Advantages and disadvantages of different break crops in organic grass/arable rotations (OF0143)

Summary

This is the final report of Defra project OF0143.
Choice of break crops to grow in addition to cereals and the fertility building phase is crucial to the agronomic and economic success of organic arable rotations. There are four specific functions that a break crop may perform, namely: addition, conservation and cycling of nutrients; pest and/or disease control; weed control and improvement in soil physical characteristics. Individual break crops may perform one or several of these functions. A good break crop must also produce satisfactory yields, be of marketable quality and produce an economic return for the farmer.
This project analysed the overall suitability of new break crops by simultaneous assessment of key agronomic, economic and environmental factors. The objectives of the project (in brief) were as follows:
1. To review the scientific literature in order to evaluate known agronomic advantages and disadvantages of 15 potential break crops for organic grass/arable rotations.
2. To evaluate the economic potential of these 15 crops.
3. To assess the suitability of nine different break crops (and oat control) grown between winter wheat and spring barley in small scale experimental plots in seven replicated field trials throughout the UK.
4. To evaluate a further diversified arable/grass rotation which includes three break crops (potato, carrot and swede) with and without grazing livestock.
5. To assess consumer acceptability, organoleptic characteristics and market potential of crops produced in the large scale field trials described under Objective 4.
Main project findings
• Yields of individual break crop varied greatly between the seven different trials
• Break crop yields were strongly correlated with soil nutrient concentrations
• Cereal yields were affected more by soil fertility status than by preceding break crop
• Over 50% of break crops were deficient in N, P and/or K (according to established values for nutrient concentrations for healthy crops) with N deficiency being the most common. Subsequent cereal crops mostly had adequate nutrient concentrations, although some were deficient in trace elements
• Break crops suffered varying degrees of pest and disease pressure. Hemp and linola had almost no recorded pest/disease damage at any site. Swede, rape and potato were severely affected by pests and/or diseases on most sites
• Different weed burdens were recorded in different break crops. Limited meaningful conclusions can be drawn from this result for five of the crops tested (bean, carrot, potato, swede, sugar beet), due to the different weed control practices at different trial sites.
• Significantly lower weed burdens were recorded in cereals following hemp and linola.
• The break crops with the highest potential net margin grown in this study were carrot, swede and potato.
• The break crops with the lowest net margins based on 1999 prices were sugar beet and oilseed rape (osr price included an assumed 50% organic premium); organic premiums are now (2002) available for sugar beet.
• Crop quality and yields (and therefore economic returns) from carrot and potato from field scale trials run on a commercial organic farm were much higher than those from small scale plot trials
• All samples of marketable crop (carrot and potato) from the small scale plot trials and field scale trials were classed as acceptable for human consumption under Tesco's current quality standards for organic produce.
The executive summary at the start of the main report includes a summary of the properties of the nine test break crops
Further work is required in order to investigate some of the less well-documented break crop characteristics such as allelopathy (hemp, lupin). It is possible that new varieties bred specifically for organic agriculture may perform better than the varieties used here and additional research is required to investigate this potential. Long-term trials are also needed if reliable conclusions are to be reached on the performance of break crops in different UK climatic areas and soil types.