814 EXPERIMENT STATION EECORD. [Vol. 38 



Humus in mulched "basins, relation of humus content to orange production, 

 and effect of mulches on orange production, C. A. Jensen (U. S. Dept. Agr., 

 Jour. Agr. Research, 12 {1918), No. 8, pp. 505-518).— This is a report of a study 

 made at Riverside, Cal., on (1) the changes in tlie humus content of soils in 

 basins mulched \vith different organic substances, (2) the effect of lime on 

 the humus content of the soils, and (3) the relation of the humus content of 

 the soil to fruit production. " Humus " was determined colorimetrically in the 

 extract obtained by boiling the soil, which had previously been freed from lime 

 by extraction with 1 per cent hydrochloric acid, in 7.5 per cent sodium-hydrate 

 solution for 2 minutes. The " basins " referred to were areas in the citrus 

 grove inclosed in earth embankments for purposes of irrigation. The materials 

 used as mulches included alfalfa, sweet clover, bur clover, bean straw, barley 

 hay, pine shavings, and cow manure. The mulches were iised with and with- 

 out the addition of lime, and in one exiieriment dried blood, tanlcage, phosphate, 

 bone meal, and sulphur were used in addition to alfalfa and manure mulches. 



The percentage of humus in the soil of the mulched basins varied from time 

 to time. With manure and alfalfa mulches it increased more rapidly in clay- 

 loam soils than in lighter soils. As a rule, the increase was greater mth 

 manure than with alfalfa. The addition of lime to the manure did not increase 

 the humus, but in most cases there was an increase of humus when lime was 

 used with^the alfalfa mulch. Blood, tankage, acid phosphate, bone meal, or 

 sulphur did not appreciably affect the humus content. There was no evidence 

 of appreciable accumulation of humus in the lower depths of the soil as a 

 result of leaching; there was no evident correlation between the humus content 

 of the soil in the mulched basins and the amount of fruit produced ; and there 

 was no evident effect of lime on orange production. "Alfalfa and bean-straw 

 mulch in basins on the heavier soil types produced from 30 to 100 per cent more 

 oranges per tree than manure mulch. Manure mulch produced more oranges 

 per ti-ee than either barley hay, sweet clover, bur clover, or pine shavings. 

 These differences were obtained in the summer following the application of the 

 mulches in the preceding fall." Apparently alfalfa and manure mulches had 

 no effect on fruit production of lemons during the first year on lighter soils. 



In all experiments so far conducted the mulched-basin system has produced 

 favorable growth response in a few months on the heavier soil types, a longer 

 time being required to produce appreciable response on the lighter soil types. 



" It would appear directly from the work here reported, and indirectly from 

 work elsewhere reported, that the degradation products from freshly decompos- 

 ing organic substances are more effective in orange production than the amount 

 of 'humus' formed. And the value of a given mulch does not necessarily 

 depend upon its being a legume or nonlegume." 



The relation of weed growth to nitric nitrogen accumulation in the soil, 

 L. E. Call and M. C. Sewell (Jour. Amer. Soc. Agron., 10 {1918), No. 1, pp. 

 35-U; abs. in Chem. Abs., 12 {1918), No. 5, p. 511). — This paper reviews the re- 

 sults of experimental work conducted at the Kansas Experiment Station, in an 

 effort to show that "in the past too much emphasis has been placed on tillage 

 as an agent directly contributing to the formation of nitrates through its effect 

 on [the incorporation of organic matter, the distribution of bacterial flora, 

 aeration, and moisture], and too little emphasis on it as an indirect means of 

 assisting in the accumulation of nitrates by preventing weeds from using them 

 in their growth." 



Briefly reviewing previous investigations by the senior author (E. S. R., 33, 

 p. 217), additional experimental work is described in which the nitrates in the 

 soil were determined on plats left uncultivated and weeds allowed to grow, 

 cultivated 3 in. deep, cultivated G in. deep, and left uncultivated but the weeds 



