Hot on the heels of its open-access Database of Pollinator Interactions (DoPI), the University of Sussex has published the results of a new project that links the use of fertilisers to agricultural productivity and the decline in our wildflowers and pollinators.
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Although it’s very much a work in progress, it has already thrown up some surprises. For example, who would have guessed that creeping buttercup would turn out to have the highest number of pollinator species (240) of any of our wildflowers?
The newer study combines flower and pollinator abundance with soil-nutrient data at the world’s longest running ecological experiment, Park Grass at Rothamsted Research. The finding that high agricultural productivity means low pollinator abundance (and, conversely, lower productivity equals more pollinators) has presented farmers as well as conservationists and even governments with the mother
of all dilemmas. With this outcome, how can farmers hope to integrate conservation with food production successfully?
The results may have come as a surprise to the scientists involved, but gardeners might be forgiven for thinking: so what? We have been following the mantra of NPK – nitrogen (N) for leaf, phosphorus (P) for roots and potassium (K) for flowers and fruit – for decades, so we know that nitrogen-rich fertilisers promote leafy growth at the expense of flowers (with a knock-on effect for pollinators). There are, however, new aspects to the research that are worth bearing in mind.
We can help the world if we reduce our NPK usage in gardens. This is not necessarily a problem
First, we habitually apply NPK for the benefit of individual plants, or of a single species such as a crop, whereas the Park Grass study looks at the effect of NPK on the interactions between the constituent members of a plant community, that of grassland. At this level, nitrogen has a huge effect, and it doesn’t seem to matter where it comes from; pelleted chicken manure has as big an effect as artificial nitrogen, and even farmyard manure has some effect. It is also clear now that legumes hate high nitrogen. Worse, it isn’t just nitrogen that reduces the abundance of flowers, but phosphorus and potassium also have a negative effect; except on legumes, which seem to enjoy both. Finally, there is firm evidence to show that adding lime helps plants, flowers and pollinators on acid soils. Researchers also point out that fertilisers can have more subtle effects, such as upon the chemical composition of nectar, or upon the decomposition pathway in the soil through their effect on fungi and bacteria.
The discovery of resilience has moved biodiversity to the forefront of the debate about the future of our environment.
Both the DoPI and the Park Grass study belong to a general trend in ecological research away from looking at individual plants or species, and towards analysing the interactions between different species within a habitat. Such work has resulted in a seismic shift in how ecologists view the natural world, particularly through the discovery of resilience, which is usually defined as the ability of a community to spring back from a shock. Resilience depends on the number of interactions between species, in that more interactions equals higher resilience, and the number of interactions depends largely on the number of species. The discovery of resilience has moved biodiversity to the forefront of the debate about the future of our environment.
So, it now seems that we can help the world if we reduce our NPK usage in gardens. This is not necessarily a problem. We are often encouraged to ‘grow plants hard’ to improve resistance to pests and diseases. Plants may not grow to quite the same size, but this surely is a planting opportunity and a way of increasing biodiversity. Many plants have never in their evolutionary history encountered soils as rich as the ones we give them, and are happy to grow in lower-nutrient soils, although most won’t turn down the opportunity to use a little extra NPK if it comes along. Nerines, for example, will enjoy a nutrient boost (which is why we feed them), but in the wild live happily in some of the world’s most impoverished soils.
The research indicates that farmers need to find a way around the productivity/biodiversity link.
Gardeners, without the economic imperative of having to grow crops for money, have the advantage in that we can apply these new ideas to our plots without worry. A lot of us have begun to do so already, with low-nutrient wildflower meadows, but we can look to do more, especially with our beds and borders.