At the start of experiment and at the end of each year (2007, 2008, and 2009) we measured soil parameters (phosphorus, potassium, calcium, and magnesium) to quantify the effect of treatments at different depths and different parts of the plots, aka, “loc” (IR-at the planting row; BR- between two planting rows). My second question in the original post came from the idea to quantify how much soil phosphorus increased or decreased for top 18 cm (weighted means of 0-5, 5-10, and 10-18) at the end of each year from initial values as well as from the first year. This can be calculate for locations separately and also for overall each plot.
Soybean experiment (2007 – 09) was planned as RCBD with split split plot arrangements of treatments with three replications. Three tillage treatments (NTBC, NTDP, and STDP) were done in three blocks as main treatments which I am calling as whole plots. Each block (whole plot) was divided into four parts to apply four phosphorus levels (0, 12, 24, and 36 kg/ha) which I am calling as sub-plots. These sub-plots were further divided into four parts to apply four potassium levels (0, 42, 84, and 168 kg/ha) which I am calling as sub-sub-plots or “PLOTS”. For year 2008 and 2009, we sampled all the plots but in the third year, we sampled plots only receiving 5 particular fertility treatments out of 16 combinations of P and K. Therefore, I have fertility (P-K) as category.
We sampled soil at two particular “locations” (within two planting rows and at the planting rows) and four depths (0-5, 5-10, 10-20, and 20-40) within PLOTS.
To handle this analysis, I need to subset this data for each MIXED model. I just want to keep only one data file to avoid confusion.