' Apparent Infertility of the Soil around Trees. 255 



on the stock of soluble mineral matter in the soil it is not likely that 

 even the smaller proportion of water present in the soil near the trees 

 would become appreciably more highly charged with mineral salts 

 than the water in the soil away from the influence of the trees. 



In order to test the validity of the theory mentioned above, 

 viz., the undue deprivation of soluble plant-food by the trees, a series 

 of samples of soils were taken (I) in the immediate vicinity of four 

 different wattle belts and plantations on this farm, and (2) at an 

 appreciable distance (about 20 or 30 yards) away from the same belts 

 and plantations. A complete chemical analysis of all these samples 

 was made, and the results, when closely compared, do not sIjow any 

 distinct evidence that the roots of the trees had appreciably deprived 

 the soil near them of plant-food as compared with the composition of 

 the soil 20 or 30 yards away. 



With the object of testing* this theory further, the amount of 

 water-soluble matter in each sample of soil was ascertained, and the 

 results again show no greater amount of soluble plant-food in the soil 

 away from the trees than immediately under them. 



With regard to the contention that the soil solution near the trees 

 contains an excess of mineral salts, the results obtained do not bear 

 this out either, for, although allowing for the smaller amount of 

 moisture in the soil in the vicinity of the trees, the concentration of 

 mineral matter in the soil- water there Avould not be nny thing like 

 enough to be harmful. 



SciEiSTiric Explanation. 



Most scientists who have studied this question seem to be of the 

 opinion that the sole, or at any rate the main, reason for the barren- 

 ness of the land in proximity to a plantation is the deprivation by the 

 trees of the moisture of tlie soil through which tlieir roots range. 

 When it is comprehended that the limiting factor governing the 

 fertility of South African soils is generally moisture (as witness the 

 large increase of crops from lands when put under irrigation) this 

 question becomes of considerable importance. 



In a soil of good physical texture the roots iDcuetrate to a great 

 depth and ramify to a considerable extent outwards, and when we 

 consider the enormous amount of moisture transpired by an average 

 sized tree through its leaves, it is realized that a belt or clump of trees 

 will deprive the soil in its immediate neighbourhood of water at a 

 tremendous rate, especially during a hot, drj, windy day. The 

 amount of water exhaled by a tree would depend chiefly on the amount 

 of leaf surface and on the number and size of the stomata or leaf pores, 

 so that some kinds of trees tend to deprive the soil of its moisture at 

 a far greater rate than others. For instance, poplars are often planted 

 in swampy areas in order to dry out such localities by the rapid 

 pumping of the water through their roots, up the stems, and finally 

 out through the pores of the leaves into the surounding air. During 

 the last summer a crop of pumpkins was grown in a field contiguous 

 to a wattle shelter-belt on tliis farm. The season was a dry one, and 

 it was soon noticed that the portion of the large-leaved crop near the 

 trees did not make such good growth as that at an appreciable distance 

 away. Furthermore, during the hot afternoons the leaves of the 

 plants near the trees were all limp and drooping, but regained their 

 usual turgid appearance as soon as the cool evenings came on. During 



