l vs University of California Publication* in Agricultural Sciences [Vol. 3 



tures were incubated for four weeks at 2-i°C-30°C, at the end of which time bac- 

 terial action was stopped by drying in the oven for 24 hours. Subsequently, the 

 samples were broken up in a mortar, and 10 grams weighed out for the determina- 

 tion of the total nitrogen. 



Pot Cultures in the Greenhouse 



The large samples of the surface foot of soil were stored in the greenhouse 

 until used. The preparation of the samples was in most cases as follows : The 

 sample was placed on a large table and screened through a quarter inch sieve. 

 This treatment of screening was attempted with the Diablo clay adobe and the 

 Altamont clay loam, but was abandoned as practically hopeless. The samples of 

 these two types had been collected in the late summer, when the ground was very 

 hard and dry, hence the clods defied any efforts to break them up. As an alterna- 

 tive the samples were as thoroughly mixed as possible and weighed out into the 

 pots. Several waterings during a week, together with carefully breaking up the 

 lumps by hand, rendered the soils finely divided enough to permit the planting of 

 the seeds. The Hanford and San Joaquin types were readily screened. 



All the soils were weighed out into nine inch flower pots. In most cases the 

 pots had been previously paraffined. Care was taken to clean the pots thor- 

 oughly, as far as surface material was concerned ; many of the pots were scrubbed 

 with a brush and water. All previously used pots were examined to exclude the 

 use of such as had formerly been used for soils containing high percentages of 

 soluble salts, but such examination was not always successful in eliminating the 

 undesirable pots, as was afterwards evident. In the Diablo, Altamont, and Han- 

 ford soils the quantity of soil used was five kilos per pot. In the San Joaquin 

 soils six kilos were used. 



Enough soil was collected to fill eighteen pots. This would allow for the 

 arrangement of six sets of triplicates of every sample; and the planting of a dif- 

 ferent crop in each of the sets would allow for the growing simultaneously of six 

 different crops on every soil. For example, there were placed together in the 

 greenhouse and considered as a unit in the culture work the series of the Diablo 

 clay adobe, including three pots of the sample taken from San Juan Capistrano, 

 three from that taken near Los Angeles, three from that of the San Fernando 

 valley, and lastly three from the sample taken in the Danville region. This group 

 of pots was planted to oats, barley, bur clover, or any one other crop. The pots 

 were kept together in the greenhouse, that the conditions for each one in the set 

 would be as nearly uniform as possible, for even a slightly different location in 

 the greenhouse was found to affect the crop appreciably. The other five sets of 

 pots were similarly treated. No fertilizing materials were added to any of the 

 soils. All were used in their normal condition. The aim was to compare the crop 

 producing power of the representatives of a given type of soil from various 

 localities. 



Several crops were grown, as the desire was to get a series of plants that 

 would grow well under greenhouse conditions, and act as indicators. It was 

 known that barley was about the best crop to use, but supplementary plants were 

 desired. Barley, wheat, oats, rye, millet, milo, cowpeas (black eye beans), soy 

 beans, beans (small white), bur clover (Medicago denticulata) , sweet clover (Hcli- 

 lotus indica), and oats and bur clover in combination were tried. Some were 

 a marked success under greenhouse conditions, and others were practically total 

 failures; the better crops were given by barley, soy beans, bur clover, and millet. 

 Sweet clover gives excellent results. This wide range of varieties of plants was 



