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Context. Many regions in the world have undergone rapid land use change and intensification of agricultural land, such as through irrigation expansion, upgrading irrigation systems, and changing grassland, stock, and nutrient management practices. With more intensive land use, changes to soil properties can occur, such as soil compaction and changes in soil water storage. The effects of modern sprinkler-irrigated pastoral farming on soil physical properties are not well quantified internationally, particularly for temperate climates. Aims. This regional study evaluates the effect of irrigation on soil physical properties in topsoil and subsoil, under modern pastoral grazing and sprinkler irrigation, across Canterbury, New Zealand. Methods. Paired sites were sampled, consisting of a spray-irrigated paddock (field) and an adjoined part of the same paddock that was dryland (unirrigated), with other management the same for each pair. Key results. Under irrigation there was a shift towards a greater abundance of smaller pores. This was reflected in macroporosity and readily available water capacity being significantly lower under irrigation, while semi-available water capacity and unavailable water held below permanent wilting point both increased. Conclusions. These differences reflect increased compaction under irrigated grazed pasture, particularly under dairy grazing, consistent with findings in similar studies. This study quantified changes in both the topsoil and subsoil but showed that most differences were confined to the topsoil (30 cm depth). Implications. For irrigation management, our study indicates the lower readily available water capacity on irrigated pasture is significant, with farmers potentially having to irrigate more frequently. Adopting deficit irrigation could minimise impacts of compaction. Keywords: available water capacity, compaction, crop lower limit, land use change, macroporosity, readily available water capacity, soil health, soil quality., Introduction Global population growth is increasing the demand for food and agricultural products. Land use change is occurring to support this demand on agricultural food production, with expansion and intensification [...]

Abstract: Although there is an opportunity to increase the productivity of Pinus radiata plantations in New Zealand through nitrogen (N) fertilisation, this treatment may reduce the quality of drainage water through leaching of nitrate-N. To improve our understanding of the effects of N fertilisation on potential N leaching, N concentrations in soil water below the root zone and potential losses were investigated after N fertiliser was applied as urea at 200kgha−1 of N to 7–9year-old operational plantations at 10 sites in New Zealand. A water balance model was used to estimate soil water drainage on a daily basis. Annual drainage ranged from 70 to 1,199mm and was closely correlated with annual rainfall. Nitrate-N, ammonium-N and organic-N concentrations in unfertilised control plots ranged between 0.03–2.26mgL−1, 0.06–0.49mgL−1 and 0.44–0.95mgL−1 respectively. Fertilisation significantly increased nitrate-N concentrations at four sites but did not affect ammonium-N or organic-N concentrations. In the 2years after fertiliser application, fertiliser increased nitrate-N leaching at eight of the 10 sites by 0–15kgha−1 (average 6.4kgha−1 or 3.2% of the N applied). These values underestimate total nitrate-N loss as fertiliser enhanced leaching at two sites had not ceased after 2years. Nitrogen fertilisation caused much greater increases in nitrate-N loss at a low productivity, high rainfall site (28kgha−1of N), and a coastal sand site (90kgha−1of N). To reduce losses at such sites, fertiliser should be applied at reduced rates in multiple applications. Factors that seem to have pre-disposed sites to nitrate-N leaching following N fertilisation include a pasture land-use history, the presence of a high component of the N-fixer Ulex europaeus in the understory, and soil C/N ratios of 15 or lower. Organic-N dominated leaching at 7 of the 10 sites, consistent with the pattern observed in unpolluted old-growth southern hemisphere forests, but mineral-N dominated at three sites, two of which had a recent land-use history of fertilised pasture. [Copyright &y& Elsevier]

