THE MONTHLY BULLETIN. 25 



THE MAINTENANCE OF SOIL FERTILITY.* 



By W. P. Kki.ley, University nf fiilifornia, Citrus Expei'imont Station, Ilivcrsidc, Cal. 



I shall oonfino myself to a brief cliscnssion of some of the broader 

 aspects of the question of soil maintenance, dwellino: on wliat appears to 

 me to be both essential to a ])erniaiieiit system of afjrienltnre, and timely 

 at the present stage of agricultural development in California. How- 

 ever, it is not my purpose to discuss the several details involved in the 

 maintenance of a given farm. The specific rules for the best manage- 

 ment of a given tract of land necessarily vary on different farms and can 

 only be arrived at by actual experience on the farm in (juestion. Tliis 

 fact, it seems to me, is often not sufficiently recognized, either by the 

 farmer or many agricultural investigators. One of the commonest 

 inquiries at the experiment stations has to do with the management and 

 fertilization of a given soil and crop ; but unfortunately it is seldom that 

 definite answers can be given, for the reason that all the conditions and 

 previous history of the soil are seldom given, and also because experi- 

 mental experience has usuall.y been insufficiently general to warrant 

 definite conclusions. It is not quite certain, for example, -whether 

 ammonium sulfate or lime nitrate will always produce better effects, as 

 an orchard fertilizer, than organic forms of nitrogen, or whether the 

 extensive use of lime, as it is applied in the east, will or will not be 

 profitable on many fruit farms of California. 



Soil fertility has at different times been variously defined. The sense 

 in which I shall use the term is that of the crop producing powder ; and I 

 may state in passing that the crop producing power of a soil is a much 

 larger question than merely the plant food involved, although the plant 

 food is an important phase of the question. There are chemical, physical 

 and biological factors involved, each of which is equally as fundamental 

 as the plant food itself. 



We have heard much during recent years of the abandoned farms of 

 the east, and it is well known that unless the greatest care be taken, the 

 time usually comes when the yields go down. The facts that virgin soils 

 as a rule are fertile and that cultivated lands are likely to become less 

 productive are generally recognized. Here in California we are culti- 

 vating a virgin soil, comparatively speaking; but in fruit culture, under 

 artifical irrigation and perennially growing w'eather, we have a far more 

 intensive SA^stem and one that certainly makes stronger demands on the 

 soil than in the culture of field crops in the humid sections of the east. 

 The methods employed in this State, however, do not differ in principle 

 from those that have been follow^ed during the earlier years of agricul- 

 ture in older sections. The common system at the outset everywhere 

 has been that of the continuous culture of a single crop. 



The first essential to soil maintenance is that of maintaining the 

 organic matter. The humus content of California soils is low and the 

 nitrogen likewise low. but it is not so much the absolute amounts of 

 humus in a soil that determine its fertility as the processes involved in 

 the formation of hunms. Under the climatic conditions prevailing here 

 it is doubtful whether it will ever be found practicable to increase 



♦Address before State Fruit Growers' Convention, Palo Alto, Cal., July, 1915. 



