810 EXPERIMENT STATION RECOED. 



Studies in the drying of soils, M. A. Klein {Jour. Amer. Soo. Agron., 7 

 (1915), No. 2, pp. 49-77, fig. 1). — In this article the work of other's bearing on the 

 subject is reviewed, and two experiments made to determine the efEect of 

 drying the soil on its chemical and biological condition and on plant growth 

 are reported. 



The object of the first experiment was to determine, under controlled condi- 

 tions, the effect of drying the soil to different moisture contents on plant food 

 in the soil and on plant growth. Two heavy clay-loam soils, differing only in 

 content of organic matter, were placed in 3-gal. pots, saturated, and then al- 

 lowed to dry until they reached their permanent moisture content, which 

 varied from 15 to 30 per cent in the soil containing little organic matter and 

 from 15 to 40 per cent in the other, the highest figTires indicating saturation. 

 They were then divided into two series, one being planted to wheat at 25 per 

 cent moisture content and the other kept bare at the different moisture con- 

 tents. The wheat, after being harvested, was followed by millet and buck- 

 wheat in turn. 



It was found in this experiment that the drying of soil previous to planting 

 had a beneficial effect on plant growth. In the clay loam with little organic 

 matter, which had been previously held at saturation, the yield of dry matter 

 was smallest, while in the clay loam containing considerable organic matter 

 and which had been held at saturation the yield was as large as in those with 

 the lowest moisture content. The factor causing the beneficial effect due to 

 drying is, therefore, considered to be affected by the organic matter in the soil. 



Previous drying of the soil had no effect on the total nitrogen in the dry 

 matter of the crop. The water-soluble matter in the clay loam containing little 

 organic matter was increased by drying, while in the same soil with a high 

 content of organic matter the opposite occurred. In the planted series of both 

 soils drying resulted in a decrease in the nitrates in the soil, but no effect was 

 observed in the unplanted series. Denitrification occurred in the soil samples 

 when incubated at 30° C. for seven days. Drying had little effect on the avail- 

 able potassium, calcium, or phosphorus in the soil. 



The object of the second experiment was to determine the effect of drying a 

 soil on its physiological condition as measured by carbon dioxid production and 

 nitrification. The clay loam soil was transferred to new pots and kept at an 

 optimum moisture content for 14 months, after which different pots were sub- 

 mitted to from one to three wettings and dryings in a drying room at 30° before 

 determinations of carbon dioxid production and nitrification were made. 



It was found that bacterial activity as measured by the carbon dioxid pro- 

 duction was greatly increased by a previous drying of the soil. In the soil 

 that was not wet again after drying the bacterial activity was greatly inhibited 

 and the cai-bon dioxid production ceased after seven days. One drying of the 

 soil greatly increased the activity over the original soil. In the soil kept at an 

 optimum moisture content for 35 days after drying the production of carbon 

 dioxid became normal again. A soil dried twice did not show a much greater 

 activity than when dried once, while three dryings showed no increase over 

 two dryings. 



Drying the soil greatly reduced the nitrates, and rewetting of the dry soil for 

 a period of 16 days further decreased nitrification. In the soil held moist for 

 35 days after one drying and in those previously dried twice and three times, 

 an increase in nitrification was found over that in the sample dried once. The 

 maximum was, however, reached at two dryings. " These results show that the 

 activity of the nitrifying organisms is increased by a previous drying of the 

 soil, but reaches a maximum at two dryings." Adding organic or inorganic 



