Productivity and nutrient cycling of a Javanese homegarden

In a 0.13 ha homegarden in West Java, Indonesia, a 16-week study of production, nutrient in- and outputs as well as internal circulation was carried out in 1989. Total annual agricultural production was 11.4 t ha^–1, of which 6.8 t ha^–1 were timber and firewood. Two thirds of the production was sold, the rest consumed by the owners. The productivity is more than twice the productivity of ricefields in the area, but can be raised further. Nutrient inputs in rainfall, streamwater and via N-fixation were estimated to a total of: 33 kg N, 7 kg P, 115 kg K, 79 kg Ca and 55 kg Mg ha^–1 yr^–1. Outputs in streamwater, harvest sold and erosion were estimated at: 42 kg N, 11 kg P, 151 kg K, 278 kg Ca and 83 kg Mg. Litterfall and pruning returned 10.0 and 7.5 t dry matter, respectively, per hectare to the soil annually. Throughfall was on average 92% of incident rainfall. Total amounts of nutrients circulated internally in the homegarden each year were estimated at: 223 kg N, 38 kg P, 373 kg K, 135 kg Ca and 50 kg Mg per hectare. This corresponded to 22, 44, 50, 20 and 30% of nutrients stored in the plant biomass, respectively. The balance is negative for all elements, the magnitude depending on whether the part of harvest consumed by the family itself is regarded as internal circulation or as an output. Compared to available soil reserves the system is likely to be sustainable for many years ahead, but may be vulnerable because of the high fraction of plant nutrient storage cycled annually.     

Influence of nitrogen and phosphorus fertilizers on amount and nutrient content of litterfall in a regrowth eucalypt forest

The effects of fertilizer treatment on nutrient transfers to the forest floor were examined in regrowth Eucalyptus diversicolor F. Muell. forest. Dry weight and nutrient content of leaf litterfall and total litterfall were measured for 3 years in a stand to which two levels of N (0, 200 kg ha^-1 year^-1) were applied each year at each of three levels of a single initial application of P (0, 30, 200 kg ha^-1). Annual accessions of litter to the forest floor were significantly increased by additions of both N (by 17%, 18% and 21% in the 3 years) and 200 kg P ha^-1 (by 8%, 8% and 4% in the 3 years) but there was no interaction between effects of N and P treatments. Fertilizer application also had a significant effect on the nutrient content of leaf litterfall and total litterfall. Concentration of N in leaf litterfall was 9% to 23% greater on plots treated with N fertilizer compared to untreated plots. The amounts of N in litterfall were about 30% greater on N-treated compared to untreated plots. On plots treated with 200 kg P ha^-1, P concentrations in leaf litter were 50% to 100% greater than in litter from plots receiving no P. Application of 200 kg P ha^-1 increased the amounts of P in annual litterfall by 32% to 87%. The greatest increase in P accessions occurred soon after fertilizer treatment. The amounts of Ca, K, and Na in litterfall were also significantly increased by fertilizer application. For Ca and K this was due partly to increases in element concentrations in litterfall following application of treatments. The effect of fertilizers on internal recycling of plant nutrients and on litter accumulation and nutrient dynamics in forest floor litter is discussed.     

The use of Sesbania (Sesbania rostrata) and urea in lowland rice production in Sierra Leone

The suitability of sesbania (Sesbania rostrata) as green manure for lowland rice was evaluated in the Inland Valley Swamp (IVS) of Sierra Leone, and attempts were made to identify appropriate methods of its management in combination with urea. Sesbania — rice intercropping and sesbania — rice rotation treatments were compared with 60 kg N ha^–1 applied in two splits and 30 kg N ha^–1 as basal or top dressed to rice grown in the two cropping systems. The ¹⁵N isotope dilution technique was used to quantify N uptake from the green manure and urea and its utilization by rice. Rotating 40–50 days old sesbania two days prior to transplanting and top dressing with 30 kg N ha^–1 as urea at nine weeks after transplanting gave highest rice grain yield (121% over the control without sesbania and urea). However intercropping sesbania with rice tended to increase N uptake and N fertilizer utilization more than the rotation treatments. The higher grain yield of rice in rotation despite lower N uptake than intercropping shows that other effects than only N explain the beneficial effect of sesbania on rice.This revised version was published online in November 2005 with corrections to the Cover Date.     

