousand and 23.8 parts per thousand) and biochar (16.8 parts per thousand and 24.1 parts per thousand), was also applied to partition the C from three sources: 1) root respiration, 2) organic amendment mineralisation, and 3) SOC priming. The SOC mineralisation was increased following both surface-applied and incorporated residues, over the nil organic amendment (control) by 72.3 and 78.3 CO2-C m(-2) respectively over 84 days. In contrast, biochar lowered the mineralisation of SOC by 62.9 g CO2-C m(-2) compared to the control. The cumulative mineralisation of sugarcane residue biochar (18.9 g CO2-C m(-2)) was lower (P = 0.03) than surface applied residue (50.1 g CO2-C m(-2)) and incorporated residue (71.9 g CO2-C m(-2)) over the study period. While there were no differences in total crop N uptake between the organic-amended soils and the control, the source of N was significantly different. The sugarcane plants utilised 31.0% and 29.4% of the supplied urea N in the nil organic-amended control and biochar treatment, respectively. This was significantly reduced to 24.8% and 20.6% in the surface residue and incorporated residue treatments, respectively. In comparison, the plant uptake of N derived from the organic amendments was 27.8%, 15.4% and 6.4% from incorporated residues, surface-applied residues and biochar, respectively (P < 0.001). Results suggest that the increased mineralisation of SOC, partly driven by the high C:N ratio (73:1) and the unbalanced nutrient stoichiometry may lead to low SOC accumulation from surface residue application and that sugarcane residue biochar results in SOC stabilisation and an increase in the use efficiency of fertiliser N in sugarcane systems.

Microplastics and nanoplastics are emerging pollutants of global importance. They are small enough to be ingested by a wide range of organisms and at nano-scale, they may cross some biological barriers. However, our understanding of their ecological impact on the terrestrial environment is limited. Plastic particle loading in agroecosystems could be high due to inputs of some recycled organic waste and plastic film mulching, so it is vital that we develop a greater understanding of any potentially harmful or adverse impacts of these pollutants to agroecosystems. In this article, we discuss the sources of plastic particles in agroecosystems, the mechanisms, constraints and dynamic behaviour of plastic during aging on land, and explore the responses of soil organisms and plants at different levels of biological organisation to plastic particles of micro and nano-scale. Based on limited evidence at this point and understanding that the lack of evidence of ecological impact from microplastic and nanoplastic in agroecosystems does not equate to the evidence of absence, we propose considerations for addressing the gaps in knowledge so that we can adequately safeguard world food supply.

A long-term field experiment in western Sydney evaluated the effect of source-separated green-waste (garden organics) compost on peri-urban vegetable crop yields and economic returns, compared to farmer practice. Comparisons were made over 10 vegetable crops between a compost (COMP) treatment (one off application of 125 dry t ha −1 of green waste compost at the start and then every five crops, supplemented with urea when required), a mixed (MIX) treatment (one-off compost application of 62.5 dry t ha −1 at start and then every five crops, but with inorganic NPK fertiliser inputs for each crop) and a conventional farmer practice (FP). Both COMP and MIX treatments consistently achieved similar or higher yields than FP, but the yield gains were more pronounced for COMP. COMP and MIX treatments delivered benefit–cost ratios of 3.3 and 2.6 respectively compared to FP over the 10 crops, indicating that this system could deliver economic benefits to growers as well as improve soil quality and the environment. Follow up large applications of compost generated more substantial yield increases in responsive vegetable crops and economic benefits. The substantial capsicum crop yield response provided a classic example of closing a crops ‘yield gap’ through improvements to soil quality with organic inputs, with implications for food security. The COMP treatment lifted the capsicum yield to ~ 60 t ha −1 , 50% above its perceived maximum potential crop yield for Eastern Australia. The value of larger applications of compost for soil quality, fertiliser savings, crop yield and farm income was apparent.

