A Beginner’s Guide to Soil Science

About a month ago, our local – and extremely helpful – proper farmer arrived with an enormous trailer attached to his enormous tractor with lots of enormous bags of fertiliser and lime on the back of it. I watched in awe as he picked them effortlessly up off the back of his trailer with the tractor’s forks as if they weren’t each the weight of six well fed chaps and just about managed to get it together in time to ask him to drag half of them to the other vineyard. Which is as well, because it’s about a quarter of a mile away, and to the best of my knowledge, I can’t, ahem, pick up six well fed men. Once I had profusely thanked our occasional hero and sent him on his way full of biscuits and coffee, I went for a walk to look at our huge bags of fertiliser and devise a plan of action.

If you are unfamiliar with lime, it is used in agriculture – and in gardens – to raise the pH of soil from more acidic to more alkaline. It is important to monitor the pH of soil as it has a habit of becoming more acidic over time – usually because intensive farming requires the addition of lots and lots of nitrogen, which is essential but makes acidic compounds in the soil – and that acidic soil prevents the vines from picking up some of the nutrients whether they are in the soil or not. Soils that have lots of chalk in can have the opposite problem, as the chalk does the same job as the lime and they tend to be alkaline, which causes a whole host of different nutrients to be unavailable to the plant. The advantage with chalky soils is that the direction of travel using modern (and traditional, for that matter) fertilisers is towards acidity, so ignoring the problem tends to help these push/pull factors meet somewhere near the middle.

So where is the sweet spot? In my experience, it’s a moving target depending on who you ask. If you ask a chap who is constantly booting huge lumps of chalk out of the way as he walks around his vineyard, he will tell you that alkaline is the way to go. Astonishingly enough, the opposite is true when you interview someone who is tripping over something other than chalk. What is absolutely the case is that you can spend all the money in the world on fertiliser, but if your soil pH is out of sync too much in either direction, the vines are ultimately going to keel over and die despite your best efforts. The lab that we send our soil samples to recommends an absolute floor of pH 6, which is fairly acidic, and everyone, irrespective of what their soil looks like, will tell you that a number lower than this is bad news.

As one part of one of the fields – interestingly enough, the weakest part – had dropped below 6 and everywhere else was well on the way, we decided that it was time for action. The only fly in the ointment was that changing the pH of a lot of soil takes a lot of lime, in our case, literally tonnes of the stuff. And that’s (mostly) the end of the chemistry lesson, let’s get on to the impracticalities of getting all that good stuff onto our soil.

Old hands here will be aware of the unique way in which we have historically spread fertiliser. To the uninitiated, it involves a bucket, an eggcup and a childish obstinacy to go out and buy the appropriate piece of equipment to make this happen with the minimum of effort. There is a certain amount of logic in this approach – no, really – as spreading fertiliser directly under the vines in an area that is habitually kept clear of grass and weeds means that that fertiliser doesn’t end up feeding the grass that runs up and down between the vines and causing it to take over. As an added bonus, as you are applying it directly, you can apply less of it, save some cash and, in theory, prevent unnecessary acidification of the soil.

The huge bags of lime posed a new and exciting problem as we have never before had to apply such vast quantities. I placed my trusty bucket next to the bag of lime and stood back. Even the most naïve optimist would be hard pressed to deny that the bucket was much, much smaller than the bag of lime. I put it to my farming mate that I may have bitten off rather more than I could chew and was thinking of hiring a spreader for my tractor and the very next day, the perfect machine for the job magically arrived on the driveway. Once I had wiped away the tears joy, I was ready to farm like a man living on the leeward side of the industrial revolution.

What we were applying with the spreader up and down the rows was a mixture made up principally of lime. We had also added some potassium and phosphorous that the soil needed, but which were unlikely to make the weeds take over or undo any of the good work that the lime was doing in the soil (potassium actually helps a little with acidity). We had the huge bags of fertiliser dealt with in short order. On reflection, this should have come as no surprise as the spreader is significantly bigger than my bucket and I was putting the tractor away and trying to catch the empty bags of fertiliser that were blowing across the fields at the end of three days of not very hard work.

And here endeth the egg cup? Not a bit of it! The vines were still missing their dose of a veritable alphabet of nutrients for the year. Carefully calculating the dose of the all in one fertiliser to be precisely one egg cup’s worth per vine, I grabbed bucket, egg cup and running shoes and went back to work like it’s 1799.