Field microplot studies were conducted under zero-till conditions on a fine sandy loam (Orthic Black Chernozem) to determine the effect of the urease inhibitors N-(n-butyl) thiophosphoric triamide (NBPT) and ammonium thiosulphate (ATS) on volatile losses of NH3 from urea and urea ammonium nitrate (UAN). Two studies were conducted, one in late May and one in early August. Losses of NH3 were measured on days 1, 2, 4 and 7 after fertilizer application, using ammonia traps. Ammonia losses were higher in the second study due to the higher soil temperatures and lower soil moisture later in the growing season. Total NH3 losses increased in the order Control < UAN + NBPT = Urea + NBPT < UAN + ATS = UAN < Urea. Total loss of NH3 during the 7 d after fertilizer application was higher from urea than from UAN, particularly in the first study. Use of NBPT was effective in reducing NH3 volatilization from both UAN and urea during 7 d after fertilizer application while use of ATS had little influence on NH3 loss from UAN. The NBPT may delay losses by slowing the hydrolysis of urea, but volatilization may persist for a longer duration. The delay in urea hydrolysis could allow time for rainfall to carry the urea into the soil, thus reducing total volatilization losses from surface fertilizer application. Key words: N-(n-butyl) thiophosphoric triamide, zero tillage

The late D. B. Edmond was a pioneer in New Zealand of systematic investigations into the influences of treading on pasture. His published work and data in preparation at the time of his dealh are reviewed by colleagues in Grasslands Division, DSIR, and the direction of further work in this field is indicated.

. 2001. Influence of source, timing and placement of nitrogen on grain yield and nitrogen removal of durum wheat under reduced-and conventional-tillage management. Can. J. Plant Sci. 81: 17-27. Effective fertilizer management is critical to maintain economic production and protect long-term environmental quality. Field studies were conducted over 4 yr at two locations in southwestern Manitoba to determine the effect of source, timing and placement of N on grain yield and N recovery of durum wheat (Triticum durum L. 'Sceptre') under reduced-tillage (RT) and conventional-tillage (CT) management. The effect of N management on durum grain yield and N recovery differed with soil type and tillage system. On the clay loam (CL) soil, lower yields with fall-as compared with spring-banded N were more frequent under RT than CT. Lower yields occurred more frequently with fall-applied as compared with spring-applied urea ammonium nitrate (UAN) than when urea or NH 3 was the N source. On the drier fine sandy loam (FSL) soil, fall applications of N generally produced similar to higher grain yield than did spring applications. Differences among fertilizer sources and tillage systems were much less frequent with spring than fall applications of N. Where differences occurred, durum grain yields were higher with insoil than surface applications of urea or UAN. In-soil applications of urea and UAN increased durum grain yield as compared with surface applications more frequently under RT than CT on the CL soil where yield potential was high, whereas increases on the FSL were as common under CT as under RT. On soils with a high yield potential, enhanced immobilisation and/or volatilisation of surface-applied N may reduce grain yield by reducing available N, particularly under RT. Selection of a suitable source-timing and placement combination to optimise crop yield may be more important under RT than CT. . La fumure minérale doit être conduite de façon, à la fois, à maintenir la production à un niveau rentable et à préserver à terme la qualité environnementale. Des travaux au champ réalisés sur une période de 4 ans à deux emplacements du sud-ouest du Manitoba avaient pour objet d'établir l'effet de la forme d'utilisation et de la période et du mode d'épandage de N sur le rendement grainier et sur l'exportation de l'azote par une culture de blé dur (Triticum durum L. 'Sceptre') conduite en régime de travail réduit (TR) et de travail classique (TC) du sol. L'effet des modalités de conduite de la fumure sur les deux paramètres étudiés différaient selon le type de sol et selon le régime de travail. Sur loam argileux (LA), les rendements étaient plus fréquemment moins bons après épandage d'automne en bandes latérales qu'après l'é-pandage de printemps en régime TR qu'en régime TC. De même, il était plus fréquemment moins bon en épandage d'automne que de printemps quand N était fourni sous forme de nitrate d'ammonium-urée (NAU), plutôt que d'ammoniac anhydre. Sur le loam sableux fin plus sec (LSF), la fumure d'automne donnait, en général, d...

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To cite this article: K. R. Brown (1968) The influence of herbage height at treading and treading intensity on the yields and botanical composition of a perennial ryegrass-white clover pasture, New Zealand Journal of Agricultural Research, 11:1, 131-137, DOI: 10.1080/00288233.1968 ABSTRACTThe effects of sheep treading and herbage cover at treading on the yield and botanical composition of a perennial ryegrass-white clover pasture were assessed at four rates of treading.Where pasture was trodden before the herbage was removed, compared with treading pasture after defoliation, higher yields of total herbage and sown species were recorded in winter and spring, but not in autumn and summer.At the highest treading intensity marked reduction in herbage yields were recorded in all seasons, but at treading intensities of 24 sheep equivalents per acre or less, reductions were much less marked in some seasons.The implications of the results obtained on extrapolations from experimental treading investigations to farm practice, on the significance of herbage cover at treading in farm practice, and on farm management systems, are discussed.