I try to be rational, semi-scientific, pragmatic and provisional about agricultural practices. It's a field rife with voodoo enthusiasms - like health care perhaps - that is subject to fads and fashions. We are so ignorant that it's easy to be superstitious. Since no one has definitive answers, wild claims about miracle products and practices crop up like weeds and are difficult to root out.

Despite my skeptical and pragmatic stance there are two soil amendments that I struggle to stay rational about. One is the recent enthusiasm for bio-char and the other is the ancient enthusiasm for lime. I usually tell those I work with that the first thing they should do is sweeten their soil with lime. If they can't afford the time and expense to do much, at least do that. Unless they have calcareous soils that are already too sweet, this is the single most effective thing they can do and is the foundation for all other amendments.

One of the myriad effects of bio-char that has been observed though not explained is that it seems to stimulate microbial life in the soil. Healthy populations of bacteria, archaea and fungi are indications of fertile and resilient soil. Lime does that too.

The objectives of the work were to establish whether liming had any immediate and residual benefits for rhizobia and plants and, if so, to determine if the two events were linked. . .

In the first year (pea crop), there was a very large and highly significant response to inoculation on populations of rhizobia in soil and rhizosphere. The number of rhizobia that occurred naturally in uninoculated plots increased rapidly in high-lime plots until, by the third year, they were substantial and, by the fourth year, equal to those in the inoculated treatment. By the end of the experiment, the mean population of rhizobia in the 4 t/ha lime treatment was 7250 per g soil, compared with <4 rhizobia per g in the nil lime treatment. . .

By the third and fourth years, soil populations of pea rhizobia in the plus inoculation and minus inoculation treatments were approximately equal, and inoculation was no longer a determinant of crop production. On the other hand, application of lime, which had only an underlying effect on pea production in the first year, significantly enhanced several parameters of the symbiosis and growth of the chickpea and pea crops, including legume nodulation and percentage nitrogen in the seed.

R. leguminosarum bv. viciae, legumes and cereals each responded differently to increasing rates of lime application. Populations of rhizobia in soil and plant rhizospheres increased with each additional rate of liming. Legume productivity responded to additional lime up to 2 t/ha. There was no significant evidence that liming per se had any effect at any time on wheat production.

That's worth unpacking a bit. Though liming per se had no effect on wheat, the indirect effect of increased soil health, especially nitrogen but other factors as well, did have an effect. Over a period of four years the original paltry population of rhizobia increased with lime amendment alone to equal that of soils that had been inoculated with imported rhizobia as well as being limed.

This supports my views and claims I make to those I'm working with. Inoculating soil with all manner of good bugs can't hurt, but it's expensive and the real question is why they aren't there already? If the soil was right the bugs would thrive, and if it's not right they won't persevere. Spend your time and energy on the basics - lime, char etc. - and the rest will follow.