Eucalyptus growth in relation to combined nitrogen and phosphorus fertiliser and soil chemistry in Tasmania

Two experiments were established to determine the early nutrient requirements for plantations of Eucalyptus globulus (Nabowla site) and E. nitens (Westfield site) in Tasmania, Australia. Nitrogen (N) and phosphorus (P) were broadcast together, 2 and 26 months after planting, at cumulative rates of up to 1200 kg N ha^?1 600 kg P ha^?1. Soil chemistry was characterised at each site in three profiles, and in all plots at the Westfield site. Nabowla has a relatively infertile, poorly structured soil, low in N and P, and receives about 800 mm of rainfall per annum. Growth was very poor without fertiliser, but trees responded rapidly and strongly to added NP. Stem volume increased directly with the rate of applied fertiliser, with no evidence that the response had peaked at the highest rate. Even at the highest rate of NP fertiliser, however, productivity was relatively low (mean annual increment about 15 m ha^?1 y^?1). Establishment of plantations on such sites is unlikely to be economically viable, with or without fertiliser, but fertile ex-pasture sites that are otherwise similar should be considered. Westfield has a relatively fertile, well-structured soil, and receives 1400–1500 mm of rainfall per annum. Response to NP fertiliser was delayed at this site, with first responses measured 33 months after planting. The response in stem volume was sigmoidal in relation to fertiliser rate, with a plateau at an application rate of 400 kg N ha^?1 and 200 kg P ha^?1. This rate of fertiliser is expected to increase mean annual increment from 20 (without fertiliser) to 25 m ha^?1 y^?1. Splitting applications of fertiliser at the highest rate did not alter the growth response.

Although high rates of N and P fertiliser may be required to maximise growth of eucalypt plantations in Tasmania on ex-forest sites, rates required during the first few years might be lower than those reported here if the timing and placement of fertiliser is optimised. Soil chemical analyses were indicative of N and P requirements, and about a third of the variation in growth across the Westfield site was accounted for by natural variability in initial concentrations of total P and exchangeable K in surface soil.     

Effects of fertiliser applications after thinning of Pinus radiata on a high-elevation site in south-eastern Australia

A trial to assess the effects of fertiliser applied after thinning was established in a ten-year-old Pinus radiata stand growing on a high elevation site in south-eastern Australia. The trial had two components. The first studied the effects of fertilisers applied in a factorial design with two levels of phosphorus (0 and 50 kg P ha^–1) and three of nitrogen (0, 150 and 300 kg N ha^–1) plus a mixed nutrient treatment to areas thinned to a routine intensity. In the second part, levels of thinning intensity were assessed with and without a fertiliser (N₁P₁) application. Over the seven years of the study, growth was affected by below average rainfall in four of the years. Significant responses to fertiliser were achieved with all treatments; the best was 150 kg N ha^–1 + 50 kg P ha^–1 plus trace elements. The volume increment was increased by 28%, however this was not significantly different from the N₁P₁ alone. The N₁P₁ fertiliser increased productivity at all thinning levels including the unthinned treatment. Models predicting relative growth response based on foliage nutrient levels gave reasonable predictions, that is, 29% increase in volume periodic increment and this was slightly higher than that achieved. On such low rainfall sites, rather than having multiple thinnings, one option is a relatively heavy thinning at a young age with fertiliser application and then leaving the stand until final harvest. Estate optimisation models provide forest managers with the means to evaluate fertiliser-thinning treatment options against objectives such as maximising the present value of expected future cash flow within production and budget constraints.     

Managing wood production from small grower acacia hybrid plantations on eroded soils in central Vietnam