Methanotrophs use methane (CH4) as a carbon source. They are particularly active in temperate forest soils. However, the rate of change of CH4 oxidation in soil with afforestation or reforestation is poorly understood. Here, soil CH4 oxidation was examined in New Zealand volcanic soils under regenerating native forests following burning, and in a mature native forest. Results were compared with data for pasture to pine land-use change at nearby sites. We show that following soil disturbance, as little as 47 years may be needed for development of a stable methanotrophic community similar to that in the undisturbed native forest soil. Corresponding soil CH4-oxidation rates in the regenerating forest soil have the potential to reach those of the mature forest, but climo-edaphic fators appear limiting. The observed changes in CH4-oxidation rate were directly linked to a prior shift in methanotrophic communities, which suggests microbial control of the terrestrial CH4 flux and identifies the need to account for this response to afforestation and reforestation in global prediction of CH4 emission. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative information on the relationships between site quality and plantation productivity (dominated by the exotic species Pinus radiata) is required to achieve goals for sustainable forest production. Soil quality is a key component of site quality. A nationwide study of soil quality measurements is reported for 35 representative forest sites, covering a wide range of climatic and edaphic conditions found throughout New Zealand''s plantation forest estate, representing most of the soils used for plantation forestry in New Zealand. The objectives of the study were to find the most important soil properties that discriminated among eight New Zealand Soil Orders and determine relationships between Soil Orders and early tree growth rates for P. radiata and Cupressus lusitanica. Soil physical and chemical properties were measured to identify key soil indicators of soil quality related to tree productivity. Tree growth was measured after four years on small plots planted at very high stand density (40000stemsha−1). A factorial design was used to examine the influence of three factors on tree productivity: two species, P. radiata D. Don (ectomycorrhizal) and C. lusitanica Miller (endomycorrhizal); with and without fertilizer; and low or high disturbance (soil compaction and/or topsoil scalping by machinery). Carbon content, Phosphorus (P) retention, and soil physical properties that index the degree of soil compactness were strongly correlated to Soil Order. These properties are similar to soil quality factors that correlated with tree growth. Discriminant analyses of soil quality parameters by Soil Order clustered soils based on P retention (phosphate absorption capacity), subsoil Carbon (C), and subsoil air capacity (volume % of voids at 10kPa matric potential). Allophanic Soils and Podzols clustered (from plots of first versus second canonical variates) separately from the other Soil Orders, which were somewhat clustered on the second variate within a broad clustering on the first variate. Soil Orders were ranked for tree growth rates for both species: pumice Andisols>Inceptisols>tephric Andisols>Entisols>Ultisols>Spodosols (NZ classification: for P. radiata is Pumice>Brown>Pallic>Allophanic>Recent>Raw>Ultic>Podzol and for C. lusitanica Pumice>Pallic>Allophanic>Brown>Raw>Ultic>Recent>Podzol). [Copyright &y& Elsevier]

Abstract: New Zealand is committed to developing sustainable forest management practices as evidenced through Government involvement in international forestry agreements such as the Montreal Process, and the forestry sector''s adoption of forest certification mechanisms. Despite this, there is little quantitative evidence of how plantation forestry affects site quality and long-term site productivity. To address this issue, a nationwide study of site quality was established at 31 key sites covering the range of edaphic and environmental conditions for New Zealand plantation forests. At each location, eight short-term site quality plots were planted at a very high stand density (40,000stemsha−1) to rapidly identify key soil indicators of growth which may be useful for determining site sustainability. The plots at each site were arranged in a factorial design with the following three factors: species (Pinus radiata D. Don and Cupressus lusitanica Mill.), fertiliser (no fertiliser and nutrients supplied in excess of crop demands) and disturbance (low and high disturbance). These plots were harvested after 4 years and data was used to (i) examine treatment and site effects on volume mean annual increment (MAI) and (ii) identify key soil properties that influence volume MAI for the two species. Volume MAI significantly ranged 7-fold across sites. For the treatments, species accounted for most of the variance in volume MAI, with values for P. radiata significantly exceeding those of C. lusitanica by 95%. Volume MAI was significantly affected by fertilisation which induced gains of 33%. Disturbance did not significantly affect volume MAI. After correction had been made for climatic variables, soil properties that were most strongly related to volume MAI for both species included C:N ratio, total phosphorus (P), and organic P. When soil properties were included in combination, the best predictive models of volume MAI formulated for P. radiata included total P and C:N ratio while the best predictive model for C. lusitanica included C:N ratio and Olsen P. Variation in species sensitivity to total P and C:N ratio is likely to be attributable to their different mycorrhizal associations. For both species, the most important soil physical property influenced by management operations was total porosity. This research suggests that total P, C:N ratio, Olsen P and total porosity should be used as indicator properties for determining sustainability of plantation grown P. radiata and C. lusitanica. [Copyright &y& Elsevier]

