Fertilizer banding influence on spatial and temporal distribution of soil inorganic nitrogen in a corn field

Fertilizer N is commonly applied as a sidedress band application in corn (Z ea mays L.) fields. The objectives of this study were to determine the impl ications of fertilizer band application on spatial and temporal variations in soil inorganic N and to evaluate different sampling strategies for their suitability in estimating the average soil inorganic N concentration of a field, Treatments were 0, 60, and 120 kg N ha(-1) in 1994, and 0, 120, and 240 kg N ha(-1) in 1995, replicated three times at each of two sites, Ferti lizer was applied as a band of NH4NO3 15 cm on each side of each corn row a t the corn six-leaf stage, Soil samples taken at eight interrow locations 0 , 5, 10, 15, 20, 25, 30, and 35 cm from the corn row and at depth increment s of 0 to 15, 15 to 30, and 30 to 60 cm and on five sampling dates were ana lyzed for soil NO3 and NH4 concentrations. Random sampling and five systema tic sampling strategies were evaluated with respect to bias in estimation o f field soil NO3 and NH4 concentration for three depth increments, and with respect to the number of samples required to achieve a given precision and probability level combination for soil NOB concentration for the 0- to 15- cm depth, All systematic sampling strategies provided adequate estimates of the true soil inorganic N concentration as estimated based on uniform samp ling across all interrow locations. There was no consistent benefit to usin g any one systematic strategy with respect to the number of cores required to obtain a given level of precision in soil NO3 concentration at a given l evel of probability, Systematic sampling strategies were at least as good a s, or superior to, random sampling, particularly after fertilizer band appl ication and at high N rates. The apparent insensitivity of estimated field soil NO3 concentration to sampling strategy was attributed to the relativel y high mobility of NO3 in soil and variation in placement of the fertilizer band relative to the corn row during sidedressing.