An experiment in a second rotation acacia hybrid (Acacia mangium × A. auriculiformis) clonal plantation in central Vietnam examined factors determining total wood production and its apportionment to sawlog and pulpwood. Growth and stand characteristics were compared with those in nearby plantations owned by small growers. The experimental site was on sloping land damaged and eroded by war and previous land use. The soil was shallow, with 20–30% laterised stones by volume and had lost part of the A horizon. Mean annual increment (MAI, in standing merchantable volume over bark) of the first rotation at age 8.8 years was 17 m³ ha^?1 y^?1. In the second rotation at age 7.6 years it was 20 m³ ha^?1 y^?1. Application of P fertiliser at three rates ranging from 14 to 86 kg ha^?1 increased stem diameter over the second rotation although stand volume response to P was not significant by rotation end. Potassium (14 kg ha^?1) gave no growth response. Growth rate was similar under weed control by herbicide and manual means. MAI increased progressively from 16.5 m³ ha^?1 y^?1 at the hilltop to 25.0 m³ ha^?1 y^?1 at the lowest part of the experiment; slope position influenced growth more than management practices. Key soil properties, pH, N, Bray-1 P and organic C were maintained from the first to the second rotation. With simple management practices including conservation of site organic matter and early stand management, appropriate for local small growers, the second rotation yielded 46% of harvested volume as sawlogs and the balance as pulpwood. Although small growers achieved similar growth rates, their current management regime does not yield sawlogs. They can influence the log categories produced and stand value through changes to stocking rate, stand management and rotation age.     

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

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.     

Wood properties of Eucalyptus globulus at three sites in Western Australia: effects of fertiliser and plantation stocking

Wood properties of 10-year-old trees in Eucalyptus globulus plantations at three sites in Western Australia were examined. Silvicultural treatments applied at age two years were stocking (unthinned, 1250 stems ha^–1; thinned to 600 stems ha^–1 or 300 stems ha^–1) and nitrogen fertiliser application (0 or 250 kg ha^–1 elemental nitrogen) in factorial combination. The three sites differed markedly in their annual rainfall (620–1100 mm), open-pan evaporation and soil water-holding capacity. Wood cores were collected at breast height from a total of 263 trees (~15 trees for each site-by-treatment combination), and radial samples prepared for analysis by SilviScan to produce radial profiles of air-dry density and microfibril angle (MFA) and modulus of elasticity (MOE), and by radial near infrared (NIR) surface scanning to produce radial profiles of NIR-predicted Kraft pulp yield (KPY) and cellulose content (CC). Sampling interval was 0.025 mm for density and 5 mm for the other properties. For wood property mean values (i.e. wood property averages of each pith-to-cambium sample), sites differed significantly only in air-dry density. The Boyup Brook site, which had low annual rainfall, the lowest climate wetness index and soil water-storage capacity and the slowest diameter growth, had the highest mean wood density (648 kg m^–3), while Scott River, with the highest rainfall, had mean density that was 10% lower. The Wellstead site (low rainfall but highest soil water-storage capacity) was intermediate for density. The only other significant differences for mean wood properties were caused by fertiliser addition, which reduced NIR-predicted KPY from 54.6% (without fertiliser) to 54.1% and predicted CC from 43.7% to 43.1%. Clear radial trends were evident for all wood properties. Density, MOE, KPY and CC all increased from pith to the cambium, while MFA declined. From the innermost (pith) 10% to the outermost (cambial) 10% of the radius, density increased on average by 21%, MOE by 103%, KPY by 9% and cellulose by 11%, while MFA declined by 47%. NIR calibrations developed using the SilviScan and NIR spectral data explained 71% of variance in MOE for an independent set of radial wood samples of E. globulus from Victoria, but less than 50% of variance for density and MFA. Implications for paper pulp and veneer manufacture are briefly considered.     

Establishing Eucalyptus nitens plantations using controlled-release fertilisers

Field trials were installed in three Tasmanian Eucalyptus nitens plantations to quantify growth responses and operational factors associated with applying controlled-release fertilisers (CRF) at planting. A range of CRF products, blends and rates of application was evaluated and compared with the industry standard (di-ammonium phosphate (DAP), 100 g seedling^–1). Trees treated with CRF were between 26 and 35% taller than unfertilised trees by age 2 years, with height equivalent to or greater than height using DAP. The use of CRF enabled the planting and fertilising operations to be combined, resulting in improved operational and financial efficiencies. Two suitable alternative primary CRF treatments were identified: Basacote® 9M applied at 20 g or 40 g seedling^–1 (B9M20 or B9M40). The B9M20 fertiliser provided equivalent height at a lower cost than DAP, while B9M40 provided greater height than DAP but at an equivalent cost. Height response was strongest and lasted longest at the low–moderate fertility site compared to the higher fertility sites. Both CRF treatments achieved rapid early growth in height, necessary for successful establishment by age 2 years, which helped reduce the period of susceptibility to browsing mammals and overtopping from weeds. Additional benefits from using CRF include significantly reduced fertiliser inputs, lower risk of leaching and lower risk of competitive uptake by weeds. These benefits are consistent with the objectives of developing more efficient operational systems, site-specific management and reducing environmental impacts.     

