Effects of liming on soil magnesium on some soils in New Zealand

Abstract

Results from 2 pastoral field lime trials showed that liming reduced exchangeable Mg. This effect increased with increasing rate of lime and with time following lime application, and was greatest in the top 0–50 mm depth. Soil solutions, sampled 2 years after liming, showed that solution Mg increased in increasing rate of lime. This effect was greatest in the top 20 mm of soil.

Lime incubation studies indicated that Mg fixation did occur on some of the soil studied, at pH >6.2. However, this did not account for the size of the observed effects of liming on exchangeable Mg in the field or explain the observed effects of liming at pH <6.2.

It is suggested therefore, that the major mechanism by which liming reduces exchangeable Mg, on these soils, is through displacement of exchangeable Mg into solution by the added Ca in lime, and subsequent leaching.

Results from other field trials suggest that liming will decrease exchangeable Mg if the change in pH‐dependent CEC (?ECEC) per unit change in soil pH is <15 me 100 g‐¹.     

Effects of cropping systems on soil organic matter in a pair of conventional and biodynamic mixed cropping farms in Canterbury, New Zealand

Effects of cropping systems on soil organic matter (SOM) in a pair of conventional and biodynamic mixed cropping farms were investigated. Soil samples (0–75 and 75–150-mm depths) were analysed for total carbon (TC), total nitrogen (TN), microbial biomass C (BC) and microbial biomass N (BN), and sequentially extracted for labile and stable SOM using cold water, hot water, acid mixtures and alkalis. In the biodynamic farm, TC and TN decreased with increasing period of cropping but the reverse occurred under pastures. These were not shown in soils from the conventional farm, probably due to N fertilizer additions. Under pastures, increases in SOM were attributed to greater biological N₂ fixation and the return of plant residues and excreta from grazing animals. Overall, sensitive SOM quality indicators found for labile SOM were BN, BN:TN and HC:TC, and for stable SOM were HCl/HFC, HCl/HFC:TC, humin C, humin N, humin C:TC and humin N:TN. The BN and BN:TN were better indicators than BC and BC:TC. The humin fraction was strongly related to both labile and stable SOM fractions suggesting that humin contained non-extractable strongly complexed SOM components with mineral matter and also non-extractable plant and microbial residual components. Received: 10 October 1996     

Effects of air-drying on the adsorption and desorption of phosphate and levels of extractable phosphate in a group of acid soils,New Zealand

The effects of air-drying field-moist soils on the adsorption and desorption of added phosphate and on the levels of extractable native soil phosphate were examined using the A and B horizons of a group of four acid soils.Air-drying increased the capacity of all the soil samples to adsorb phosphate. At an equilibrium solution concentration of 0.5 μg P ml^?1, the increase in the quantity of phosphate adsorbed following drying ranged from 23% to 70% of that adsorbed by the moist samples. Considerable hysteresis in phosphate adsorption—desorption isotherms was observed for both moist and dried soil samples indicating that the additional phosphate adsorbed by the dried samples was held with the same strength as that held by the moist samples.Air-drying the soil samples caused a small decrease in soil pH of approximately 0.1 pH unit and a general increase in levels of EDTA-extractable Fe, Al and organic matter. Quantities of native soil phosphate extractable with EDTA, resin and NaHCO₃ were also increased. Concentrations of oxalate- and pyrophosphate-extractable Fe and Al and exchangeable Al were, however, unaffected by drying.It was also shown that when the phosphate content of NaHCO₃ extracts is measured using the conventional molybdenum blue method, orthophosphate plus a differing amount of acid-hydrolysable organic P present in the extract is measured.     

Effects of drying on the ion exchange capacity and cation adsorption properties of some New Zealand soils

Abstract

The effect of drying on the cation (CEC) and anion (AEC) exchange capacity, and on potassium (K) and magnesium (Mg) adsorption by three New Zealand soils was investigated. Air‐drying resulted in no significant changes in these properties compared with the field‐moist samples. Oven‐drying at 105°C significantly decreased the CEC and increased the AEC of most soils compared with air‐dried samples. The decrease in CEC was related to increased solubility of organic matter and a decrease in surface area on which charge could be developed. The increase in AEC was attributed to a decrease in soil pH.

Potassium and Mg adsorption by two soils decreased following oven‐drying. This was consistent with the effect of drying on CEC. For the remaining soil, K adsorption increased following oven‐drying. This was attributed to K fixation.     

