Thomas G. Baker

Distribution and forms of phosphorus and aluminum in acidic topsoils under pastures in south-eastern Australia

The vertical distributions of pH, and forms of phosphorus (P) and aluminium (Al) in acidic topsoils (0-100 mm depth) under pastures were examined at 15 sites in New South Wales and Victoria. The soils were characterized by shallow surface strata of moderate pH, high P and low Al concentrations overlying more acidic, P-deficient and Al-rich subsurface strata. Significant amounts (35-65%) of the total P in acidic pasture topsoils were present in organic forms (Po). Some 20-40% of this Po was extractable using 0.5 M NaHCO3, and is regarded as easily mineralizable and a potential source of P for plant uptake. Substantial amounts of Al were present in crystalline and non-crystalline oxides (2000- 6000 mg kg-1) and complexed to organic matter (up to 400 mg kg-1). The amount of aluminium extracted using reagents commonly accepted to indicate Al toxicity in soils (1 M KCl and 0.01 M CaCl2) was not related to the amounts of those Al forms (extracted by ammonium oxalate, sodium citrate-dithionite) typically identified in pedological and mineralogical studies. Sampling and analysis of soils for determining P fertilizer requirements and diagnosing acidity and related problems (e.g. Al toxicity, Ca deficiency) should take into account the vertical heterogeneity in soil properties in the top 100 mm of the profile.

Distribution and cycling of nutrients in Pinus radiata as affected by past lupin growth and fertiliser

Abstract The effect of past lupin ( Lupinus arboreus Sims) growth and the application of a balanced mixture of fertiliser on the distribution and cycling of nutrients (N, P, K, Ca and Mg) in a 14-year-old stand of Pinus radiata D. Don growing on a stabilised coastal sand dune was studied. Tree growth continued to respond to fertiliser (960 kg ha −1 N applied during the first 10 years) but growth in the lupin treatment (where lupin was effectively absent since the stand was 5 years of age) was similar to that in the control. Biological N 2 -fixation by lupin growing under the developing pine canopy was estimated to average at least 80 kg ha −1 year −1 over 5 years. Ecosystem-N (exclusive of roots) in the control, lupin, fertiliser, and lupin-with-fertiliser treatments was 820, 1220, 1440 and 1610 kg ha −1 respectively. Most of the differences between treatments were due to soil-N (measured to 1 m depth). Current drainage losses of N were low ( −1 year −1 ) but there were clearly significant losses in the past. For example, 560 kg ha −1 of the estimated inputs of 1360 kg ha −1 of N to the lupin-with-fertiliser treatment were unaccounted for. The N-content (kg ha −1 year −1 ) of litterfall averaged 10 (control), 20 (lupin), 23 (fertiliser) and 25 (lupin-with-fertiliser). Nitrogen was immobilised in decomposing litter for at least 22 months in all treatments. There was little net leaching of total-N from the tree crowns ( −1 year −1 ), and there was net absorption by trees of both NO 3 N and NH 4 N from rainwater. Bulk precipitation contained 3.1 kg ha −1 year −1 of N, and aerosols captured by the tree crowns were estimated to contribute 1.1 to 2.0 kg ha −1 year −1 . Across the treatments the gross annual demand for N for above-ground new growth varied from 22 to 87 kg ha −1 year −1 , of which 27–41% was supplied by internal redistribution, and 5–19% from atmospheric inputs. Despite the large inputs of N in the past the trees in all treatments are currently N-deficient and would respond to N-fertiliser. The highly N-immobilising nature of the ecosystem suggests that continuing N-inputs by either biological N 2 -fixation or by fertiliser will be necessary to maintain growth rates in the long term.

Modelling and prediction of dominant height and site index of Eucalyptus globulus plantations using a nonlinear mixed-effects model approach

A nonlinear mixed-effects model approach was used to model dominant height and site index for Eucalyptus globulus Labill. plantations in southeastern Australia. Mixed effects were considered initially for all three parameters of a modified Chapman–Richards model. Inclusion of random effects improved fitting and accounted for the within-plot heteroscedasticity. To correct for within-plot autocorrelation, a power autocorrelation model allowing for irregular intervals for remeasurements was found to be most appropriate. Additional fertilizer application at age 1 year and a number of environmental variables were related to the fixed-effects parameters, but these were not statistically significant, whereas mean annual rainfall and average daily maximum temperature in July (winter) greatly reduced the residual variability among plots. The resulting nonlinear mixed-effects model combines dominant height and site index prediction into a single model and predicts polymorphic height growth rates on different sites....

