Liebig's Modern Agriculture. 



comparatively unproductive if it is not thoroughly 

 mixed with the Soil ; The roots of a crop dhninish 

 the Mineral Food in those portions of tlie Soil in 

 contact with them ; Fertility is restored to those 

 portions by ploughing and other mechanicul means, 

 which miX' the soil and allow the roots to ramify 

 freely; Reason of the value of Green Manures; 

 . Estimation of amount of Mineral Food in the Soil 

 to produce different Remunerative Crops ; Law of 

 Exhaustion in soils for different crops : Action of 

 Organic Remains in the Soil on the Mineral Con- 

 stituents ; Progress of diminution in Grain and 

 Straw of cultivated crops, when the Ash Consti- 

 tuents are not restored to the soil, and when those 

 of the Straw alone are returned ; Relation between 

 the production of Leaves and of Grain; Relative 

 proportions of Mineral Food required for Grain and 

 for Root or Leaf-producing Crops ; The increase of 

 Organic Matter and Nitrogen in the Soil by Green 

 Crops, without the addition of Mineral Food, aug- 

 ments the produce of Grain, hut hastens the period 

 of Exhaustion of the Soil ; Progress of tlie Exhaus- 

 tion of a Soil by the cultivation of shallow and of 

 deep-rooting Plants; The manner in which the 

 Subsoil contributes to the prolongation of the fer- 

 tility of land; Importance of the formation of large 

 roots after germination ; Exhausted fields in an 

 Agi-icultural sense; Fertility restored by Manures ; 

 The nature of Manures; The part played by the 

 Organic and Inorganic Matter of Manures ; Farm- 

 yard Manure. 



Letteh 9.— Constant relation between the Sulpluir 

 and Nitrogen of Organic Compounds and the Alka- 

 line Phosphates and Alkaline Earths of Cereals and 

 Leguminous Plants; Mineral substances are as in- 

 dispensable to the liife of Animals as to that of 

 Plants : Tlie amount of Phosiphoric Acid and of 

 Potasli ascertained by analysis as existing in Soils 

 is very small; The errors of Practical Teachers 

 proved from the writings of Practical Agriculturists; 

 Fertility of land cannot be maintained by Nitro- 

 genous and Carbonaceous Manures alone, but by 

 the Restoration of the Ash Constituents of Plants; 

 Critical examination of the views of Walz, a prac- 

 tical teacher, on the Nutrition of Plants; The 

 Mineral Food of Plants in Arable Soils is not Inex- 

 haustible ; The Volatile and Organic Matters of 

 Manures are not the most important ; The nature 

 of Guano and its active Constituents. 



Letteb 10.— The Empirical Agriculturist is a Trader; 

 The duties of the empirical and rational Agricul- 

 turist: Viewsof Albrecht IJlock; Rotation of Crops 

 not unimi>ortant— an Underground Crop is followed 

 by a belter Cereal; Cropping of land withoutmanure, 

 and the removal of produce, cause Exhaustion ; 

 The Spoliation system of Agriculture ; Exhaustion 

 of the lands in North America by this system ; 

 Exhaustion of the Minas Geraes Fields; High 

 farming is a more subtle system of Spoliation of the 

 Soil ; Mutual relation of Clover, Turnip, and Corn 

 Crops, and the results of removing from the lands 

 the Mineral Constituents of these Crops respec- 

 tively ; The German system of Farming before the 

 Thirty Years' War; The German three-field system 

 of rotation ; Introduction of Clover Cultivation into 

 Germany ; Opposition to its introduction ; False 

 teaching in connection with the value of maimres. 



