This is the final report of Defra project OF0187. The attached report starts with a detailed Executive Summary, from which this text is a short extract.
The aim of this experiment (1999-2001) was to investigate the agronomic effects of applying treated and untreated farmyard manure and slurry to an organically managed, upland clover/ryegrass pasture. Seven main treatments were imposed in a split plot, randomised complete block design, simulating inputs from organic and conventional systems at ADAS Redesdale. The main treatments were; composted (Treatment A) and uncomposted (B) FYM; aerated (C) and unaerated (D) cattle slurry; ammonium nitrate (E); and a zero nitrogen control (F). A further control treatment (G), to which slurry was applied only in 1996, was added to provide a common control treatment during an earlier phase of the experiment. Target application rates were 150 kg total N/ha for untreated slurry and FYM treatments. Following aeration, the same volume of slurry as for the unaerated slurry treatments was applied. Allowing for losses, composted FYM was applied at a rate calculated to supply 80% (120 kg/ha) of total N compared to the untreated FYM treatment. Ammonium nitrate was used as a conventional control treatment, applied at an annual rate of 240 kg/N/ha.
To determine the effect of phosphate and potash, one half of the plots were supplemented when soil levels of these nutrients fell below theoretically optimum levels. Highland Slag and Seagreen K were used as organic sources of P and K, while muriate of potash and superphosphate were used on the conventionally managed plots. Application rates were based on the results of soil analysis, according to standard recommendations for organic (Glenside Organics, Ltd) and conventional (Anon. 2000) production.
Overall, the results indicate that high clover swards and the return of major nutrients in slurry and FYM can support a high level of productivity from an organically managed pasture, without the requirement for exogenous fertiliser inputs. Under a conservation system of management, it was clear that soil potassium could be a major limiting factor to herbage yield. However, FYM/slurry maintained an acceptable concentration of herbage K, despite a Soil Index of 0/1. The information generated on nutrient cycling, on output and other measures of productivity raises questions as to the optimum level of soil nutrients required for organic production, the role of soil microbial activity and the potential to better exploit composted FYM. The balance of crop offtake from more modest yields, with nutrients released from the soil, may dictate that high levels of extractable nutrients in the soil may not be a prerequisite for good performance from an organic system
