Soil Fertility: A Weapon Against Weeds

Stop the spread of poverty weeds by rebuilding your soil.

It is becoming a more common complaint that “Broom sedge and Tickle grass are taking our pastures.” Others say, “Those weeds have moved in from the South.” All this has happened in spite of statutes against the spread of noxious weed seeds.

Broom sedge has come into prominence, especially as a left-over for winter notice, because the cows refuse to eat it. Tickle grass comes under the same category. That refusal has been the cow’s way of telling us that such plant growth does not deliver enough feed value for her trouble of eating it.

Broom Sedge (Andropogon virginicus)

Sanborn Field, at the Missouri Experiment Station, is giving its wise answer to the question of how to get rid of these noxious plants. It tells us clearly that Broom sedge and Tickle grass have come in because the higher level of soil fertility required for more nutritious feed plants has gone out. Rebuilding the soil is the answer.

Pasture farming with continuous grass must already have been in the mind of Professor J. W. Sanborn when, in planning this now historic field, he included two plots of continuous timothy. One has been given six tons of barnyard manure annually, the other no treatment, ever since the field was started. The manured plot has always been a fine timothy sward with early spring and late fall growths, and a quality hay crop of two and one-half tons every summer. The one with no treatment has been getting so foul with growths other than timothy as to require plowing and reseeding about every five or six years. This called for the same treatment, for uniformity’s sake, of the companion plot, even though weed-free. Broom sedge soon takes over the no-treatment plot as the major trouble maker.

These plots tell us that the trouble is not in the particular “invading power” of the Broom sedge, even if its fluffy, wind-borne seeds travel profusely and go everywhere. Both plots are equally invaded by the seed of this nest. However, Broom sedge appears on only the untreated plot, cropped to poor hay now much of the time. It grows right up to the soil line dividing these two plots. It does not cross that border. None has grown on the manured plot, always covered with a dense growth of good timothy. Other plots equally as low in soil fertility on this field are gradually being taken over by Broom sedge. Those with higher levels of productivity are free of it.

Prof. Sanborn says: “Fertilize the soil so it will grow grasses that make nutritious feed and these troublesome plants of no feed value stay out.” “Poverty bluestem,” as Broom sedge is sometimes called, is a mark of the kind of farming that fails to consider the fertility of the soil as the foundation of it. This pest has been coming more and more into what has been “pasture farming” because past cropping to grass, like to any other crop, without soil treatments, has brought the fertility down to where crops of feed value are failing and only those woody growths like this poor bluestem the cows reject are all that can be produced.

Tickle Grass (Aristida dichotoma)

Tickle grass is also invading Sanborn Field. It has been taking over the last half of the six year rotation of corn, oats, wheat, clover, timothy and timothy where no soil treatments are used. The plots alongside given manure, phosphate, and limestone are free of it right to the straight line separating the plots and treatments. This poverty grass means poverty of soil fertility and thereby poverty in crop output of yields and of nutritional values. No other crop can grow luxuriantly enough on such low fertility to drive this pest out.

This weed has come in when the rotation was as long as six years. This is one claimed by some to be helpful for better yields and crops. It certainly has not been such. It has simply rotated the fertility of the soil out so much faster than Tickle grass now comes in as major cover during those three years when there ought to be clover and timothy. Crops requiring no plowing have been rotated out and Tickle grass has been rotated in.

Chemical analyses of these pest crops confirm the suggestions by the cow and Sanborn Field. As pounds per ton, Broom sedge contained 2.14 of calcium, 2.18 of phosphorus and 88 of crude protein. For Tickle grass the corresponding figures were 3.04; 1.9; and 69. In marked contrast for a mixture of clover and grass from fertile soil and at similar growth stage the corresponding values per ton were 26, 4, and 181 pounds.

Nature’s pattern of different crops growing on different places is the pattern of different levels of soil fertility nourishing them and correspondingly a pattern of different feed values in them. Declining soil fertility is pushing some crops out and letting others come in. According to these simple soil differences, then, we can drive out Broom sedge and Tickle grass by lime, manure and other soil treatments offering better nourishment for better crops that will keep these pest crops out. That Broom sedge and Tickle grass should go out when you put soil fertility in is merely the converse of the fact that they come in when the fertility goes out.