818 EXPERIMENT STATION RECOBD. 



The moisture couteut varied from 40 to SO per cent of tlie water capacity of the 

 soil. Oats eitlier without addition of straw or with amounts varying from 0.25 

 to 1 per cent of the weight of soil in the pots gi-ew best with a moisture content 

 equivalent to 80 per cent of the water capacity of the soil. The moisture con- 

 tent remaining constant, the yield of oats decreased with increasing amounts of 

 straw. The rapidity of decline in yield was greatest with SO per cent of the 

 water capacity, and appreciably decreased with a lowering of the water content. 

 The influence of the straw in diminishing the yield increased with the mois- 

 ture content in presence of sodium nitrate as well as in presence of ammonium 

 sulphate. The reduction of yield resulting from the addition of 0.25 per cent of 

 straw was about the same as that resulting from a reduction of the moisture 

 content of the soil to 20 per cent of its capacity. 



The addition of calcium carbonate with the straw reduced to an appreciable 

 extent the injurious effect of the latter, but did not wholly overcome it. The 

 maximum beneficial effect of the calcium carbonate was obtained when it was 

 used at the rate of 0.25 per cent of the weight of the soil. 



Sugar, starch, and straw, in amounts of from 0.125 to 1 per cent, were used 

 in sand cultures, and it was found that the smallest growth of mustard and 

 oats was obtained in the culture to which sugar had been added, followed in 

 order by starch and straw. The diminished growth resulting from the addi- 

 tion of these organic substances to the sand cultures was not due to denitriflca- 

 tion in a strict sense, but to the fact that the nitrates in the soil were converted 

 into albuminoid compounds which are less assimilable by green plants than 

 nitrates. It was observed that the nitrogen content of the plants was higher 

 the greater the reduction of growth. The addition of the organic substances in 

 the presence of nitrates produced an alkaline medium in exact proportion to the 

 amount of organic matter added. 



Some relations of certain hig'her plants to the formation of nitrates in 

 soils, T. L. Lyon and J. A. Bizzell {l^ew York Cornell Sta. Man. 1, pp. 9-109, 

 pis. 5, figs. 22).— Investigations which showed that "the nitrate content of soil 

 under timothy, maize, potatoes, oats, millet, and soy beans was different for 

 each crop when on the same soil " are reported in detail. " There was charac- 

 teristic relationship between the crop and the nitrate content of the soil at 

 different stages of growth. During the most active growing period of the maize 

 crop, nitrates were frequently higher under maize than in cultivated soil bear- 

 ing no crop. Under a mixture of maize and millet, nitrates at this period were 

 higher than under millet alone, although the crop yields were about the same 

 on both plats. . . . 



" Under both maize and oats the nitrate content was higher during the period 

 when the crop was making its greatest draft on the soil nitrogen than in the 

 later stages of growth, in spite of the fact that the nitrates in the uncropped 

 soil were increasing while those in the cropped soil were disappearing. Nitrates 

 under these crops and under millet failed to increase late in the season, when 

 nitrogen absorption had practicaUy ceased, although uncropped soil showed a 

 very large increase in nitrates at that time. . . . 



" Aside from the influence of cultivation, the source of the great differences in 

 the nitrates under the crops mentioned may be sought in the inherent differences 

 between plants of different species in their stimulating or inhibiting influence 

 on the production of nitrates, as well as in their relative rates, amounts, and 

 forms of nitrogen absorption. 



" Changes in the moisture content or in the temperature of the soil after early 

 summer had no important effect on the nitrate content of the soil under plants. 

 On the uncropped soil an increase in moisture content was sometimes accom- 

 panied by an increase in nitrates and sometimes by a decrease. 



