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    The role of earthworms in nitrogen release from herbage residues : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Soil Science at Massey University
    (Massey University, 1987) Ruz-Jerez, Belarmino Emilio
    Decomposition and nutrient release from pasture litter were examined in two biotic systems; either with or without large organisms ("macrobes"). Earthworms were the test macrobe and nitrogen (N) the test nutrient. This experiment addressed the hypothesis that consumption of herbage residues by macrobes, as opposed to microbes, should result in more of the contained N becoming available for uptake by plants or for loss processes, because macrobes oxidise a greater proportion of the contained carbon (C) by energetics. Earthworms influenced both soil metabolism and mineral N availability, irrespective of litter type (ryegrass or clover) and temperature (15 or 22.5 C). Carbon dioxide evolution and oxygen consumption increased by 26% and 39%, respectively, in the presence of earthworms. After an 11-week incubation about 50% more mineral N was recorded in the soils containing earthworms. Moreover, less microbial biomass was recorded in the presence of worms. This influence of macrobes carried over into a subsequent, exhaustive cropping experiment, using ryegrass as the test plant. Where soils had been previously influenced by earthworms, there was a significant increase in plant growth and N uptake. Carbon dioxide evolved during incubation was highly correlated with soil mineral N (r= 0.84** ) present at the conclusion of incubation, and also with subsequent plant dry matter yield (r= 0.75** ) and plant N yield (r=0.85** ). The link between elaborated C and contained N has long been recognised as providing stability to organic residues in soils. In the design of this experiment, other influences of macrobes (e.g. mixing or structural influences) were largely obviated, so one can conclude that nitrogen availability was increased primarily through carbon respiration by the macrobial population. These results offer a fresh perspective on the balance between mineralisation and immobilisation in the soil-plant complex and, hence, on the dynamics of nutrients contained in organic matter. Better understanding of these relationships may allow improved management of the dynamics of soil organic matter in temperate grassland ecosystems.
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    Nitrification activity in New Zealand soils and the variable effectiveness of dicyandiamide : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Ph.D.) in Soil Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2011) Rajendran, Janice
    A perfusion technique was developed by which the rate of nitrification could be monitored as it changed over time following one or more additions of a nitrification inhibitor called dicyandiamide (DCD) in two contrasting soils - namely Manawatu Silt Loam (MSL) and Manawatu Fine Sandy Loam (MFSL). The modes of action of DCD in both soils were similar but the effectiveness of DCD varied between the two soils, with greater inhibition of nitrification in the MFSL than in the MSL when expressed as a percentage of the control soil. However when expressed in actual nitrification rates (absolute terms), greater inhibition of nitrification was obtained in the MSL as compared to MFSL. The actual reductions in nitrification rates between the two soils were almost similar, but the effect of DCD on the NO3 --N reduction in the MSL was slightly higher than in the MFSL. The nitrification rates in both soils gradually recover following the addition of DCD, but it didn’t return to the initial levels in either soil. This ongoing inhibition effect was more obvious in the MFSL. The effect of DCD on the ammonia oxidising bacteria (AOB) populations in both soils followed a similar pattern to the nitrification activities, with an inhibition of nitrifier population in the presence of DCD and a recovery of the temporarily suppressed nitrifier populations when the DCD solution was removed from the system and was replaced with a fresh nitrogen source. Again, there was a residual effect of DCD on AOB numbers and this appeared to be greater in the MFSL than in the MSL. In a separate experiment the effectiveness of DCD in the two soils was similar to that obtained in Chapter 3, in which it differed when expressed as percentage and absolute terms. DCD was more effective, with higher inhibition was obtained, in the MFSL than in the MSL when expressed as a percentage of the control. This was probably due to the differences in the rate of DCD degradation in both soils, in which DCD degraded two times slower in the MFSL than in the MSL. The effectiveness of DCD was also different between the two soils, when the same amount of DCD remained in both soils, with higher inhibition was obtained in the MSL than in the MFSL. Thus, in absolute terms DCD was more effective in the MSL. In a further experiment it was demonstrated that soils collected from steep slopes (SS) in a hill country paddock had low nitrification rates compared to soils collected from adjacent camp sites (CS). These low nitrification rates were associated with similarly low populations of AOB in the SS soils. Of interest was the observation that the numbers of AOB and the nitrification rate in absolute terms in the SS did not increase greatly over the time, even with a plentiful supply of NH4 + substrate from added urea and the associated higher pH. It was not clear whether the low initial population of AOB in SS resulted from low inputs of NH4 + substrate over many years, or whether in addition there was an inhibitory effect that may have prevented a build-up of the nitrifiers. A subsequent investigation suggested that the low nitrifying SS soil may exert a small inhibiting effect when mixed with high nitrifying CS soils. In conclusion DCD was found to vary in its effectiveness in soil types. The effectiveness of DCD in reducing NO3-N production in grazed pasture systems is a function of both its half life in the soil and also the extent of inhibition of nitrification at a given concentration of DCD in the soil.
