The Effect of the Use of Lime, Soil Fumigants, and Mulch on the Solubility of Manganese in Hawaiian Soils

G. DONALD SHERMAN AND CHARLES K. FujiMOTo THE production of some vegetable crops in Hawaii has not been successful because of certain soil factors. One of the foremost of these limiting factors has been the high content of available manganese in the soil. Kelley ( j ) z was the first worker to report the abnormal manganese content of Hawaiian soils and its effect on plant growth. Later, Johnson (6) discovered that the chlorosis which developed in pineapples grown on soils rich in manganese could be corrected by the application of a spray containing iron sulfate to the diseased plant's. He concluded that the large amount of manganese in the soil oxidized the iron to the ferric state in which form it is unavailable to the pineapple plants. More recently, Fujimoto and Sherman (3) have demonstrated that the quantity of available manganese present in lateritic soils depends on the soil temperature and the degree of hydration of the manganese oxides. They found that the available manganese increased with a rise in soil temperature, and if the manganese oxides are dehydrated, large quantities of soluble manganese will be released. Manganese toxicity to plant growth has been recognized in other soil areas.. Funchess (4) reported that certain nitrogenous fertilizers increased the soluble manganese content of the' soil. Bortner (i) corrected manganese toxicity in certain Kentucky soils with the application of lime and superphosphate. Snider (14) has shown that the application of lime to the acid soils of Illinois materially reduced the manganese content of the crops. Recently, Fried and Peech (2) have made a critical study to ascertain if acid soils requiredlime to correct a calcium deficiency or to correct other soil conditions. They concluded that one of the benefits of the application of lime to acid soils was the reduction of 'the soluble .manganese. The application of lime to the Hawaiian soils having a high content' of available manganese has produced a marked improvement in" plant growth, how, ever, this effect has not been as good as expected with those crops which are grown in rows. Another disadvantage found in the application of lime to Hawaiian soils has been the limited amount of lime which can be applied without the occurrence of overliming effects. Heavy applications of lime which are necessary to reduce the level of available manganese will depress the .growth of plants very markedly. The maximum application of lime to Hawaiian soils without depression of plant growth is limited to 2 tons per acre. Thus, it is possible that the full benefit of the application of lime has not been obtained with crops commonly grown in rows due to the exposure of the soil to the sun which would produce a high soil temperature and which in turn would increase the soluble manganese in the soil. For some time it has been a common practice for the pineapple growers to use a paper mulch between the rows of pineapples. The purpose of the paper mulch has been for the control of the growth of weeds and for conservation of soil moisture. The use of the paper has produced an increase in the growth of the pineapple plant. The use of mulches would have a marked influence on the soil temperature in addition to the conservation of soil moisture. Vageler (16) has reported temperatures in bare soils ranging from 50° C to 86° C in East Africa. Leather (8) has shown in India that the temperature of a bare soil would average 20° C higher than the same soil under a shade. Mohr (u, page 43), quoting from Wind's work, found the maximum temperature of a surface soil exposed to the sun to be 44° C; when lightly shaded, it was 30° C; and when fully shaded, it was 26.5° C. McCalla and Duley (10) reported much lower soil temperatures under straw mulches. Makarevsky (9) has shown that the use of a. white mulch paper on a subtropical soil has resulted in a marked increase in plant growth over that produced by plants grown on a bare soil. Likewise, plants grown in soil covered with black paper yielded less than those grown on a bare soil. Linford, working in Hawaii, has obtained identical results with white and black mulch papers. He has grown several vegetables and .in most cases those growing in soils covered with white paper have produced the largest yields. The pineapple growers have used several soil fumigants for the purpose of controlling nematodes in the soil. Two of these fumigants, chloropicrin and D'D' mixture (1,2, dichloropropane, and 1,3, dichloropropylene), have produced marked increases in yields. According to some growers, the latter has reduced the need for the use of iron sulfate sprays on the pineapples. The applications of chloropicrin and D'D' mixture in certain instances produce much greener plants than are normally produced in Hawaiian soils and for this reason they may have an influence in the nutrition of plants. Since the application of lime, soil fumigants, and mulches have individually produced improvement in plant growth through the alleviation of the chlorotic condition of the plant, it was considered that each of these treatments, in some way, affected the solubility