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In-field estimates of green leaf area index for treatments with varying amounts of yellow rust (Puccinia striiformis (Westend.)) were directly proportional to laboratory measured green leaf area index (R2 = 0.75). The field technique depended on shoot counts and a leaf form factor (F = 0.83) which was derived from 20 varieties of winter wheat by relating the product of their leaf lengths and widths to leaf areas measured by a planimeter (R2 = 0.95). In two experiments at ADAS Terrington, UK, on the susceptible winter wheat variety Slejpner, epidemics of yellow rust ranged from nil to severe with 60 (1994) and 52 (1995) different combinations of fungicide dose and timing. Assessments of disease severity (%) integrated as the area under the disease progress curve accounted for yield differences within each season, but the relationship differed markedly between seasons. In-field assessments of green leaf area index integrated over time, or healthy area duration, showed a curvilinear relationship with grain yield (1994, R2 = 0.63; 1995, R2 = 0.73), but any healthy area duration value in the brighter year of 1995 related to larger yields than the equivalent value in 1994. Intercepted radiation by green leaf tissue accumulated after flowering (20 June in both years), estimated through the Beer’s Law analogy from field-measured green leaf area index and total incident radiation (i.e., healthy area absorption), accounted for more variation in grain yield (1994, R2 = 0.80; 1995, R2 = 0.92). There was no seasonal difference in the conversion coefficient between grain dry matter and the amount of incident radiation absorbed by green leaf tissue (1.4 g/MJ) but the intercepts of the relationships were sensitive to the date from which integration began. It is suggested that in-field green leaf area index assessments, interpreted through a simple model which provides estimates of differences in intercepted light energy, may prove useful in the analysis of experiments on disease control. © 1997 Elsevier Science B.V.

Summary Field trials to examine the effect of pea bacterial blight (Pseudomonas syringae pv. pisi) (Psp) on the yield of combining peas were carried out at five sites (HRI Wellesbourne, ADAS Rosemaund, ADAS Terrington, PGRO, SASA East Craigs) in the UK in 1990, 1991 and 1992. Healthy seed, cv. Solara, and seed naturally infected with Psp Race 2 was sown in large plots (c. 200 m2) in the open or under nets to prevent bird damage by pigeons. Despite relatively low disease severity levels (< 15% leaf area) and separation by at least 12 m of cv. Consort (resistant to Race 2) between plots there was considerable spread of disease into plots sown with healthy seed. Regression analysis demonstrated a significant relationship between yield and disease. Of the disease measurements examined, disease severity on the leaves (stipules) at growth stage 208 was found to be the best predictor of yield. A model containing environmental and bird damage terms, in addition to disease, suggested that a yield loss of 0.98 t/ha would be expected for a disease severity score of 1, equivalent to 5% leaf area affected, at growth stage 208.

There is a running joke at Tauranga-based software business Embark Open Homes that the co-founders Mark Murphy and Joshua Terrington are going to buy each other ice skates this Christmas [...]

An experiment was carried out at Terrington to investigate the effect of pre-weaning solid feed or no pre-weaning feed for suckling piglets using diets of either high or low protein levels. Previous work at Terrington with 3 week weaned pigs showed that post-weaning performance had a big effect on subsequent performance so the trial pigs were monitored through to slaughter. Research at Bristol University showed that “abrupt weaning”, i.e. no pre-weaning feed can reduce post-weaning diarrhoea.

This report was presented at the UK Organic Research 2002 Conference. Perennial weeds with spreading root systems, e.g. Cirsium arvense, are difficult to control in organic arable rotations, particularly in those without grazed leys. Competitive crops and repeated mowing are proven methods of control that can be applied to the legume fertility-building crops in stockless rotations. An experiment at ADAS Terrington in 2000 compared a standard treatment of mowing at 45 cm legume height (x4) with mowing every two weeks (x8), and mowing when thistle flower buds were visible (x3). Thistle shoot numbers counted in July 2001 were around 75% less than at start of mowing in April 2000 (mean of 9.5 shoots per m2). The results suggest that achieving and maintaining a dense competitive crop has more influence than mowing frequency on creeping thistle survival under a clover fertility-building crop.

This is the final report of Defra project OF0145. If organic farming is to expand in the arable east of England, where the knowledge, infrastructure and capital for livestock are not available, viable stockless systems will be needed. The aim is to maximise economic performance and in turn encourage conversion. Project OF0112 showed that a stockless arable rotation was consistently more profitable that a comparable conventional rotation on the fertile silty clay loam at ADAS Terrington. Project OF0145 researched challenges to sustaining that level of performance into the second crop rotation. The project was a combination of systems comparison, replicated experiments and monitoring of commercial farms. The core of the project was an unreplicated systems comparison with field-scale plots to allow meaningful study of patchy problems such as perennial weeds and give confidence to farmers that the system could work on a farm scale. Conversion was completed in 1995 and the rotation has since been clover, potatoes, winter wheat, spring beans, undersown spring barley. The greatest agronomic challenges continued to be with the establishment of fertility-building legumes. Despite these problems, crop yields have been maintained with good rolling average yields of 25 t/ha for potatoes, 7.5 t/ha for winter wheat, 3.5 t/ha for spring beans and 4.1 t/ha for spring cereals. Disease levels in cereals have remained low and posed minimum threat to yields. Slugs and blight have affected potatoes in wet years; control of these is particularly difficult in an organic system leading to greater yield variability than would be expected in a non-organic rotation. Calabrese has grown and yielded well with few problems but weed control in onions proved both difficult and expensive and they have been dropped in the successor project OF0301. Weighted rolling-average gross margins show a consistent and large advantage to organic (£912/ha conventional, £1757/ha stockless with potatoes and £1148/ha stockless with vegetables). The advantage to organic has increased with time as yields and prices have been maintained whilst conventional crop prices have fallen. Soil fertility as measured by carbon and nitrogen contents has shown little change since the start of conversion in 1990. Soil available P and K have remained at ADAS Index 1 to 2 despite continued crop offtakes. However both are showing a slow progressive decline, less so with P, perhaps partly due to the rotational applications of Aluminium Calcium Phosphate. Annual weeds are proving relatively easy to control, being worst where crop growth is poor for reasons such as compaction on headlands. However, the perennial weeds couch grass, creeping thistles and docks are an increasing problem. Hand pulling of thistles and docks is containing the problem but the cost of this has risen dramatically in the last two years. The distribution of potato cyst nematodes (PCN) was mapped within all five plots in January 1998, 1999 and 2000. Sampling was in 25 m x 25 m sub-plots. In January 2000 viable cysts were found in 7.6 % of sub-plots, all at fewer than 10 eggs per g of soil. There was no evidence of a significant multiplication of PCN following potatoes. Growing a variety other than the resistant Sante may have allowed multiplication. A manure utilisation booklet was compiled in association with Elm Farm Research Centre. The text was agreed with MAFF in May 2001 and it should be published by July 2001. Specific challenges deserving further study include: • The ecology of perennial weeds and agronomic strategies for their control. • Quantification of net nitrogen fixation by legumes and subsequent release to crops. • The impact of potato cultivar on PCN multiplication. • Better and more reliable grain quality. • Control of slugs and potato blight. The development of companion and bi-cropping systems for arable rotations (linked to results from OF0181 and OF0173).