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Friday, July 27, 2012

Drought and Despite

Temperatures have moderated a little the past couple days – 80s and 90s, but the drought is relentless and there is no rain in the forecast. The survival of plant life depends on the amount of water in the soil column that can be extracted in the root zone, and evapotranspirative demand by the plant. The following chart indicates ET at several stations in the state, calculated with Penman's equation and using a crop coefficient of 1, simulating conditions for well-watered turf. The coefficient and thus ET becomes lower with exposed soil and with water in the root zone at less than field capacity (the amount of water the soil will hold just before it begins to drain).

The chart shows an ET value of 0.28 inches at the Muscatine station yesterday, in line with what have been daily values of 0.25-0.33 inches for the past several weeks. Depending on soil composition (relative proportions of sand, silt, clay, humus) and structure (for instance, the size, shape, and number of voids), a foot of soil might hold 1-4 inches of water at field capacity. Depending on the crop, the root zone might be 1-4 feet. The issue with drought in rainfall-dependent areas becomes obvious.

A corn crop requires about 32 inches of water for maximum yield, which is almost exactly the annual rainfall across Iowa. So far this year, we've received only a third of the rainfall expected as a long-term average. It's a tenuous situation.

The Sonoran Desert of Arizona gets less than 2 inches of rain per year, yet this is where most of your iceberg lettuce comes from, thanks to canals and pipelines that deliver enormous volumes of water from river systems hundreds of miles away. Each of the several crops per year of lettuce use about 12 inches of water. A lot of alfalfa is grown there, too, for hay and silage animal feed, mostly beef, and it demands 60 inches a year over four or more cuttings. One begins to appreciate, perhaps, the true costs of delivering a Big Mac to the blithe customer at a seemingly bargain price.

Two nights ago we had a nice shower of rain but the gauges captured only 0.2 inches. It infiltrated less than an inch into the soil. We've become reluctant to irrigate the gardens because we know nothing about the depth, yield, drawdown curve, etc. of our well, the only source we can deliver to the gardens at present (the rain barrels captured only about 30 gallons from the shower), and our sole source of household water.

The pond, with no inflow the past couple months, is drying up at that same relentless pace of a quarter to a third of an inch every day.

The garden is stressed. The sweet corn and popcorn have some leaf curl but seems to be slowly filling the ears. But some critters larger than rabbits, probably raccoons, are scaling the fence now, breaking down the stalks and leaving half-eaten ears on the ground. I see electric fencing in our future.

A few individual fruits in the Concord grape clusters are beginning to show some purple. These are old vines with a well-established root structure, so we'll probably have a harvest and then another method of preservation to learn – jelly!

The cucurbits (the plant family that includes squashes, melons, and cucumbers) wilt alarmingly in the heat of the day but recover again in the evening, and so far are bearing prolifically. The winter squash are filling, and the melon are ready to eat and are delicious. Today I cleared the cucumber vines of all the overripe fruit. They're still blossoming profusely and now we can try again to harvest them while they're still pickle-sized. Our attempts at pickling the first batch of overripe fruit have been a mixed bag as the skins of some were just too bitter for the vinegar, sugar, and spices to overcome.

The tomatoes are really coming on now from both the transplants and the volunteers, several varieties of shape, color, texture, and flavor, and they taste great. So far our preservation method is dehydration. This image show the loaded dehydrator, the rest of today's harvest, dried fruit from a few days ago, and melons.

The mustards have bolted but for the time being the leaves remain a good source of salad greens. They, and the turnip greens, are also good cooked. I've got kale transplants ready to put in the ground if and when the weather turns, and they should then last into the first frosts. Once it cools down we can plant some more lettuce.

This is my nemesis, purslane, and at last I seem to have gotten ahead of it, but it ruined an area of the garden where I'd planted herbs and stole a lot of water from the vegetables. It was blossoming and had it gone to seed the situation would have been even worse next year. It's an edible, small-leaved succulent with a tangy flavor, more commonly used in Europe than here. It's good in salads, but after hoeing and pulling great mounds of it only to find more after a couple days, I've little appetite for it.

The infestations come one upon another, noxious weeds and insects and invasive plants: thistle, poison ivy, Japanese beetle, honeysuckle. The latest is Queen Anne's Lace or wild carrot. Eradication is a long-term project and yearly control laborious. In this weather I've only been able to work outdoors for an hour or two at a time, and some things just don't get done.

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