Simulation of Herbicide Persistence in Soil

.\. WalkerTable 3. Simulation of linuron persistence in uncropped plotsDatesprayedResidue (kgi ha)Dose Weeks after(kg/ha) application Observed Simulated12.6.645.8.&28.tO.6425.5.65zt.t.6J2.24t.t2l 68I .68I .680807l206t2l82329080bl21.820. 9l2.52| .47t.262.66l .541 .260. 98r .050.77l .401 .332.943.36.3.992.24r.042.16l.200. 902. 58l .931.55| .250. 990. 64) ?fI .042.72L59l.0la From this ooint onwards the observedata become unreliable.and linuron to this particular soil will not lead to a buildup of residues of either herbicide. Theyconfirm the conclusions of Fryer and Kirklandr that repeated applications of simazine for 5 yearsdid not alter the soil's capacity to degrade the herbicide, but the discrepancies between observedand predicted linuron residues following three applications of relatively high doses in each of fivesuccessive years suggest the possibility that some change did occur.AcknowledgementsThanks are expressed to Mr H. A. Roberts for his encouragement during this work and to MissP. A. Brown for technical assistance.Referencesl. Fryer, J. D.; Kirkland, K. ll'eed Res. I970, 10, 133.2. Walker, A. J. Environ. Quality 1974,3,396.3. Walker, A. Pestic. Sci. 1976,7, 41.4. Bray, G. A. Analvt. Biochem. 1960, 1,279.5. Katz, S. "/. l.rs. of. anolyt. Chem. 1967,50,912.6. Hance, R. J. Pesrlc. Sci. 1973, 4. 817.7. Usoroh, N. J.; Hance, R. J. l4eed Res. 1974, 14, 19.8. Obien, S. R.; Creen, R. E. lleed Sci. 1969, 17, 509.9. Walker, A. In Proceedings European lYeed Research Council Synposiunt, Herbicidts and the Soil Paris, 1973,p.240.10" Borner, H. Z. P.flnnzenkrankh Pfanzensthutz 1965,7?-,516.Ycgetable Rcsrccelved 19Thc effects ofof propyzamidHalf-lives in srfrom 63 to I Icapacity was fiwith the relevaprogxam, predplots were inresidues of Prtments concerthose observecomputer progJto predict theiments.z The mrare made undermoisture contenlmodel are in goobe specific to thtThe present experpropertisoil type, and to drapply to oth(in lettuce,thharvest was also (2.1. MaterialsSoils from flve fieldproperties are showrconcrete slabs sunkiof about 25 cm withraked level, andfrom the field uThe herbicide use