'MOVEMENTS OF SALTS IN SOILS. Ill 



water-soluble salts in the zone of greatest, root activity may in- 

 fluence yield, good surface cultivation must be beneficial in 

 holding the nitric acid, lime, magnesia and potash well down 

 within the zone of 3 to 15 inches, where the roots of crops are 

 usually most abundant, and for this reason, where the salts may 

 be expected to be most immediately available. 



The table on p. 108 shows that, for an average of 6 soil types, 

 the amounts of nitric acid (NO 3 ) in the layer of soil 3 to 6 

 inches below the surface, had come to be in the ratio of 172.7 

 under the good 3-inch mulch, to 51.2, where no mulch was 

 maintained ; and this difference, so far as can be seen, was due 

 wholly to the effect of the mulch. In the 6 to 9 inches the 

 mean ratio was 139.4 to 49, or nearly three times as much ni- 

 trates had accumulated under the mulch; and even at 12 to 15 

 inches below the surface the ratio had come to be 69.8 tot 34.2, 

 or twice as much nitric acid existed there; and this is one of 

 the most essential plant food materials, for it is the immediate 

 source of all the nitrogen of cultivated crops, at least so far as 

 is as yet demonstrated. 



In Figures 8 and 9, p. 112, there are two illustrations 

 of a form of surface cultivation very generally practiced 

 in the South, but which, for all except very unusual soils in 

 very wet seasons, or for certain special cro^s, is far from the 

 best. In both of the fields there shown a small plow had been 

 run close to the row, first throwing the dirt away from the 

 plants, leaving a firm, moist furrow bottom exposed to the dry- 

 ing action of the hot sun and winds and, at the same time, the 

 loose earth turned away left in a condition to dry out com- 

 pletely. After a day or two the dried and loose earth was 

 again turned back against the row with the plow and another 

 furrow bottom left exposed to the drying action which brings 

 the nitrates, lime and other soluble salts to the immediate sur- 

 face where they are useless to the crop and where the first heavy 

 rain is liable to carry much of them away in the surface drain- 

 age. The curled condition of the leaves of the corn, as shown 

 in the engraving, Fig. 8, is the direct effect of this faulty cul- 

 tivation rather than the result of a necessary deficiency of soil 

 moisture at the time. 