Nutrient release from silvicultural slash: Leaching and decomposition of Pinus radiata needles

The loss of nine nutrient due to leaching and decomposition of green needles present as part of silvicultural slash in Pinus radiata D. Don forests was studied in the laboratory and in the field for a period of 12 months. There was negligible immediate leaching of nutrients from intact, live or dried needles, and only after 3 months decomposition in the field was there any appreciable nutrient release. The proportions of macronutrients loss after 12 months was in the order: nitrogen (16%) < calcium (19%) < magnesium (34%) < phosphorus (38%) < sulphur (52%) < potassium (92%). For the micronutrients, 76% of boron was lost after 12 months, but less than 10% of manganese and zinc were lost. It is suggested that the retention of N in silvicultural slash resulting from green-cron pruning may cause a significant reduction in total N availability in young stands gron on N-poor sites

Effect of irrigation with sewage effluent on decomposition of litter in Pinus radiata forests

Abstract Two Pinus radiata D. Don forests (aged 18 and 25 years) were spray-irrigated for 32 months with domestic sewage effluent from a secondary oxidation pond. Effluent was applied at rates of 25 and 50 mm week −1 . Irrigation decreased litter organic matter by 43%–57% but there was no change in organic matter in the soil (0–50 mm). Annual loss-constants determined from a litter-bag study in one forest approached 1.0 in the irrigated plots, compared to 0.48 in the control. Irrigation increased the pH and the availability of P, Ca and Mg in the soil. Increased concentrations of N, P, Ca and Mg in irrigated litterbags were closely correlated with increases in the rate of decomposition of the organic matter. The effect of irrigation on decomposition rates was due, in part, to the maintenance throughout the year of a more suitable environment in the litter for decomposers, particularly during dry summer periods.

Effect of timing and rate of hexazinone application on weed control and early growth of Pinus radiata on two contrasting sites

Summary The effects of timing (1–12 months after planting) and rate (1–8 kg ha −1) of hexazinone application on weed control and the growth of Pinus radiata two years after planting were studied in two field trials established on contrasting sites at Longford and Neerim in Gippsland, Victoria. Hexazinone applications were compared with a routine treatment of amitrole + atrazine in mixture (1 + 4 kg ha −1), also applied from 1 to 12 months after planting. Growth of P. radiata was closely correlated with live-weed cover. At Longford, maximum weed control and growth response occurred with 4 kg ha −1 hexazinone, whereas at Neerim, growth of P. radiata continued to increase to 8 kg ha −1 hexazinone. Maximum tree growth at Longford was achieved for hexazinone application in August-September, 1–2 months after planting. At Neerim, there appeared to be greater flexibility in time of application than at Longford, with best responses being recorded for applications in the September to December period. Amitrole + atr...

A regionalised growth model for Eucalyptus globulus plantations in south-eastern Australia

Summary A whole-stand distribution growth and yield model was developed for Eucalyptus globulus plantations in south-eastern Australia. The model was developed and parameterised using growth measurements from permanent sample or experimental plots established within plantation estates across the Gippsland, Central Victorian and Green Triangle regions. Regional variation of stand height and basal area growth, and mortality, was statistically tested using selected base models and indicator variables. Stand-level component models were constructed for projecting the stand heights, basal areas and stockings sampled in inventories into the future. Tree-level component models were developed for estimating the relationship between height and diameter, stem taper, and bark thickness at 1.3 m height from ground. To derive the diameter distributions of trees at any age, models were developed for predicting the 0th, 25th, 50th and 95th percentiles of cumulative diameter distributions. The Weibull distribution-based diameter distributions are estimated using the diameter percentiles and quadratic mean diameter predicted at the ages of interest (parameter recovery). In general, the developed models represent the mean growth of the E. globulus plantations in the three regions, and the observed and predicted yield trajectories agreed well for stand height, basal area and stocking. The accuracy of the developed stand models was evaluated using an independent data set. In general, for a prediction interval of 5 y or less, average bias in stand height, basal area and volume predictions is within ±1.0 m, ±0.5 m2 ha−1 and ±1.0 m3 ha−1 respectively. The models are reliable for projecting the stand parameters sampled in inventories at ages 5 or 6 y to the end of the rotation at about age 10 y. The developed growth model is particularly useful for strategic planning and wood flow analysis.

Mid-infrared spectroscopy for rapid assessment of soil properties after land use change from pastures to Eucalyptus globulus plantations

