FIELD CROPS. 433 



Swoet potatoes are considered a valuable fecdinj: stutt", and it is pointed out 

 that they may contain as hijih as ;>7 per cent of dry matter while 30 per cent is 

 about the average. Kstimatinj: that under ordinary conditions land yielding 

 20 bu. of corn would be able to produce about 200 bu. of sweet potatoes, it is 

 stated that the potatoes will furnish more than 3 times as much nitrogen-free 

 extract and as much, or more, of each of the other proximate constituents of a 

 feeding stuff as that contained in corn. Analysis of all the varieties did not 

 disclose the presence of amids. The different varieties here tested gave an 

 average yield of 250 bu. per acre, with the following average composition : 68.1 

 per cent of water, l.G per cent of protein, 0.5 per cent of fat, 0.9 per cent of fiber, 

 1 per cent of ash, and 27.9 per cent of nitrogen-free extract. The vines of 4 

 varieties calculated to the water-free basis contained an average of 12.48 per 

 cent of protein, 4.86 per cent of fat, 18.22 per cent of fiber, 8.73 per cent of ash, 

 and 55.71 per cent of nitrogen-free extract. This composition of sweet potato 

 vines is compared with an average composition of the water-free material of 

 red clover, crimson clover, and cowpea and soy bean hay. 



In determining the fertilizing elements removed by a crop of sweet potatoes 

 it was found that the crop removes about 4.3 ets. worth of phosphoric acid, 

 nitrogen, and potash per bushel, or about $8.60 worth in a yield of 200 bu. per 

 acre. A table is given showing the percentage composition in fertilizing in- 

 gredients of the moisture-free vines. A determination of the content of water, 

 protein, starch, and sugar at different stages of growth seems to indicate that 

 the sweet potato reaches maturity just about the time when the starch content 

 is at its maximum and the sugars at their minimum. 



Work at the tobacco experiment stations, E. H. Mathewson {Virginia Sta. 

 Rpt. 1908, pp. 27-39, Jigs. 10). — This article is a review of the tobacco experi- 

 ments conducted by the Virginia Station in cooperation with the Bureau of 

 Plant Industry of this Department. Work is in progress at five stations upon 

 the same general plan but modified sufficiently to be suited to the type of 

 tobacco produced in the particular localities. The experiments include fertil- 

 izer, rotation, and tobacco breeding work. Some of the results here reported 

 have already been noted from another source (E. S. R., 20, p. 33). 



The use of potash was found more striking on the light, thin tobacco soil 

 at Chatham than on the stronger and more clayey soil at Appomattox. It is 

 stated that the finest and brightest tobacco was obtained only when the fertilizer 

 mixture used contained relatively high proportions of phosphoric acid and, in the 

 case of bright tobacco particularly, of potash also. A heavy application of nitro- 

 gen gave a striking increase in yield over either phosphoric acid or potash, but 

 the tobacco was both coarser and darker. The result is regarded as showing 

 that with heavy applications of nitrogenous manure adequate quantities of 

 phosphoric acid and potash should also be applied in order to balance the appli- 

 cation. 



A general lesson brought out by the experiments is that the ordinary unim- 

 proved tobacco soil of ^'irginia is uni)roductive to a large extent at least because 

 it supplies too little nitrogen to the growing crop. This may be remedied by 

 the use of commercial fertilizers, barnyard manure, and the increase of the 

 supply of humus by the growth of grasses and leguminous plants. The last 

 method suggested requires the introduction of crop rotation, and to those in 

 charge of the work it has become evident that the real solution of the problem 

 lies in the diversification of crops or the introduction into the crop rotation of 

 soil-improving crops, particularly the grasses and the leguminous plants. 



Observations made on the residual effect of the fertilizer used on tobacco 

 indicate that nearly all the soils in the tobacco-growing sections of the State 

 can be made to produce excellent, profitable crops of hay and clover. The effect 



