For example, to determine how much you can reduce nitrogen in corn after a hairy vetch cover crop, the split-plot design could be used in the following manner. Such experimental designs are particularly well suited to farmers. Treatments can be laid out in strips, with length of the plots determined by the length of the field and the width by the equipment you use. Considerations in Applying Treatments and Collecting Data Variation within your experiment can come from many sources. Some of those sources are known and some are not.
Some variation can result from how treatments are applied and data is collected.
With that, comparing the zero-rate plots to the other treatments was like comparing apples to oranges. An element of variation was introduced to one treatment that was not applied to all treatments. Data collection is another potential source for mistakes. All measurements should be taken under the same conditions using the same methods. Be as uniform as possible when applying treatments and collecting data.