I recently noticed an interesting article in an agricultural trade paper that described the results of a Michigan State University tomato trial.The researchers designed a program to test plant response to various water inputs, and found that withholding water for three to five weeks after transplanting resulted in a yield increases of up to 15% while using 40% less irrigation water.
These results were duplicated in two consecutive growing seasons, working in partnership with southwestern Michigan farmers. The article did note that it is critical that the soil be moist at planting time - see www.greeen.msu.edu
As an explanation for the findings, the project coordinator said that over-irrigation after transplanting probably washes away nutrients from the soil.This is consistent with almost all ag-college studies -suggesting that there is some chemical reason behind all observations.
If thes echemistry-oriented researchers would have wandered over to MSU's Biology department for a few minutes, they might have gained a different perspective/explanation.It is well-documented that mycorrhizal fungi, which bring nutrients and moisture to plants on an as-needed basis, can go into a "higher gear" when their host plants are stressed.Withholding water is a routine part of the propagation process when creating mycorrhizal inoculants.
When a plant senses a shortage of water, it sends a specific "help" signal through its roots,which causes beneficial fungi to step up their efforts to keep the plant from dying.This is simply the way that nature gets plants through drought years.
As I have suggested many times in past newsletters, by putting some research investment behind soil biology we can learn to manipulate natural biological relationships for agriculture.Bio methods could save enormous amounts of fertilizer and water, reduce environmental run-off problems, and prevent soil degradation. But soil researchers must acknowledge first, that soil biology actually exists, and secondly, that living organisms in the soil serve any useful purpose.
The MSU results were completely predictable to anyone with even the slightest awareness of how mycorrhizal fungi function.These are powerful organisms that can be the key to achieving superior plant performance with lower grower input.
I do hope these scientists keep experimenting with watering practices...but hope that they recognize that overabundant irrigation has biological as well as chemical implications."Washing away nutrients"might not be the best explanation for their observations."Not calling up the fungi" could be a better answer, or at least one that should be mentioned in any modern ag article.
By the way, this is about the time of year that I stop watering my tomatoes and melons - another effect of water stress is for plants to ripen their fruit quicker.You might be surprised to find how long they will go before showing any wilting in the morning hours.(Note that this strategy may not be appropriate for container plants that have a restricted foraging zone.)
Good growing, friends,
Don Chapman
President, BioOrganics, Inc.