A 49week soil incubation study employing 15 recycled organic (RO) wastes was conducted to investigate relations (through Kendall correlation analysis) between plant available nitrogen (PAN) supply and soil recalcitrant carbon (C) parameters with those of the RO waste chemical properties as determined by wet chemistry and spectroscopic methods. The hot water extractable organic C to hot water extractable nitrogen (N) ratio (HWOC:HWN ratio) was often the highest correlating property for mineral N supply (mg mineral N kgdrywaste−1), while many of the 13C NMR functional group parameters such as the aromatic C to N ratio, phenyl C to N ratio, and aryl C to carbonyl C ratio were also significantly correlated with mineral N supply. These functional group C properties were significantly correlated with mineral N release in the later phase of the incubation (i.e. 12–49weeks), while HWOC:HWN ratio was highly correlated with the early period (0–2weeks) but this period had a dominant influence on the total supply. The fore mentioned 13C NMR functional group properties were also significantly correlated with recalcitrant C, but the fraction of total RO waste C as aromatic C (110–165ppm) was the parameter most highly correlated with this property. Molecular C component composition had no predictive advantage over functional group data. Future work should focus on narrow classes of organic amendments for predictive correlations.

Alternative management practices need to be developed to improve the sustainability of intensive vegetable production in peri-urban areas. A field trial was established in 2005 at Camden, near Sydney, Australia to evaluate the effect of garden organic compost on vegetable production and soil quality relative to conventional practice and under low and high soil P status. The trial comprised seven treatments; compost (garden organic), conventional practice (fertiliser and poultry manure) and a mixture of compost and inorganic fertiliser, all replicated at high and low soil P, plus a nil control. Compost was applied once at the beginning of the trial and again before the 6th crop (125 dry t/ha/application). Results are reported for 7 consecutive vegetable crops: broccoli, eggplant, cabbage, capsicum, leek, capsicum and broccoli. Production and crop quality parameters were recorded. Soil samples were collected and chemical, physical and biological properties analysed at the time of planting all crops and prior to harvest for crops 4 to 6. Soil biological indicators measured include basal respiration, microbial biomass carbon, hydrolysis of fluorescein diacetate (FDA) and fungal DNA. Compost application significantly increased soil respiration in the first crop but the benefit was diminished in subsequent crops. The response was more pronounced in the crop soils following the second compost application with respiration, biomass and FDA higher in the compost treatments. Preliminary DNA analysis of soil samples collected in the second capsicum crop found a greater diversity of fungal organisms in the low P compost treatment. Future work will look at expanding the assessment of soil biological indicators and the potential for pathogen suppression.

A field experiment was established near Camden in south west Sydney, Australia in 2005 to evaluate the effect of garden organics compost on vegetable production and soil quality relative to conventional practice. Treatments were full compost (125 dry t/ha), half compost (62.5 dry t/ha supplemented by inorganic fertilisers), conventional farmers practice (mixture of poultry manure and inorganic fertilisers), and control (nil inputs) in a fully randomised and replicated experiment with 4 blocks. It was evident at the start of the experiment (i.e., crop 1), that compared to the conventional farmers practice treatment, the full compost treatment (120 dry t/ha) had produced significantly (P<0.05) higher soil carbon levels (2.1 vs. 1.3%), eCEC (11.5 vs. 7.5 cmol (+)/kg), bicarbonate extractable P (108 vs. 59 mg/kg), NO3--N (123 vs. 63), exchangeable K (1.2 vs. 0.5 cmol(+)/kg), exchangeable Ca (7.6 vs. 5.6 cmol (+)/kg), and pH (5.8 vs. 5.2), but also higher EC (0.38 vs. 0.16 mu S/cm) and exchangeable Na (0.4 vs. 0.2 cmol (+)/kg) levels in the 0-15 cm soil layer. These soil properties were monitored over 5 successive crops to determine trends over time. The trend in soil carbon levels in the compost treatments over time fluctuated up and down partly due to the influence of variable inputs from crop residues which were incorporated into the soil, but by the fourth crop had been reduced slightly from 2.1 to 1.9 g/100 g and the ECEC from 11.5 to 11.2 cmol (+)/kg. The conventional farmers practice treatment revealed how currently recommended P application rates are excessive and lead to elevated Colwell P levels in the soil. The compost system supplied P to the crop with lower risk to the environment. The compost treatment also improved soil structure relative to the conventional practice treatment, resulting in a higher proportion of the soil as water stable aggregates >0.25 mm. This study demonstrated that a 125 dry t/ha compost application rejuvenated soil quality and maintained many soil quality benefits over the five crops, despite the high tillage associated with rotary hoe use in this system.

