Gardening Without Irrigation VII (Increasing Soil Fertility Saves Water)

Increasing Soil Fertility Saves Water

Does crop growth equal water use? Most people would say this statement seems likely to be true.

Actually, faster−growing crops use much less soil moisture than slower−growing ones. As early as 1882 it was determined that less water is required to produce a pound of plant material when soil is fertilized than when it is not fertilized. One experiment required 1,100 pounds of water to grow 1 pound of dry matter on infertile soil, but only 575 pounds of water to produce a pound of dry matter on rich land. Perhaps the single most important thing a water−wise gardener can do is to increase the fertility of the soil, especially the subsoil.

Poor plant nutrition increases the water cost of every pound of dry matter produced._Using foliar fertilizers requires a little caution and forethought. Spinach, beet, and chard leaves seem particularly sensitive to foliars (and even to organic insecticides) and may be damaged by even half−strength applications. And the cabbage family coats its leaf surfaces with a waxy, moisture−retentive sealant that makes sprays bead up and run off rather than stick and be absorbed. Mixing foliar feed solutions with a little spreader/sticker, Safer's Soap, or, if bugs are also a problem, with a liquid organic insecticide like Red Arrow(pyrethrum−rotenone mix), eliminates surface tension and allows the fertilizer to have an effect on brassicas.

Sadly, in terms of nutrient balance, the poorest foliar sprays are organic. That's because it is nearly impossible to get significant quantities of phosphorus or calcium into solution using any combination of fish emulsion and seaweed or liquid kelp. The most useful possible organic foliar is 1/2 to 1 tablespoon each of fish emulsion and liquid seaweed concentrate per gallon of water.

Foliar spraying and fertigation are two occasions when I am comfortable supplementing my organic fertilizers with water−soluble chemical fertilizers. The best and most expensive brand is Rapid−Gro. Less costly concoctions such as Peters 20−20−20 or the other "Grows," don't provide as complete trace mineral support or use as many sources of nutrition. One thing fertilizer makers find expensive to accomplish is concocting a mixture of soluble nutrients that also contains calcium, a vital plant food. If you dissolve calcium nitrate into a solution containing other soluble plant nutrients, many of them will precipitate out because few calcium compounds are soluble. Even Rapid−Gro doesn't attempt to supply calcium. Recently I've discovered better−quality hydroponic nutrient solutions that do use chemicals that provide soluble calcium. These also make excellent foliar sprays. Brands of hydroponic nutrient solutions seem to appear and vanish rapidly. I've had great luck with Dyna−Gro 7−9−5. All these chemicals are mixed at about 1 tablespoon per gallon.