Interpreting data from on-farm fertilizer trials for use where soil-test values are not available
1988
Jones, M.J. (ICARDA, Aleppo (Syria))
Results from fertilizer trials for soil-test calibration may be used to develop general fertilizer recommendations to apply where soil-test values are not available. From the data of 32 on-farm barley trials, quadratic equations (response surfaces) relating yield and cash value of crops to rates of N and P fertilizers have been computed for different subgroups of sites (recommendation domains), and the profitability of different fertilizer rates in those different domains calculated. The most clear-cut differences lay between rotation "domains" (barley preceded by fallow vs barley preceded by barley); between northwest and northeast Syria, and between different rainfall ranges. Phosphate fertilizer was fairly generally profitable, but profitability was often enhanced by the concurrent use of nitrogen. Nitrogen fertilizer was most profitable in barley-barley rotations, in high rainfall areas, and in northwest Syria but usually only in the presence of phosphate fertilizer. The limitations of the methods used are discussed
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