Using solid state (13)C NMR data and elemental composition in a molecular mixing model, we estimated the molecular components of the organic matter in 16 recycled organic (RO) wastes representative of the major materials generated in the Sydney basin area. Close correspondence was found between the measured NMR signal intensities and those predicted by the model for all RO wastes except for poultry manure char. Molecular nature of the organic matter differed widely between the RO wastes. As a proportion of organic C, carbohydrate C ranged from 0.07 to 0.63, protein C from <0.01 to 0.66, lignin C from <0.01 to 0.31, aliphatic C from 0.09 to 0.73, carbonyl C from 0.02 to 0.23, and char C from 0 to 0.45. This method is considered preferable to techniques involving imprecise extraction methods for RO wastes. Molecular composition data has great potential as a predictor of RO waste soil carbon and nutrient outcomes.

Forages cover extensive areas of agricultural land in Australia, but only limited data is available on the potential of these different forages to sequester soil organic carbon (SOC) under best practice management. This study was undertaken on a brown dermosol in the warm temperate climate of Camden, Australia, over three years, to evaluate a range of perennial and annual forages for their impact on SOC and soil nitrogen (N). The C4 perennial forages kikuyu (Pennisetum clandestinum Hochst. ex. Chivov.) and paspalum (Paspalum dilatatum Poir.) increased (P < 0.05) SOC by 7 g/kg from 27 g/kg initially over the three years which was equivalent to an annual increase of approximately 2.6 t C/ha. For the other forage species, the SOC did not change (P > 0.05). The high productivity of legumes led to high mean estimate of N fixation of up to 726 kg N ha/year over the three years. However, as most of the legume shoot production of the forage species was removed there, was a negligible increase in soil N levels. This study has shown that the choice of forage has a large impact on the amount of carbon that can be sequestered into the soil.

Background, aim, and scope Current Australian legislation permits the beneficial application of grease trap waste (GTW) to agricultural soil, viewing it as a beneficial source of organic matter and soil conditioner containing no/low amounts of metals or pathogenic organisms. However, little is known about the influence of GTW on soil bacterial community. A field experiment was established at Menangle in south western Sydney in Australia to quantitatively assess the impacts of different types (GTW CO and GTW CL) and amounts of GTW application on the soil bacterial community and diversity. Furthermore, a municipal solid waste (MSW) compost was simultaneously examined to compare against the other organic wastes. Knowledge about the shifts in microbial community structure and diversity following the applications of organic wastes could help to evaluate the ecological consequences on the soil and thus to develop sound regulatory guidelines for the beneficial reuse of organic wastes in agricultural lands. Materials and methods Soil samples were collected from recycled organics plots treated with different types and quantity of organic wastes. The field experimental treatments included control (CK, without application of any organic wastes), low amount of GTW CO (COL), GTW CL (CLL), and MSW (ML), and high amounts of GTW CO (COH), GTW CL (CLH), and MSW compost (MH). Microbial DNA was extracted from soil samples and the 16S rRNA genes were polymerase chain reaction (PCR)-amplified. The PCR products were analyzed by denaturing gradient gel electrophoresis (DGGE), cloning, and sequencing. The bacterial community structures and diversity were assessed using the DGGE profiles and clone libraries constructed from the excised DGGE bands. Results DGGE-based analyses showed that application of the GTW CO, regardless of the amount applied, had significant negative effects on soil bacterial genotypic diversity and community structure compared with the control, while the applications of other organic wastes including the GTW CL and MSW had no clear effects. The effects of the rate of organic waste application on soil bacterial community characteristics varied with the types of organic wastes applied. Sequence-based analyses of 126 clones indicated that Proteobacteria (53.2%) was the dominant taxa at the experimental site, followed by Actinobacteria (9.5%), Bacteroidetes (7.9%), Firmicutes (7.9%), Gemmatimonadetes (5.6%), Chloroflexi (2.4%), Acidobacteria (1.6%) and the unclassified group (11.9%). In the COH treatment, Acidobacteria , Bacteroidetes , and Gemmatimonadetes were not detected; the percentages of Firmicutes , Proteobacteria , and Actinobacteria in the COH treatment were significantly different from those in CK. There is a significant positive correlation ( r = 0.71, p = 0.002) between the C/N ratio of organic wastes and the bacterial genotypic communities. Discussion Both the type and the amount of GTW applied affected soil bacterial genotypic diversity and community structure. The different effects of various types of organic wastes on soil bacterial characteristics may be predicted by the differences in specific properties of organic wastes such as C/N ratio, as evidenced by the strong and significant positive relationship between the bacterial community distance and the environmental distance of C/N ratio. This also indicates that the C/N ratio of GTW applied can be a major driver for the shift in the soil bacterial community. Conclusions Our results revealed that the effects of organic wastes on soil bacterial communities varied with the types of organic wastes, and depending on the rate of application. Application of the GTW CO led to significant shifts in soil bacterial community diversity and structure. The effects of different types of organic wastes on the soil bacterial characteristics can be predicted by the differences of specific properties of organic wastes, such as the C/N ratio. Sequence-based analyses of 126 clones indicated that Proteobacteria was the dominant taxa at the experimental site. Recommendations and perspectives Our results have important implications for developing sound regulatory guidelines for the beneficial reuse of organic wastes, indicating that GTW CO and similar organic waste treatments may not be suitable for application in agricultural soils due to its significant negative effect on soil bacterial community.

