Abstract:
Nearly 2 million hectares of farmland have been intercropped with rows of paulownia
(Paulownia elongata) trees in the North Central Plain of China. Paulownia provides an
important timber source and long term income as a "saving bank". It is in harmony both
ecologically and economically with the understorey winter wheat (Triticum spp.), the
farmers' "survival food". Funded by ODA (Overseas Development Administration,
UK), the present study investigates the role of the paulownia-crop intercropping (PCI)
system in rural socio-economic development. It also identifies the socio-economic and
technical factors that affect the promotion and success of PCI and examines the needs
and problems encountered in the development of PCI under the present "Individual
Responsibility System" (IRS). A socio-economic survey on PCI in Chengwu,
Shandong Province, as a case study, shows that paulownia intercropping is an important
component of socio-economic development in the poor areas.
Existing policy on paulownia intercropping and land distribution causes some problems
for farmers, and technical guidance on optimum tree spacing, management and
maximum production of PCI with emphasis on wheat yield is eagerly awaited.
An adaptive research approach to address the farmers' needs was applied in this study by
interpreting scientific research to produce a useful, simple and practical model to
optimise tree spacing for a range of scenarios.
Data used for analysis were collected during 1983 - 1992 from an experiment station at
Dangshan, Anhui Province, on a project supported by The International Development
Research Centre (IDRC) of Canada. The important components of the PCI system
including tree growth, growth and yield of understorey crops, and light, as a key
microclimate factor affecting understorey crops, were analysed to further understanding
on the natural functioning of the PCI system. The denser the spacing, the earlier the
fast-growth stage of the trees occurs. However, there was no significant difference
among the spacings in any of the growth variables at the end of the study in the 10th
intercropping year. There are always reductions in light transmissivity (LT) and
Photosynthesis Active Radiation (PAR) and the proportion of PAR to total solar
radiation in the intercropped fields due to light interception by the trees. These effects
are more apparent in areas near the trees, in denser spacings, in older paulownia, and
when the paulownia have fully developed leaves. Intercropped wheat benefits from the
modified microclimate, such as reduced temperature and increased soil water contents
and relative humidity. Air temperature is the only microclimatic factor determining
wheat leaf conductance, which gives a negative effect. Wheat yields start to decrease
when LT is reduced to 81.8% as an average and about 10% higher for dense spacing and
older trees and 10% lower for larger spacing and younger trees. Leaf conductance,
biomass and yield of the intercropped wheat are slightly above those in open fields
when the trees are young and widely spaced, but lower otherwise. The distribution of
wheat yield across the alley in the intercropped field was similar to that of light, apart
from in the dense spacing of older age trees where the competition of tree roots for
nutrients probably also reduces yields near the tree rows. The reduction of leaf
conductance and yield of summer crops by paulownia is greater than for the winter crop
due to shading by the trees and different response of the crops. The yield reduction of
cotton and maize is 15% at the edge of the tree canopy and as much as 50% near the tree
rows.
Regression models were developed to express DBH (used as an index of tree growth) as
a function of age; light transmissivity as a function of distance across the alley for
different spacings and ages of trees; understorey wheat yield as a function of distance
across the alley for different spacings and ages of trees; and understorey wheat yield as a
function of light transmissivity. The models can yield information on rates of tree
growth and changes in understorey wheat yield and LT, by inputting tree age, and
distance from west row under a given tree spacing. The output will help farmers
optimise the tree-row spacing depending on whether their objective is to maximise
timber production, crop production or the economic return from both. The models
could also provide useful and practical technical guidance to help decision-making and
settle disputes among farmers and between farmers and the local authority.
Models were validated by the data collected during 1993 - 1994 from farmers' fields in
Chengwu, Shandong Province. All the models perform well in these conditions and it is
recommended that they be applied to PCI in all parts of North Central Plain of China
due to the similarity of climate and soil conditions. Optimum tree spacings under
different scenarios were also recommended.
The present study demonstrated the approach of adaptive research in PCI agroforestry
by linking scientific findings to rural socio-economics and farmers' needs. It indicated
the equal importance of three components: socio-economic survey, experimental data
analysis and interpretation, and application of scientific findings. Socio-economic
survey at the village or farm level is essential for identifying the needs of farmers from
PCI under IRS conditions. Data analysis helps scientists and extension officers to
understand and interpret the dynamic eco-biological interactions of PCI systems
. Regression modelling is a practical, efficient, simple and easy way of interpreting and
applying scientific findings to a realistic PCI system.