Abstract: As erosion control and water conservation are almost always important issues, information on water use between different plantation species may be of significant management value for guiding decisions on species selection. The main and interactive effects of species and fertilisation on annual water loss and drainage in three-year old Cupressus lusitanica Mill. and Pinus radiata D. Don were examined across an environmental gradient at eight sites in New Zealand using small highly stocked plots designed to compress the rotation length. Annual average fractional available volumetric water content (θ a), total annual water loss and total annual drainage for each treatment at each of the eight sites was determined using a daily water balance model, validated against two-monthly measurements of θ a. Modelled annual average θ a, total annual water loss and total annual drainage were all significantly influenced by site and species (P <0.001 for all variables), but not fertilisation or the interaction between species and fertilisation (P >0.05 for all variables). Averaged across the eight sites, annual average θ a for C. lusitanica was higher than that of P. radiata by 0.15 (0.58 vs. 0.43). Total annual water loss for P. radiata was on average 104mm higher, than that of C. lusitanica (893mm vs. 789mm), while total annual drainage for C. lusitanica was on average 129mm higher than that of P. radiata (285mm vs. 156mm). Combining average values for drainage and water loss indicated that there was on average 233mm more available water per annum in soils under C. lusitanica than P. radiata, which equated to an average of 22% of total annual rainfall. [Copyright &y& Elsevier]

Abstract: Data taken from 261 4-year-old trees growing within a nationwide set of site quality plots where Pinus radiata D. Don and Cupressus lusitanica Mill. were established at high stand densities (40,000stemsha−1) were analysed to (i) determine how site, species and fertilisation influence the wood properties basic density and green dynamic modulus of elasticity (MOE) for the stem at the tree base, and (ii) develop predictive models of basic density and MOE for both species. A further objective was to examine the utility of the “experimentation in miniature” (EIM) approach used here, to identify key determinants of wood properties across an environmental gradient. Site mean variation for both wood properties was highly significant with treatment-averaged values ranging from 27% (365 to 465kgm−3) for density to twofold for MOE (2.4–5.9GPa). Basic density of C. lusitanica significantly exceeded that of P. radiata by 12% (457 versus 407kgm−3), while MOE of P. radiata significantly exceeded that of C. lusitanica by 33% (4.4 versus 3.3GPa). Neither fertilisation nor the interaction of fertilisation and species had a significant effect on either basic density or MOE. Although key determinants of basic density were very different between species, they exhibited considerable similarity for MOE. In the final multiple regression model of basic density for C. lusitanica ground-line diameter accounted for 88% of the variance, while for P. radiata 90% of the variance in basic density was explained by total soil phosphorus (P), average leaf area index (LAI), total annual radiation, and average minimum air temperature during winter. The final multiple regression model of MOE for C. lusitanica accounted for 90% of the variance using stem slenderness, average air temperature during winter, and average LAI, while stem slenderness and total soil P accounted for 96% of the variance in P. radiata MOE. Key determinants of P. radiata basic density previously identified across an environmental gradient at conventional stockings were consistent with our results. Results from our study also demonstrate that previously unmeasured variables, within these conventionally stocked stands, such as total soil P and LAI may also have an important influence on P. radiata basic density. Although preliminary and limited to a single wood property in P. radiata this comparison suggests that EIM has some utility for identifying key determinants of wood quality across environmental gradients. [Copyright &y& Elsevier]

