H.—34.

solubility in dilute acids of certain iron compounds which have been used as stock-licks with apparently good results on land where bush-sickness or allied stock-ailments have caused serious trouble ; (6) the effect of fine grinding on the solubility of iron compounds in dilute acids ; (c) the amounts of soil iron which can be extracted by dilute acids from typical samples of all the soil-forming volcanic showers in the Central North Island Territory. In earlier reports it has been shown that 5 per cent, oxalicacid solution extracts very different amounts of iron from typical bush-sick soils on the one hand, and from other volcanic soils which have been considered healthy by stock men. This strength of oxalic acid has been employed to determine the solubility of limonite, spathic iron-ore, and magnetite, the former two of which have been shown to be helpful in combating bush sickness. The results of the analyses, using this reagent, have shown that in the case of limonite relatively large amounts of iron were extracted, but in the case of ferrous carbonate the quantity of iron extracted by this reagent was relatively small. The analyses have also shown that even 1 per cent, oxalic acid extracted a large amount of iron from limonite and that the fineness of grinding of the limonite ore materially affected the analytical results. The results indicated that in order to secure maximum solubility the limonite ore should be ground to pass a sieve with not less than sixty meshes to the inch. In view of the fact that hydroxide of iron must form a considerable percentage on well-aerated soils of the more easily soluble iron compounds, the use of dilute oxalic acid would appear to be valuable in determining the relative amounts of more easily available soil-iron compounds in different volcanic soils. A number of determinations on different volcanic soils using both N/10 oxalic acid and N/10 hydrochloric acid indicated that the results obtained with oxalic acid were more consistent with the known iron deficiencies of the soils. The Available Iron Content of Typical Bush-sick Soils—Determinations of available iron, using N/10 oxalic acid, have been made on nine typical bush-sick soils. The soils comprise a sample from the granite formation at Glenhope, Nelson ; a sample from the Kaharoa series at Waerenga, Rotorua ; and°seven samples from different locations on the Taupo series of soils. In every case bush sickness has caused serious trouble, and in several instances has greatly hindered the use of the land for animal husbandry. In the case of the nine samples, the percentages of available iron range from 0-43 to 0-69, giving an average figure of 0-57 per cent, iron oxide (Fe 2 o 3 ). The lowest percentages were found in the case of the Glenhope granite soil and the Kaharoa sample. The Taupo samples, with one exception, were considerably higher in available iron. Determinations of available iron made on three other samples taken from properties on which bush sickness, although present, did not give serious trouble showed a somewhat higher percentage of iron. The percentages in the three samples range from 0-71 to 0-82 iron oxide (Fe 2 o 3 ), the average being 0-77. Estimation of Available Iron in Typical Healthy Volcanic Soils.—A large number of soil-samples taken from other volcanic-soil types on which bush sickness is not known has been examined and the amount of available iron soluble in N/10 oxalic acid has been determined. Four samples taken from the Rotomahana series showed a variation in iron of 1-51 to 1-82 per cent., the average percentage being 1-61 iron oxide. Three samples from known healthy locations on the Mairoa series gave figures varying from 1-97 to 2-24 per cent., the average being 2-15 per cent, iron oxide. In the case of the Tongariro series two samples of soil gave 1-68 and 2-35 per cent, iron oxide respectively. Five samples of soil taken from different locations in connection with the Egmont volcanic soils gave figures ranging from 1-38 to 2-5 per cent, iron oxide, the average being 1-94 per cent. In the case of the Hamilton series, four samples of soil taken in the vicinity of Hamilton and Te Awamutu gave figures varying from 2-9 to 3-80 per cent, iron oxide, the average being 3-34 per cent. Two samples taken from the Tirau series near Putaruru ga.ve 1-29 and 1-32 per cent, respectively of iron oxide. A sample taken from Eskdale, on the Taupo series, and which is stated to be healthy for stock, contained 1-12 per cent, of iron oxide. Several samples taken from the healthy soils of the Waikato Plains gave figures ranging from 1-74 to 2-50 per cent, The results of the iron estimation made on bush-sick soils and healthy volcanic soils definitely show much lower percentages of iron soluble in N/10 oxalic acid where bush sickness occurs, and the use of this reagent appears to have considerable value in predicting the probable incidence of bush-sickness or healthiness of soil in the case of land which is in process of development. Further confirmation of the association of comparatively high iron figures on healthy volcanic soils is provided from our examinations of soils taken from what are known as " change " fields. These fields are used as change pastures for ailing stock in districts where bush sickness is experienced. They have been found by experience to enable recovery of the affected animals to take place in a comparatively short time. Five samples taken from Hamurana, from lakeside flats, Rotorua district, and from Tirau, all gave comparatively high figures for available iron. The percentages range from 1-29 iron oxide to 4-26, the average being 2*Bl. Field observations in conjunction with estimations of available iron have shown that variations in the amount of available iron may be experienced on any property located on those showers which are known to be associated with bush sickness. The presence of a coating of Rotomahana ash even of a depth of 3 in. confers distinct benefit to the soil in so far as stock is concerned. The outcropping of underlying volcanic showers higher in available iron is thought to be responsible for the freedom from bush sickness of certain areas on different farm properties. The action of streams and rivers in resorting volcanic-ash material and in depositing fragments of rock brought sometimes from a considerable distance has in a number of cases resulted in the formation of soils healthy to stock. These soils contain much larger amounts of available iron than typical volcanic-ash samples which have not undergone resortment.

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