My own opinion is, that these superphosphates are not the most economical artificial manures that could be used for wheat. They contain too little nitrogen. Peruvian guano containing nitrogen equal to 10 per cent of ammonia, would be, I think, a much more effective and profitable manure. But before we discuss this question, it will be necessary to study the results of actual experiments in the use of various fertilizers for wheat. CHAPTER XXVII. LAWES AND GILBERT’S EXPERIMENTS ON WHEAT. I hardly know how to commence an account of the wonderful experiments made at Rothamsted, England, by John Bennett Lawes, Esq., and Dr. Joseph H. Gilbert. Mr. Lawes’ first systematic experiment on wheat, commenced in the autumn of 1843. A field of 14 acres of rather heavy clay soil, resting on chalk, was selected for the purpose. Nineteen plots were accurately measured and staked off. The plots ran the long way of the field, and up a slight ascent. On each side of the field, alongside the plots, there was some land not included, the first year, in the experiment proper. This land was either left without manure, or a mixture of the manures used in the experiments was sown on it. I have heard it said that Mr. Lawes, at this time, was a believer in what was called “Liebig’s Mineral Manure Theory.” Liebig had said that “The crops on a field, diminish or increase in exact proportion to the diminution or increase of the mineral substances conveyed to it in manure.” And enthusiastic gentlemen have been known to tell farmers who were engaged in drawing out farm-yard manure to their land, that they were wasting their strength; all they needed was the mineral elements of the manure. “And you might,” they said, “burn your manure, and sow the ashes, and thus save much time and labor. The ashes will do just as much good as the manure itself.” Whether Mr. Lawes did, or did not entertain such an opinion, I do not know. It looks as though the experiments the first year or two, were made with the expectation that mineral manures, or the ashes of plants, were what the wheat needed. The following table gives the kind and quantities of manures used per acre, and the yield of wheat per acre, as carefully cleaned for market. Also the total weight of grain per acre, and the weight of straw and chaff per acre. Experiments at Rothamsted on the Growth of Wheat, Year After Year, on the Same Land. Table 1.--Manures And Produce; 1st Season, 1843-4. Manures and Seed (Old Red Lammas) Sown Autumn 1843. Manures: FM Farmyard Manure. FMA Farmyard Manure Ashes.[1] SiP Silicate of Potass.[2] PhP Phosphate of Potass.[3] PhS Phosphate of Soda.[3] PhM Phosphate of Magnesia.[3] SPL Superphosphate of Lime.[3] SAm Sulphate of Ammonia. RC Rape Cake.