1919] FIELD CROPS. 185 



Uredinales of Guatemala based on collections by E. W. D. Holway, II— IV, 

 J. C. Arthur {Atner. Jour. Bot., 5 (1918), Nos. 8, pp. 420-U6; 9, pp. 462-489; 

 10, pp. 522-550). — The present series, which is consecutive with the contribu- 

 tion previously noted (E. S. R., 40, p. 327), deals with the ^cidiacase (Pucci- 

 niacese), some genera having been placed out of their usual order to express the 

 author's conception of their affinities. 



FIELD CROPS. 



The influence of crop plants on those which follow, II, B. L. Hartwell, 

 F. R. Pember, and G. E. Merkle {Rhode Island Sta. Bui. 116 {1919), pp. 4-^8, 

 figs. 7). — Supplementing experimental work conducted in the field (E. S. R., 40, 

 p. 623), pot experiments begun in 1911 are described in which further observa- 

 tions were made on the effect of different crops on those grown subsequently. 

 The investigations were divided into two parts, one conducted in Wiley pots in 

 the greenhouse to study the effect of onions, buckwheat, rye, and redtop on 

 onions and buckwheat when grown with an optimum supply of nutrients ; with 

 nitrogen, phosphorus, and potassium eacli omitted ; and with half more than 

 the optimum supply of nutrients ; and the other made in ash cans sunk in the 

 ground out of doors in which observations were made on the effect of onions, 

 buckwheat, rye, redtop, and mangels on onions and buckwheat when the crops 

 were grown with different amounts of nitrogen. Applications of lime were 

 made to all pots at the beginning of the experiment and again 3 or 4 years later. 

 Data showing tlie crop yields and the amount of nutrients removed in the dif- 

 ferent crops are presented in tabular form with full discussion and may be 

 summarized as follows : 



When onions were grown after the different crops had occupied the soil 2 or 3 

 successive seasons, the yields increased after the crops in about the following 

 order: Buckwheat, mangels, rye, onions, and redtop. When buckwheat was 

 grown uniformly, the yield increased in order after redtop, buckwheat, mangels, 

 rye, and onions. With the different fertilizer treatments the relative effect of 

 the several crops varied somewhat, depending upon the treatment, but not so 

 much as generally expected. Chemical analyses of the crops are held to indi- 

 cate that changes in the percentage composition of a crop brought about by a 

 given application of a nutrient depended not only upon its effect upon the rate 

 of growth but also upon the abundance of the other nutrients in relation to the 

 needs of the crop. In general it appeared that the nutrients actually required 

 for the normal growth of the crops need not exceed in dry material 2 per cent 

 nitrogen, 1.5 per cent potassium oxid, and 0.5 per cent phosphoric oxid, provid- 

 ing an adequate supply of other ingredients is available to furnish the indiffer- 

 ent ash. As indicated by the field experiments, "the divergent effect of crops 

 on those which follow seems not to be attributable, at least principally, to dif- 

 ferences in the amount of nutrients removed by the crops grown previously — that 

 is, tlie smallest yield may not occur after the crop which removed the largest 

 amount of even the most-needed nutrient." 



The soil acidity was affected differently by the various crops. Onions, said 

 to be sensitive to conditions accompanying acidity, showed the best yields after 

 crops giving rise to the least acidity. The effects of the crops on those which 

 followed were observed to be much less divergent when the soil acidity was re- 

 duced by liming. Even the preceding crop effects may prove to be relatively 

 unimportant on neutralized soil. It is suggested that for practical purposes 

 the potent influences observed in these investigations should receive careful at- 

 tention, since many soils exhibit a higher degree of acidity than existed in the 



