| No. |
| 1. Nothing plot. |
| 2. Nitrogen. |
| 3. Phosphates. |
| 4. Potash. |
| 5. Nitrogen and phosphates. |
| 6. Nitrogen and potash. |
| 7. Phosphates and potash. |
The subjects of other experiments might be such as the respective values of nitrogen in the different forms of sulphate of ammonia and nitrate of soda; phosphoric acid as superphosphate, and in an undissolved form as Thomas-slag; the relative importance of artificial and farmyard manure; the effect of manures applied at different times, as well as the effect of different quantities of the same manure; the most economical manures for different kinds of crops; and numerous other interesting problems connected with the practical application of manures.
In carrying out these experiments, care should be taken not to have the experimental plots immediately adjoining one another, as the manure applied to the one plot may, by soaking through the soil, affect the result on the adjoining plot. Especial note ought to be taken of the weather during the progress of the experiment. In order to make such experiments as valuable as possible, they ought to be continued year after year. At the conclusion of the experiment the produce obtained from each plot should be carefully weighed.
Educational Value of Field Experiments.
The educative value of such experiments is very great, and in this connection the remarks made by Mr F. J. Cooke, in a recent lecture delivered to the London Farmers' Club, are worthy of most careful consideration.
"Local experiments," he says, "teach the simple principles which should determine the selection of manures, as well as scientific accuracy and method in their use. The value of experiments is thus brought home to men who would not go far to discover it; and the practice of a few simple trials upon a correct system, each on his own farm, is encouraged. That such trials may be conducted with very little expense to the farmer, or other difficult qualifications, and yet to his great practical advantage, I will venture to assert on the ground of my own personal experience. For some twenty years I have annually conducted private experiments on a very humble scale, and am not aware of any other separate practice which has been so useful to me. It has been pursued upon two light-land farms in different parts of the same county. Yet, in respect of manurial requirements, the proper treatment for one of them has differed so essentially from the other that a common practice upon both would have been simply ruinous."
Value of Manures deduced from Experiments.
Tables have been constructed for the purpose of showing the comparative value of different kinds of manures as deduced from such experiments, and may be fittingly compared with the tables giving the trade prices. We have already quoted some of these tables in the Appendix to the chapter on Mineral Phosphates. These tables show the relative intrinsic value of different forms of phosphatic manures. In the Appendix[252] to this chapter tables showing the relative value of different kinds of nitrogenous and potash manures will be found.
Value of Unexhausted Manures.
A subject which has had much attention devoted to it of late years is the question of the value of unexhausted manures in the soil. In the Agricultural Holdings Act special provision is made for giving compensation to the out-going tenant of a farm for unexhausted manures in the soil. The Act has given rise to endless disputes between landlord and tenant, owing to the extreme difficulty of arriving at a satisfactory estimate of what the value of the unexhausted manures in reality is. The difficulty arises from the fact that we have not sufficient data available for guiding us in estimating this value, which further varies under different conditions. The fertilising ingredients of a soil are present in the soil for the most part in an inert condition, from which they are only slowly converted into an available form.