wet seasons. If the topography be one of very sharp ridges and valleys, or of steep slopes, leaching will be modified in two directions: (1) The ratio of soakage to run-off will be lowered, less water sinking into the soil, or sinking through in more restricted areas; (2) The water which does soak through and leach the higher levels will often seep out again, bearing its load of soluble plant food to the plants at lower levels. In such a case where seep-age springs and creeks are bordered by swampy pasture, even in rela-tively small areas, stock having access to the pasture do not develop iron starvation. If the springs are localized, or the streams sharply entrenched so as to leave no room for wet seepage or unaerated soil pasture, the incidence of the disease is but little affected.

Some examples of how the various factors operate together to produce the different degrees of iron starvation actually observed may be given. On portions of the Kapakapa Road, and at Te Pu and Ngawaro (Rotorua County), perhaps the most acute degree of the disease is manifest. All the factors enumerated are present (see N. Z. Journal of Agriculture for January, 1925, p. 2). The situation is relatively high above permanent water, the soil is a fine gravelly sand or a coarse sand, the substrata are pervious, consisting of sands and tuffs, the topography is that of a plateau, or is gently valleyed and hummocky, and the rainfall is heavy, resulting in a leached soil and an absence of springs and seepage areas.

At Mamaku, the chief factor modified is the texture of the soil, which is a sandy silt, rather fine and less pervious than the soils mentioned above. Sickness is less acute, but still severe (see N. Z. Journ. Agr., vol. 29, November, 1924, page 324).

At Oturoa the soil is finer, being a sandy loam, and the altitude less. Springs and creeks occur. Sickness is absent or of a light degree.

Farms at the blind ends of Kapakapa and Kaharoa Roads, and in parts of Ngawaro and on the northern side of Rotoiti Lake, are either free, or exhibit only a mild form of the trouble. The soils and other factors are practically the same here as in other parts of the Kaharoa and Ngawaro districts, with the exception of topography, which is usually found to be well dissected, with springs, swamps and seepage areas, and streams.

At Hamurana, and generally on the low-lying land bordering the lakes, not only is no sickness found, but sick animals from other areas recover quite rapidly. The soils vary from sandy silts to fine gravelly sands, and the only modified factor appears to be the altitude above permanent water, which is often but a few feet, or even inches, and in winter some land may be submerged. Springs, seepage areas, and swamps, occur under the hills and higher terraces to the lake edge.

The higher terrace lands, which are intermediate in altitude and position between the low-lying healthy lakeside soils (as at Rotorua) and the high sick soils (as at Mamaku) are also found to be inter-mediate as regards the incidence of sickness.

(b) Texture of the soil: Of the two possible ways in which this could be amended—namely, by increasing either the clay or the humus —the latter is alone likely to be practicable. As recommended by Aston (N. Z. Jour. Agr. for August, 1912, p. 122, May, 1912, p. 377, and August, 1924, p. 90) of all avenues open to the farmer, green manuring appears to be the most immediately promising for diminish-ing the trouble. By this means a closer and less pervious structure is given to the soil, the store of material capable of reducing the insoluble ferric to the more soluble ferrous form of iron salts is added to, and the general fertility of the soil increased. Somewhat the same end is attained by the establishment of a close and well-compacted turf of approved pasture plants; and it is probably for this reason that with ageing of the pasture iron starvation generally diminishes, while reploughing and resowing is said frequently to produce a tem-porary return to a more acute stage. Rolling, trampling by stock, or other means of consolidation also should be beneficial, both by decreasing the air space in the soil and by tending to restrict soakage and leaching.

(c) Neither the nature of the substrata nor (d) the amount of rainfall, nor (e) the general nature of the topography are factors amenable to practical control.

(f) Building up of the store of iron in the soil should be aimed at, even though much of it may be rendered for the time being practically unavailable. Especially is the use of basic slag (or, better still, of a slag super mixture), or a mixture of iron sulphate with superphosphate likely to be beneficial, as the phosphate encourages root growth, and by bringing the roots into close association with the iron, may tend towards a greater degree of absorption. Mr. Aston has recently recommended the trial of “ferrous superphosphate,” a mixture of superphosphate, sulphate of iron (hydrated ferrous sul-phate), and hydrated sulphate of lime (gypsum). This mixture contains 12 per cent. of iron sulphate (see Griffiths's Treatise on Manures, 1892, p. 283, Whittaker, London).

(g) The utilization of any areas of seepage, swamp, or river flat existing on “bush-sick” farms should be zealously aimed at, pasture grown under such conditions being usually rich in iron and an anti-dote to the sickness.

To make his paper complete, the reviewer here summarizes some of the remedial treatment recommended or adopted at the Government Farm, Mamaku, as the result of many years' experience of officers who have assisted in this investigation, together with some recommenda-tions of his own. This may be compared with the last authoritative advice published by the Department (see N. Z. Journ. Agr., vol. 33, p. 98):—

“(1) Farm more highly; get the plough in; compact the soil; grow plenty of winter feed, and save plenty of hay; subdivide into smaller paddocks, and keep the pasture eaten short. Topdress with phosphate—preferably containing iron, or in conjunction with iron sulphate—as frequently as is the practice to topdress in the Waikato. Treat the stock well, especially in the matter of water-supply.