Effects of long-term phosphatic fertilizer applications on amounts and forms of phosphorus in soils under irrigated pasture in New Zealand

In this study a detailed sequential fractionation scheme was used to examine the effects of long-term annual applications of phosphatic fertilizer on the amounts and forms of phosphorus (P) in soils under intensively grazed irrigated pasture over a 25 year period (1952–1977). Results showed that increases in soil inorganic and organic P occurred in response to continued P fertilizer addition, although inorganic P decreased with time following the cessation of P fertilizer inputs in the residual fertilizer and control treatments. The rate of organic P accumulation in soils decreased with time, while a marked decline in soil organic P in all treatments between 1971 and 1974 was attributed to increased mineralization as a result of lime addition in 1972. Furthermore, changes in the forms of inorganic P which accumulated in the continually fertilized soils after 1971 were attributed to the combined effects of liming and changes in the chemical nature of applied fertilizer P.     

Pyrolysis-gas chromatography studies on a climosequence of soils in tussock grasslands,New Zealand

The nature of the organic matter in the A horizons of seven New Zealand soils in tussock grasslands has been shown by pyrolysis-gas chromatography of the whole soils to be strongly influenced by climate. A ratio relating the a abundances of four pyrolysis products varies systematically from 1.20 for a brown-grey earth to 3.82 for a high-country podzolized yellow-brown earth, and shown significant correlations with altitude, precipitation, and mean annual temperature; this is in accord with the concept of the seven soils forming members of a climosequence. Similarities with the mull/mor humus sequence in Scottish soils are also noted.     

Probability distributions for concentrations of nine nutrient elements in the foliage of black walnut (Juglans Nigra L.) in a New Zealand population

Abstract

Black walnut foliage samples collected from a wide range of sites during a national survey of the New Zealand (NZ) resource conducted in 1979 were analysed for N, P, K, Ca, Mg, B, Fe, Mn, and Zn. Provisional American standards applied to the foliar data indicate that only very small proportions of the field population (individually 1 to 2%) have foliar levels of N, P, Fe, Mn, or Zn rating deficient. For K, Ca, Mg, or B foliar levels consistently exceeded the deficiency threshold. The proportions of the population rating intermediate were very large (40 to 95%) for certain elements (P, Mg, Fe, Zn), and fairly large (16 to 27%) for the remainder. In this transitional bracket response to fertiliser is uncertain. As the applicability of the American criteria to NZ conditions is unproven, this evaluation must remain tentative.

To study the distributions for the foliar concentrations of the elements determined, two functions of the Weibull distribution were used ‐ one for cumulative density and the other for probability density. The cumulative density function fitted the arrayed data for each nutrient very closely (R = 0.992 to 0.998). Quartile values for cumulative probability are given for each nutrient; these allow a preliminary ranking of individual foliar analyses as an aid in assessing nutrient status relative to the expected NZ norm. Estimated parameters of the same function are given for each nutrient so that percentile values can easily be calculated.     

Estimating the minimum viable population size of kaka (Nestor meridionalis), a potential surrogate species in New Zealand lowland forest

While conservation management is increasingly turning towards an ecosystem-level framework, the focus on a small subset of surrogate species has recognised merit given insufficient time, resources, and expertise. The kaka (Nestor meridionalis), a large threatened New Zealand parrot, is an iconic, visible species in lowland forests. As kaka populations are sensitive to mustelid predation and habitat loss, kaka can act as both a flagship and indicator species for healthy lowland forest ecosystems in New Zealand. To ensure the sustained protection of kaka over a sufficient area, this research aims to estimate the minimum viable population (MVP) size of kaka in the Eglinton Valley, Fiordland, and the management required for population persistence. A post-breeding census, stochastic, age structured Leslie matrix model was developed to estimate the population size having a 95% probability of persistence over 100 years. Scenarios modeling current and alternate management regimes, uncertain life-history traits, and environmental unpredictability were run. The most ‘realistic’ scenario resulted in an MVP size of 258 kaka (155 adults). Maintaining current levels of predator control appears essential to ensure kaka population persistence. An area of >500 km² is proposed to maintain the MVP of kaka based on detailed information on home range size and territory overlap derived from radio-tracking studies. As one of a group of surrogate species in lowland forest ecosystems, kaka may be used to guide management decisions regarding large-scale mustelid trapping and the delineation of habitat area requiring protection in the face of proposed human developments in the region.     