Vegetable production is often located in the peri-urban areas close to large cities. In Sydney, Australia, excessive levels of phosphorus (P) have been reported in the soils, and vegetable farms have long been regarded as a potential source of the P that enters Sydney's waterways. We report vegetable production under varying soil P conditions and the consequent changes in soil P, as well as water quality of runoff and leachate after growing 5 crops in a field trial where inputs in the form of garden organic compost were compared to current farmers' practice. No difference in vegetable yield was observed between 100 and 400 mg/kg of soil Colwell P (0-0.10 m); therefore, our results indicate that the excessive soil P levels in the vegetable farms around Sydney are not important for optimal vegetable production. Results from runoff and leachate studies clearly demonstrate that high concentrations of P in soils used for vegetable production under the current farming practice around Sydney have increased the potential to export P and to negatively affect water quality of receiving environments. The significant increases in soluble P concentrations found in the soil and runoff water from the current farming practice can be attributed to the use of poultry litter. In contrast, using compost in place of poultry litter resulted in significantly reduced soil P accumulation and P concentration in runoff and leachate. Training and education programs for farmers and their advisors are recommended to encourage more sustainable fertiliser management practices and reduce the accumulation of P in the environment.

This soil monolith production method, initially developed in the late 1990s, has now been successfully applied to over 100 soil profiles, dealing with the majority of Australian soils ranging from clays to sands, from uniform to texture contrast profiles, and from alkaline soils to even acid sulphate soils. The method outlined utilises intact soil profiles (150 mm diameter undisturbed soil cores collected with a Proline hollow flight auger). This technique is rapid and minimises site disturbance. A modern acrylic bonding compound (Bondcryl 737(R)) was selected as the bonding agent because it is strong, durable, UV resistant, and non-toxic. The bonding agent is applied to the soil profile as a series of fine misty sprays using a hand pump action spray bottle. After several applications the solution permeates through the outer 5 mm or more of the soil, bonding the whole profile together. The finished soil monolith has a moist soil colour, but with a natural non-glossy appearance. A decade has now passed since the first monoliths were made using this method, and those monoliths are still being transported and displayed regularly. They remain in good condition, giving us some confidence in the reliability of this method. (C) 2009 Elsevier B.V. All rights reserved.

