| 1. | Control. | ||
| 2. | 1/5,000 | manganese sulphate. | |
| 3. | 1/10,000 | „ | „ |
| 4. | 1/25,000 | „ | „ |
| 5. | 1/50,000 | „ | „ |
| 6. | 1/100,000 | „ | „ |
| 7. | 1/250,000 | „ | „ |
| 8. | 1/500,000 | „ | „ |
| 9. | 1/1,000,000 | „ | „ |
(b) Stimulation in soil cultures.
[Roxas] carried out pot experiments with rice in soil to which was added varying proportions of manganese sulphate, with and without the addition of nutrient salts of ammonium, potassium, and calcium. The criterion of stimulation was the length of the growing leaves as measured daily, a strength of M/1000 MnSO4 (M = molecular weight) giving a favourable result.
In the [Hills Experiments (1903)] an increase of produce was obtained with wheat by manuring with manganese phosphate, chloride, sulphate, or oxide (MnO2), while an increase of straw was gained with nitrate, though this compound decreased the yield of corn. With barley no evidence of stimulation is set forth for any compound, except that the root growth was improved by the addition of manganese iodide, in spite of the general unfavourable action this substance exerted upon germination and growth.
[Bertrand (1905)] whose work will later be considered in detail, experimented on arable land, adding quantities of manganese sulphate (?) equivalent to about 1·6 gm. Mn to each square metre, growing oats from February to May. Increase of weight was found in the plants growing on the manganese plots, the differences in favour of manganese being
| For | total crops | 22·5%. |
| „ | grain only | 17·4%. |
| „ | straw only | 26·0%. |
A certain alteration in the quality of the grain was also noted from the manganese plots, the weight per hectolitre exceeding that from the untreated plot, the % of water and of total nitrogen being somewhat lower than that from the untreated, while the ash and the quantity of manganese present was the same in the grain from both plots. Bertrand suggested that these results might indicate a new line to follow in the study of the causes of the soil fertility.
[Strampelli (1907)] tested the effect of manganese dioxide, carbonate, and sulphate, and of a manganiferous mineral from the Argentine upon wheat, and found that while all four substances exercised a favourable influence on the vegetation, the best result was obtained with the sulphate. When however other manures were used in conjunction with the manganese compounds the balance of improvement shifted. With nitrogen, applied as nitrate of soda, manganese dioxide proved the most beneficial, with farmyard manure the manganiferous mineral[14], and with blood the carbonate. It was also found that a manganese compost did not increase production when phosphatic manure was applied as basic slag.
[Feilitzen (1907)] indicated that the nature of the soil plays its part in determining whether manganese acts as a stimulant or not. His experiments were made in the field on poor moor soil, which carried a little Sphagnum turf and Eriophorum, and which was poor in food salts. The soil was prepared and manured and then the plots were watered with a solution of ·1 gm. MnSO4 . 4H2O per litre at the rate of 10 kgm. sulphate per hectare, six control plots being left untreated. Oats were sown and the soil rolled. During growth no difference was noted between the various plots, and after harvesting the weights of the different crops showed that the manganese had not caused increase of crop in either grain or straw on this poor moor soil.
The great bulk of the work on this problem has been carried out by various Japanese investigators, whose work extends over several years. [Loew and Sawa (1902)] found that small quantities of manganese sulphate in soil cultures stimulated the growth of rice, pea, and cabbage. They suggested that soils of great natural fertility contain manganese in an easily absorbed condition, and that this forms one of the characteristics of such soils.