6 row does produce less uniform kernels, for sure. The mid kernel is exactly the same between 2 row and 6 row, but on the 6 row, the outside 2 kernels, so 2/3 of the kernels, would be smaller than the mid kernel. However, to say that 6 row is smaller kernels is not always the case. Metcalfe, for eg, a very popular but declining market share variety, has quite small kernels compared to newer 2 row varieties. On the other hand, newer 2 row varieties often produce kernels that dwarf older 2 row varieties. So breeding has increased kernel size quite dramatically over the last few years.
I am not going to be anywhere near an expert on all the data, so I am not going to be able to comment on that, however, on the protein side, the differences must be noted that soluble protein in 6 row CAN be considered higher on an overall basis, but total protein is often very similar, again VERY dependent on weather and agronomic practices. I can not make any comment on a year to year soluble protein difference, but total protein is so influenced by weather conditions, that there would need to be major correlation put together for weather, previous years moisture carryover, fertilization practices, disease pressure and finally total protein. I'm sure the data is out there, but for what I do, all I am concerned with is the year to year total protein.
Recent breeding has been a push (on 2 row for sure as that is where a major portion of breeding $ goes to) to bring protein levels down, but allowing for higher fertilization by the producer to maintain yields. The old school method of keeping protein levels down was to cut back on fertilizer usage, however that also had the effect of lowering total grain produced, and if the barley did not meet malt specs, you get a second kick in the butt by not having higher yields. The newer varieties are able to be more heavily fertilized, so producing more volume, but the breeding keeps protein levels in malting range.
Cons of 6 row barley, besides the lack of any money being put into it to produce better varieties, is the structure of the 6 row head. Having all the kernels develop, it creates an atmosphere inside the barley head to stay wet after rains for a longer time, thus increasing the chance of disease development, fungal issues, staining of the kernels, etc. Disease wise, saying every agronomic practice is being used, is the number 1 reason why 6 row is inferior to 2 row. And like I said before, with the new varieties being bread to do what 6 row was specialized to do years ago, ie higher enzyme packages, the pros of growing 6 row are very few. Up to a couple years ago, you could say that 6 rows yields kept them above two row, but that has also been covered by the newer 2 row varieties.
