Harvesting the Research: Insect Pollination Maintains High Yields with Lower Nitrogen Inputs

From foodtank.com, by Emily Nink
Harvesting the Research: Insect Pollination Maintains High Yields with Lower Nitrogen Inputs

Food Tank spoke with Giovanni Tamburini, a co-author of a study on insect pollination and nutrient availability published in Agriculture, Ecosystems & Environment.

The overall message: Researchers found that insect pollination compensated for low levels of fertilizer application, indicating economic implications of ecosystem services, which are the benefits provided to humans by nature.

The research: The field experiment involved stripcropping three cultivars of oilseed rape and using cages to exclude pollinators from areas of the field. Areas of the strips received different nitrogen applications (low and high). Researchers repositioned the cages were throughout the experiment to compensate for differences in sunlight, and observed the visitation rates of honeybees, wild bees, and other insects. The researchers then measured the yield (quantified by seed weight, number of seeds per pod, and number of pods per plant) to determine the interacting effects of nitrogen application, insect pollination, and crop variety selection.

Food Tank (FT): What are two key points of your paper?      

Giovanni Tamburini (GT): First, we found that nutrient availability and insect pollination interact to impact yields. Second, we found that crop variety selection can also play a role in harnessing these ecosystem services. This is very exciting because pollination benefit to yield is often studied independently rather than in conjunction with other ecosystem services. Although the correlation between yield formation and pollinator abundance has been studied before, our results show that variation in this effect could be explained by interactions that are not usually considered.

FT: Why is your research relevant for the transition to sustainable agriculture?

GT: We have identified actual options for reducing inputs that are already in the hands of farmers. Insect pollination is 100 percent sustainable and reduction of inputs can mitigate the negative effects of agriculture on the natural environment. From the beginning of our research, we attempted to be as practical and realistic as possible in order to provide not only theoretical relationships between nutrient availability and insect pollination but also to provide effective management recommendations.

FT: Could you describe some of these management practices? How do they differ from current conventional practices?

GT: We consider three factors that are known to affect or accelerate yield formation, which are nitrogen fertilizer, crop variety selection, and pollinator abundance. Both nitrogen input and crop variety selection are direct management choices, and pollinator abundance can also be affected by farm decisions. We can work with farmers to combine these three factors at different levels to achieve high yields. For example, if a field is rich in pollinators, a farmer can choose a crop variety that is highly dependent on pollination and thereby work to reduce nitrogen inputs into the cropping system. By tweaking this balance, the farmer will lower production costs, and also reduce negative effects on the environment. If instead, a field is located in a landscape that is actually poor in pollinators, then the farmers could enhance pollinator abundance by adding honeybee hives close to the field.

FT: Your paper’s abstract observes the “increased access of nitrogen seems to partly compensate yield losses from poor insect pollination.” Is it possible to see this as the glass half-full rather than half-empty: decreased applications of fertilizer may nonetheless sustain yields through good insect pollination? How would the research implications differ if this causality were reversed?

GT: We formulated that statement at the beginning to emphasize the farmer perspective. For a farmer, it is more difficult to manage pollinator abundance locally in the field than it is to adjust nitrogen input levels. But from an academic standpoint, we can reverse this causality through our research design and think about the interests of society as a whole. Our results suggest that good pollination service will have qualitative effects on agricultural economics and environmental health. These outcomes are important to both farmers and society as a whole, so it’s important to put pollination in the economic balance of farming.

Nitrogen fertilization is a direct cost for farmers, and results in indirect costs to society due to the environmental impacts. For example, it contributes to climate change from the emissions of carbon dioxide to the atmosphere. Furthermore, only about half of nitrogen that is applied to the crop is taken up from the land harvested; the rest is leached from the soil into groundwater or runs off, creating huge problems worldwide. So if we can successfully reduce nitrogen input through good pollination service, we could actually reduce agriculture’s most harmful effect on the environment.

FT: To what extent can farmers be sure that insect pollination is compensating for lower applications of nitrogen fertilizer in a given season? What exactly would they need to be doing on site?

GT: The starting point is to observe and quantify the pollination service at a given location. That will determine if it is possible to decrease the nitrogen level in a given field or not. Next, the farmer can work to select the right crop variety. However, it is quite difficult to tell from the available information which crop varieties are more dependent on pollinators and which are not. Making this information more accessible to farmers would be an important step.

FT: And could this occur in crops other than the ones that you studied?

GT: Yes. We are now looking at peas, and we have researched other crops as well. It seems from our results that the relationship between nutrient availability and pollination benefit is really important. More research is needed, because different crop species can have different flowering strategies that can affect this kind of interaction. But I think the fact that we have found interactive effects between ecosystem services encourages the idea that this could work for other crops.

FT: Would it be possible to extrapolate the cost-savings of switching cultivars, improving conservation, and reducing inputs to a landscape scale?

GT: I definitely think this is the next step. In the last few years, studies have been compiled into new models that examine how biodiversity and related ecosystem services contribute to agricultural productivity or farm income. The creation of new policy and management recommendations will depend on these economic and ecological analyses at larger scales.

There’s also potential for better collaboration between traditional agronomists and plant breeders with ecologists and economists. Agronomists are experts in predicting yield formations from agricultural inputs locally, but they often fail to consider the effects of ecosystem services and plant species composition. So the challenge now is to use interdisciplinary thinking to predict yield formation more correctly and to observe if there are any tradeoffs between the provision of ecosystem services and the productivity of agricultural systems. Our results on cultivar selection also show that stakeholders such as plant breeders may be interested in further genetic research on the suitability of different cultivars for ecological intensification.

FT: Where is future research going, and how do you think it will contribute to agricultural sustainability?

GT: My main focus for future research is to dig deeper into the mechanisms behind the relationship between nutrient availability and insect pollination. Recent papers have shown that insect pollination can be useful to differing extents depending on many factors, so we still don’t really understand how exactly it is working. We are starting to see study designs that examine the interacting effects of multiple ecosystem services, which is really exciting to me. The preliminary research showing that these synergies exist is important to communicating the importance of ecosystems services to farmers and jump-starting adoption of ecological intensification; meanwhile, further research should focus on really understanding the mechanisms behind these synergies, which is our next goal. We want to understand how to use ecosystem services to our advantage to grow food without creating such harmful impacts on the environment.