Letter 11.— Ammonia is an element of food indis- 

 pensable to Plants; Comparison of the action of 

 Water and Ammonia ; Ammonia is an element of 

 Food and a Solvent of Mineral Matters in the Soil ; 

 Ammonia alone, or its Salts, useless to Plants, 

 without Mineral Food ; Vast amount of Ammonia 

 in Arable Soils; The 'Nitrogen' Theory of Manures; 



The error of attributing the chief value of a 

 Manure to its Nitrogen ; The reason why the quan- 

 tity of Nitrogen in Guano and Excrements may be 

 taken as a standard of their Agricultural value ; 

 Proper mode of Comparing the relative effects of 

 Guano, Ground Bones, and Chili-saltpetre ; The 

 Loss of Fertilising Matter in the Flesh and Grain 

 carried to large towns ; the constant Loss of Phos- 

 phates in the Excrements of the Inhabitants ; The 

 importation of Guano most inadequate to replace 

 this loss; Superiority of Human Excrement over 

 Guano as a Manure for Corn Fields; Tobacco, Po- 

 tatoes, and Beet-root are more exhausting to a soil 

 than Wheat ; Injurious influence of extensive Cul- 

 tivation of the Vine on the production of Corn and 

 Wheat; Effect of the Subdivision of the Land. 



Letter 12.— Modern Agriculture has no history ; The 

 reason of this ; The history of Roman Agriculture 

 shows the existence of the Spoliation system at that 

 period; The works of Cato, Virgil, Varro, and Pliny 

 inculcate, two thousand years ago, the same pre- 

 cepts that ai-e now taught by many Teachers of 

 Agriculture ; Quotations from these writers, to 

 show their opinions on tlie Exhaustion of the 

 Ground— on the different kinds of Soils, and the 

 modes of improving them— on the selection of Plants 

 for the soils which are suitable for them- on fal- 

 lowing-on the cultivation of Green Crops for ma- 

 nures—on the different kinds of manure and their 

 relative values, and modes of managing them ; The 

 various precepts inculcated of old only hastened the 

 ruin of Roman Agriculture. 



Letter 13.— The true object to be kept in view in 

 establishing Scientific Principles ; In scientific 

 Agriculture, ' Manure,' like the term 'Phlogiston,' 

 has no longer a meaning ; The cultivation of Green 

 Crops for the purpose of keeping a stock of Cattle 

 for manure is not necessary in the cultivation of 

 land; The distinction between the Necessity and 

 the Utility of keeping Cattle ; No necessary con- 

 nection exists between the production of Corn, 

 and that of Flesh and Cheese ; The fundamental 

 principles of German Agriculture quite unknown in 

 China; Chinese Agriculture; The Maimres em- 

 ployed; Great value set by Chinese on human 

 excrements— their mode of collecting and using 

 them; Ch inese compost ; Their mode of sowing and 

 transplanting Wheat : Plants cultivated as green 

 manure for Rice Fields ; Tl'.e lesson taught by the 

 Chinese system of Agriculture. 



Letter 14.— The Law of Compensation is of universal 

 application; Elementary information on Chemical 

 subjects connected with Agriculture easily im- 

 pirted ; Importance of instructing youth at school 

 in these fundamental truths; Theoretical instruc- 

 tions should always precede Practical; The proper 

 mode of instructing Agriculturists in the Theory 

 and Practice of Agriculture; The present consti- 

 tution of Agricultural Institutions very defective; 

 ThefalsepositionofScience in Practical Agriculture 

 is the result of the teachings of these Schools; The 

 demands made by Science on Agriculturists are 

 simple, and a knowledge of them cannot prove in- 

 jurious; Scienc3 demands that Agriculturists should 

 test the Truths she advances ; The Truihs in the>e 

 Letters expressed by a Formula; Thevalue of Guano 

 first discovered by Science; The establishment of 

 Reservoirs for animal excreta strongly recom- 

 mended ; Reliance to be placed upon such Excreta 

 rather than on Guano ; Chemistry can only help 

 Agriculturists after they have exhausted all the 

 means at their disposal ; Notes on supply of Guano 

 and on the Agriculture of Tuscany. 



London : WALTON & MABERLY, Upper Gowei- Streef, and Ivy Lane, 

 Paternoster Eow. 



