H.—34,

Effect of Soil-type and Fertilizer on the Iron Content of Pasture Plants. —Several series of pot experiments have been conducted at the Gawthron Institute in order to determine whether plants grown on different soils elaborate different amounts of iron in their tissue, and whether treatment with lime, superphosphate, or iron salts in any way affects the amount of iron elaborated by the plants. White clover, red clover, perennial rye, Danthonia pilosa, and Agrostis alba have all been grown on the Glenhope granite soil under controlled moisture conditions. Analyses of the plant material cut from the pots during the course of the experiment showed that the plants elaborated different amounts of iron. The highest figures for iron were obtained with white clover and perennial rye, and the lowest figures were associated with Agrostis alba and Danthonia pilosa. Red clover occupied an intermediate position. Although treatment with lime, superphosphate, and lime plus superphosphate increased materially the yield of crop, practically no difference resulted in the percentage of iron in the plants. The use of iron sulphate or iron citrate in the case of white clover, red clover, and Danthonia pilosa had practically no effect in improving the iron intake of the plants. In the case of Agrostis alba the use of iron sulphate appeared to effect a small increase in the iron content of the crop, but in the case of perennial rye the use of iron citrate seemed to depress somewhat the iron content. It must be remarked that the pots were maintained at a 70-per-cent. water saturation of the soil, and rapid growth was made by the different crops. It is possible that the somewhat high figures for iron obtained for the majority of the crops grown in the pots is connected with the rapidity of growth. The results, however, do indicate that plants have little difficulty in obtaining a supply of iron from the Glenhope granite soil and that fertilizer treatment has little effect on the intake of iron by the plants. In regard to crops grown on different soils possessing great variation in their content of available iron, the amounts of iron found in unit weights of dry matter grown on different soils did not vary greatly. In a number of cases there was a very marked difference in crop yields on all soils, but these differences were not associated with a higher iron content in unit weight of the crops. It would almost appear that crop weights are affected more by deficiency of iron than is the actual percentage of iron contained in the material grown. (c) Field Experiments at Glenhope. During the past season trials have been conducted using different drenches in the case of a new line of sheep brought in from a healthy locality and held on typical bush-sick pastures at Glenhope. At the commencement of the experiment in October, 1932, sheep were divided into four groups of seven to eight hoggets, and arrangements were made for the sheep to receive the following drenches : — Group I: Received no drench. Group II : Received a drench of iron ammonium citrate. Group 111 : Received a drench of limonite ore obtained from Onekaka. Group IV : Received a drench of Nelson soil taken from the Gawthron Institute grounds. The drenches were given twice a week, the sheep being weighed every fortnight, and notes were made regularly concerning their health and condition. The sheep receiving iron ammonium citrate were dosed with 1 fluid ounce of a 10-per-cent. solution. In the case of limonite ore a suspension was made in water and approximately 3 fluid ounces of the suspension was given as a dose. It is estimated that each dose of limonite suspension contained 3-4 grammes of iron oxide. In the case of the Nelson soil a suspension was made in water, and this was administered by bottle in a similar way to the limonite ore. In making the soil suspension approximately 1 lb. of Nelson soil was pestled with 40 oz. of water, and then 100 c.c. of the suspension was used for drenching each sheep. Nelson soil was selected for use as a drench because of its comparatively high content of available iron (6 per cent. Fe 2 0 3 , soluble in N/10 oxalic acid). With the exception of the use of different drenches, the sheep were held under uniform conditions and grazed in rotation two fields which in previous, years had been proved to be associated with bush sickness. Very favourable weather was experienced during the early part of the season, the rainfall being much lower than the normal for the Glenhope district. Up till the end of December the sheep did relatively well, and it was not until the middle of January that definite symptoms of ailment were noticed in the case of certain sheep. The average live weights for the different groups of hoggets from the 12th October up till the 16th April are shown in Table I below.

Table I. — Control of Bush Sickness: Glenhope Experiments.

21

Average Weight (Pounds). Group. Drench. j ■ Oct. 12. Nov. 12. Dec. 31. Feb. 2. March 2. April 2. ' April 16. I .. No drench .. .. 70-8 79-6 84-5 , 84-8 85-4 88-8 85-6 II .. Ferric ammonium citrate 65-3 76-3 85-3 83-5 85-5 89-0 88-2 III .. Limonite ore .. .. 65-1 77-4 84-9 j 84-6 82-3 79-7 75-9 IV .. Nelson soil .. .. 68-1 80-6 87-8 91-3 93-9 97-8* 96-6* ■ I ' * Note. —One sheep got badly staked and fell off in condition, lowering the average weight thereby.