Composition and availability of bioreactor feedstock from New Zealand agribusiness – Progress report

The purpose of this report is to supply information so that users of the bioreactor Feedstock Table and associated summary tables can confidently use them as designed. Included is a description of the layout of the bioreactor Feedstock Table. This table lists published details of the volume and characteristics of feedstock produced by a range of farms and primary processing industries within the New Zealand agricultural sector. Summary tables describing the volume and composition of differing types of feedstocks from various sources are also discussed.Report no. RE450/2023/074</p

A comparison of the threshold concentrations of DCD, DMPP and nitrapyrin to reduce urinary nitrogen nitrification rates on pasture soils: A laboratory study

  Context: Using nitrification inhibitors (NIs) for the targeted management of urine patches, to reduce nitrous oxide (N2O) emissions, requires determining the threshold concentrations of the NIs in urine for effective nitrification inhibition. Aims: This study comparatively assessed the threshold concentrations of three NIs: dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP) and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) to reduce urinary nitrogen (N) nitrification rates on two contrasting pasture soils. Methods: Four rates of each NI (3–27 mg DCD kg−1 soil, 1–13 mg DMPP kg−1 soil and 1–14 mg nitrapyrin kg−1 soil) were added to urine-amended soils and incubated at laboratory room temperature. The amended soils were sampled periodically to monitor changes in mineral-N concentrations. Key results: The threshold concentration of DCD (3 mg kg−1 soil, lowest rate tested) was lower than that of nitrapyrin (5–7 mg kg−1 soil) and DMPP (13 mg kg−1 soil, highest rate tested) on both soils. Greater NI effectiveness corresponded to greater NI persistence, with higher (P P  Conclusions: Compared with DCD and nitrapyrin, a higher DMPP concentration was required to effectively inhibit urinary N nitrification rates in the pasture soils. Implications: Choosing the ideal application rate of NIs to inhibit nitrification under field condition, and hence mitigate N2O emissions from urine patches, requires consideration of the factors that affect NI loss.</p

Differential immediate and long-term effects of nitrogen input on denitrification N₂O/(N₂O +N₂) ratio along a 0–5.2 m soil profile

High nitrogen (N) input to soil can cause higher nitrous oxide (N2O) emissions, that is, a higher N2O/(N2O+N2) ratio, through an inhibition of N2O reductase activity and/or a decrease in soil pH. We assumed that there were two mechanisms for the effects of N input on N2O emissions, immediate and long-term effect. The immediate effect (field applied fertilizer N) can be eliminated by decreasing the N input, but not the long-term effect (soil accumulated N caused by long–term fertilization). Therefore, it is important to separate these effects to mitigate N2O emissions. To this end, soil samples along a 0–5.2 m profile were collected from a long-term N fertilization experiment field with two N application rates, that is, 600 kg N ha-1 year-1 (N600) and no fertilizer N input (N0). External N addition was conducted for each subsample in the laboratory incubation study to produce two additional treatments, which were denoted as N600+N and N0+N treatments. The results showed that the combined immediate and long-term effects led to an increase in the N2O/(N2O+N2) ratio by 6.8%. Approximately 32.6% and 67.4% of increase could be explained by the immediate and long-term effects of N input, respectively. Meanwhile, the long-term effects were significantly positively correlated to soil organic carbon (SOC). These results indicate that excessive N fertilizer input to the soil can lead to increased N2O emissions if the soil has a high SOC content. The long-term effect of N input on the N2O/(N2O+N2) ratio should be considered when predicting soil N2O emissions under global environmental change scenarios. </p

Significance of inhibitor volume in on-farm mitigation of nitrous oxide emission from dairy cattle urine patches

Technologies are being developed for the targeted mitigation of nitrogen (N) losses from livestock urine patches using urease and nitrification inhibitors (UIs and Nls). In our earlier study, we identified a major limitation for inhibitor efficiency, specifically, the application of a 40 mL volume of inhibitor solution to a 2L of urine patch (i.e., 1:50, based on New Zealand recommended dicyandiamide [DCD] application rate of 10 kg DCD dissolved in 800 L water ha-1).This ongoing research evaluates the effect of inhibitor treatments by varying the inhibitor: urine volume ratio from 1:50 to 1:10 (200 mL of inhibitor to the 2L of urine patch) on nitrous oxide (N2O) mitigation of five nitrification inhibitors: DCD, 3,4-dimethylpyrazole phosphate (DMPP), 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin), and two confidential compounds (named A and C, provided by AgResearch). These inhibitors were applied 24 hours after creating 2L simulated urine patches (within 0.5 m2 chambers) in two dairy-grazed pasture soils with contrasting drainage (poorly vs well drained). Results showed that the N2O emissions reduction efficiency from urine patches was the highest (35.8%–46.7%) with DCD followed by inhibitor C (26.9%–27.9%). The reductions in emission from the other inhibitors were not significant (11.0%–23.0% with DMPP and nitrapyrin, respectively; and 1.5%–15.6% with inhibitor A). In this study, diluting the inhibitor solutions resulted in retention of only 3% to 18% of the NIs by the pasture canopy compared with up to 59% (with 1:50) in our previous study. This dilution increases the amount of inhibitor reaching the soil, offering a potential option for effectively reducing N2O emissions from cattle urine patches. However, dilution may result in concentrations below threshold levels of DMPP, nitrapyrin and inhibitor A, compromising their effectiveness. These results warrant further research to optimise inhibitor application rate and volume and measure inhibitor residues for developing best practice for targeted application of inhibitors to urine patches while addressing unintended food and human health risks.</div

