SOILS — FERTILIZERS. 515 



growth of the plants not interfered with, the soil zone occupied bj- the roots 

 must be uniformly supplied with n sufficient quantity of available water (as a 

 rule more than 10 per cent in the clay soil experimented with). 



The depth of the moist layer at seedtime in the spring is of vital importance 

 in relation to subsequent droughts. It was found in the experiments at Odessa, 

 where the useful rainfall is only about 5.85 in., that every year at the end of 

 June or at the beginning of July, and with a dry spring season at the end of 

 May, cereals have consumed all of the reserve water which had accumulated 

 in the root zone in the preceding autumn, winter, and spring, and that with ' 

 continuous culture of cereals there was a pronounced and complete drying of -. 

 the soil of the root zone and almost complete cessation therein of formation of 

 soluble plant food. 



An elaborate study of the distribution of roots of different kinds of plants 

 in the soil (E. 8. R.. 2(ju P- 732) showed wide differences in the depth and 

 extent to which different plants exhausted the soil moisture. Potato and flax 

 roots were found to grow to a depth of approximately 2* ft., sunflowers and 

 beets about 4* ft., and most cereals about 3* ft. 



On the basis of his studies of the root systems of plants and their relation jl 

 to the exhaustion of soil moisture the author recommends very strongly rota- ' I 

 tions which will alternate short-rooted and dense-rooted crops with those hav- 1 ? 

 ing longer and more scattering root systems. ' 



The conditions conducive to drought are summarized in brief as follows: 

 (1) Uneven distribution of moisture in the soil zone at the time of seeding, (2) 

 persistent and perennial dryness of the intermediate layer of the soil and a 

 deficiency of soluble plant food therein as a result of continuous cropping with 

 the same kind of plants, and (3) great depth of the permanent water table. 



Among the measures recommended for lessening or controlling the effects of 

 drought in addition to the rotation of crops of different rooting habits, already 

 referred to, are surface tillage and the destruction of weeds, the latter being 

 considered " the bitterest enemy of . . . field culture and the best friend of 

 drought." 



It is pointed out that A. Shishkin about forty years ago formulated quite 

 fully the means of combating drought, anticipating much that is now current 

 practice in dry farming. 



Forests and floods, J. Aitken {Nature [London], 93 (1914), No. 2333, p. 

 506). — Tests with garden soil in pots are reported to show that stirred soil 

 absorbs and retains much more moisture than compact, undisturbed soil, and 

 it is maintained that soils under trees are loosened by the constant growth and 

 expansion of the roots and thus put into condition for absorbing and retaining 

 more rainfall than bare soils. 



The chemistry of the soil: The evolution of acid amins, G. Chardet (Rev. 

 Gen. Chim., 11 [WW, No. 9, pp. i37-i4^).— This article discusses the theo- 

 retical and practical value of the determination of acid amins in soils, review- 

 ing briefly the chemistry of the metabolism of these substances, their evolution, 

 and their transformation into products which are either toxic or fertilizing to 

 plants. Attention is also called to the numerous points of similarity between 

 the nutrition of the plant cell and the animal cell and the relation thereto 

 of nutritive substances and excretory products. 



The application of the Sorensen method for the rapid determination of acid 

 amins in the study of soils is discussed and examinations of the nitrogenous 

 compounds of four soils by this means are reported. It was found that the 

 proportion of nitrogen in the form of acid amins varied from 49 per cent of the 

 total nitrogen in peat to 52 per cent in swamp soil, 66 per cent in humus garden 

 soil, and 68 per cent in compost. 



