INTENSIVE TILLAGE EFFECTS ON SPATIAL VARIABILITY OF SOIL TEST, PLANT GROWTH, AND NUTRIENT UPTAKE MEASUREMENTS

Spatial variability and relationships between soil chemical properties, plant growth, and nutrient uptake in an intensively tilled field have not been well documented. Our objective was to examine the spatial variability and positional similarities between soil chemical and plant properties and to determine sample size requirements for assessing these relationships. The research was conducted on a Bertie silt loam (fine-loamy, mixed, mesic Aquic Hapludult) near Wye Research and Education Center at Wye Mills, Maryland. Tillage-related operations are provided in the accompanying manuscript. Rye grass (Secale cereale L.) was planted in October 1987. Samples were taken at 1-m intervals in April 1988 along two parallel 45-m transects in the East-West direction and two parallel 37-m transects in the North-South direction. Plant tissue was hand-clipped from an area of 0.1 m2 and subsequently analyzed for biomass, plant nitrogen (N), phosphorus (P), and potassium (K). Disturbed soil samples were taken from the 0- to 15-cm depth and analyzed for soil nitrate nitrogen (NO3-N), P, K, calcium (Ca), magnesium (Mg), pH, and organic matter (OM). Plant tissue macronutrients exhibited minimal differences in the coefficients of variation (CV) with values near 25%. Soil N,P,K, and Ca generally showed similar CV values of 15 to 20%. Magnesium, pH, and OM concentrations generally exhibited CVs of less than 10%. Plant N and P exhibited strong spatial dependence, whereas biomass and plant K exhibited moderate spatial dependence. With the exception of P and Ca, all soil chemical properties exhibited moderate spatial dependence. There were few positional similarities between biomass production and plant macronutrient concentrations. Biomass exhibited strong positional similarities with soil NO3-N and pH, whereas soil NO3-N and plant N indicated positional similarities with increasing values. Soil OM and NO3-N had similar patterns for high measured values. Soil and plant P exhibited strong positional similarities, but this was not true for soil K or plant K uptake, indicating other factors may be involved. After intensive tillage, the sample size requirements were lower for soil properties than for plant properties. We conclude that it is inappropriate to make recommendations on equal sample size for plant and soil properties unless the properties exhibit the same degree of variability.