Calliandra calothyrsus (Meissn.) in an alley cropping system with sequentially cropped maize and cowpea in southwestern Nigeria

Alley cropping is increasingly becoming accepted as an appropriate technology with the potential to provide stable and sustainable food production in the tropics. However, only a few of the potential trees/shrubs have been tested. The performance of Calliandra calothyrsus (Meissn) as an alley cropping species was evaluated on an Oxic Paleustalf. The treatments were: prunings removal, prunings application; and three N levels, 0,45, and 90 kg N ha^–1, in a factorial arrangement. The cropping sequence was maize (main season) follwed by cowpea (minor season). Nitrogen fertilizer treatments were applied to the maize crop only. Four annual prunings of Calliandra hedgerows produced a total of 6 t ha^–1 of dry matter prunings containing about 200 kg ha^–1 of N. Maize yields were increased by the application of prunings but no benefits were obtained by supplementing the prunings with inorganic N. An average maize grain yield of 3.1 t ha^–1 per year was maintained without any chemical fertilizer input. However, without any prunings, maize yields were substantially increased by the application of inorganic N. Cowpea yield did not respond to application of prunings but plants grown adjacent to the hedgerows had reduced yield probably due to shading. Our results suggest that six rows (0.57 m inter-row spacing) between Calliandra hedgerows spaced at 4 m are optimum for this cowpea variety. The performance of Calliandra was comparable to that of Leucaena which has been widely shown to be effective in alley cropping systems of the region.     

Fine root dynamics of shaded cacao plantations in Costa Rica

Root turnover may contribute a significant proportion of recycled nutrients in agroforestry systems and competition between trees and crops for nutrients and water may depend on temporal fine root regrowth patterns. Fine root biomass ( 2 mm) and fine root productivity were measured during one year in plantations of cacao (Theobroma cacao) shaded by Erythrina poeppigiana or Cordia alliodora planted on a deep alluvial soil in Turrialba, Costa Rica. Fine root biomass of approximately 1.0 Mg ha^–1 varied little during the year with maximum values at the beginning of the rainy season of 1.85 Mg ha^–1 in the cacao-C. alliodora system compared to 1.20 Mg ha^–1 for cacao-E. poeppigiana. Fine root productivity of C. alliodora and E. poeppigiana (maximum of 205 and 120 kg ha^–1 4 week^–1, respectively) was greatest at the end of the rainy season, while for cacao it was greatest at the beginning of the rainy season (34–68 kg ha^–1 4 week^–1), which suggests that if nutrient competition occurs between the shade trees and the cacao, it could be minimized by early fertilization during the beginning of the rains immediately after pruning the shade trees. Annual fine root turnover was close to 1.0 in both systems. Assuming that fine root biomass in these mature plantations was constant on an annual basis, nutrient inputs from fine root turnover were estimated as 23–24 (N), 2 (P), 14–16 (K), 7–11 (Ca) and 3–10 (Mg) kg ha^–1 year^–1, representing 6–13% and 3–6% of total nutrient input in organic matter in the C. alliodora and E. poeppigiana systems, respectively.     

Long-term effect of wood and peat ash fertilization on nutrient content in peat and trees on a drained peatland

ABSTRACT

Total and soluble nutrients in peat were studied after ash fertilization on an oligotroph peatland in southeast Norway. Plots 15?m?×?15?m in size were fertilized with 0, 4, 7, and 10 tons ha¹ of wood or peat ash in 1944. Chemical analyses after 18, 35 and 48 years showed a gradual reduction of phosphorus (P) and calcium (Ca) from the 0 to 10?cm surface peat layer. Some of the leached Ca was recovered in the layers 10–20 and 20–40?cm, while hardly any of the lost P was recovered in this way. The amount of potassium (K) in the surface layer declined by 75% over the first 18 years, and remained stable thereafter. Nothing of the lost K was recovered in deeper layers. The pH reflected the Ca levels. Over the years, an increasing proportion of the applied P, K and Ca was retrieved in the trees. Needle analyses indicated that declining tree vigor on plots fertilized with 4 and 7 tons of ash ha^?1 was due to P limitations. After 48 years, the peat content of P and Ca was still significantly higher in fertilized than in control plots, thus demonstrating the long-lasting effect of ash fertilization.     