Abstract: The objectives of this study were to determine the influence of site, fertilisation and age on fibre length and develop predictive models of fibre length from a comprehensive set of climatic, edaphic and stand variables. Data were collected from a nationwide set of 22 site quality plots where Pinus radiata D. Don was established at high stand densities (40000stemsha−1) and grown over a period of 4 years. The main environmental drivers of fibre length were identified by assessing the strength of bivariate correlations and use of multiple regression. Path analysis was used as an extension to multiple regression to separate cause from effect and quantify the direct influence of variables significantly related to fibre length. Fibre length exhibited significant variation between sites. When averaged across fertiliser treatments, site variation for fibre length in rings 1–4 ranged from 1.08 to 1.76mm. Fertilisation did not significantly affect fibre length. Fibre length significantly increased with age from an average of 1.10mm in rings 1–2 to 1.62mm in rings 3–4. The interaction between age and fertilisation was insignificant. In total 16 variables were significantly related to fibre length. For rings 1–4, fibre length exhibited the strongest significant relationships with stem slenderness (r =0.69), mean minimum air temperature (r =0.67), green crown height (r =0.66), tree height (r =0.64) and average air temperature (r =0.62). The best multiple regression models for both age classes and the whole stem included mean minimum air temperature and stem slenderness in a linear formulation. Path analysis indicated that the direct positive contribution of both these variables to fibre length was of a similar magnitude (path coefficients of 0.52 versus 0.49). Significant determinants of P. radiata fibre length in our study were similar to those identified in trees grown at conventional stockings across a similar environmental gradient in New Zealand. Although these studies did not examine how stem slenderness influences fibre length, they found average air temperature to be the strongest environmental determinant of fibre length, and that soil fertility, as indexed by Olsen phosphorus and total nitrogen and pH had little influence on fibre length. Further research is needed in conventionally stocked stands to confirm the link found here between stem slenderness and fibre length. [Copyright &y& Elsevier]

Abstract: Data from a nationwide set of Pinus radiata site quality plots established at high stand densities and grown over a period of 4 years were analysed to (i) determine how site and fertiliser influence dynamic modulus of elasticity (E) of the stem at the tree base, and (ii) develop a predictive model of E for basal stemwood. Site had a highly significant (P <0.001) influence on E, which exhibited an almost three-fold range from 2.3 to 6.3GPa, across the 21 site quality plots. When compared to the unfertilised controls, fertilisation had a relatively minor and insignificant effect on E, reducing values by on average 6%. This demonstrated the insensitivity of E to Bray phosphorus (P), Olsen P, inorganic P, and exchangeable potassium which were elevated in the soil by on average two- to three-fold by application of fertiliser. In total, 13 variables were found to be significantly related to E. Minimum temperature during early autumn (March) and tree slenderness (determined as tree height/ground-line tree diameter), also known as taper, exhibited the strongest correlations with E, accounting for 61 and 60% of the variance in this property, respectively. A multiple regression model with these two variables predicted 75% of the variance in E. Residuals from this model exhibited little apparent bias with predicted values, or independent variables. Results indicate that E may be relatively simple to predict across environments as stem slenderness can be readily obtained from either regional growth models or stand inventory, while temperature data can be obtained from regional or national climate surfaces. The relationship found between E and stem slenderness is consistent with the Euler buckling formula which suggests in a competitive situation increases in stem slenderness will induce increases in E to reduce the risk of stem buckling. The significant influence of temperature during early autumn on E may be mediated through regulation of latewood development. Given that latewood with high E is forming during early autumn, sites with higher temperatures and increased growth rates over this month are likely to develop a greater percentage of high E latewood, and as a consequence a higher overall stem E. [Copyright &y& Elsevier]

