Februabt 2, 1922 



The Rorists' Review 



FERTILIZERS FOR FLORISTS' SOILS 



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PROPER USE OF FERTILIZERS. 



By DR. P. A. LEHENBAUER, 



of Illinois Experiment Station. 



A Complicated Problem. 



The practice of soil fertilization is 

 based on the fact that plants, during 

 their period of growth, take from the 

 soil certain chemical elements — a fact 

 which has been established by means of 

 repeated, rigid experiments. We know 

 rather definitely what chemical elements 

 are necessary for plant growth and, 

 therefore, it is but natural to assume 

 that in order to prevent depletion of the 

 soil, all that we need to do is to put 

 back in the soil those substances which 

 the plant removes. 



The problem of soil fertility, however, 

 is not so simple. Many factors are in- 

 volved; in fact, the question of the 

 maintenance of soil fertility is so va- 

 ried and complex that only general prin- 

 ciples can be discussed. I should hesi- 

 tate to give to a group of experienced 

 growers, such as my readers, specific di- 

 rections on how to fertilize a particular 

 crop and how to treat the soil in order 

 to get maximum results. We who have 

 been working in the experimental field 

 have learned long ago that extreme cau- 

 tion is necessary in giving advice on 

 the problem of soil fertilization and 

 that only general prin,ciples can be 

 given. There are many types of soil, 

 differing in chemical composition and 

 in physical structure, and each green- 

 house no doubt has a soil which re- 

 sponds differently, in some degree, from 

 the soil in other greenhouses. 



Under Indoor Conditions. 



The problem, therefore, is one which 

 must be solved in its details by each in- 

 dividual grower — solved with a full 

 knowledge and a true understanding of 

 the principles involved. 



The problem of soil fertilization for 

 greenhouse crops is in many respects 

 distinct from that of fertilization for 

 outdoor crops. In the greenhouse we 

 are dealing with conditions of tempera- 

 ture, soil moisture and humidity in 

 many respects unlike those outside. The 

 bacterial flora of the soil, too, probably 

 differs at times from that of the soil 

 outside. When we ndd to this the fact 

 that many greenhouse crops are grown, 

 in part or wholly, in porous pots, a prac- 

 tice which adds to the problem still 

 other complex factors, all of which must 

 be considered, we pan see that the prac- 

 tice of growing plants under glass is full 

 of uncertainties, and, from the stand- 

 point of exact information, is decidedly 

 incomplete. However, thanks to the 

 ]iainstaking labors of many investiga- 

 tors, we have a foundation of certain 

 I)rinpiples upon which we can build and 

 construct a system of treating our soils 

 so that we may be reasonitbly sure of 

 maximum results. 



For (lur greenhouse crops we have 

 been deiii>nding to a great extent upon 

 farmyard manures. From the standpoint 

 of food materials natural manures fur- 

 nish some ])liospliorus and potash, but 

 they are chiefly nitrogenous fertilizers. 

 The nitrogen is largely in the organic 

 form, a form which is not ntili/ed di- 



rectly by plants, but one which must be 

 changed first, through the agency of 

 bacteria, into an available form. The 

 rate at which this nitrogen becomes 

 available varies with a number of con- 

 ditions, such as temperature, soil mois- 

 ture, composition of soil, number of bac- 

 teria and the degree of decomposition of 

 the manure when applied. However, in 

 our greenhouses, where ideal conditions 

 for decomposition usually prevail, un- 

 questionably the nitrogen becomes 

 available quickly. 



Useful Bacteria. 



Manures, however, furnish relatively 

 small quantities of available nitrogen. 

 A ton of manure contains, on the aver- 

 age, only about ten pounds of nitrogen. 

