Mexicowichan: The Soils of Chorus Frog Farm

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Recently Pauline was helping her co-workers at the Salt Spring Island Conservancy clean out some old resourses in their library. They had an extra copy of “Soils of the Gulf Islands of British Columbia: Volume 1 Salt Spring Island” survey done in 1987 so she was allowed to take it.

What a gold mine. The publication itself is comprised of a 4’X6′ full color map that depicts all the occurences of about 30 different types of soils on the island. The book describes the island’s topography, geology, hydrology etc and then discusses each of the soil types depicted on the map with comments on their suitability for agriculture.

Roads are not drawn particularly well nor are there a lot of other obvious landmarks or street addresses to help the individual pinpoint his or her property. But based on the roads that are shown and some topographic clues, plus my own observations of the soil itself on the property, I’m pretty sure that the two distinct types I have observed on the property are the same two that appear contiguously on the map, in about the same place.

The one we first encountered from last year’s initial two plots (one of which was then abandoned), is called Mexicana. From the book: “Mexicana soils are moderately well drained soils that have developed on gravelly sandy loam to gravelly loam morainal deposits overlying deep, compact, unweathered till within 100cm from the surface”. I can attest to this description in that, after harvesting many tons of stones last year, there are still many bumper crops remaining. A few weeks ago I tilled up a couple of beds. This is itself evidence of the soil type; few other soil types could be rototilled safely in January after months of rain. The second giveaway is the new crop of stones that came up when I did that.

If this were our land, I would probably plant a nut orchard, a berry patch and an asparagus patch. The fertility is probably decent but the drainage excellent. Not having to work the soil again would be a huge bonus. From the book: “The major limitations for agricultural use are the droughtiness, topography and stoniness. Mexicana soils on slopes not exceeding 15% could be improved with irrigation and stone picking to grow a small range of annual crops. Tree fruits and berries seems to do well on these soils under irrigation”.

The other soil type is Cowichan which, contrary to the Mexicana, is described as one of the best types on the island. Damp and mucky until the water table drops but…full of nutrition. “Cowichan soils are poorly drained soils that have developed on deep (>100cm) silty clay loam to silty clay marine deposits that are usually stone free.”

Under ‘Land Uses’, it goes on to say:

“Cowichan soils represent one of the most important agricultural soils on Salt Spring Island. The surface soil is well supplied with organic matter and nitrogen. They are strongly acid (pH 5.1-5.5) soils. Poor drainage is the major limitation for growing a large variety of agricultural crops on these soils and, for this reason, they are mainly used for pasture and hay crops particularly on Salt Spring Island. With improved drainage, these soils are good for growing a wide variety of crops including vegetables, berries and small fruits.”

Now, I’m not sure whether I’ve got the whole drainage thing licked on that patch but, if so, all I need is a couple of loads of lime and it should be pretty good for my heavy feeders. Having said that, tomatoes apparently shouldn’t get too much N or else they put on too much foliage at the expense of fruit but I’m willing to live with that problem.

Now to find the on-line version of the map…

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