Dirt Matters!

Michelle Dacombe Feb 2015Michelle Dacombe, Vineyard Manager at Misha’s Vineyard talks about soil health in a very tough environment.

Not many things in life are more intimidating than looking at your first soil analysis and attempting to decipher its secret code: I just didn’t understand what I was looking at. All the numbers next to the elements that were measured seemed to be within the expected healthy range – but what exactly was I looking at? Dirt Matters 4How exactly was I to manage the nutrition available to the vines when I only get a snapshot of the soils fertility every second year?

Well, that’s what specialist suppliers are for, right? They give you the best advice available and make suggestions about what your soils may need. The soils couldn’t need too much – after all, we grow a tall green canopy and have a good fruit set and we are harvesting beautiful fruit every year. Well, that’s just it. Each season we are doing the things we think are best for the vines health and nutrition and we have had a good run, but could we be doing more or possibly even less?

Dirt Matters 1In May I went down to Invercargill, (New Zealand’s southernmost and westernmost city) for a three-day soil fertility course. The focus on the course is the Albrecht/Kinsey system. Albrecht was a soil microbiologist whose focus on soil was to correct chemical imbalances (chemistry) which can then correct soil structure (physics) to build the “house” for the microbes (biology). His belief was that soil pH was an effect of the chemical make-up, not the cause. So adjusting the chemical make-up of the soil through a fertiliser program can in turn shift your pH. A pH may need shifting to create an environment where the plants have better access to other nutrients. In a soil system, there is a limiting factor. An out of balance element can limit access to another element. Too much of any one element in the soil profile can “tie up” other elements.

Every soil is different and as many growers know soil pits may be dug before development, but consistency throughout a block is not guaranteed. This can make fertilising difficult, but a program should be developed that is generally good for the entire block. When soil tests are taken one of the important measurements is the soil’s nutrient supplying capacity. This is measured as the CEC or the Cation Exchange Capacity of the soil. The CEC of a soil is determined by the amount of colloids (negative charges) present, which is the ability of the soil to attract and hold plant nutrients from fertilisers (which are positively charged). The soil’s CEC is a reflection of the structure as well. Clay particles in soil have more colloids hence more negative charges to hold more nutrients. But a high clay component in soil can also be a detriment. The nature of clay is a fine texture which is a small pore space with little air and a strong ability to hold water tightly. Many high clay soils can experience pugging after significant rain events and in places like Central Otago very dry summers can turn clay rock hard. A soil’s CEC is difficult to shift. It can be increased by increasing humus content, but this is very difficult and natural organic matter in soils can take hundreds of years to build up. Not a commercial undertaking!

Dirt Matters 3Throughout the three-day course we swept through the periodic table ticking off the boxes of all the major and micro nutrient requirements for healthy soils and in turn healthy crops. The amount of information was rather overwhelming, but I was assured by folks attending their third event you take away more and more information each time.
I just received our soil tests back from last month and I am happy to say I can now read and understand them and even ask my supplier some technical questions! It has given me a newer vantage point on the ground I walk every day at work and also a deeper appreciation for the beauty and brains in nature. I think now I’ll be fretting less about soil fertility and the vines ability to cope with the stresses the natural environment of Central Otago throws at us. I’m looking forward to the next year’s course to enable me to crack a little more of our soil code.