Spatio-temporal variation of net anthropogenic nitrogen inputs (NANI) from 1991 to 2019 and its impacts analysis from parameters in Northwest China

At present, excessive nutrient inputs caused by human activities have resulted in environmental problems such as agricultural non-point source pollution and water eutrophication. The Net Anthropogenic Nitrogen Inputs (NANI) model can be used to estimate the nitrogen (N) inputs to a region that are related to human activities. To explore the net nitrogen input of human activities in the main grain-producing areas of Northwestern China, the county-level statistical data for the Ningxia province and NANI model parameters were collected, the spatio-temporal distribution characteristics of NANI were analyzed and the uncertainty and sensitivity of the parameters for each component of NANI were quantitatively studied. The results showed that: (1) The average value of NANI in Ningxia from 1991 to 2019 was 7752 kg N km-2 yr-1. Over the study period, the inputs first showed an overall increase, followed by a decrease, and then tended to stabilize. Fertilizer N application was the main contributing factor, accounting for 55.6%. The high value of NANI in Ningxia was mainly concentrated in the Yellow River Diversion Irrigation Area. (2) The 95% confidence interval of NANI obtained by the Monte Carlo approach was compared with the results from common parameters in existing literature. The simulation results varied from -6.4% to 27.4% under the influence of the changing parameters. Net food and animal feed imports were the most uncertain input components affected by parameters, the variation range was -20.7%-77%. (3) The parameters of inputs that accounted for higher proportions of the NANI were more sensitive than the inputs with lower contributions. The sensitivity indexes of the parameters contained in the fertilizer N applications were higher than those of net food and animal feed imports and agricultural N-fixation. This study quantified the uncertainty and sensitivity of parameters in the process of NANI simulation and provides a reference for global peers in the application and selection of parameters to obtain more accurate simulation results. </p

Rice root Fe plaque increases paddy soil CH4 emissions via the promotion of electron transfer for syntrophic methanogenesis

Iron (Fe) plaque is a concentrated form of microbially available Fe oxide that coats rice plant root surfaces, representing a high density of Fe oxide and which potentially mediates paddy soil CH4 emissions. Using a combination of methods including Fe plaque induction, isotopic labeling, pure microbial strains, and Fe oxide addition experiments, we investigated the impact of Fe plaque on methane (CH4) emissions from paddy soils and explored the associated mechanisms underlying the influence of Fe plaque on CH4 emissions. A 13C–CH4 isotopic labeling experiment showed that Fe plaque did not significantly affect CH4 oxidation and associated gene expression, whereas Fe plaque significantly enriched methanogenic archaea and their expression of genes associated with methanogenesis. Pure microbial strain and Fe oxide addition experiments showed that the enhancement of CH4 production in the presence of Fe plaque was caused by the (semi) conductive minerals within the Fe plaque, specifically, hematite, which promoted the extracellular electron transfer between the methanogenic archaea and their syntrophic bacteria, resulting in enhancement of methanogenesis. Our results imply that the presence of Fe plaque will accelerate CH4 emissions from paddy soils and suppressing Fe plaque has the potential to mitigate CH4 emissions.</p

Anthropogenic N input increases global warming potential by awakening the “sleeping” ancient C in deep critical zones

Even a small net increase in soil organic carbon (SOC) mineralization will cause a substantial increase in the atmospheric CO2 concentration. It is widely recognized that the SOC mineralization within deep critical zones (2 to 12 m depth) is slower and much less influenced by anthropogenic disturbance when compared to that of surface soil. Here, we showed that 20 years of nitrogen (N) fertilization enriched a deep critical zone with nitrate, almost doubling the SOC mineralization rate. This result was supported by corresponding increases in the expressions of functional genes typical of recalcitrant SOC degradation and enzyme activities. The CO2 released and the SOC had a similar 14C age (6000 to 10,000 years before the present). Our results indicate that N fertilization of crops may enhance CO2 emissions from deep critical zones to the atmosphere through a previously disregarded mechanism. This provides another reason for markedly improving N management in fertilized agricultural soils. </p

Foliar N₂O emissions constitute a significant source to atmosphere

Nitrous oxide (N2O) is a potent greenhouse gas and causes stratospheric ozone depletion. While the emissions of N2O from soil are widely recognized, recent research has shown that terrestrial plants may also emit N2O from their leaves under controlled laboratory conditions. However, it is unclear whether foliar N2O emissions are universal across varying plant taxa, what the global significance of foliar N2O emissions is, and how the foliage produces N2O in situ. Here we investigated the abilities of 25 common plant taxa, including trees, shrubs and herbs, to emit N2O under in situ conditions. Using 15N isotopic labeling, we demonstrated that the foliage-emitted N2O was predominantly derived from nitrate. Moreover, by selectively injecting biocide in conjunction with the isolating and back-inoculating of endophytes, we demonstrated that the foliar N2O emissions were driven by endophytic bacteria. The seasonal N2O emission rates ranged from 3.2 to 9.2 ng N2O–N g−1 dried foliage h−1. Extrapolating these emission rates to global foliar biomass and plant N uptake, we estimated global foliar N2O emission to be 1.21 and 1.01 Tg N2O–N year−1, respectively. These estimates account for 6%–7% of the current global annual N2O emission of 17 Tg N2O–N year−1, indicating that in situ foliar N2O emission is a universal process for terrestrial plants and contributes significantly to the global N2O inventory. This finding highlights the importance of measuring foliar N2O emissions in future studies to enable the accurate assigning of mechanisms and the development of effective mitigation.</p