Sowing Rates and Planting Time
There are some controlled factors which are relatively straightforward.
Planting time refers to the choice between Winter sowing and Spring sowing. There has been a long running debate about whether early farmers would risk the "loss" perceived to be greater with Spring sowing. The reality has proved to be that there are years in which both sowings succeed and others in which either one or the other fail (this gives a good insurance against total loss). The chances of both failing are very low.
One necessary latitude in the design of an experiment is to leave it to the trialist "farmer's" judgement as to the exact timing of sowing, depending wholly, as it does, on the prevailing weather and how wet/dry and cold/warm the soil is at the prescribed sowing "season".
Nevertheless, the fact that sowing at either time, in experiments, can be demonstrated to form a practical strategy, does not of itself give proof that early farmers were that percipient.
Sowing rates are self-
The germinability of cereal seed decays rapidly from about 95% in Year 1 to about 85% in Year 2 and about 70% in Year 3, until after 7 years the seed is essentially dead. Thus, known farming practice is to keep a reserve stock which is no older than 3 years.
In the case of sowing rates, these were set at the original site, which was on very poor soil and with no intention to use any other improvement method than manure. After discussion with a local farmer, the rate was set at 56 lb per acre (67.5kg/ha), which proved to give sound, and to some, surprising, yields. This rate was maintained until 2007.
Recently, a trial on an associated site has indicated, as expected, that higher rates are likely to be inefficient in many circumstances and not give proportionate, if any, gains.