NA TURE 



54: 



THURSDAY, OCTOBER 26, 1911. 



AGRICULTURE IN DRY COUNTRIES. 

 Drv Farming: a System of Agriculture for Countries 

 under a Low Rainfall. By Dr. J. A. Widtsoe. Pp. 

 xxii + 445. (New York : The Macmillan Co.; 

 London: Macmillan and Co., Ltd., igi 1.) Price 

 6s. 6d. net. 



ACCORDING to the author's calculations, nearly 

 six-tenths of the land surface of the earth re- 

 ceives less than twenty inches of rain per annum, 

 and therefore requires the adoption of special agricul- 

 tural methods differing From those in use in moister 

 regions, in the strid historical sense it may be that 

 the "dry farming" methods .ue really the older, for 

 some of the ancient civilisations — Babylon and Egypt 

 — flourished in "dry" regions. But to-day the dry 

 farming methods are new, and are rapidly being ex- 

 tended over the regions of deficient rainfall that are 

 now coming into cultivation. 



Drv farming is different from irrigation, which is 

 not touched upon in the present book. It consists in 

 cultivation methods that reduce the loss of water from 

 the soil by evaporation, and thus leave a maximum 

 amount for the crop. Hence it implies a certain rain- 

 fall ; at least tin inches a year are wanted, and 

 success is not certain with less than fifteen inches. 



A clear account is given of the differences between 

 the soils of semi-arid and of humid regions, so far 

 as these can be connected with the differences in rain- 

 fall. In humid regions the fertility of the soil is 

 largely bound up with the clay fraction; a good deal 

 of washing has gone on, and there is a tendency for 

 the clay to wash into the subsoil, thus limiting the 

 distance to which air can penetrate. A sharp distinc- 

 tion therefore arises between the surface and the sub- 

 soil, the latter being unsuited to plant growth. In 

 semi-arid regions, on the other hand, the washing is 

 reduced to a minimum ; clay does not wash into the 

 subsoil (it is said that clay does not even form to any 

 ■.lent, but no evidence is set forth), and the 

 diffe nee between surface and subsoil does not arise ; 

 hence all parts of the soil are adapted to plant 

 grow 1I1. Two deductions are drawn: the semi-arid 

 soils aie richer in plant food and stand in less need 

 of fertilisers than humid soils; and recourse can be 

 had more freely to deep ploughing. 



Dry farming in the States, in its modern sense, is 

 said to have been begun h_\ Brigham Young and his 

 followers when, in 1S47, they went into the Great Salt 

 Lake Valley. In this arid region starvation seemed 

 to be the only possible ending to the colony, but 

 suitable methods of farming were gradually evolved, 

 and the results are matters of history. But the 

 methods w-ere not put together until H. \Y. Campbell, 

 in 1895, published his " Soil Culture and Farm 

 Journal." Then a boom began. The railway com- 

 panies, with true commercial instinct, set up demon- 

 stration farms in dry regions for the benefit of intend- 

 ing settlers, and glowing accounts were given of what 

 dry farming methods would do. The question aroused 

 gieat interest in the British colonies, where large semi- 

 arid tracts occur, and commissions and deputations 

 NO. 2IQI, VOL. 87] 



were sent to study the methods on the spot. It is un- 

 fortunate that commercial interests were ever involved, 

 because for a time the whole system was looked on 

 with considerable suspicion by agriculturists, but 

 Mr. Widtsoe's book will go far to satisfy the most 

 sceptical that the methods are really effective. 



Naturally there has been a good deal of change in 

 methods, but the general conclusions to which Mr. 

 Widtsoe is led are as follows. The soil should be a 

 clay loam, uniform to a depth of at least eighl feet. 

 After the land has been cleared and broken it should 

 lie fallow for one year, all weeds being rigorously 

 hoed down ; ii should then be ploughed deepl} in 

 autumn. If crops are to be sown immediately las 



they should be if the winter season is not t Id) 



the plough is followed 1>\ the disk cultivator and the 

 harrow; if not, the land should lie up rough during 

 winter, be further ploughed in spring, disk cultivated 

 and harrowed. After every shower of rain the land is 

 to be cultivated; the hoe or the harrow must be kept 

 going all the season, and directly after harvest the 

 land must be disked. Two great principles are thai a 

 fine laver of drv soil is to be maintained on the sur- 

 face ; and every weed must be killed. 



It was originally thought necessary to compress the 

 soil below this surface layer, but later experience 

 shows this operation to be superfluous. A recent 

 development, however, is the summer-cultivated 

 fallow, adopted every third or fourth year in regions 

 of fifteen to twenty inches rainfall, and every alternate 

 year in regions of less than fifteen inches rainfall. By 

 constant cultivation a large proportion of the rainfall 

 can be kept in the soil for the next crop. 



Wheat is the best crop, maize the second best ; but a 

 rotation is desirable, including a leguminous crop. As 

 cattle cannot be kept the straw is not wanted ; the 

 grain is therefore cut off with a "header" and the 

 -.traw ploughed in. Up to the present fertilisers have 

 not been used, and the soil, so far from showing signs 

 of impoverishment, is said actually to increase in 

 fertility. However, the author does not counsel disuse 

 of fertilisers, but insists that the soil must give out 

 unless manure is added. 



The necessitv for a summer fallow arises from the fact 

 that crop production is only possible where sufficient 

 moisture is present. It is particularly to be noticed that 

 no economy is attempted so far as the plant itself is 

 concerned : extraneous sources of loss only are cut oil. 



As in other branches of agriculture, the facts are 

 ahead of the hypothesis. The distribution of water 

 over a complex mass of particles like the soil has not 

 been worked out, but it is clearly regulated by the 

 surface attractions between the particles and the 

 water. Further, it is supposed that evaporation takes 

 place only at the surface, and scarcely at all— only 

 about o"2 inch per annum— from the layers below, 

 Iml this supposition is a little difficult to reconcile with 

 the phenomena of diffusion of air into the soil. 



Soil students and agriculturists will welcome the 

 book as a useful summary by a man on the spot of 

 what has been achieved so far, and they will be put 

 in a position better than before to disentangle the real 

 from the imaginary in the accounts of dry farming 

 they come across. E. J. R. 



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