We investigated how multiple-crop forestry has influenced the magnitude and variability of soil and plant phosphorus (P) fertility and site disturbance. Kinleith Forest, on Mamaku Plateau, covers >100,000 ha and comprises mainly plantation Pinus radiata. Three study areas in the forest were chosen to represent natural state (native forest), first crop of P. radiata (24 years growth), and second crop of P. radiata (4 years growth of second crop). The adjacent areas have similar relief and climate, and the soils are all the same age, being predominantly Andic Haplohumods developed in 1770 calendar-year-old non-welded tephra (Taupo Ignimbrite, ca. 0.5–0.8 m in thickness) and overlying a buried paleosol on earlier tephric material.
Soil properties were compared using a random geometric sampling scheme stratified in a 40-m grid. Soil samples (0–20 cm) were taken at 1.5, 4.5 and 13 m spatial intervals in random directions away from each primary node, providing 192 sample sites for each study area. Additionally at selected sites, samples of the current year's foliage from the upper crowns were collected, the thickness of Taupo Ignimbrite (i.e. depth to buried paleosol) was recorded by augering, and site disturbance was assessed using a new six-point scale based on change relative to a modal soil profile. Geostatistics and geographical information systems (GIS) were used to assess variability and effects of forest management on the measured properties. Soil Bray-2 P concentrations were below guidelines for satisfactory growth (12 mg kg−1) at all sites, and no differences were recorded between the different management areas. However, the amount of within-site variability in Bray-2 P increased with the number of crops. Foliar P concentrations were only marginally deficient in both the first and second crops, indicating that P is currently not significantly limiting growth. The lack of difference in foliar P between first and second crops indicates no crop-to-crop decline in foliar P status and suggests that no site P fertility decline has occurred. The soils have an unusual ability to continue releasing P through successive sequential extractions in the Bray-2 P test, indicating a strong buffering capacity, and this may explain the apparent lack of deficiency even with Bray-2 P values of <12 mg kg−1. The site disturbance index increased and the spatial distribution of P data became increasingly variable with crop rotation.
GIS, inverse-distance weighting and kriging proved useful in illustrating the trends between crops. The spatial variability of results indicated that there was no obvious pattern to the variability and that more site-specific forest management in the region would be difficult. However, there was some evidence that less disturbance during harvesting may minimise variability of soil P supply. 相似文献
Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems
of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica.
For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference
between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests)
of the system are considered.
The implications of the models are discussed in detail.
Aspects of net primary production in the systems studied are considered.
N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall
patterns and pruning of theE. poeppigiana.
For part I see Vol. 4, No. 3, 1986 For part II see this issue
Agroforestry Project, CATIE/GTZ (Tropical Agricultural Research and Training Center/Gesellschaft für Technische Zusammenarbeit),
Turrialba, Costa Rica 相似文献
This article reports the regeneration dynamics of a temperate Abies–Tsuga forest in Kirishima Yaku National Park, southwestern Japan, and examines the influence of species coexistence mediated by
gap disturbances on biomass production. All trees taller than 2 m in a 1-ha plot were monitored over four growing seasons.
Three growth-form groups occupied different vertical layers. Evergreen conifers and deciduous broad-leaved trees tended to
be spatially segregated from evergreen broad-leaved trees, which formed thickets in the understorey. The regeneration of understorey
evergreen broad-leaved trees was affected by canopy gaps. The recruitment of conifers and deciduous broad-leaved species was
not observed during the four growing seasons. This suggests that regeneration is sporadic and the present environmental conditions
are not favorable for these canopy species. The mortality and unsuccessful recruitment of conifers and deciduous trees appeared
to cause fluctuations in the productivity of the stand. However, an abundance of canopy gaps accelerates the regrowth of shorter
species, and the fluctuation of productivity resulting from the population dynamics of canopy species would be partly mitigated
by the regeneration of evergreen understorey species. The horizontal and vertical heterogeneity of the temperate mixed forest
was a result of the patch structures of the three growth-form groups. The different regeneration patterns among the three
groups, which were driven by interactions of species-specific regeneration niches and disturbance regimes, might be an important
factor in maintaining the aboveground productivity in a transitional mixed forest between warm-temperate and cool-temperate
zones. 相似文献
Separate assessment of nutrient uptake by individual plants in mixed cropping with trees is impossible without tracer techniques.
The different 15N-to-14N isotope ratio of atmospheric and soil N can be used to study the contribution of biologically fixed N to the nutrition of
associated trees. In most cases, the assessment of nutrient uptake distribution is an appropriate way of evaluating how to
improve the transfer of biologically fixed N. Radioisotopes (e.g., 32P), stable isotopes (e.g., 15N) and rare elements (e.g., Sr) can be used to determine relative root activity distribution by applying the tracer to different
soil depths or distances from trees. A broadcast application of the tracer instead of point application makes it possibe to
calculate uptake values per unit area. The direct determination of nutrient pathways with such robust experiments offers considerable
advantages for improving nutrient use efficiency and complementarity in multistrata agroforestry systems.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献