Roger L. Parfitt

Rapid development of phosphorus limitation in temperate rainforest along the Franz Josef soil chronosequence

The aim of this study was to examine how shifts in soil nutrient availability along a soil chronosequence affected temperate rainforest vegetation. Soil nutrient availability, woody plant diversity, composition and structure, and woody species leaf and litter nutrient concentrations were quantified along the sequence through ecosystem progression and retrogression. In this super-wet, high leaching environment, the chronosequence exhibited rapid soil development and decline within 120,000 years. There were strong gradients of soil pH, N, P and C, and these had a profound effect on vegetation. N:Pleaf increased along the chronosequence as vegetation shifted from being N- to P- limited. However, high N:Pleaf ratios, which indicate P-limitation, were obtained on soils with both high and low soil P availability. This was because the high N-inputs from an N-fixing shrub caused vegetation to be P-limited in spite of high soil P availability. Woody species nutrient resorption increased with site age, as availability of N and P declined. Soil P declined 8-fold along the sequence and P resorption proficiency decreased from 0.07 to 0.01%, correspondingly. N resorption proficiency decreased from 1.54 to 0.26%, corresponding to shifts in mineralisable N. Woody plant species richness, vegetation cover and tree height increased through ecosystem progression and then declined. During retrogression, the forest became shorter, more open and less diverse, and there were compositional shifts towards stress-tolerant species. Conifers (of the Podocarpaceae) were the only group to increase in richness along the sequence. Conifers maintained a lower N:Pleaf than other groups, suggesting superior acquisition of P on poor soils. In conclusion, there was evidence that P limitation and retrogressive forests developed on old soils, but N limitation on very young soils was not apparent because of inputs from an abundant N-fixing shrub.

Effects of clay minerals and land use on organic matter pools

The organic matter in density and particle size fractions of an Andisol and an Inceptisol has been characterised by its C and N contents and infrared spectra. The soils have a similar texture but different clay mineralogy and are under two contrasting land uses represented by pasture and cropping. The Andisol samples were taken from sites which have been under perennial pasture for 100 years and from a pasture site which has been cultivated and cropped with barley and brassica for 20 years. The Inceptisol samples were from sites under native forest and perennial pasture, and from a pasture site which had been cropped with maize for 20 years. The Andisol contained allophane and ferrihydrite whereas the Inceptisol contained mica as the main clay mineral. The CN ratios of the dispersed-light fractions and heavy particle size fractions from the Andisol were in a narrow range of 9–12, and this may be related to the presence of allophane and ferrihydrite. By comparison, the CN ratio of the Inceptisol was close to 9 for the 20 μm fraction, and generally highest for the light fractions. This is consistent with the presence of clay minerals with low specific surface area. Infrared spectra indicated that the organic matter associated with the < 2 μm fraction was enriched in aliphatic groups. Soil carbon in the 0–20 cm layer of the Andisol was 10 T/ha lower under cropping (134 T/ha) than under pasture (144 T/ha). By comparison, the Inceptisol was 23 T/ha lower under cropping (50 T/ha) than under pasture (73 T/ha) suggesting that the turnover of C was more rapid in the Inceptisol. Simulations of C and N turnover for the Andisol using CENTURY indicated that the pool of passive organic matter was very large. For soils with variable charge, of which the Andisol is an example, a modifying factor such as specific surface area may be required in order to give a close simulation of C and N turnover. The data indicate that the stability of organic matter is greater in the Andisol than in the Inceptisol, and it is less likely to be affected by cropping. Allophane and ferrihydrite appear to have a stabilising influence on a large part of the organic matter in the Andisol.

Soil and solution chemistry under pasture and radiata pine in New Zealand

The conversion of hill country pasture to exotic forest plantations is occurring rapidly (70,000 ha yr−1) in New Zealand. Impacts of this land-use change on soil properties, soil fertility, and water quality are only beginning to be investigated. This study examines the effects of radiata pine (Pinus radiata) on soil and soil solution chemistry, in a region of low atmospheric pollution, 20 years after plantation establishment, assuming that the pasture and pine research sites had comparable soil properties before planting pine. The primary effects of conversion on soil chemistry were a decrease of organic carbon in the mineral soil that was balanced by an accumulation of the surface litter layer, a decrease in soil N, soil acidification, and increased pools of exchangeable Mg, K, and Na. Soil solution studies revealed a large input of sea salts by enhanced canopy capture of sea salts that contributed to much larger solute concentrations and elemental fluxes in the pine soil. Sea salts appear to accumulate in the micropores of pine soil during the dry summer period and are slowly released to macropore flow during the rainy season. This results in a progressive decrease in solute concentrations over the period of active leaching. While chloride originating from sea salt deposition was the dominant anion in the pine soil, bicarbonate originating from root and microbial respiration was the dominant anion in the pasture soil. Carbon dioxide concentrations in the soil atmosphere were 12.5-fold greater in the pasture soil than in the pine soil due to greater rates of root and microbial respiration and to slower diffusion rates resulting from wetter soil conditions in the pasture. Although elemental fluxes from the upper 20 cm of the soil profile were substantially greater in the pine soil, these losses were compensated for by increased elemental inputs resulting from nutrient cycling and enhanced canopy capture of sea salts.

