For Au^u>l, 1121 



677 



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A Lesson on the Conservation of Plant Food in Soil | 



Being One of a Series of Lessons of ;i Home Study Course on Gardening Appearing Regularly in The Gardeners' Cjironici.e 1 



Under the Direction of ARTHUR SMITH 1 



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SO far as crop raising is concerned, the advent of Sep- 

 tember, or earlier, brings a cessation from seed sowing 

 out of doors in the more northern parts of the country; 

 but it does not, or should not, bring about a cessation from 

 gardening. 



Each season of the \ear has its own special work which is of 

 the utmost importance at that time, but there is no period of 

 greater importance than the Autumn because the effects of what 

 is done, or left undone, then are felt for good or evil through- 

 out the entire following year. 



There are far too many garden owners, both large and small, 

 who think that when the cropping season is over there is little 

 or nothing to do in a garden until the following Spring. This 

 idea is a complete fallacy, and all real gardeners find themselves 

 just as busy during the Autumn as in the Spring. One cannot 

 put too much emphasis upon the ^reat benefits connected with 

 making every possible use of the I'all season. There are many 

 things which can be better done then than at any other time; 

 there are other things which must be done then or thev can- 

 not be done at all ; and the .\utumn is the best time to carry 

 out all kinds of permanent planting and other improvements or 

 extensions. 



From the point of view of economy and of continually increas- 

 ing permanent soil fertility the conservation of plant food is at 

 this season of great importance. 



-A properly cared for vegetable garden — and it is to this de- 

 partment which our remarks now mainly refer — will have been 

 kept free from weeds and the ground between the plants re- 

 ligiously cultivated througliout the season. This cultivation not 

 only prevents the existence of weeds and renders watering less 

 necessary, but the continual stirring of the ground greatly 

 assists in bringing the plant food which the soil may contain 

 into an available condition. 



Like all other livi'"!.g organisms, plants require for their sus- 

 tenance food containing several ingredients, hut unless some pro- 

 portion of all these ingredients exists in the soil in a proper 

 condition for the plant to make use of thev might just as well 

 not be there at all. The great difference between the available 

 and the unavailable plant food of a soil is the reason for the 

 fact that a chemical analysis of a soil gives no criterion of its 

 fertility, although such analysis may give some idea of a soil's 

 potentialities in that direction. 



Not only do plants require several different food elements 

 for their growth but these elements are required in certain pro- 

 portions and excess of one or more will not compensate for 

 deficiency in others. Every species of plant has practically the 

 same composition wherever it may be grown, and from this we 

 know how much of any element a crop of a given weight will 

 remove from a given area of .ground. For example a medium 

 crop (150 bushels) of potatoes removes twenty pounds of phos- 

 phoric acid from an acre, but as plant roots do not come into 

 contact W'ith all the soil it follows that there must be considerably 

 more than twenty pounds of phosphoric acid available in an acre 

 to enable this amiunit of potatoes to be produced. Tt has been 

 estimated that there must be four times the quantity of plant 

 food in an available state than is used to produce a crop of a 

 given bulk ; therefore when a crop is removed there is always 

 a con.-;idcrable quantity of plant food in an available state re- 

 maining in the soil. It also follows as a matter of course that 

 the larger the crop the larger is the amount of available plant 

 food remaining unused. 



If the ground is allowed to remain bare with nothing growing 

 upon it then nndoubtedlv the greater part of this unused avail- 

 able plant food is wasted by being washed down into the subsoil 

 by Autumn rains, the waste being greatest upon a .sandv soil 

 and least upon one of a clayey nature. Further, available nitrogen 

 is lost with much greater ease than other food ingredients. In 

 this _ connection Dr. Russell, of the Rothamsted Experimental 

 Station, has carried out some epoch-making experiments con- 

 cerning the loss of nitrogen in drainage water. As the results 

 of his investigations, he fcnmd that from .September 13 to I'ebru- 

 ary IS, the richest soil Ic^t the equivalent of S04 pounds of 

 nitrate of soda per acre, and the poorest lost the equivalent of 

 168 pounds of nitrate of soda per acre; this makes the average 

 loss to be practicallv fifteen dollars per acre in nitrogen alone. 