Abstract: Afforestation of pastures in New Zealand reduces methane (CH4) production from soil, while also stimulating oxidation of atmospheric CH4 by soil methanotrophs. However, neither the mechanisms by which soil CH4 oxidation is enhanced by afforestation, nor how long after forest planting tree-dependent responses in CH4 oxidation become detectable are fully known. Here, we investigated the effects of different-aged stands (5–20 y) of the exotic pine (Pinus radiata (D. Don)) on CH4 oxidation and methanotrophic community structure in soils, compared with adjacent, long-established pastures. Two of the pastures were on volcanic soils and two were on non-volcanic soils. Although the CH4 fluxes in soils from these young stands were not significantly different from those in the associated pastures, the rate of oxidation of added 13CH4 was higher in the pine soils. Both fluxes and 13CH4 oxidation rates were higher in the volcanic than the non-volcanic soils. Combined phospholipid fatty acid (PLFA) and stable isotope probe (SIP) analyses suggested that type II methanotrophs (PLFA C18:1ω7) were most active in all soils followed by uncultivable bacteria (C17:0ai). Molecular analysis of the methanotrophic community structure using pmoA (particulate methane monooxygenase) genes suggested that a particular type II methanotroph (TRF 35) was dominant in all soils, but more so in the pine than in pasture soils. A type I methanotroph (TRF 245) was more prevalent in the pasture than in associated pine soils, whereas TRF 128 (a type II methanotroph) was slightly more dominant in soils under pine. Cloning and sequencing data suggest TRFs 35 and 128, which differ from one another, belong to distant relatives of Methylocapsa sp; TRF 245 is related to Methylococcus capsulatus. Land-use change resulted in changes in soil bulk density, porosity, moisture contents and in methanotrophic community structure. Methane oxidation rates were most closely related to soil moisture, as well as to the methanotrophic community structure, and nitrate-N, extractable C and total C concentrations. Stepwise multiple regression also suggested a weak effect (P = 0.06) of stand age on CH4 oxidation rate. By contrast, the responses of the methanotrophic community structure to this land-use change were more readily detected by the specific molecular analyses, and indicated a predominance of type II methanotrophs in pine soils. [Copyright &y& Elsevier]

Abstract: Afforestation and deforestation are key land-use changes across the world, and are considered to be dominant factors controlling ecosystem functioning and biodiversity. However, the responses of soil microbial communities to these land-use changes are not well understood. Because changes in soil microbial abundance and community structure have consequences for nutrient cycling, C-sequestration and long-term sustainability, we investigated impacts of land-use change, age of stand and soil physico-chemical properties on fungal and bacterial communities and their metabolic activities. This study was carried out at four sites in two geographical locations that were afforested on long-established pastures with Pinus radiata D. Don (pine). Two of the sites were on volcanic soils and two on non-volcanic soils and stand age ranged from 5 to 20 y. Microbial communities were analysed by biochemical (phospho-lipid fatty acids; PLFA) and molecular (multiplex-terminal restriction fragment length polymorphism; M-TRFLP) approaches. Both site and stand age influenced microbial properties, with changes being least detectable in the 5-y-old stand. Land use was a key factor influencing soil metabolic activities as measured by physiological profiling using MicroResp. Pasture soils had higher microbial biomass (P < 0.001), and metabolic activities (P < 0.001), and basal respiration rates were up to 2.8-times higher than in the pine soils. Microbial abundance analysis by PLFA showed that the fungal to bacterial ratio was higher in the pine soils (P < 0.01). Community analysis suggested that soil bacterial communities were more responsive to site (principal component 1; P < 0.001) than to land use (principal component 5; P < 0.001). In contrast, the fungal community was more affected by land-use change (principal component 1; P < 0.001) than by site, although site still had some influence on fungal community structure (principal component 2; P < 0.001). Redundancy analysis also suggested that bacterial and fungal communities responded differently to various soil abiotic properties, land-use change and location of sites. Overall, our results indicate that the change in land use from pasture to P. radiata stands had a direct impact on soil fungal communities but an indirect effect, through its effects on soil abiotic properties, on bacterial communities. Most of the changes in bacterial communities could be explained by altered soil physico-chemical properties associated with afforestation of pastures. [Copyright &y& Elsevier]