Land-use change effects on soil C and N transformations in soils of high N status: comparisons under indigenous forest, pasture and pine plantation

Globally, land-use change is occurring rapidly, and impacts on biogeochemical cycling may be influenced by previous land uses. We examined differences in soil C and N cycling during long-term laboratory incubations for the following land-use sequence: indigenous forest (soil age = 1800 yr); 70-year-old pasture planted after forest clearance; 22-year-old pine (Pinus radiata) planted into pasture. No N fertilizer had been applied but the pasture contained N-fixing legumes. The sites were adjacent and received 3–6 kg ha−1 yr−1“volcanic” N in rain; NO3−-N leaching losses to streamwater were 5–21 kg ha−1 yr−1, and followed the order forest < pasture = pine. Soil C concentration in 0–10 cm mineral soil followed the order: pasture > pine = forest, and total N: pasture > pine > forest. Nitrogen mineralization followed the order: pasture > pine > forest for mineral soil, and was weakly related to C mineralization. Based on radiocarbon data, the indigenous forest 0–10 cm soil contained more pre-bomb C than the other soils, partly as a result of microbial processing of recent C in the surface litter layer. Heterotrophic activity appeared to be somewhat N limited in the indigenous forest soil, and gross nitrification was delayed. In contrast, the pasture soil was rich in labile N arising from N fixation by clover, and net nitrification occurred readily. Gross N cycling rates in the pine mineral soil (per unit N) were similar to those under pasture, reflecting the legacy of N inputs by the previous pasture. Change in land use from indigenous forest to pasture and pine resulted in increased gross nitrification, net nitrification and thence leaching of NO3−-N.

Comparison of some soil properties under Pinus radiata and improved pasture

Abstract Some properties of surface mineral soils under Pinus radiata were compared with those under adjacent pasture at ten farm‐forestry sites in the Manawatu, New Zealand. None of the sites had received lime in the last 10 years. Generally, the soil samples under P. radiata had lower pH and higher extractable aluminium concentrations than their counterparts under pasture. Exchangeable calcium values were lower under P. radiata, by 96–1275 kg/ha. Tree uptake and forest floor development can account for up to 550 kg/ha; at six sites the difference was less than 550 kg/ha, suggesting that calcium generally was conserved by the P. radiata ecosystem. Soil exchangeable sodium and magnesium values were usually greater under P. radiata than under pasture; this probably resulted from the interception of airborne sea‐salt by the P. radiata canopy and subsequent transfer to the soil. There were no general trends in the data for available phosphorus and exchangeable potassium. Total nitrogen was often lower in the...

Carbon and phosphorus transformations during decomposition of pine forest floor with different phosphorus status

Summary Information on the mineralization of inorganic phosphate (Pi) from organically bound P (Po) during decomposition of forest floor and soil organic matter is vital for understanding P supply in forest ecosystems. Carbon (C) and phosphorus (P) fluxes were determined for forest floor samples from three Pinus radiata plots which had received no P (Control), 62.5 kg P ha–1 (Low P) and 125 kg P ha–1 (High P) 20 years before sampling. The P concentration of the forest floor samples had increased with fertilizer application, and the C:P ratio ranged between 585 and 1465. During a 9-week laboratory incubation 8.2–19.0% of the forest floor C was evolved as CO2-C. The amount of CO2 evolved from the forest floor of the Control plot was more than twice the amounts from the Low P and High P plots. There was little change in net P mineralization in the Control and Low P treatments throughout the incubation, but it increased slightly for the High P samples, suggesting a critical forest floor C:P ratio of 550 for net P mineralization. Changes in the 32P-specific activities of the Pi and microbial P pools during incubation, and concurrent changes in microbial-32P and 32Pi, indicated internal P cycling between these pools. The rate of internal P cycling varied with forest floor quality, and was highest in the High P forest floor. The High P samples had microbial C:P ratios of 22 : 1 which remained constant during the incubation, suggesting the microorganisms had adequate P levels.

Assessment of multiple ecosystem services in New Zealand at the catchment scale

The ecosystem services approach to resource management considers all services provided by ecosystems to all sections of the community. As such, it could be used to assess sustainability of human development and equity in resource use. To facilitate the approach, tools are required at the level of detail at which policy and management decisions are made. We have developed spatially explicit models of indicators of important ecosystem services in New Zealand: regulation of climate, control of soil erosion, regulation of water flow (quantity), provision of clean water (quality), provision of food and fibre, and provision of natural habitat. The models were developed using lookup tables from process-based models to allow rapid evaluation of land-use scenarios. We demonstrate the application of the models to assess ecosystem services in a simulation of hill-country afforestation in the Manawatu catchment, which has recently seen increasing soil erosion in the hills leading to sedimentation of waterways. Each ecosystem service was assessed by calculating the change in the indicator relative to two extremes. The ecosystem services with the largest relative changes were control of soil erosion, carbon sequestration, and provision of wood.

