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Normally, the data generated from farmer participatory trials (FPT) are
highly unbalanced due to variation in the number of replicates of different
treatments, the use of different varieties, farmers' management of the
trials, and their preferences for testing different treatments. The
incomplete nature of the data makes mixed models the preferred class of
models for the analysis. When assessing the relative performances of
technologies, stability over a range of environments is an important
attribute to consider. Most of the common models for stability may be
fitted in a mixed-model framework where environments are a random factor
and treatments are fixed. Data from on-farm trials conducted in the
Indo-Gangetic Plain (IGP) of South Asia under the umbrella of Rice-Wheat
Consortium (RWC) were analyzed for grain yield stability using different
stability models. The objective was to compare improved resource management
technologies with farmers' practice. The variance components of an
appropriate mixed model serve as measures of stability. Stability models
were compared allowing for (i) heterogeneity of error variances and (ii)
heterogeneity of variances between environments for
farmers-within-environment effects. Mean comparisons of the treatments were
made on the basis of the best fitting stability model. Reduced-till
(non-puddled) transplanted rice (RT-TPR) and reduced-till drill-seeded
wheat using a power tiller - operated seeder with integrated crop and
resource management RTDSW(PTOS)ICRM ranked first in terms of both adjusted
mean yield and stability.
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