Herbicides for use in management of certified Pinus radiata plantations in New Zealand

Post-planting vegetation control in commercial Pinus radiata D.Don forests within New Zealand almost exclusively uses a mixture of the two triazine herbicides, terbuthylazine and hexazinone. However, neither of these herbicides is endorsed for use on land certified by the Forest Stewardship Council (FSC), based on criteria relating to their persistence or toxicity in the environment. This is a problem for the forest industry as these herbicides are inexpensive, are not phytotoxic to P. radiata, and their residual action enables continued control of competing vegetation for up to a year following application. Using measurements obtained from three short-term field trials where herbicides were applied as pre- and post-emergent, post-planting treatments to a wide range of competitive vegetation species, the efficacy of alternative mixes of herbicides was compared to the triazine mix (the current industry standard). As the restrictions on the use of terbuthylazine by FSC may be lifted, this herbicide was also trialled in mixes with herbicides other than hexazinone. Tree growth was quantified one year after herbicide application using a biomass index. Results from all three trials showed that the triazine mix provided the greatest level of vegetation control, with the trees in this treatment attaining the highest biomass index. Where herbicide mixes were applied as pre-emergent treatments, the best alternative herbicide, as assessed by tree growth at one year, was indaziflam applied at 300 g active ingredient (a.i.) ha^–1. Compared to the triazine mix, the biomass index for this treatment was reduced by <1%. Where herbicides were applied as post-emergent treatments, the best alternatives to the triazine mix were very similar across trials and included treatments where terbuthylazine (at 7000 g a.i. ha^–1) had been applied in combination with one of either mesotrione (at 150 g a.i. ha^–1; 300 g a.i. ha^–1), triclopyr (at 113 g a.i. ha^–1), or clopyralid (at 1500 g a.i. ha^–1) or where a mixture of clopyralid, triclopyr and haloxyfop (1125 g a.i. ha^–1, 113 g a.i. ha^–1 and 250 g a.i. ha^–1) was used. Reductions in biomass index at one year in these five treatments, relative to the triazine mix, ranged between 5% and 35%, with smallest reductions being recorded for terbuthylazine used in combination with either clopyralid or mesotrione.     

Nutrient management of contrasting Acacia mangium genotypes and weed management strategies in South Sumatra,Indonesia

ABSTRACT

Tropical plantations are an important source of forest products both to meet the growing demand for wood, and to facilitate the transition from native forests to more sustainably produced forest resources. Management of these plantations for optimal productivity and resource-use efficiency is vitally important, and nutrient management is a critical component of sustainable plantation production. In this study, we explored the response of Acacia mangium plantations in South Sumatra, Indonesia, to fertiliser and their requirement for fertiliser, focusing on phosphorus (P) at establishment. Almost all plantations across a series of 11 sites were highly responsive to P fertiliser, with nine of the 11 sites having more than double the productivity in P-fertilised treatments at age 1 year compared with control treatments. However, the quantity of P required for 90% of maximum growth was generally low by age 2 or 3 years, and 10 kg P ha^–1 at establishment was sufficient to ensure that at least 90% of maximum growth was captured across all the experimental sites. At a 12^th site, we explored the interactions between genotype and weed control, and found that both effects were additive in the response of the plantations to P, and thus there was no substitutability between management types: weed control, genotype and P needed to be managed in combination to achieve maximum productivity.     

Changes in Dry-weight and Nutrient Distribution in Maritime Pine after Fertilization

A single application of urea (206 kg N/hectare) and superphosphate (90 kg P/hectare) increased the dry weight of a 13-year-old stand of unthrifty maritime pine (Pinus pinaster Ait.) after 3 years from 28.8 × 10³ to 52.6 × 10³ kg per hectare. One third of the dry-weight increase was in clear bole beneath the living crown.