The effects of copper on microbial activity and the degradation of atrazine and indoxacarb in a New Zealand soil

Copper is present in a range of fungicides as well as in some animal manures and biosolids that are applied to agricultural soils as fertilisers. Elevated and increasing levels of copper in agricultural soils are of worldwide concern. Copper is toxic to soil microorganisms and has been reported to reduce the ability of soil microorganisms to degrade pesticides. A glasshouse study was undertaken to determine if copper inhibited the degradation of atrazine and indoxacarb in soil. A fine sandy loam agricultural soil was fortified with copper at five concentrations over a concentration range of 0–1000 mg/kg copper, then field-aged for 6 months prior to treatment with either indoxacarb or atrazine at a rate of 2 mg/kg. The soils were sampled twice at intervals based on published half-lives. The samples were analysed for a range of parameters including total and bioavailable copper, urease and phosphatase activity, ergosterol and either indoxacarb or atrazine and its degradation products. The soil microbial biomass and enzyme activities decreased with increasing copper concentration (p < 0.05). There were no significant differences in soil atrazine and indoxacarb concentrations between the copper levels. At sampling time two, the concentrations of hydroxyatrazine in treatments containing the three highest copper concentrations were significantly greater (p < 0.05) than for the control soil. Our results indicate that copper does not inhibit the first step of indoxacarb and atrazine degradation, but may affect degradation of secondary metabolites like hydroxyatrazine in soil.     

Past and future trajectories of forest loss in New Zealand

Historically, New Zealand was dominated by forest below the alpine treeline, but about 1000 years of Polynesian and European colonisation has resulted in the destruction of nearly three-quarters of the indigenous forest cover. In this study, the historical patterns of deforestation and forest fragmentation were assessed in relation to major topographical, climatic and anthropogenic variables that may drive forest loss. Deforestation has occurred almost equally on the two main islands, the North and South Islands, although the remaining indigenous forest is more fragmented in the North Island. Most deforestation has occurred in regions with a high-density of road networks, although gradients in climatic water availability and soil fertility also had weak effects. Deforestation rates over the period 1997-2002 were very low (nationwide deforestation rate of just −0.01% p.a.), but varied widely among political districts. Expansion of plantation forestry was the single most important driver of recent deforestation. Only 10 of 73 political districts are afforded long-term protection of native forest cover (having more than 30% forest cover that is managed by the Department of Conservation). Forest cover in the majority of New Zealand landscapes has been reduced below the level of an expected ‘extinction threshold’ (circa 30% native habitat cover) in 55 political districts, and long-term trajectories predict that ongoing deforestation threatens to force another five districts below the critical threshold within the next 45 years. Except for the most heavily deforested regions, relatively modest annual rates of habitat restoration could bring forest cover back above the extinction threshold by the year 2050.     

The genesis and classification of soils on wet terraces and moraines in New Zealand

Six soils on glacial outwash terraces and one on moraine are discussed; four are formed partly in loess of unknown age. Evidence of podzolization is apparent in all profiles, but the vertical drainage under very high rainfall is insufficient to remove surplus water. Gley processes appear to dominate, in a perched-water environment.
Podzolic B horizons were identified in the same five profiles following both the Canadian system and that used by the Soil Survey of England and Wales. However, only three of these profiles could be allocated to existing podzolic subgroups in the latter system. Spodic horizons were identified in a different group of five profiles. Differences in classification are discussed with reference to the criteria used and in relation to proposals for revision of the New Zealand Soil Classification.     

Nested spatial biodiversity patterns of nematode genera in a New Zealand forest and pasture soil

Biodiversity has a spatial dimension, which we estimated by examining generic turnover (beta diversity) of nematodes in adjacent forest and pasture sites. Dissimilarity was estimated in small and intermediate scale transects, the distribution of sampling points being determined by spatial simulated annealing. On an average, the forest yielded fewer nematodes per 24 mm dia 0-10 cm deep core than did pasture (435 vs 2818) but more genera (23.7 vs 19.1). Dissimilarity analysis suggests generic turnover is higher in forest than pasture, at both scales. At the small scale both communities have comparable dissimilarities up to 0.6 m, but only in forest does increasing distance increase dissimilarity. At the intermediate scale no spatial structure was apparent in the pasture nematode community, but in forest dissimilarity increased with distance, with no plateau. Quantifying the difference in spatial patterns between ecosystems illustrates the utility of geostatistical methods for addressing soil biodiversity.     