Alley cropping on an Ultisol in subhumid Benin. Part 2: Changes in crop physiology and tree crop competition

From 1986–92 alley cropping with Leucaena leucocephala (Lam.) de Wit and Cajanus cajan (L.) Millsp. was compared to a no-tree control, and fertilisation with 90, 39 and 75 kg ha^–1 N, P and K vs. no fertilisation were studied in maize and cassava grown intercropped or in rotation. Light transmission measurements and row position effects on food crop yield did not indicate any decisive shading effect in tree-crop competition when trees were pruned 2–3 times a year. In the last three years, with NPK in solecropping the crop growth rates (CGR) of maize reached a peak of 100 g m^–1 wk^–1 around 70 days after planting (DAP). CGR in unfertilised Cajanus alleys was as high as in corresponding fertilised treatments but delayed by one month. For cassava, the highest growth rates of 60–130 g m^–1 wk^–1 lasted from 60 to 190 DAP with NPK in solecropping. The harvest index (HI) of cassaca reached 40–50% in all intercropping and unfertilised solecropping treatments. The HI in solecropping was reduced by fertilisation to 30–40% due to excessive leaf growth at 60–190 DAP. The increase in number of thickened roots starting at 30 DAP in solecropping was delayed by one month in intercropping. The reason for significantly higher cassava root yields in Cajanus alleys as compared to no trees in the fertilised solecrop was attributed to the enhanced root formation at 85 DAP due to a slower release of nutrients subject to leaching such as N and K from tree prunings than from mineral fertiliser.     

Leucaena + maize alley cropping in Malawi. Part 1: Effects of N, P, and leaf application on maize yields and soil properties

Yields under alley cropping might be improved if the most limiting nutrients not adequately supplied or cycled by the leaves could be added as an inorganic fertilizer supplement. Three historic leaf management strategies had been in effect for 3 years ina Leucaena leucocephala alley cropping trial on the Lilongwe Plain of central Malawi : 1) leaves returned; 2) leaves removed; and 3) leaves removed, with 100 kg inorganic N ha⁻¹ added. An initial soil analysis showed P status to be suboptimal under all strategies. A confounded 3⁴ factorial experiment was conducted with the following treatments: leaf management strategy (as above), N fertilizer rate (0, 30, and 60 kg N ha⁻¹), P fertilizer rate (0, 18, and 35 kg P ha⁻¹), and maize population (14,800, 29,600, and 44,400 plants ha⁻¹). Both N and P were yield limiting, and interacted positively to improve yields. The addition of 30 kg N and 18 kg P ha⁻¹ improved yields similarly under all leaf management strategies by an average of 2440 kg ha⁻¹. Increasing the rates to 60 kg N and 35 kg P ha⁻¹ improved yields an additional 1990 kg ha⁻¹ in the ‘leaves returned’ and leaves removed + N’ strategies, but did not improve yields under the ‘leaves removed’ strategy. Lower yields were related to lack of P response at the highest P rate in this treatment, which may have induced Zn deficiency. Plots receiving leaves had higher organic C, total N, pH, exchangeable Ca, Mg, K, and S, and lower C/N ratios in the 0–15 cm soil layer than did plots where leaves had been removed. Leaf removal with N addition was similar to leaf removal alone for all soil factors measured except for organic C and total N, which were higher where N had been added. The results show that N and P were the primary yield-limiting nutrients. Historic N application maintained the soil's ability to respond to N and P on par with leaf additions.     

Long-term effect of wood and peat ash on the growth of Pinus sylvestris on drained peatland

The effect of ash fertilization on height growth and volume production of Scots pine (Pinus sylvestris L.) was studied on oligotroph peatland in southeast Norway. In the year 1944, plots 15 m × 15 m size were fertilized with 0, 4, 7, and 10 tons ha^?1 of wood or peat ash. The area was treeless, but a satisfactory number of pine seedlings were present. All measurements were confined to the central inner plot, 10 m × 10 m area. Most plots were re-fertilized with 10 tons of wood ash ha^?1 in the year 1993. Wood ash had higher content of nutrients, and generally, it had greater growth enhancement effect than peat ash. When the amount of ash was increased, volume production significantly increased for the age period 38–50 years and the total production at age 50 years. The mean annual increment during the first 50 years was about 6 m³ ha^?1 for the plots applied with 10 tons of ash ha^?1. Trees on plots fertilized with 7 or 10 tons in 1944 and replenished with 10 tons ha^?1 at age 50 years (1993) had a mean annual increment of 14 m³ ha^?1 for the stand age period 51–68 years. Over time some tree roots from control plots and plots fertilized with 4 tons ha^?1 have captured nutrients from richer plots. Such effect is to a smaller extent relevant for treatment 7 tons. It is concluded that the content of mineral nutrients of wood and peat ash makes these ashes well suited as fertilizers on peatland.     

