Dk. Cassel et al., Assessing spatial variability in an agricultural experiment station field:Opportunities arising from spatial dependence, AGRON J, 92(4), 2000, pp. 706-714
Spatio-temporal field soil and crop processes are important for site-specif
ic farming. The objectives of this study were to spatially evaluate selecte
d soil physical and chemical properties and their relationship to wheat (Tr
iticum aestivum L.) yield, and to discuss stochastic approaches to help ide
ntify processes underlying yield variability in heterogeneous field sites.
Modified grid sampling included 330 sites including a primary transect. Soi
l properties measured for the Ap, E if present, and upper B horizons at eac
h site included pH, P, Zn, Cu, exchangeable rations, percentage base satura
tion, ration exchange capacity, bulk density, soil water contents at -10, -
33, and -1500 kPa, texture, and humic matter content. Wheat grain and straw
were hand-harvested on 1- by 2-m plots centered on each site. Soil water c
ontent on the primary transect was determined by neutron attenuation on nin
e dates. Field and primary transect means and semivariograms for a given so
il or plant parameter were similar. The range of spatial dependence or auto
correlation of soil parameters ranged from 10 m for Ap horizon depth to 100
m for -1500 kPa water content of the Ap. Base saturation and available wat
er storage capacity were cross-correlated with grain yield to a distance of
+/-15 and 12.5 m, respectively. State-spare analysis was used to develop a
grain yield model using these two variables, Spearman rank correlation of
the soil water content data suggests that the temporal stability of soil wa
ter storage is less for shallow than for deeper soil layers.