. Agriculture for southern schools. leaves are generally burned. Thisdoes not mean that exhausting crops should not be grown,but that something must be returned to the land in exchangefor what is removed. Lack of drainage makes soils unproductive. — All thecauses of soil-impoverishment mentioned are due to sub-stances taken from the soil. They have all been formsof subtraction. There is, however, an addition to thesoil that may make it poor. Too much water injuresthe soil and the crop if it is not drained away either by HOW THE SOIL BECOMES POOR 85 the porous nature of the soil or by ditches c
. Agriculture for southern schools. leaves are generally burned. Thisdoes not mean that exhausting crops should not be grown,but that something must be returned to the land in exchangefor what is removed. Lack of drainage makes soils unproductive. — All thecauses of soil-impoverishment mentioned are due to sub-stances taken from the soil. They have all been formsof subtraction. There is, however, an addition to thesoil that may make it poor. Too much water injuresthe soil and the crop if it is not drained away either by HOW THE SOIL BECOMES POOR 85 the porous nature of the soil or by ditches cat bythe farmer. This subject was discussed in the last section. Note to the Teacher. — Ask your pupils to explain how lye ismade from ashes kept in hoppers. Point out that this process isleaching. Leaching does more harm to rich than to poor soils. Thisprocess removes from the soil chiefly nitrogen and little or no phosphateand potash. The loss of plant-food due to the sale of lint cotton andof cotton seed is shown in Fig. Fig. 54.—The Poor SubsoilIn the foreground the top soil has been removed by grading,with the corn on normal soil. Note the contrast SECTION XV. HOW TREES AND LEGUMI-NOUS PLANTS IMPROVE THE LAND In a forest, year after year, the trees drop their leaves;the decayed leaves and roots make the soil very loose andrith. When the trees are removed, the new-ground pro-duces good crops that use the vegetable matter as crops are good on new-ground also, becausethe humus in dry weather holds moisture like a , therefore, is not much felt by crops on land con-taining much humus. When plowed, the dark, loose soilcrumbles readily, for the reason that vegetable matter inthe soil keeps the particles of clay from sticking together^and from turning up in great useless clods. Resting land not the quickest way to enrich it. — Farm-ers have learned that even a crop of weeds adds vegetablematter, and so they sometimes leave certain poor fieldsunc
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