1919] FIELD CROPS. 143 



supplied from nitrate, one-third from ammonium sulplaate, and one-tliird from 

 laigh-grade organic matter. 



Further observations on the omission of potash in fertilizer tests with pota- 

 toes begun on Aroostooli farm in 1915 have led to the following conclusions: 

 Good yields were secured without potash. The application of 300 lbs, of com- 

 mon salt per acre resulted in a small but uniform increase in yield over the 

 untreated plat. The application of 45 lbs. of potash per acre (equivalent to 

 1,500 lbs. of 3 per cent goods) produced a uniform and profitable increase in 

 yield on Caribou loam, while larger applications were not proportionately more 

 profitable. Finally, nitrogen and not potash appeared to be the limiting factor 

 in potato production on this soil. 



How to control potato enemies (Maine Sta. Doc. 535 (1918), pp. 16, fig. 1). 



Brief popular descriptions of the insects and diseases affecting potatoes and the 

 nature of the injury produced by each are presented, together with recommenda- 

 tions for their control. Directions as to the time and manner of spraying and 

 formulas for the preparation of insecticidal and fungicidal sprays are included. 



Fertilizer experiments with, tobacco, W., W. Garner and D. E. Brown (Mary- 

 land Sta. Bui. 225 (1919), pp. 157-183, figs. 4).— This bulletin describes rather 

 extensive fertilizer tests with tobacco conducted in cooperation with the 

 U. S. Department of Agriculture in Prince George County (southern Mary- 

 land). Observations were made on the effect upon the yield and quality of 

 tobacco of applying different combinations and amounts of commercial ferti- 

 lizers and on the use of lime. The results secured may be summarized as 

 follows : 



An analysis of the leaves and stalks of tobacco grown on the experiment 

 field showed that a crop ranging from 1,300 to 1,600 lbs. per acre removed from 

 the soil approximately 35 to 55 lbs. of nitrogen, 10 to 12 lbs. of phosphoric acid, 

 and 55 to 70 lbs. of potash, about one-third of which was contained in the 

 stalks and should be returned to the soil. Nitrogen appeared to be the limiting 

 factor on these soils, inorganic forms such as nitrate of soda and sulphate of 

 ammonia giving better yields than organic forms such as cottonseed meal and 

 tankage, although the latter resulted in a better quality of tobacco than the 

 former. Phosphates failed to increase the yield of tobacco but stimulated 

 growth and promoted the proper ripening of the crop to a marked extent, re- 

 sulting in a lighter color in the cured leaf. Wheat and other crops following 

 tobacco shoAved a decided residual benefit from phosphate fertilizing. Potash 

 gave only small increases in yield on " rested " land, while under continuous 

 cropping to tobacco the soil showed a decided need of potash. 



The proper ratio between the nitrogen and phosphoric acid in tobacco fer- 

 tilizers is deemed to be most important, a nitrogen content amounting to from 

 one-half to two-thirds of the phosphoric acid content being recommended for 

 all except quite fertile soil or where a legume has been plowed under. For 

 average soil conditions it is suggested that a fertilizer containing 4 or 5 per 

 cent niti'ogen, 8 per cent available phosphoric acid, and 4 per cent potash be 

 applied at the rate of 600 lbs. per acre. Somewhat increased yields resulted 

 from applying the fertilizer in the drill over broadcasting, while the crop also 

 secured an earlier start and usually matured earlier. 



Liming produced increased yields of tobacco only when nitrogen was not 

 liberally supplied in the fertilizer through the liberation of nitrogen from the 

 reserve supply in the soil. The darker color of tobacco following liming is said 

 to be due to the excess nitrogen made available to the plant. It is suggested 

 that lime, when used on tobacco soils, be applied to the crop immediately 

 following tobacco in the rotation rather than to the tobacco crop itself. 



