NUTRIENT CYCLING AND SUSTAINABILITY IN ALLEY-CROPPING SYSTEMS
IN THE HUMID TROPICS : II : PHOSPHORUS, LABILE SOIL
ORGANIC PHOSPHORUS AND BASE-CATIONS
Objectives
1.
To maintain the experimental alley-cropping (AC) and open field (control) plots in lowland tropical-rain-forest sites in Costa Rica that were established under the original STD2 funding (1988-92).
2.
In both AC and control plots, to analyse the cycling of phosphorus, by means of ecosystem budgets and isotopic root-uptake studies.
3.
To investigate the potential role of nutrient supplements in AC systems, in particular base cations, so as to provide guidelines for sustainable land use on acid, leached soils.
4.
To experiment further on the role of permanent mulch cover in the context of mycorrhizal and free-living microbiota and their phosphatase activity.
Activities
We originally worked on two sites, La Conquista, Sarapiqui (LaC), and Co-ope San Juan, San Carlos (CSJ), but from 1992 onwards the research will focus on CSJ. Here the AC trials will, by the end of the project, have been monitored continuously for 5 years, following an initial slash-and-burn operation in 1989. The whole CSJ site covers 2 ha and corresponds to the size and scale of a family holding. It comprises 8 AC and 8 control plots, each with or without additions of rock phosphate, plus supplementary plots and experiments. We are intentionally maintaining an intense and stressful regime of two crops per year, with maize and beans alternating (a simple analogue of indigenous practice), together with 4 prunings per year in the alley plots.
01/02. Cambridge : project co-ordinator T. Bayliss-Smith will be based in U.K. while Research Associate M.R. Hands will be stationed in Costa Rica organising the field trials, managing the local labour force and overseeing the lab work at UCR?
03. ITE : A.F. Harrison and J. Dighton are to conduct fieldwork at CSJ on isotopic root uptake in mid-1993.
04. Granada : R. Azcon will visit Costa Rica in mid-1993 to liaise with UCR project researcher M. Bermudez on the on-going experiments on VAM mycorrhizae, using soils from the experimental sites at CSJ.
05. UCR : A. Alvarado, Director of Centro de Investigaciones Agronomicas, will be liaising with M.R. Hands on the facilities needed for the ITE work on isotopes and for analysis of soils and biomass at University of Costa Rica.
Expected Outcome
The environmental context in Costa Rica is typical of rain forests in the lowland humid tropics : acid, leached latasols and a high rainfall. The project is about the sustainability of alley cropping for small farmers in this environment : to what extent is this from of agroforestry, using minimal inputs, a viable alternative to shifting cultivation ? We aim to gain an understanding of the cycling of phosphorus, with or without the benefit of tree mulch from the AC hedgerows, in sustaining the productivity of agricultural systems in the tropical rain forest zone. There are anticipated benefits to development planning as well as to our scientific knowledge of this important agro-ecosystem.
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