There is an increasing demand for rapid and cost effective techniques to accurately measure the effects of land use change on soil properties. This study evaluated the ability of mid-infrared spectroscopy (MIRS) coupled with partial least squares regression (PLSR) to rapidly predict soil properties affected by land use change from agriculture (mainly pasture) to Eucalyptus globulus plantations in south-western Australia. We measured total organic carbon (TOC), total nitrogen (Total N), TOC/Total N (C/N ratio), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and total phosphorus (Total P). The PLSR calibration models were developed using mid-infrared (MIR) spectra (4000 to 450 cm(-1)) and square root transformed measured soil data (n = 180) from 23 paired pasture and E. globulus plantation sites representing the soils and climate of E. globulus plantation estates in south-western Australia. The calibration models for TOC, Total N, C/N ratio and Total P showed excellent correlations between measured and predicted data with coefficient of determination (R(2)) exceeding 0.91 and minimum root-mean-square error (RMSE) of calibration [TOC (R(2) = 0.95, RMSE = 0.36), Total N (R(2) = 0.96, RMSE = 0.10), C/N ratio (R(2) = 0.92, RMSE = 0.14) and Total P (R(2) = 0.91, RMSE = 0.06)]. The calibration models had reasonable predictions for MBC (R(2) = 0.66, RMSE = 0.07) and MBN (R(2) = 0.63, RMSE = 0.06). The calibrated models were validated using soils from 8 independent paired pasture and E. globulus sites (n = 64). The validated predictions were excellent for TOC (R(2) = 0.92, RMSE = 0.40) and Total N (R(2) = 0.91, RMSE = 0.12), but less so for C/N ratio (R(2) = 0.80, RMSE = 0.35), MBC (R(2) = 0.70, RMSE = 0.08) and Total P (R(2) = 0.75, RMSE = 0.12). The results demonstrate the potential of MIRS-PLSR to rapidly, accurately and simultaneously determine several properties in land use change affected soils.

Selection of cold-tolerant Eucalyptus species and provenances for inland frost-susceptible, humid subtropical regions of southern China

Summary Inland humid subtropical regions of China’s southern provinces have substantial areas of land potentially available for forest plantation development. Such development would help address a substantial deficit in domestic production compared with demand for timber and fibre raw materials. However, the tropical and subtropical eucalypt varieties that are the basis of highly productive and commercially successful plantations in China’s warmer coastal regions have proved poorly adapted to inland regions which are characterised by hot humid summers and frequent winter frosts and cold events with temperatures down to –8°C or lower. To evaluate a range of Eucalyptus species and provenances for plantation development in this subtropical environment, three species–provenance trials were established in southern and central Hunan province from 2001 to 2004. Included in these trials were 64 provenance seedlots representing 22 species and a locally selected Eucalyptus camaldulensis clone. Five of these seedlots represented somewhat improved sources from South Africa, whilst the others were unimproved natural stand provenances. Species that demonstrated the best growth and survival at age 6 years were E. amplifolia var. amplifolia, E. benthamii, E. dunnii and E. dorrigoensis. Species which showed reasonable performance in at least one trial and warrant further investigation include E. saligna × E. botryoides and E. deanei. Whilst E. macarthurii had the best cold tolerance, it had relatively poor performance for growth and survival. Provenances from imported improved sources (from South Africa) in most cases proved inferior to, or no better than, the best natural-stand provenances of the same species, providing salutary guidance for prospective growers.

Relative, but not absolute, thinning responses decline with increasing thinning age in a Eucalyptus nitens plantation

Summary Growth rates of trees and stand structure change as stands age, and therefore absolute and relative thinning responses may also vary with thinning age. The study examined whether thinning age influenced the relative and absolute thinning responses in Eucalyptus nitens plantations near Carrajung, Victoria, Australia, and whether this effect was influenced by nitrogen (N) fertiliser application. Two levels of thinning and fertiliser application were applied in a factorial design replicated three times in a randomised block layout in each of two trials established in September 2006 in adjacent plantations aged 3.2 y and 13.2 y respectively and from the same seed source. Treatments included: unthinned or thinned non-commercially from below to 300 trees ha–1; fertiliser treatments were nil or 300 kg ha–1 N as urea in the younger trial and nil or mixed fertiliser supplying 256 kg ha–1 N, 80 kg ha–1 P and 100 kg ha–1 K in the older trial. Five years after thinning, basal areas of the largest 200 sawlog crop trees ha–1 (SCTs) were about 4.1 m2 ha–1 greater in thinned than in unthinned stands, regardless of thinning age, and volumes of SCTs were 30.1 m3 ha–1 greater in thinned stands. As a result of the greater standing basal area and volumes in the older trial, relative thinning responses of SCTs were greater in the younger trial, such that thinning increased the basal area of the SCT200 by about 42% (and volume by 32%) in the younger trial, but by only 21% (and volume by 17%) in the older trial. Fertiliser application also increased absolute thinning responses. Smaller relative thinning responses in the older stand were associated with age-related changes in stand structure of unthinned stands, including increasing skewness and decreasing kurtosis of diameter distributions as stands aged. The absence of a thinning-age effect on absolute responses suggests that there is some flexibility in the thinning age in E. nitens plantations. However, it is important to note that while the absolute thinning response may be slow to decline, the size of the SCTs will be smaller after later-age thinning owing to the extended period of competition they experience prior to thinning.