rERSlSTRNCE OF AKSENITE. 32/ 



Retention of Arsenite in the Soil. 



For spraying fruit trees, arsenical compounds which are 

 relatively insoluble {e.g. arsenate of lead) are used as a rule; 

 but for the destruction of the house-fly a soluble compound like 

 arsenite of soda is clearly desirable on account of its quicker 

 action on the flies, and the greater likelihood of its being carried 

 away under the leaching influence of rain. 



To get some idea of the effect and persistence of arsenite of 

 soda in varying quantities in the soil, two series of experimental 

 plots were started. May, 191 5, at the Entomological Experiment 

 Station at Rosebank, C.P. The plots (including two control 

 plots for each series) were 16 feet long b}' 6 feet wide, and 

 separated by isolation plots 3 feet wide. The plots in the first 

 series were treated with arsenite of soda at the rate of 500, 400, 

 300, 200, 100, 50, 25, 12^, 514 pounds per acre, prepared as for 

 fly bait, according to the formula given above, and mixed with 

 stable manure at the rate of 10 tons per acre. The plots in the 

 second series were treated with the same strength of arsenite of 

 soda dissolved in water and applied evenly by means of a 

 garden syringe. In comparison the two series would show 

 whether the presence of the sugar and the manure increased or 

 decreased the injurious effect of the arsenite. After the applica- 

 tion of the poison, the ground in each plot was w^ell dug over 

 (8-10 inches deep), and the following seeds and transplants were 

 ])lanted across the line of the plots so as to insure uniformity : — 

 Wheat, oats, barley, ny^e, maize, peas, beans, potatoes, and 

 cabbage. 



The ground had been trenched to a depth of 2 to 3 feet in 

 1913, forming a deep, stiff, clayey soil. The plots are nearly 

 level ; but a few yards beyond the second series the ground slo})es 

 off rapidly, so that both series are fairly well drained. The 

 annual rainfall is approximately 25 inches, the rainy season 

 extending from May to October. 



Results. 



All the plots were kejjt under close observation by Mr 

 C. P. van der Merwe, who was then Assistant Entomologist, and 

 in immediate charge of the work, and myself. The results show 

 that in the stronger plots (500, 400, and 300 lb. per acre) the 

 transplants, as well as the seedlings of all kinds, presented a 

 very sickly, spindly appearance from the start, being stunted in 

 growth, and of a reddish yellow colour, especially at the tips and 

 along the edges of the leaves. On the whole, the sickly apjiear- 

 ance was less pronounced from plot tO' plot as the strength of 

 the arsenite decreased ; but there was not much to choose between 

 the 500, 400. and 300 lb. plots. In the 200 lb. plot the injury 

 was less severe, and in the 100 lb. plot only noticeable. In the 

 weaker strengths no injury was manifest in com]~)arison with the 

 control and the isolation idiots. 