Increase of nitrogen and phosphorus content of the above ground parts of the trees amounted to 33 per cent of the nitrogen applied, but only 7.3 per cent of the phosphorus. Approximately two thirds of the increases in nitrogen and phosphorus contents were in the foliage.

Potassium and magnesium were not applied but the concentrations in the trees increased by factors of 3.6 and 2.3 respectively as a result of the improved vigour of the trees, and the foliage accounted for more than two thirds of these increases. Calcium was added in the superphosphate but only doubled its content in the stand with slightly less than two thirds in the foliage.     

Quantitative and qualitative assessment of timber harvesting residues: a case study of a balsa plantation in Papua New Guinea

The quantity and quality of the harvesting residues in a balsa plantation in East New Britain Province of Papua New Guinea are reported in this paper. The plantation was harvested manually with a chainsaw and manpower to extract the industrial wood at age 6 years. A modified standard harvesting residue assessment method using plots on line transects was applied. The total weight of the harvest residues remaining on the site after wood extraction was 211.7 t_GREEN ha^?1 (tonnes (green) per hectare). The major component was un-merchantable stem wood (121.3 t_GREEN ha^?1; 57.3%), followed by bark (59.3 t_GREEN ha^?1; 28.0%). This level of harvest residue was relatively greater than that reported in other studies, reflecting the combination of the log specification applied and the nature of the stem defects in balsa trees. The level of residues indicates the possibility of additional woody material recovery for bioenergy after consideration of sustainability issues.

The average moisture content of the wood components of the residues was determined over two days. The average moisture content on the first day after harvesting was 50%, falling in the following day to about 48%. The abundance of five elements in the harvest residues was estimated using data from a single sample tree; of the elements assessed potassium was the most abundant while calcium was the least.     

Effect of Mycorrhizal Infection on Phosphorus Efficiency of Maize (Zea mays L.) Cultivars

Phosphorus is considered as one of the least available plant nutrients found in the rhizosphere. The large variation in phosphorus acquisition efficiency of different crop cultivars provides opportunities for screening cultivars that perform well on low phosphorus soil for sustainable agriculture. To assess phosphorus efficiency of maize cultivars viz.: Paras and JH 3459, a field experiment was conducted for 2 years at Indian Institute of Technology, Kharagpur, India on sandy loam soil, having pH 5.1, organic carbon 4.1 g kg^?1 soil and as low as 11.2 kg ha^?1 available phosphorus. Phosphorus was applied at a rate of 0 (low) and 400 kg ha^?1 (high) with and without the application of fungicide Benomyl at 500 kg ha^?1 for eradication of arbuscular mycorrhiza. Maize plants were harvested at 24, 48, and 74 days after sowing and final harvest was taken at maturity. In low phosphorus soil without Benomyl, cv. Paras produced 29, 18, and 69 %, while cv. JH 3459 produced 19, 9, and 57 % of their maximum shoot dry weight at 24, 48, and 74 days after sowing, respectively during the first year and the trend was same during the second year. The results indicate that relative shoot dry weight varies with growth stages and therefore, grain yield should be used to assess phosphorus efficiency. At maturity, maize cv. Paras produced 91 and 80 % while JH 3459 produced 71 and 60 % of their maximum grain yield during the first and second year respectively, proving that cv. Paras was more phosphorus efficient than cv. JH 3459. Root growth of both the cultivars was restricted under phosphorus deficiency conditions; however, cv. Paras produced 1.4–2.6 times more root length than cv. JH 3459 at different growth stages. Cultivar Paras had lower phosphorus influx than cv. JH 3459, but it was more phosphorus efficient because of more roots, lower internal phosphorus requirement and higher root length/shoot dry weight ratio. Application of Benomyl was completely effective in suppressing arbuscular mycorrhiza infections up to 48 days after sowing. Its effect started diminishing thereafter and some infection occurred, which however was significantly less than that observed in untreated plots. Thus, the yield difference between Benomyl treated and untreated plots can be attributed to arbuscular mycorrhiza. In low phosphorus soil, Benomyl application reduced the growth of cultivars by 12–45 % and the maximum reduction of growth was at 48 days after sowing. However, in high P soil, Benomyl application had no significant effect on dry matter yield of the cultivars.     

