Conclusions
Although considerable research efforts were made to
investigate fertilizer response in rainfed lowland rice of
northeast Thailand, the particular characteristics of this
environment and the cropping system led to greatly
diverging results. Simplified characterizations go from
‘‘inherently poor soils’’ to ‘‘soils with abnormally poor
fertilizer response’’ or ‘‘soils that can be productive only
when using organic fertilizers’’ to ‘‘soils with normal to high
fertilizer response’’. Our analysis indicates that most of the
statements outlined above are correct, but that they need to
be understood in the context of a landscape with high spatial
variability of soil and water resources. This variability has a
strong influence on the efficiency of resources used to
increase rice yields and therefore needs to be taken into
account when formulating recommendations for farmers.
We concluded that efficient fertilizer use in rainfed rice of
northeast Thailand can be achieved, but that existing
uniform recommendations provide farmers with not much
useful advice. Thus, we proposed a set of guidelines for
improved nutrient management, which, after further efforts
of all stakeholders involved (tool development and
participatory on-farm testing by researchers, farmers, and
extensionists), could contribute to increased system productivity.
Acknowledgments
The authors are grateful to Bruce Linquist for very
helpful discussions and thank the various reviewers for their
valuable comments on the manuscript. Agnes Padre was a
great help in conducting the statistical analysis. The original
data set was produced with support from the Asian
Development Bank in the Philippines and the Directorate
General for International Cooperation in the Netherlands,
with additional support to IRRI from the