Spatial variability of soil nutrients in paddy field and their appropriate sampling sizes

An understanding of the spatial components of variability in soil nutrients is essential,before any decision can be made as to how many fertilizer rates are likely to be appropriate for the field.The objectives of the present study were to examine the spatial variabilities of soil pH and nutrients,and to determine their appropriate sampling size by the means of conventional statistics and geostatistics.The area selected for this study was a 0.52 hectare paddy field divided into four blocks,which were cultivated separately by four farmers,at Taozhuang farm in Jiashan county.The soil nutrients analyzed consisted of total N,total C,available K,available P,available Mg,available Mn,available Cu,available Zn.The results showed that the data sets of soil properties except pH and total N were all normally distributed,and the data set of total N was also normally distributed through log transformation.All the soil nutrients were found to vary across the field to some extent.And that soil pH had the least difference within the field,whilst available Mn had the greatest one.The spatial patterns of main nutrients,such as total N,total C,available K and available P,were zonal in south-north direction,same as the direction of the blocks.The difference among 4 blocks cultivated by four farmers was prominent.For a 95% confidence with 5% of population mean,the estimated number for pH would be only one,which meant that only one sample was needed for the whole area.Those for soil total N and total C would be 4 to 5 samples,i.e.,one block needed only one sample.All these results indicated that the farmers' fertilization habits could affect the spatial variability of those soil nutrients.It was concluded that soil could be sampled in farmer unit for site-specific management to N fertilization at this farm.