20 research outputs found
Nitrogen Cycling in Leucaena Alley Cropping
No full textField experiments were conducted on an Alfisol in the semi-arid tropics of northern Australia to investigate nitrogen (N) cycling in the leucaena (Leucaena leucocephala) alley cropping system. This is a farming system in which maize (Zea mays L.) is grown in alleys formed by leucaena hedgerows spaced 4.5 metres apart. Mineralization of N from Ieucaena (prunings) and maize residues was studied under field conditions. Response of maize growth to addition of N fertilizer and plant residues was evaluated both in field plot and microplot experiments. The fate of fertilizer N and leucaena N was examined over four consecutive seasons. The decomposition (loss of mass) of dry, cut 15N-labelled leucaena residues differed from that of intact fresh leucaena prunings in the first cropping season although no difference was detected after one year. At the end of one cropping season, 3 months after application, 58-72% of 15N-labelled leucaena had decomposed compared to only 34-36% of fresh leucaena prunings. Similar trends occurred at 20 and 52 days after application. The extent of decomposition of fresh leucaena prunings (28-33%) was similar at two loading rates (2.4 and 4.7 t DM ha -1) by 3 months after addition. About 72% of young 15N labled maize residues was decomposed by 3 months after addition in the presence of fresh leucaena prunings. Decomposition of 15N-labelled leucaena residues and unlabelled fresh prunings was 91% and 88% respectively 14 months after addition. After 2 years the corresponding values were 96% and 94%. When N content of the recovered residues was taken into account, the values were 95% and 94% after 14 months, and the same (97%) after 2 years. Maize yield and N uptake were significantly increased following addition of either unlabelled fresh leucaena residues or 15N-labelled thy Ieucaena residues. Application of N ferilizer produced a thither increase in the presence of the residues. The maize yield and N uptake with the 15N-labelled leucaena were not different from those with the unlabelled residues. There was a significant positive interaction between N fertilizer and leucaena prunings which increased maize production. Addition of maize residues decreased the yield and N uptake of maize compared with that obtained in the presence of N fertilizer at 40 kg N ha~1 and leucaena residues (2.4 t DM ha-1). There was a marked residual benefit of N fertilizer applied in the first season at 36 kgN hat in the presence of leucaena prunings on the second maize crop yield and N uptake, but not on the third crop. However, a significant residual benefit of leucaena prunings added in the first season was found in DM yield and N uptake of the second and third maize crop. The short-term fate of 15N applied in plant residues was examined during two separate cropping seasons. By 20 days after application of separate 15N-labelled leucaena leaves, stems and petioles, 3-9% of the added 15N could be found in maize plants, 33-49% was in surface residues, 36-48% in the 2 m soil proffle and 0.3-22% unaccounted for. In a separate experiment when leucaena components were not separated, 5% of 15N applied in leucaena residues was taken up by maize 52 days after addition, 45% was in residues, 25% was in soil and 25% was unaccounted for. Jn another experiment, maize recovered 6% of added leucaena 15N after 2 months, 39% remained in residues, 28% was in soil and 27% was not recovered. Incorporation of 15N-labelled leucaena residues in the soil did not increase recoveiy of leucaena 15N by maize compared with placement of the residues on the soil surface. By the end of one cropping season (3 months after application), 9% of added 15N was recovered by maize from 15N-labelled leucaena. There was a similar 15N recoveiy from 15N-labelled maize residues applied as mulch at 1.7 t DM ha1 together with unlabelled leucaena prunings at 2.4 t DM ha ~. In both cases, 30-32% of added 15N was detected in soil, 28% in residues, and 31-34% apparently lost. The short-term fate of fertilizer 15N was different from that of 15N added in plant residues. In a 52-day experiment, maize recovered 65-79% of fertilizer 15N applied at low rates (6.1 and 12.2 kg N ha -1) in the presence of leucaena prunings, 21-34% was present in soil, and less than 1% was not recovered. By 2 months after application, recoveiy of fertilizer 15N by maize was 41% from N fertilizer added at 80 kg N ha -1, 35% from N fertilizer at 40 kg N ha -1 in the presence of leucaena prunings, and 24% from N fertilizer at 40 kg N ha -1 in the presence of maize residues and leucaena prunings. The corresponding deficits (unaccounted-for 15N) were 37%, 38% and 47% respectively. A small but significant amount of the fertilizer 15N was present in the unlabelled leucaena residues (3%) and in the mixture of unlabelled leucaena and maize residues (7%) present on the soil surface. However, application of the plant residues did not affect recoveiy of the fertilizer 15N in soil (21-24%). When N fertilizer was applied at 40 kg N hi1 in the presence of leucaena prunings, 43% of fertilizer 15N was recovered by maize at the end of cropping season, 20% in soil, 2% in residues, and 35% unaccounted for. The long-term fate of fertilizer 15N was compared with that of leucaena 15N in an experiment over four cropping seasons. In the first season, maize tops recovered 50% of the fertilizer 15N but only 4% of the leucaena 15N. In the second, third and fourth seasons, maize (tops + roots) recovered 0.7%, 0.4% and 0.3% of the initial fertilizer 15N compared with 2.6%, 1.8% and 1.4% of the initial leucaena 15N. In the second, third and fourth seasons, recovery of the initial fertilizer 15N (12-14%) in soil was much lower than that of the initial leucaena 15N (38-40%). There was no further loss of the fertilizer 15N after the first season. However, the cumulative 15N deficit for the leucaena 1N in the first two seasons was 50%--thissuggested an additional loss of 23% since the end of the first season. There was no further loss of 15N from either residual fertilizer 15N or residual leucaena 15N in the third and fourth seasons. In conclusion, application of leucaena prunings could substantially increase maize yield and N uptake although some supplementary N fertilizer may be required to achieve maximum crop yield. Maize recovered only a small amount of added leucaena N in the first year. Most of the leucaena residue N was present in the soil and remaining residues after one season. This residue N would be gradually available for plant uptake by subsequent crops. Of course, annual additions of leucaena prunings would appreciably increase the pool of available N over time. Thus, application of leucaena prunings could substantially improve soil fertility in the long term.Thesis (PhD Doctorate)Doctor of Philosophy (PhD)Division of Australian Environmental StudiesFull Tex
Prevention of 15N cross-contamination during distillation and potentiometric titration of 15N-labelled samples
No full textRetention of cotton stubble enhances N fertilizer recovery and lint yield of irrigated cotton
No full textSpatial-temporal variability of soil moisture, nitrogen availability indices and other chemical properties in hoop pine (Araucaria cunninghamii) plantations of subtropical Australian forest plantations
No full textThe spatial variability of soil moisture, nitrogen (N) availability indices (total N, NO3--N, NH4+-N, potential mineralizable N (PMN)), and other chemical properties (organic C (OC), available P, pH, CEC, exchangeable K, Ca, Mg, Mn, Na) was investigated in two plots (1.36 ha each) of eight-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) progeny tests located in south-east Queensland, Australia, for dry and wet seasons. Following a nested sampling pattern, soil samples of 0-10 cm depth stratified at three different sampling scales (378, 42 and 2.6 m(2)) were taken. The hierarchical model of analysis of variance was used to analyse the spatial structure of these soil properties. The objectives of this study were to: (1) evaluate the spatial-temporal variability of soil properties in the two plots, and (2) develop an effective sampling strategy for similar test plots. At the wet season in the study plot 1, it was shown that for soil total N, CEC, pH, exchangeable Ca, Mg, and Na there were significant differences between means of 42 m(2) plots within 378 m(2) plots and between those of 378 m(2) plots within the 1.36 ha plot. For available P, PMN, mineral N, CC, and exchangeable Mn only differences between means of 42 m(2) plots within 378 m(2) plots were significant. For soil moisture, NH4+-N and exchangeable K there were significant differences between means of 378 m(2) plots within the 1.36 ha plot. For all of these properties there were no significant differences between means of 2.6 m(2) plots within 42 m(2) plots, mainly due to substantial variation (30-70% of total variance) of the soil properties within 42 m(2) plots. No spatial structure was found for soil NO3--N. For the dry season in the study plot 1, the patterns of the spatial variability only for soil total N, mineral N and available P remained the same as for those of the wet season. For study plot 2 at the wet season, the patterns of spatial variability for such soil properties were less pronounced. The sampling strategy for evaluating tree productivity potential of the plots and for monitoring the soil properties was highly dependent on set of the properties chosen, and on expected changes in means of soil properties from date to date. The findings are discussed in relation to the issues concerning assessment of tree growth performance in forest plantations. (C) 2000 Elsevier Science B.V. All rights reserved
Variation in branchlet ?13C in relation to branchlet nitrogen concentration and growth in 8-year-old hoop pine families (Araucaria cunninghamii) in subtropical Australia
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Carbon isotope composition (delta(13)C) of branchlet tissue at nine canopy positions, and nitrogen concentration (N-mass) at four canopy positions, were assessed in 8-year-old hoop pine (Araucaria cunninghamii Ait. exD. Don) trees from 23 half-sib families, grown in six blocks of a progeny test in southeastern Queensland, Australia. There was considerable variation among sampling positions, families and blocks in both delta(13)C and N-mass. The delta(13)C was positively related to N-mass only for samples from the upper outer crown (P < 0.005). Phenotypic correlations existed between tree growth and canopy delta(13)C. Branchlet delta(13)C of th, inner and lower outer crown was positively related (P < 0.037) to tree height, but delta(13)C in branchlets of the upper outer crown was not related to tree height, or was related negatively (P < 0.045). There were significant differences in delta(13)C between hoop pine families for six canopy positions (upper canopy positions as well as lower canopy positions on the northern side), with heritabilities greater than 0.40. The significance of these findings is discussed in relation to water and light competition within the tree canopy of hoop pine
