Speaker
Description
Introduction
Organic farming restricts the import of fertilisers to support crop and grassland production because it aims to rely on supplying nutrients to crops through managing soil fertility via rotations and the use of on-farm manures and crop residues rather than direct intervention. Designing rotations that effectively use nitrogen fixed by legumes is challenging, as the release of fixed nitrogen through mineralisation is difficult to predict. Some import of nutrients from outside the farm is allowed but restricted via certification rules. This paper explores yield, nutrient uptake and soil fertility in contrasting stocked and stockless organic farming rotations in a long-term experiment in Scotland.
Materials & methods
A replicated experiment comparing two 6 course crop rotations with different ratios of ley to arable cropping was established at Tulloch, Aberdeen (02°15’W, 57°11’N), UK in 1991. From 1991–2006, the experiment compared two rotations, the first with 3 years of grass/white clover ley and 3 years of arable cropping (T50) and the second with 4 years of grass/white clover ley and 2 years of arable crops (T67). These rotations are described in detail in Watson et al. (2011). In 2007, T67 was changed to a stockless or “plant based” rotation (T0), with a one-year grass/red clover green manure followed by 5 years of arable cropping. The stockless rotation is described in Ball et al. (2014). Crop yield and quality, soil nutrient contents and soil organic matter have been measured over 32 years. Nutrient budgets have been calculated on a rotational basis to address relationships between yield and nutrient inputs in stocked and stockless systems. Yields have been analysed over rotational cycles.
Results
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Figure 1: Yields (85% dry matter) of spring oats and spring barley with and without undersowing (u/s) of red clover (RC) or white clover (WC) in a stocked rotation with 3 years of grass/clover ley (T50) or a stockless rotation (T0) in the 4th (2008-2013) and 5th cycle (2014-2019) of the experiment.
The median yields of spring barley and spring oats declined between the 4th and 5th rotational cycle of the experiment (Figure 1) in all rotations. The decline in yield was larger in the stockless system. The median yields of organic grass/white clover year 2 in T50 and T67 declined over time. Silage yields of the 4th and 5th cycles for T50 were lower than the median yields for cycles 1–3 (data not shown). Maximum yields for the organic grass/white clover leys were 15.8, 13.3 and 10.1 t DM/ha in swards aged 2, 3 and 4 years respectively. Extractable P and K in soil has declined over time in all the rotations. Soil organic matter declined in the stockless (T0) system but did not show a clear trend in the stocked rotation (T50) (data not shown).
Discussion
The decline in cereal yields over time reflects declining levels of soil P and K. Maintaining soil P and K levels from acceptable sources is widely accepted as a challenge in systems reliant on biological N fixation. The decline in soil organic matter in the stockless (T0) system reflects the difficulties of maintaining soil organic matter in systems without grazing livestock or manure additions and is a major consideration for future production systems. Nutrient budgets provide helpful information for decision making on suitable inputs for organic systems.
- References
Ball B.C., Griffiths B.S., Topp C.F.E., Wheatley R., Walker, R.L., Rees R.M., Watson C.A., Gordon H., Hallett P.D., McKenzie B.M. and Nevison I.M. (2014) Seasonal nitrous oxide emissions from field soils under reduced tillage, compost application or organic farming. Agriculture, Ecosystems and Environment 189, 171–80.
Watson C.A., Baddeley J.A., Edwards A.C., Rees R.M., Walker R.L. and Topp C.F.E. (2011) Influence of ley duration on the yield and quality of the subsequent cereal crop (spring oats) in an organically managed long-term crop rotation experiment. Organic Agriculture 1, 147–159.
| Keywords | crop yield; organic farming; livestock based; stockless; long-term experiment |
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