Leaching of propiconazole and chlorothalonil during production of pinus sylvestris seedlings in containers

The risk of environmental contamination by pesticides is not well known in container production of forest seedlings. Leaching of propiconazole (Tilt 250 EC^®) and chlorothalonil (Bravo 500^®) from peat container medium into the ground was monitored during three growing seasons in nursery production of Scots pine (Pinus sylvestris L.) seedlings. Fungicides were applied at about 20 day intervals from the end of July until November. The annual load of leached propiconazole (25–183 g active ingredients ha^‐1) was greater than that of chlorothalonil (5 to 82 g active ingredients ha^‐1). The proportion of leached to applied propiconazole was large, 4–29%, but less than 1% of the applied chlorothalonil was detected in leachates. The downstream percolation of water in the soil beneath the container area was small. After extra irrigation into the ground, the detected concentrations of chlorothalonil in soil water 0.5 m beneath the ground surface were 0.4–2.4 μg 1^‐1.     

Forage production and quality of 4 perennial grasses grown under and outside canopies of matureProsopis glandulosa Torr. var.glandulosa (mesquite)

Comparisons were made of dry matter production and forage quality of two coolseason grasses, Canada wildrye (Elymus canadensis L.), Virginia wildrye (Elymus virginicus L.), and two warm-season grasses, green panic (Panicum maximum var.trichoglume Eyles) and plains bristlegrass (Setaria leucopila Scribn. & Merr.), planted under and outside the canopies of mature honey mesquite (Prosopis glandulosa Torr. var.glandulosa). Green panic gave the greatest cumulative dry matter yield in both canopy (5120 kg ha^–1) and open (3370 kg ha^–1) locations, followed by plains bristlegrass under mesquite (1130 kg ha^–1) and in the open (570 kg ha^–1). One-time yields from Canada wildrye and Virginia wildrye, under and outside mesquite canopy, were 247 and 329 kg ha^–1, and 272 and 268 kg ha^–1, respectively. Dry matter production of green panic (p=0.001) and plains bristlegrass (p=0.026) was greater under mesquite only for the first of four harvests, although both warm-season grasses exhibited a trend for greater production under mesquite than in the open. Average nitrogen content of green panic was greater (p=0.0004) under mesquite than in the open, while plains bristlegrass exhibited a trend for greater crude protein content in the open than under mesquite. Overall, moisture content of the warm-season grasses was greater (p=0.0001) under mesquite than in the open, while Virginia wildrye was more (p=0.002) succulent under mesquite than in the open. Averagein-vitro dry matter digestibility of warm-season grasses was almost significantly greater (p=0.0501) in the open than under mesquite. Canopy soils contained significantly more organic C (p=0.0004) and total N (p=0.0001) than open soils, with differences of 8.3 Mg organic C ha^–1 and 1.3 Mg total N ha^–1. Correlations indicated that soil fertility was more limiting to grass production than light intensity.     

Role of weeds in the management of nitrogen in a young Pinus radiata plantation

Pinus radiata trees were grown on a podzolized sandy soil at a second rotation site under the following treatments: total weed control, total weed control plus ammonium nitrate, strip weed control and no weed control. During the first two summers after planting the differences in needle water potential between trees under no, strip or total weed control were very small. Despite similar rates of net N-mineralization in strip and total weed control treatments, which averaged 64 kg ha^–1 yr^–1 in the 0–15 cm soil depth, weeds in the strip weed control treatment reduced soil mineral-N concentrations by 50–80%, leaching of N by the end of the first growing season by 45%, foliar-N concentrations by 4–14% and stem biomass at 20 months after planting by 46%. Although N-uptake by above-ground vegetation (trees plus weeds) was 49% higher in the strip weed control treatment, the amount of N apportioned to trees during the first 20 months after planting was reduced from 15.5 to 9.0 kg ha^–1. These effects of weeds were even more pronounced in the no weed control treatment. Since weeds had little effect on the needle water potential of trees and the annual rates of N-mineralization, but adversely affected N-uptake by trees, results indicate that weeds directly competed with trees for N, and thereby aggravated N-deficiency in trees. Application of ammonium nitrate after complete weed control increased foliar-N concentrations, and N-uptake and growth of trees, but also induced severe stem deformation.     