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    Copper induces nitrification by ammonia-oxidizing bacteria and archaea in pastoral soils
    (Wiley, 12/12/2022) Matse D; Jeyakumar P; Bishop P; Anderson C
    Copper (Cu) is the main co-factor in the functioning of the ammonia monooxygenase (AMO) enzyme, which is responsible for the first step of ammonia oxidation. We report a greenhouse-based pot experiment that examines the response of ammonia-oxidizing bacteria and archaea (AOB and AOA) to different bioavailable Cu concentrations in three pastoral soils (Recent, Pallic, and Pumice soils) planted with ryegrass (Lolium perenne L.). Five treatments were used: control (no urine and Cu), urine only at 300 mg N kg-1 soil (Cu0), urine + 1 mg Cu kg-1 soil (Cu1), urine + 10 mg Cu kg-1 soil (Cu10), and urine + 100 mg Cu kg-1 soil (Cu100). Pots were destructively sampled at Day 0, 1, 7, 15, and 25 after urine application. The AOB/AOA amoA gene abundance was analyzed by real-time quantitative polymerase chain reaction at Days 1 and 15. The AOB amoA gene abundance increased 10.0- and 22.6-fold in the Recent soil and 2.1- and 2.5-fold in the Pallic soil for the Cu10 compared with Cu0 on Days 1 and 15, respectively. In contrast, the Cu100 was associated with a reduction in AOB amoA gene abundance in the Recent and Pallic soils but not in the Pumice soil. This may be due to the influence of soil cation exchange capacity differences on the bioavailable Cu. Bioavailable Cu in the Recent and Pallic soils influenced nitrification and AOB amoA gene abundance, as evidenced by the strong positive correlation between bioavailable Cu, nitrification, and AOB amoA. However, bioavailable Cu did not influence the nitrification and AOA amoA gene abundance increase.
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    Nitrification rate in dairy cattle urine patches can be inhibited by changing soil bioavailable Cu concentration
    (Elsevier, 17/01/2023) Matse D; Jeyakumar P; Bishop P; Anderson C
    Ammonia oxidation to hydroxylamine is catalyzed by the ammonia monooxygenase enzyme and copper (Cu) is a key element for this process. We investigated the effect of soil bioavailable Cu changes induced through the application of Cu-complexing compounds on nitrification rate, ammonia-oxidizing bacteria (AOB) and archaea (AOA) amoA gene abundance, and mineral nitrogen (N) leaching in urine patches using the Manawatu Recent soil. Further, evaluated the combination of organic compound calcium lignosulphonate (LS) with a growth stimulant Gibberellic acid (GA). Treatments were applied in May 2021 as late-autumn treatments: control (no urine), urine-only at 600 kg N ha-1, urine + dicyandiamide (DCD), urine + co-poly-acrylic-maleic acid (PA-MA), urine + LS, urine + split-application of LS (2LS), and urine + combination of GA plus LS (GA + LS). In addition, another four treatments were applied in July 2021 as mid-winter treatments: control, urine-only at 600 kg N ha-1, urine + GA, and urine + GA + LS. Soil bioavailable Cu and mineral N leaching were examined during the experimental period. The AOB/AOA amoA genes were quantified using quantitative polymerase chain reaction. Changes in soil bioavailable Cu across treatments correlated with nitrification rate and AOB amoA abundance in late-autumn while the AOA amoA abundance did not change. The reduction in soil bioavailable Cu induced by the PA-MA and 2LS was linked to significant (P < 0.05) reduction in mineral N leaching of 16 and 30%, respectively, relative to the urine-only. The LS did not induce a significant effect on either bioavailable Cu or mineral N leaching relative to urine-only. The GA + LS reduced mineral N leaching by 10% relative to LS in late-autumn, however, there was no significant effect in mid-winter. This study demonstrated that reducing soil bioavailable Cu can be a potential strategy to reduce N leaching from urine patches.