Efficiency of nutrient use for biomass production of a Eucalyptus clone as a function of planting density in short-rotation cropping

ABSTRACT

The objective of this study was to assess the effects of planting density on nutrient use efficiency (NUE) in the production of biomass of a hybrid of Eucalyptus urophylla × Eucalyptus grandis. Twelve planting densities were evaluated at 36 months of age, ranging from 498 to 2564 plants ha^?1. Three trees were harvested in each treatment to determine biomass production and allocation (per plant and per area), concentration (g kg^?1), amount (kg ha^?1), and NUE of N, P, K, Ca, Mg and S in the biomass of leaves, branches, bark and wood. In summary, the increase in planting density resulted in: higher biomass production per area; a reduction in biomass production per plant; a reduction in homogeneity; an increase in the concentration of N, P and K in leaves, of N, Ca, Mg and S in bark, and of N, P and K in wood; a higher amount of nutrients exported by harvesting; and a higher NUE for wood production. The increase in NUE indicates a possible nutritional deficit in trees at higher stocking rates at the age of three years. The higher the planting density, the sooner the site will require re-fertilisation.     

A review of nutrient,water and organic matter dynamics of tropical acacias on mineral soils for improved management in Southeast Asia

ABSTRACT

More than 3 000 000 ha of tropical acacias have been established in recent decades, mostly grown on short rotations of 4–7 years, by a range of growers, from smallholders in Vietnam with less than 5 ha to large industrial growers in Sumatra managing hundreds of thousands of hectares. While the acacia estate is declining in some areas due to disease susceptibility, it is still expanding in other areas, and acacias would probably be the preferred species in many areas if the disease issues can be overcome. To date, many of the silvicultural management practices have largely been based on operational trial and error rather than backed by scientific evidence. To ensure sustained production, a deeper understanding of the mechanism for the response of acacias to management and environment is required. The objective of this paper is to review recent advances in our knowledge of the nutrient, water and organic matter dynamics of acacia plantations on mineral soils in Southeast Asia. We show that water availability is a key factor influencing productivity in many locations, but also that there are options for new approaches to management, including regional and site selection (or choice to plant or not on any given plot of land), and an understanding of nutritional requirements will help managers to adopt best practices in their plantations. While many plantations show significant responses to nutrients, particularly phosphorus (P, e.g. up to 200% stem volume increase at age one year); initial large responses to P fertiliser are reported to diminish over time, such that the response tends to be non-significant at many sites by harvest age. Only small quantities are recommended at establishment (equivalent to around 10 kg P ha^?1) to maximise productivity. Large quantities of site nutrient pools are held in harvesting debris or slash. Slash should be considered a valuable resource for sustaining productivity into the future, and its role in relation to fertiliser application needs further study.     

Growth response following variable espacement of 28-year-old Alpine Ash regeneration in New South Wales

Analysis of stand growth-response patterns have shown that small increases in sawlog volume resulted from thinning fast grown, fire regenerated alpine ash (Eucalyptus delegatensis R.T. Bak.) from below to a range of regular tree-spacings, at age 28 years. No significant correlation was found between basal area growth response and increased spacing for four treatments that ranged from 3.7 m to 7.3 m.

Rapid natural stocking-attrition occurred in both thinned and unthinned stands during the 31 post-thinning years of measurement. Maximum density diagrams indicated that these alpine ash stands were fully-stocked at lower densities than have been recorded for many other forest species. As a consequence of the propensity to self-thin, little additional stand growth was gained from the thinning treatments. The 150 trees ha^?1 with the largest diameters from all thinned stands averaged a basal area increase of only 0.59 mha^?1 over the 31 year period of measurement (<0.2 mha^?1 yr^?1), when compared with the equivalent stratum from an unthinned stand.

However, the small average nett growth response to spacing was not distributed evenly across the largest 150 trees ha^?1 dbhob. The 50 largest diameter trees ha^?1 in spaced stands showed a significant (α = 0.05) positive response, the trees ranked 51 to 100 showed no significant response and those trees ranked 101 to 150 showed a significant (α = 0.05) negative response when compared with the corresponding strata in the unthinned stand, over the same period.