Effects of soil fertility on leaching losses of N, P and C in hill country

Abstract The OVERSEER® nutrient budgets model is increasingly being used by farmers and regional councils to assess N and P inputs and outputs from farms. There are, however, few data for low fertility and high fertility soils in hill country grazed by sheep. Two farmlets at AgResearch Ballantrae, near Woodville, with no‐fertiliser (NF) and 375 kg ha‐1 year‐1 superphosphate high fertiliser (HF) added since 1980, were used to quantitatively estimate N and P cycles under sheep‐grazed pastures at two stages of N saturation. We present data on soils, N and P leaching, and uptake for a trial in which treatments to both farmlets were (a) control, (b) herbicide applied (for broadleaves), and (c) 300 kg N ha‐1 added annually. Trial plots were located on 3–9° slopes in each farmlet. In winter, seepage zones in mini‐catchments in each farmlet generated waters that allowed us to follow nutrient movement from soils to waters. Winter 2006 had above average rainfall, with one intense storm where surface runoff was observed. During other storms, water perched at about 300 mm depth in the subsoil, and moved to seeps solely by subsurface runoff. Mean nitrate‐N concentration in drainage at HF was highest in 2006, as were surface and subsurface runoff, giving a calculated annual loss of nitrate‐N of 44 kg N ha‐1, compared with 20 kg N ha‐1 in 2005 and 27 kg N ha‐1 in 2007. At NF, the losses ranged from 1–2 kg N ha‐1. P losses increased considerably during surface runoff. Mean annual losses in drainage for HF and NF, respectively, were 1.0 and 0.3 kg ha‐1 for dissolved reactive P, 8 and 4 kg ha‐1 for dissolved organic N (DON), and 121 and 228 kg ha‐1 for dissolved organic C (DOC). The DOC/DON ratio was lower at HF (16) than at NF (54). In the plots with 300 kg N added, soil N status increased at NF and losses increased from 2 to 14 kg N ha‐1 year‐1 at 200 mm depth; losses at HF were over 80 kg N ha‐1 year‐1. This suggests soils on these slopes in the HF farmlet can become saturated with N and no longer retain N; soils in the NF farmlet appeared to retain N fertiliser initially, but by years 2 and 3 they appeared to become saturated with N. Gaseous emissions of ammonia, NOx and N2 would also increase as pastures and soils become enriched with N. The OVERSEER® nutrient budgets model gave good predictions of N in waters but underestimated P losses. The pathways of both gaseous losses and immobilisation of N in soils require further study to better quantify the N cycles.

Nitrogen inputs and outputs for New Zealand from 1990 to 2010 at national and regional scales

Abstract Reactive nitrogen (N) is increasingly added to the New Zealand environment because of increased sales of N fertilizer and increased human population. The Greenhouse Gas Inventory now reports in detail on changes for N losses from grazing animals from 1990 to 2010. Using animal numbers, we made assessments of N inputs and outputs for the 16 regions of New Zealand for 1990, 2001 and 2010 to assess temporal trends. Fertilizer sales have increased from 46 Gg N in 1990 to 329 Gg N in 2010, which leads to reduced biological N fixation by pastures. The import of oil-palm kernel has increased from zero to about 28 Gg N in 2010. Total N inputs are estimated to have increased from 689 Gg to 951 Gg N. The outputs of produce, leachate, gasses and sediment have increased from 771 to 866 Gg N; outputs to rivers may increase further if increases in outputs lag behind increases in inputs. Many of the inputs and outputs are well constrained because animal numbers have been used rather than land area, but uncertainties do exist for specific land-use classes. For example, the area of lifestyle blocks is approaching 800,000 ha and there is uncertainty regarding N inputs and outputs in this land use. There are also uncertainties in the amount of N fixation, the N loss by leaching in any one year, the amounts and fate of dissolved organic N, and the N content of eroded sediment. These uncertainties need to be resolved so that the amount of N stored in soils can be assessed. It seems likely that the N concentration of soils under dairying is increasing relative to the carbon concentration (i.e. soil C/N ratios are declining) but there is conflicting evidence as to whether the total N (and C) in these soils is increasing or decreasing.

13C NMR study of pine needle decomposition

The quality of substrates in plantation forest litter, and their chemistry, can influence decomposition and N cycling. We studied the decomposition of Pinus radiata D. Don needles suspended on branches in windrows, for 3 yr after clear-cutting, using improved solid-state 13C NMR and chemical analysis. The NMR spectra suggested that the concentration of condensed tannins was 12–22%, and showed they were chemically altered during the period 4–12 months after clear-cutting. The spectra showed no evidence for further chemical modification of the tannins during the second or third years. Data for P. radiata needle decomposition in New Zealand indicated rapid loss of mass in the first 3 months, and condensed tannins did not appear to prevent mineralization of C or N. The tannin and lignin concentrations increased with decomposition of the needles, which was consistent with the early mineralization of readily available C compounds.