Good treatment of the soil not only benefits the crop crowing 



upon it at the time but also may be of considerable advantage 

 to the crop of the foUowin.g year. How great this advantage 

 may be will depend upon whether the garden is totally neglected. 

 or the reverse, after the crop-growing season is over. 



One of the most important features of Autumn gardening is the 

 using up of the plant food remaining unconsumed and preventing 

 it from being lost, and it is this which the growing of cover 

 crops accomplishes. 



In this connection a large-scale experiment was carried out 

 in Britain during 1916-1917 by Professor Wibberley on a field 

 of ei.ght acres. During the Summer of 1916 the entire field was 

 under the same crop. At the end of Summer part was sown 

 to a green crop and the remainder left uncropped. The green 

 crop was eaten oft' by sheen during March and early April. Imme- 

 diately after, the entire field was manured and cultivated uni- 

 formly throughout and planted at the same time with the same 

 variety of potatoes. Tlie crops at the end of the experiment 

 were carefully weighed, with the result that the portion under 

 cover-crop gave 360 bushels per acre and the portion uncropped 

 263 bushels per acre. A very striking illustration of the waste 

 which goes on when land is left uncropped during Autumn: 

 and in all cases the more open the Winter and the later the 

 soil freezes up the greater the waste. 



Another feature of importance in connection with Winter cover- 

 crops, especially in wet Winters when the ground is not frozen 

 up for long at a time, is that these crops, owing to leaf evapora- 

 tion and root action, help to dry the land in readiness for preparing 

 it for the succeeding Spring crop. 



Seed for the production of a cover-crop should be sown upon 

 all ground immediately after a crop for use is finished and there 

 is no further time for another one to mature for that purpose. 

 If there is only a narrow strip vacant it should he sown, followed 

 from time to time by other strips until the entire vacant ground 

 in the garden is covered. Sowing broadcast is the best method 

 so that all the soil is evenly covered. 



In deciding what species of plants should be sown for a cover- 

 crop we must bear in mind what we wish to accomplish and 

 what is possible to attain by it; having regard also to climatic 

 conditions as to whether the crop is wanted to live through the 

 Winter and make some Spring growth or whether it is intended 

 to turn it under before the ground becomes frozen up. 



First we want to use up the available nitrogen, phosphates and 

 potash remaining in the soil, and we can at the same time also 

 add nitrogen to the soil by the use of some kind of leguminous 

 plant. For the latter purpose Crimson Clover will answer for 

 sowing during August and September ; subsequently Winter 

 Vetch can be used. As these and other leguminous plants obtain 

 their nitrogen from the atmosphere, and are termed nitrogen 

 .satberers, it is doubtful if they make any use whatever of avail- 

 able soil nitrogen. To conserve the latter some plant which is 

 a user of soil nitro.gen, such as rye, should be sown at the same 

 time. Piuckwheat and rape are also good to mix in as they arc 

 good fora.gcrs and their root action is such that there will be 

 little available plant food escape them. 



The value of the rye and vetch combination for late sowing as 

 a soil renovator is very great, especially upon light soils. The 

 Winter vetch will frequently grow where other le.gumes will not 

 and as a nitrogen gatherer it is at least equal to any others of 

 its family. It has the further qualification of being extremely 

 hardy and succeeding in the more northern parts of the country. 

 The vetch may, as above noted, \k sown later in the Autumn than 

 the clover and will furnish a greater qiianlity of matter for 

 the production of humus after bein.g turned under in the Spring 

 than anything else, but the crimson clover combination is prefer- 

 able for early I'all sowing as it makes more growth before 

 Winter. During the Autumn the vetch appears to spend its 

 energies in making root .grow-th rather than top and is fre- 

 quently scarcely visible when Winter sets in. While the clover 

 is often Winter killed it grows more or less rapidly during the 

 Fall. 



For tlie earliest Spring sowin.gs the first planted cover-crops 

 hould be deeply spaded under just before hard frost prevents 

 the operation being carried out so that the vegetable matter of 

 the cover crop may have time to decay, and under ordinary 

 conditions this portion of the ground will not require spading 

 (Continued on /•a.ci" 679) 