Thus the overall result of stand spacing on the largest 150 trees ha^?1 was a widening of the stand diameter distribution and a small overall gain in the merchantable volume. For sites of higher quality, the basal area response was larger and predominantly accrued to the largest 50 trees ha^?1.     

Effects of tree spacing on branch-size development during early growth of an experimental plantation of Eucalyptus pilularis in subtropical Australia

ABSTRACT

Branch development in trees 1.6–5.7 years after planting was studied in a plantation experiment involving Eucalyptus pilularis in subtropical eastern Australia. The experiment compared stocking densities at planting in the range of 816–1667 stems ha^?1 and rectangularities of tree spacing in the range of 1–6. Branch diameters at their bases were measured on the lowest 5 m of the stems of trees judged likely to yield sawn timber of high quality at final harvest. Neither stocking density nor rectangularity had substantial effects on branch numbers or diameters. Particular interest was paid to the presence of branches with diameters in excess of 2.5 cm that might produce knots large enough to degrade the quality of sawn timber. Such branches developed on lower stems between 2–4 years of age. An average of nearly five such branches was found on more widely spaced trees, reducing to 2–3 on more closely spaced trees. The results confirmed other work suggesting that pruning of high-quality eucalypt plantations should start near 2–3 years of age to both limit the development of large branches and restrict the size of knotty cores in logs. There was no evidence that changing the rectangularity of spacing to 3 or a little more, from the more normal practice of close to square, would affect such pruning regimes: increasing the distance between rows can reduce establishment and harvest costs and allow easier access for silvicultural operations.     

Competition for nitrogen between trees in a mixed-species plantation in the Solomon Islands

ABSTRACT

As part of an ACIAR project aiming at improving community forestry in Solomon Islands, mixed-species plantations were established to assess the feasibility of inter-planting teak (Tectona grandis L. f.) and flueggea (Flueggea flexuosa Muell. Arg). Flueggea is a native hardwood used for timber and fence construction, and early removal of flueggea from a mixed-species stand could have a similar silvicultural outcome to thinning a single-species stand of teak. Using ¹⁵N-labelled ammonium sulphate, we investigated the competition for nitrogen (N) between the two species. The ¹⁵N-labelled tracer was applied to the soil surface of plots containing pairs of trees, one of each species, in 2-year-old and 4-year-old mixed-species stands, after the pairs of trees were isolated from the rest of the stand by an impermeable membrane. After 12–18 months, the isolated trees were measured and harvested, and each tree component (roots, stem, branch and foliage) was weighed and analysed for total N and ¹⁵N enrichment. There was no significant difference in the amounts of ¹⁵N between teak and flueggea components at either age, suggesting equal uptake of added ¹⁵N-labelled tracer by both species. The ¹⁵N amount was greater in stem followed by root, foliage and branch for teak and branch followed by stem, root and foliage for flueggea. About 42% and 55% of the applied ¹⁵N tracer were recovered in the 2-year and 4-year plots respectively, suggesting that higher uptake occurs with well-established root structure and that N losses decreased following canopy closure. The amount of total nitrogen was not significantly different between teak and flueggea components at age 2 and 4 years, and may indicate equal access to growth resources, and similar allocation. Although teak had significantly greater stem growth (height, basal area and volume) than flueggea in the 4-year plots, ¹⁵N uptake were similar to flueggea, which may mean that competition for growth resources was still minimal or that access to the resources was equal and growth rates differed between species.     

HIGHER FORESTRY EDUCATION IN AUSTRALIA

The results of three field trials which were established in 1976 to determine the feasibility of increasing wood production of Pinus radiata by fertilisation of thinned stands are described after four years of growth following the fertilisation treatments. The stands of about 20 years of age were producing an average of 14 m³ ha^?1 stem-wood per year.

The extra volume of wood growth resulting from fertilisation averaged 4.2 m³ ha^?1 a¹ for all sites, and 5.9 m³ ha^?1 a^?1 for the two most responsive sites, the latter being 37% over that obtained from unfertilised stands. Fifty per cent of the extra volume was added to the largest one-third of trees in the stands. A dominant tree of diameter (bhob) 27.0 cm in 1976 became 30.7 cm in 1980 if unfertilised and 32.8 cm if fertilised, an increase of 2.1 cm.