Soil nitrogen mineralisation and organic matter composition revealed by 13C NMR spectroscopy under repeated prescribed burning in eucalypt forests of south-east Queensland
No full textThe effects of burning on in situ extractable nitrogen (NH+4-N+NO-3-N) and net Nmineralisation following scheduled fuel reduction burns in repeatedly burnt dry and wet sclerophyll forest sites in south-east Queensland were assessed. In addition, soil organic matter composition in the wet sclerophyll site was assessed by 13C NMR spectroscopy. The results showed that at the dry sclerophyll site, extractable N and net N mineralisation for 1 year were largely unaffected by burning, while at the wet sclerophyll site, these parameters decreased. 13C NMR analysis of soil samples from the wet sclerophyll site revealed that there was a significant reduction in the proportion of O-alkyl (alkoxy/carbohydrate) C with increasing burning frequency. Statistically significant effects on the other chemical shift regions were not detected. The ratio of alkyl C to O-alkyl C, a proposed index of organic matter decomposition, increased with increasing burning frequency. A high ratio of alkyl C to O-alkyl C suggests low amounts of carbohydrates relative to waxes and cutins, which could in turn lead to slower mineralisation. The findings are in accord with this hypothesis. There were significant linear relationships between cumulative N mineralisation for 1 year and the proportions of alkyl C and O-alkyl C, and the ratio of alkyl C/O-alkyl C. Thus, in addition to reductions in substrate quantity (low organic C and total N for burnt soils), there was also an alteration of substrate quality as revealed by 13C NMR spectroscopy which is reflected in low N mineralisation
Canopy carbon and oxygen isotope composition of 9-year-old hoop pine families in relation to seedling carbon isotope composition, growth, field growth performance, and canopy nitrogen concentration
No full textCarbon isotope composition (delta C-13), oxygen isotope composition (delta O-18), and nitrogen concentration (N-mass) of branchlet tissue at two canopy positions were assessed for glasshouse seedlings and 9-year-old hoop pine (Araucaria cunninghamii Ait. ex D. Don) trees from 22 open-pollinated families grown in 5 blocks of a progeny test at a water-limited and nitrogen-deficient site in southeastern Queensland, Australia. Significant variations in canopy delta C-13, delta O-18, and N-mass existed among the 9-year-old hoop pine families, with a heritability estimate of 0.72 for branchlet delta C-13 from the upper inner canopy position. There was significant variation in canopy delta C-13 of glasshouse seedlings between canopy positions and among the families, with a heritability estimate of 0.66. The canopy delta C-13 was positively related to canopy N-mass only for the upper outer crown in the field (R = 0.62, p < 0.001). Phenotypic correlations existed between tree height and canopy delta C-13 (R = 0.37-0.41, p < 0.001). Strong correlations were found between family canopy delta C-13 at this site and those at a wetter site and between field canopy delta C-13 and glasshouse seedling delta C-13. The mechanisms of the variation in canopy delta C-13 are discussed in relation to canopy photosynthetic capacity as reflected in the N-mass and stomatal conductance as indexed by canopy delta O-18
Some nutrient dynamics associated with litterfall and litter decomposition in hoop pine plantations of southeast Queensland, Australia
No full textLitterfall was collected over a 12-month period with littertraps in hoop pine (Araucaria cunninghamii) plantations aged 10, 14 and 62 years in southeast Queensland, Australia. The bulk of litterfall occurred during spring, mainly as hoop pine foliage with the annual litterfall ranging between 6.0 and 10.9 t ha−1, respectively, for the younger stands (10 and 14 years) and the mature 62-year old stand. The amount of nitrogen (N) and phosphorous (P) recycled annually through litterfall was lower in the younger stands (28–37 kg N ha−1 and 4.4–5.3 kg P ha−1) compared with that of the mature stand (85 N ha−1 and 6.2 kg P ha−1). The N and P retranslocated during senescence varied across the three stands studied with a trend for N and P retranslocation to increase as availability of soil mineral-N decreased.
Decomposition of the hoop pine foliage component of litter was also studied in the same stands using a litterbag technique and mass-balance analysis. The estimated half-life of hoop pine foliage mass ranged between 1.5 and 1.8 years. Litter-mass loss was strongly correlated with litter substrate quality indicators of N, C, P, C/N ratio, lignin, lignin/N ratio and polyphenols. During the course of the study, there was no difference in litter-mass loss between the stands of different ages. During the 15-month period, the order of element release from the hoop pine litter was K>Na>C>Mg>P, with N, Ca and Mn generally demonstrating varying degrees of net accumulation. During the course of the study, the lignin/C ratio of the hoop pine litter increased from 0.61 to 0.96. This suggested that the litter-C was predominantly in a recalcitrant form and, therefore, the associated N was unlikely to be rapidly released in the hoop pine litter layer
Nitrogen response and 15N-labelled fertiliser recovery by hoop pine seedlings grown under glasshouse conditions
No full textFaculty of ScienceNo Full Tex
