FIGURE 179.—The effect of asphalt paper as applied only to the plant row. Potatoes and tomatoes in the foreground. Arlington Experiment Farm, 1928
Type A Papers
PAPER-MULCH Trials Center About Three Lines of Usefulness
The experimental trial of paper mulch as an aid to crop production in the United States is centering about three lines of usefulness—(1) The development and trial of papers suitable for field culture of annual crops, (2) the improvement and trial of papers suitable for perennial crops and home-garden use, and (3) the development and trial of papers suitable as a winter mulch. The papers utilized for these purposes have been designated arbitrarily as type A, type B, and type C, respectively. Present prices range from $30 to $200 an acre, varying both with the type of paper and the system of adapting it to the requirements of any specified crop plant. There are substantial indications that some of these papers will be of economic value, and with improvement in the papers and the methods of their application paper mulch appears to have a fair prospect of becoming an asset in agricultural practice.
While the maximum. effect of mulch paper appears to accompany complete soil coverage, confining paper to the planting row has practical advantages with many crops, reducing costs and permitting use of spray apparatus. This system 1s being tried with papers of type A in the field culture of annual crops of low per acre value, and its effectiveness is indicated by the results of some trials at the Arlington Experiment Farm as shown in Figure 179.
The use of durable papers for perennial plants (type B) appears to be of promise in trials with small fruits, young fruit trees set in permanent orchard plantings, flowering plants, young evergreens, and nursery stock, as well as for home-garden use. The stimulation characteristic of the use of paper mulch with crop plants, moreover, may be made available to an appreciable extent with ornamental plantings by covering the paper with pine straw or other material simulating natural conditions. The heat-absorbing value of the black surface is necessarily sacrificed for the sake of appearances, but substantial advantages of increased moisture and weed suppression remain.
The experimental trial of type C papers for winter mulching is developing (1) as a soil-conditioning mulch designed to insure a drier and warmer soil leading to earlier spring growth of crop plants such as asparagus and (2) as a protective mulch designed to insure a measure of frost protection with crop plants such as strawberries. Differences characterizing type C papers in asparagus trials in California are indicated in Figure 180.
In general, the measure of weed control afforded by paper mulch is of secondary importance to its stimulation of the mulched plant. In the case of particularly persistent and obnoxious weeds such as wire grass, witch grass, Bermuda grass, poison ivy, etc., however, the use of paper may become of first importance as a means of weed eradication.
From the crop-production standpoint paper mulch favors the plant over many diseases simply because hastened maturity shortens the period of susceptibility. From the disease standpoint paper mulch affords control of many soil-borne organisms either through the prevention of emergence or through the destruction of host tissues sustaining parasites.