The responses obtained were inversely proportional to both the relative growth rates of unfertilised stands following thinning, and to the nitrogen concentration in the foliage of unfertilised trees measured in the year following fertilisation. Some soil/plant relationships have been examined for nitrogen, phosphorus, potassium and sulphur.

Fertilisation at this age appeared to at least ‘break-even’ if costs were amortised at an interest rate of 6%. However, fertilisation may also be a useful means of increasing yields at relatively short notice and allow increased flexibility in harvesting and other forest operations.     

Fertilization and Crop Residue Addition Impacts on Yield Sustainability Under a Rainfed Maize–Wheat System in the Himalayas

A 9-year old experiment was conducted at Almora, India to study the effects of mineral sources of nutrients in different combinations with or without crop residue or farmyard manure (FYM) addition on crop productivity under a rainfed maize–wheat system. Plots under 100 % nitrogen–phosphorus–potassium (NPK) + FYM had maximum mean maize (5.00 Mg ha^?1) and wheat (2.61 Mg ha^?1) yields that were generally significantly higher than yields observed under other treatments. Total soil organic carbon (C) increased in all treatments except with mineral fertilization and control plots. While NPK treated plots had significantly higher benefit:cost ratio than NPK + FYM plots, organic C content in the NPK treated plots decreased over the initial soil and FYM treated plots had better soil physical and chemical properties than NPK only. Thus, the study showed that although the combined 100 % NPK and FYM application had higher productivity of the maize–wheat system, the same is as remunerative as 50 % NPK + FYM, if the cost of FYM was considered. However, depending upon the resource availability, farmers can also apply Kudzu, maize stalk and wheat straw annually along with adjusted dose of NPK to a crop and full dose of NPK to the other crop as the alternate options.     

Domestic timber harvesting affects wood quantities in Tasmanian dry eucalypt forests

Domestic fuelwood harvesters illegally reduced coarse (≥10-cm diameter) downed woody debris stocks in Tasmanian mature dry eucalypt forests, 27–34 m tall, by 96.9 m³ ha^?1 or 22.7 t ha^?1. There was no effect of domestic harvesting on quantities of dead trees or live trees. Few dead trees were encountered in natural (unharvested) sites. Domestic harvesters preferentially removed debris <70 cm in diameter, leaving domestically harvested sites with 40% less volume and biomass of downed woody debris than natural sites. Assuming domestic harvesting, at the measured intensity, extends 25 m into forests either side of the state forest road system that passes through the studied forest type, dead wood stocks in that forest type and tenure throughout the state have been reduced by 688?000 m³ or 161?000 t. Domestic harvesting potentially damages biodiversity values, diminishes habitat available for species dependent on fallen logs and reduces forest carbon stocks. Domestic harvesters are advised to obtain licences to collect fuelwood from areas with an appropriate forest practices plan.     

Efficient Nitrogen and Water Management for the Soybean–Wheat System of Madhya Pradesh,Central India,Assessed Using APSIM Model

A series of long-term simulations were carried out to investigate alternative management practices to increase grain yields of soybean and wheat by optimizing sowing dates, nitrogen (N) and water requirements, along with complimenting farmyard manure (FYM) as a N source in the soybean–wheat cropping system of Madhya Pradesh. The APSIM simulation study showed that the mean soybean yield ranged from 1.0 to 1.6 t ha^?1 for the different dates of sowing. The average wheat grain yield was 3.2–3.9 t ha^?1, whereas, the crop sown on 15 November gave the highest yield. In this region, there is a potential to increase soybean and wheat yields by 0.6 and 2.2 t ha^?1, respectively. Among the various irrigation practices simulated, five irrigations of 60 mm at 20 days interval was the best option for wheat. Application of 16 t FYM ha^?1 to soybean produced 50 % higher wheat yield than the same amount of FYM applied to wheat. The wheat yield obtained from inorganic application of N was at par with that obtained from the application of integrated and organic sources. However, the amount of N loss from the integrated use of fertilizer N was lower than that from the current recommended practice for the region. Application of FYM alone or in combination with inorganic fertilizer maintained higher soil organic carbon concentration as compared to the application of inorganic fertilizer alone. Thus, the model provided a mean of evaluating alternative crop N and water management options for effectively managing the soybean–wheat cropping system.