724 EXPERIMENT STATION RECOED. [Vol.36 



Terracing and drainage to prevent erosion of Java hill soils used for the cul- 

 tivation of tea and coffee are discussed, and the so-called " Kotak " system 

 of terracing practiced is described. In this system small rectangular terraces 

 are employed instead of long terraces with ditches. For coffee a terrace 12 

 ft. square, with one tree in the middle, is usually constructed, while for tea a 

 terrace 8 ft. square, with four plants, is used. An open drain is placed at the 

 foot of the terrace. 



The importance of soil ventilation on the alluvium, A. Howard {Agr. Jour. 

 India, Indian Hci. Cong. No., 1916, pp. 46-52).— The importance of soil aeration 

 in preventing the yellowing of peach trees, in increasing and hastening the effect 

 of green manuring, and in aiding the maturing of crops is discussed. 



Notes on the presence of nitrates in orchard soils, J. H. Gourlby and V. D. 

 Shunk {Neto Ham.pshire 8ta. Tech. Bui. 11 {1916), pp. 3-Sl, figs. 9).— Experi- 

 ments on the effect of sod, tillage, and liming on the presence of nitrates in 

 light orchard soil with very sandy subsoil are reported. 



It was found that " the formation of nitrates is greatly reduced in a sod 

 orchard and from a fertility standpoint is the first limiting factor." Stirring 

 the soil readily increased the rate of nitrification and under a good system of 

 tillage nitrates were usually present in excess of the needs of the trees. Lime 

 also consistently increased nitrification. Moisture was not the limiting factor 

 in the sod plats. 



See also a previous note (E. S. R., 33, p. 44). 



Some effects of oxygen and carbon dioxid on nitrification and ammonifl.- 

 cation in soils, J. K. Plummeb (Ne\c York Cornell Sta. Bui. 384 {1916), pp. 

 305-330, figs. 5). — Experiments with Dunkirk clay loam soil on the influence 

 of oxygen and carbon dioxid on ammoniflcation and nitrification are reported. 

 It was found that vigorous nitrification takes place in sealed flasks as long 

 as there is a supply of oxygen. Of the soil gases studied, oxygen was found to 

 be the limiting constituent. "There is an optimum mixture of this gas (one 

 containing from 35 to 60 per cent of oxygen) for nitrification." From the losses 

 of oxygen from the gas mixtures, it is considered certain that there are other 

 forms of oxidation than that caused by the nitrate bacteria. 



A large quantity of carbon dioxid was produced when lime was used, amount- 

 ing in some instances to nearly 20 per cent. The greatest production of this 

 gas accompanied the point of maximum nitrification. Ammonium sulphate, 

 when applied to the soil without the addition of lime, produced only slight in- 

 creases in nitrification even after incubation for a period of 28 days. " The 

 small quantity of carbon dioxid formed under such conditions would tend to 

 indicate that ammonium sulphate, when applied to this soil alone, depresses 

 the action of the carbon-dioxid-producing bacteria as well. Taking the results 

 as a whole it can not be said that carbon dioxid has any material effect on nitri- 

 fication so long as oxygen is present in the atmosphere. It is of little conse- 

 quence whether the oxygen is diluted with the inert gas nitrogen or with 

 carbon dioxid. When the supply of oxygen becomes limited and anaerobic con- 

 ditions are produced, denitrification sets in and this continues until practically 

 all the nitrates are destroyed. In no case with these experiments was the com- 

 bined oxygen liberated in the elementary form during the processes of denitri- 

 fication." 



The results with the distillation method for the determination of ammonia 

 showed that there is no optimum content of oxygen for the production of this 

 compound. The results of all mixtures, except the very high concentrations of 

 oxygen, were practically the same. It seemed to make little difference whether 

 the soil readily increased the rate of nitrification and under a good system of 

 dioxid. Under purely anaerobic conditions, caused by an atmosphere of pure 