 This nitrogen can be furnished to plants 



As fertilizers become scarcer 

 and more expensive, it is in- 

 creasingly desirable that grow- 

 ers be familiar with all the 

 needs of their soils and with 

 the best means of supplying 

 those needs, so as to use the 

 available fertilizers with the 

 greatest possible safety, effect- 

 iveness and economy. When 

 natural fertilizers were abund- 

 ant and cheap, the enrichment 

 of soil was a comparatively 

 simple matter, but the un- 

 scientific use of chemical fer- 

 tilizers is hazardous as well as 

 costly. Hence the value of the 

 information here given. 



more cheaply and probably as efficiently 

 by means of chemical fertilizers. But 

 the value of natural manures lies not 

 only in the fertilizing elements which 

 they contain. Tliis is probably the least 

 important function. Far more impor- 

 tant is the relation of manures to the 

 bacterial flora of the soil. 



Manures contain useful bacteria, 

 forms which bring about important 

 changes in the food materials contained 

 in soil, making them available to the 

 plant. We must keep in mind the fact 

 that the soil is not a dead, inert mate- 

 rial, but that in it are teeming millions 

 of living organisms, harmful as well as 

 useful, and it seems to be a function of 

 natural manures to supply the soil with 

 forms of life which make the soil a bet- 

 ter material to support plant growth. 

 At any rate, the applications of small 

 amounts of manure to soil often produce 

 effects on the crop which seem out ( f 

 proportion to the results that we should 



expect from the food elements contained 

 in the manure. 



In addition, natural manures have a 

 highly important effect on the physical 

 structure of soil. Soils with an ade- 

 quate amount of humus permit better 

 aeration, are more retentive of moisture 

 and are less subject to unfavorable tem- 

 peratures. Florists know well eiipugh 

 the importance of natural manures. Un- 

 fortunately, the supply of this valuable 

 material is comparatively small today. 

 Instead of larger quantities being avail- 

 able, the grower is being restricted to 

 smaller quantities. The problem, there- 

 fon^, is to find a substitute for this ma- 

 terial. Unfortunately, there is nothing 

 known which will entirely take the 

 place of it. From the standpoint of 

 plant nutrients, artificial fertilizers may 

 be substituted. By means of dried 

 blood, sodium nitrate, tankage, etc., the 

 nitrogen may be furnished to plants 

 readily enough. This is true, also, for 

 the other fertilizing ingredients of ma- 

 nure, such as the phosphorus and pot- 

 ash, which can be supplied by means of 

 chemical fertilizers easily enough. 



As a substitute for natural manures 

 when the latter are not available, the 

 use of sod is often resorted to by flo- 

 rists and this unquestionably produces 

 good results. The use of muek and peat 

 has been tried experimentally and fa- 

 vorable results have been reported. 



G-reen Crops for Humus. 



As another satisfactory substitute for 

 farmyard manures, green manures may 

 be used. Plowing under green crops of 

 legumes and other plants puts humus 

 into the soil and, since humus is the im- 

 portant constituent of natural manures, 

 the value of green manures is readily 

 seen. Any green crop may be grown 

 for this purpose, such as oats, rye, buck- 

 wheat, etc. It lias been determined ex- 

 perimentally that the greatest benefit 

 is derived when these crops are plowed 

 under at the half-grown stage. In other 

 words, the crop should not ho permitted 

 to mature, but should be plowed under 

 when about half mature, for by this 

 method humus is formed more rapidly 

 and the nitrates, also, accumulate read- 

 ily. The nitrates begin to accumulate 

 as soon as the green manures are con- 

 siderably decomposed. If, on the other 

 hand, decomposition goes too far — -that 

 is, if too much time elapses before the 

 soil is put to use — there is a loss of 

 humus and also a loss of the nitrates. 



The question often is raised if it is 

 profitable to use a soil continuously, 

 year after year, in the greenhouse for 

 the same crop. It is unquestionably 

 true that the practice of using new or 

 fresh soil in our greenhouse benches in- 

 volves not only a large amount of labor, 

 but also a waste of fertilizers. Much 

 of the fertilizing material ]>ut into 

 greenhouse soils is not used by the 

 plants in one season, due to the slow 

 rate of availability of some materials, 

 and when the soil is discarded the fer- 

 tilizing material is discarded with it. 

 But there are some growers who believe 

 that soils lose in productiveness after 

 one or two seasons, esjH'cially if the 