Amounts and forms of micronutrient cations in a group of loessial grassland soils of New Zealand

The status of micronutrient cations Fe, Mn, Zn, Cu and Co was examined in a group of soils from beneath undisturbed grassland sites. The soils were selected such that factors of soil formation besides loess accumulation and rainfall remained relatively constant. In a previous study these two factors were found to have a large effect on the K status of the soils, but results from this study showed that there had been little effect on micronutrient content. With decreasing loess accumulation the total and HCl- and EDTA-extractable micronutrient content of soils tended to decrease, but rainfall had no consistent effect. Extractable levels of Cu and Co in A horizons tended to decrease from high to potentially deficient values with decreasing loess accumulation.HCl- and EDTA-extractable Fe, Mn, Zn and Cu were clearly higher in A than B horizons although total contents tended to be lower in A horizons. A chemical fractionation procedure demonstrated that there were greater quantities of pyrophosphate- and oxalate-extractable Zn and Cu and acetic acid-extractable Zn in the A than B horizons.With the exception of HCl-extractable Cu, extractable micronutrients were significantly correlated with the organic matter content of the HCl or EDTA extracts. There were no significant correlations between extractable micronutrients and soil pH or oxalate-extractable Al or Fe.Acetic acid-extractable Co was not significantly correlated with any measured soil property. It is concluded that the cycling of nutrients and the build-up of organic matter, which characteristically occur under grassland conditions in New Zealand, were the major factors influencing the micronutrient status of the soils.     

Microbiological and biochemical characteristics of a range of New Zealand soils under established pasture

Twenty one topsoils, selected to represent major New Zealand soil groups were collected from developed, grazed pasture and examined for microbiological and biochemical characteristics. Organic C and total N levels ranged from 2.4–46% (mean 8.7%) and 0.22–2.31% (mean 0.65%), respectively. The characteristics examined included microbial biomass (mean 1240 μg Cg^?1 soil), min-N flush (mean 85 μg N g^?1 soil), microbial P (mean 52 μg P g^?1 soil), min-N and CO₂ produced, nitrification index, urease, protease, phosphatase and arylsulphatase activities. Most of these characteristics were generally higher than the values already published possibly due to high levels of organic matter.Principal component analysis of the correlation matrix showed two distinct groups of characteristics: CO₂ produced, N mineralized, total N, organic C, microbial biomass, microbial P and phosphatase comprising one group and arylsulphatase, min-N flush, urease and nitrification index comprising the other group. Protease activity and soil pH were not strongly associated with each other or the other groups.     

Site condition, fertility gradients and soil biological activity in a New Zealand frost-flat heathland

Gradients in stressed areas potentially provide a powerful tool to interpret relations between soil biodiversity and site quality. We measured soil chemistry, soil microbiology and nematodes along three transects representing a fertility gradient and at a disturbed site near a road in a Dracophyllum subulatum-dominated shrubland in which frosts are a major factor in preventing succession to forest; we used D. subulatum size as a site-quality index. Significant correlations between both shrub height and shrub growth rate and volumetric measures of total soil phosphorus and anaerobically mineralisable nitrogen indicate that nitrogen and phosphorus regulate plant growth. Microbial biomass and total nematode abundance significantly increased with greater plant growth, presumably in response to greater litter input. Conversely, neither heterotrophic microbial diversity nor nematode diversity was correlated with shrub performance along the transects. Litter was from a single species and thus likely similar in quality so changes in microbial or nematode diversity might not be expected. In this oligotrophic environment, nutrient levels were not only the important regulators of plant growth but also appeared to have an indirect influence on the size of the microbial and nematode populations.     

High frequency of virus-infected bacterial cells in a sheep grazed pasture soil in New Zealand

Viruses cause significant mortality of microbes in aquatic environments and thus play a major role in biogeochemical cycling. While viruses are known to be present in soil, the rate of infection of bacteria, and therefore the potential for mortality and lysis, are unknown. In this study we measured the frequency of viral infected of bacterial cells in soils from a New Zealand sheep grazed pasture under ambient or elevated atmospheric carbon dioxide levels at the New Zealand Free Air Carbon Dioxide Enrichment facility (NZ-FACE). Averaged across the CO₂ treatments, the frequency of visibly infected cells (FVIC) was 23%. This is far greater than the reported FVIC values for marine or fresh water environments. The average FVIC of soils under ambient and elevated atmospheric CO₂ conditions was 28% and 18% respectively. These results are discussed in relation to nutrient cycling in grazed pastures.