A simulated rainfall study was carried out on couch (Cynodon dactylon cv) turf on a Haplic Lixisol soil at Camden in South Western Sydney, Australia, to compare surface applications of a new granulated biosolids product with poultry litter (the current turf farm practice) in terms of runoff water quality impacts. The granulated biosolids were surface applied to the turf at a total N loading of 240 kg N ha−1, equivalent to the current turf farm practice of applying 18.9 m3 ha−1 of poultry litter. One week after the application of the organic fertiliser treatments, simulated rainfall was applied to each plot at an intensity of 90 mm h−1 for a period of 0.5 h, and all runoff water was collected and analysed for a range of important water quality parameters. The most significant result from this study was the finding that runoff water samples from the poultry litter treatment plots were found to contain 10 times more total P (12.3 mg l−1 compared to 1.2 mg l−1) and dissolved P (8.3 mg l−1 compared to 0.6 mg l−1) than that found in the runoff water samples from the biosolid treatment. The relationship between application total P loading (TPA) and runoff water total P concentration (RO-P) was significantly (P < 0.05) different between the biosolids (RO-P:TPA ratio = 0.01) and poultry litter (RO-P:TPA ratio = 0.16) products, reflecting the importance of the chemical nature of the applied P in addition to the total loading. The phosphorus in the poultry litter was much more easily mobilised and transported in runoff than the biosolids P. For surface applications of these organic wastes, bicarbonate extractable P loading provided a better indication of runoff P contamination risk in the first flush of runoff, than total P loading. The runoff from the biosolid treatment plots also had lower levels of NH4-N and salinity than the poultry litter plots, although both treatments had moderate levels of dissolved organic carbon in their runoff. Heavy metal levels in the runoff were below guideline limits for both organic amendments, while runoff pathogen levels were highly variable. Our findings highlight the potential benefits of using granulated biosolids as an alternative surface applied organic N fertiliser on turf farms for its lower risk to surface water quality as compared to poultry litter, the current practice.

Current State government guidelines attempt to ensure that the supply of plant available nitrogen (PAN) from land-applied biosolids does not exceed the crop's requirement for mineral nitrogen (N), in order to minimise the risk of excess nitrate contaminating surface and groundwater. In estimating a suitable application rate, current guideline methodology assumes a fixed proportion of the organic N in the biosolids will be mineralised in the first year following the application for all situations. Our study included a field trial and a field incubation study to assess N mineralisation for both a granulated biosolid and a dewatered biosolid product, together with an additional laboratory incubation study for the granulated biosolid product. The application rates were 12, 24, and 48 dry t/ha for the granulated biosolids and 22 dry t/ha for the dewatered biosolids. Our results showed that the guideline procedure underestimated the supply of mineral N from the biosolid-treated soils, with more than 3 times the predicted amount being supplied by the biosolids at all application rates. The excess supply of mineral N was due to a much larger proportion of the biosolid organic N being mineralised than the assumed 25%, as well as a significant contribution of mineral N from the soil itself (which is ignored in the estimation calculation). The proportion of biosolid organic N mineralised in the 12-month field incubation study for the 3 granulated biosolid treatments (12, 24, and 48 dry t/ha) and the dewatered biosolid treatment (22 dry t/ha) were estimated to be 54%, 48%, 45%, and 53%, respectively, in our field incubation study. Both the laboratory and field incubation studies found that most of the biosolid mineralisable organic N was mineralised rapidly during the early stages of the incubation. In the field incubation, the 24 dry t/ha granulated biosolid treatment had 35% of its organic N mineralised within the first 2 months following application, while all granulated biosolid treatments in the laboratory incubations had by, day 29, supplied >50% of the mineral N they would supply for the whole 216-day incubation. This release pattern for the supply of PAN from biosolid organic N should be factored into fertiliser application strategies. Our study reveals some of the shortcomings of the currently recommended 'one size fits all' approach for estimating the PAN supply from land-applied biosolids. Further research on the development of an effective rapid assessment for the mineralisable N content in organic wastes and soils, in combination with modelling, may improve our capacity to predict PAN supply from land-applied organic wastes in the future.