Efficiency of Blocking Basing On Contour and Ideal Block Size in RCBD Experiment in On-Farm Trials

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Seth C.A
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University of Nairobi
There is a lot of emphasis now for on-farm than on station trials. The big challenge here is how to address carefully the high variability in farmers’ fields while designing an experiment to ensure that the results from such studies are of high quality. In practice researchers fit blocks along contours in a field perceived to be uniform without necessarily subjecting the soil sample for laboratory testing to identify homogeneous sections. Chapter 1 we have Introduction, literature review, problem statement, objective and methodology of the study. Previous studies in on-farm trials have given very high Coefficient of variation (CV) of over 40% and R2 of less than 0.5, which is attributed to careless designing. The objectives of this study were to: find out if plots in the same contour across a farm are always homogeneous and if the contour is an appropriate and fast criteria for blocking in Randomised Complete Block Design (RCBD) experiment in on-farm trials, use Exploratory data analysis method to identify underlying structure of the data collected; fit several models to the data and identify the best model and recommend the length of a block that guarantees homogeneity within the same contour on-farm. The study was conducted in Meru and Embu Districts in 32 farms , 16 in each district . RCBD design was used with each block divided into 8 plots. Blocks were either 16m, 24m, 32m or 40m long. In chapter two we show how data is modelled in data anaysis. The data collected was subjected to exploratory data analysis in chapter three and was found to be normally distributed. It was then analysed by fitting linear and proc mixed models in S-Plus and SAS respectively. The result in chapter four shows that plots within blocks of 16m long did not give significantly different mean yield (p = 0.2105) while those within blocks of 24m, 32m and 40m long were significantly different at p = 0.0001,0.0256 and 0.0005 respectively. The same result was obtained in the height analysis. Plots in the blocks of length 16m long did not give significant difference in maize height. But blocks of length 24, 32 and 40 meters long were significantly different at p = 0.0018, 0.119 and 0.0011 respectively. Therefore field of land (on-farm) is not significantly different within short distance of not exceeding 20m. Contour can be used as criteria for blocking in the field perceived to be uniform so long as blocks are kept small. In chapter five I have recommend that blocks of maximum 15m long would be be ideal length to ensure homogeneity within blocks otherwise when the size of the block exceeds 20m long then balanced incomplete block design would be ideal.