Estimates of above-ground biomass and nutrient accumulation in Mimosa scabrella fallows in southern Brazil

Naturally regenerated stands of bracatinga (Mimosa scabrella Bentham) are harvested for firewood after six to eight years of unregulated growth, debris burnt and the area planted to one cycle of intercropped maize (Zea mays L.) and beans (Phaseoulus vulgaris L.). Burning breaks dormancy of bracatinga seed (> 80% germination) marking the onset of a new fallow-crop cycle. This production system has been practiced for nearly 100 years in Southern Brazil, covering some 60,000 ha in 3,000 small farms. An estimation of above-ground biomass and nutrient accumulation was made using literature data on stand age, population numbers, tree sizes, tree biomass partitioning and concentration of major nutrients in tree tissues. A simple simulation model, used to quantify above-ground nutrient pathways and their temporal dynamics, confirmed that six to eight years is the optimal rotation length. Biomass and nutrients deposited onto the soil, peak at stand age six years, which may result in significant soil fertility improvement prior to crop planting. At year six, estimated total above-ground biomass amounts to 83 Mg ha^–1; 44 Mg ha^–1 available as firewood and 39 Mg ha^–1 to be returned to the soil. Roughly half the amount of nutrients fixed in the above-ground bracatinga biomass would be exported in firewood and subsequent grain crops.     

Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production,litter production and decomposition

During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha^–1.a^–1 cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity.Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha^–1.a^–1): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m³.ha^–1.a^–1.Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha^–1.a^–1 and underC. alliodora 7.07 t.ha^–1.a^–1. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles.The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha^–1.a^–1): For part I see Vol. 4, No. 3, 1986.Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesselschaft für Technische Zusammenarbeit), Turrialba, Costa Rica     

Fine root production and turnover in Brazilian Eucalyptus plantations under contrasting nitrogen fertilization regimes

Nitrogen fertilization increased largely over the last decade in tropical eucalypt plantations but the behaviour of belowground tree components has received little attention. Sequential soil coring and ingrowth core methods were used in a randomized block experiment, from 18 to 32 months after planting Eucalyptus grandis, in Brazil, in order to estimate annual fine root production and turnover under contrasting N fertilization regimes (120 kg N ha⁻¹ vs. 0 kg N ha⁻¹). The response of growth in tree height and basal area to N fertilizer application decreased with stand age and was no longer significant at 36 months of age. The ingrowth core method provided only qualitative information about the seasonal course of fine root production and turnover. Mean fine root biomasses (diameter <2 mm) in the 0–30 cm layer measured by monthly coring amounted to 0.91 and 0.84 t ha⁻¹ in the 0 N and the 120 N treatments, respectively. Fine root production was significantly higher in the 0 N treatment (1.66 t ha⁻¹ year⁻¹) than in the 120 N treatment (1.12 t ha⁻¹ year⁻¹), probably as a result of the greater tree growth in the control treatment throughout the sampling period. Fine root turnover was 1.8 and 1.3 year⁻¹ in the 0 N and the 120 N treatments, respectively. However, large fine root biomass (diameter <1 mm) was found down to a depth of 3 m one year after planting: 1.67 and 1.61 t ha⁻¹ in the 0 N and the 120 N treatments, respectively. Fine root turnover might not be insubstantial in deep soil layers where large changes in soil water content were observed.     

Biomass,decomposition and nutrient release of Vaccinium myrtillus leaf litter in four forest stands

Biomass and nutrient transfer (N, P, K, Ca, Mg) of bilberry (Vaccinium myrtillus L.) leaf litter fall, as well as decomposition and nutrient release, were studied in four mature forest stands situated in Central and South Sweden. Bilberry leaf litter fall amounted to between 33 and 55 kg ha^‐1 yr^‐1 in the four stands. Only minor differences between sites were noted for litter concentrations of N, P and Ca, whereas K and Mg showed somewhat larger variability. Relative amounts of the five nutrient elements in the litter fall were generally in the order N > Ca > K > Mg > P. The amounts of nutrients returned to the forest floor by the annual leaf litter fall in the stands ranged from 0.4 to 0.8 kg ha^‐1 for N, 0.4 to 0.6 kg ha^‐1 for Ca, 0.2 to 0.7 kg ha^‐1 for K, 0.1 to 0.2 kg ha^‐1 for Mg and 0.04 to 0.08 kg ha^‐1 for P.

The decomposition of the local bilberry leaf litter was followed by means of litterbags during three years. At all sites there was an extremely rapid mass loss from the litter (between 45% and 54%) during the first four to five months of decomposition. After this initial phase, the decomposition rates decreased markedly and after three years the accumulated mass losses of the litters varied between 64% and 78% at the studied sites. After two and three years of decomposition, three of the sites exhibited almost similar litter mass losses whereas at the fourth site the litter was decomposed to a significantly lower degree. The pattern of nutrient release from the decomposing bilberry leaf litter differed somewhat from site to site. Minor differences were, however, noted for P, Ca and Mg while N and K were more strongly retained in the litter at one of the sites.     

Phosphorus adsorption by peat from drained mires in southern Finland

The phosphorus adsorption capacity of 20 peat soils and those soil properties likely to influence it (Al, Fe, Ca, Mg, pH, ash content) were studied. Phosphorus adsorption was correlated only weakly to the site type classification of peatlands. However, the P adsorption was strongly correlated with the concentration of Fe in the peat. Thus, soil chemical analysis should be used to support site type classification in order to assess the effectiveness of peatlands to adsorb P. When expressed on a volume basis, the P adsorption capacity varied from 7 kg ha^‐1 to 673 kg ha^‐1 in the 0–30 cm layer. Compared with the amounts of P used in practical peatland forest fertilization in Finland (40–45 kg ha^‐1), the P adsorption capacity of several peat soils studied was substantially lower. It was thus concluded that slowly soluble P fertilizers or applications <40–45 kg ha^‐1 should be used where the P adsorption capacity is low.     

Agronomic and economic appraisal of alley cropping with Leucaena diversifolia on an acid soil in the highlands of Burundi

Although alley cropping has been shown elsewhere to permit continuous cropping, it has not been widely tested in the highlands of east and central Africa where it has the additional potential of controlling soil erosion. The effect of four rates (0, 30, 60 and 90 kg N ha^–1) of inorganic N on the performance of alley cropping using Leucaena diversifolia as the hedgerow species was studied in the central highlands of Burundi. Significant increase in maize yield (average of 26%) due to alley cropping was only first realised in 1992, three years after the commencement of the trial. In 1993, the average yield advantage of the alley cropping plots was 21%. The prunings augmented the response of maize yield to inorganic N in 1992 and 1993. Compared with the control, economic benefits over the five-year period for all the treatments were negative.     

Response of western hemlock crosses to nitrogen and phosphorus supply

Seedlings of nine controlled crosses of westernhemlock (Tsuga heterophylla (Raf.) Sarg.) withknown differences in growth rate after six years inthe field were grown for one year, and then subject tothree nutrient treatments. Nutrient treatments variedthe amount of nitrogen (N) and phosphorus (P) innutrient solutions as follows (N:P): 20:4 mgL^–1,100:20 mgL^–1, and 250:60 mgL^–1. Nutrientsolutions were used to subirrigate pots containing theseedlings in a peat:perlite medium for two growingseasons. Biomass and foliar N and P concentrationsincreased while nutrient productivity (biomass/shootN content) decreased with increasing nutrient supply. The nine crosses were divided into fast, medium andslow-growing parental ranks. There was a significantparental rank × nutrient treatment interaction forshoot and total biomass, and root:shoot ratio. Theresults indicate that tree improvement programs forwestern hemlock should plant progeny trials on sitesof different fertilities to examine relative responseof crosses.     

Effect of post-planting applications of granulated atrazine and fertiliser on the early growth of Eucalyptus nitens

A factorial experiment was established in a plantation of Eucalyptus nitens in southern Tasmania on a site which had formerly carried native eucalypt forest. Before planting, the site had been cleared of weeds with foliar translocated and pre-emergence herbicides. The first factor of the experiment examined the effects on tree growth of no post-planting weed control, control by hand or with three levels of application of granulated atrazine, 0.9, 1.8 and 8 kg ha^–1. The second factor examined the effects of no fertiliser application or the application of nitrogen as urea at 200 kg ha^–1 N plus triple superphosphate at 120 kg ha^–1 P. Tree growth responses to treatments were examined at 11, 16, 23 and 29 months of age.Fertiliser application increased tree height and diameter growth. Application of atrazine generally reduced height and diameter growth, but this was statistically significant only at the highest rate of application. Growth reduction occurred even though atrazine reduced post-planting weed cover on the site and hence potential competition with the tree crop for site resources. Hand weeding reduced the weed crop on the site even more than atrazine, but this did not increase growth of the tree crop.Given satisfactory establishment practices which include the use of herbicides pre-planting, it was concluded that post-planting weed regeneration was not sufficiently vigorous to warrant post-planting weed control on these sites. The use of atrazine for post-planting weed control could even be deleterious to eucalypts.