Nitrogen (N) is the most important essential element for crop production because it is required in large amounts and is nearly always the first nutrient that becomes limiting after an ecosystem is converted to cropland. Cereal grains provide about 50% of the world’s calories, and their production has become largely dependent on the use of synthetic N fertilizer. However, fertilizer N not used by plants can degrade the environment and negatively impact both people and ecosystems. In addition, efficient use of N fertilizer generally requires phosphorus (P) fertilizer which is made from rock phosphate derived from mines. Therefore, huge amounts of N and P from outside sources are being added to the environment each successive year leading to additional environmental concerns [Stewart & Lal 2017: 124A].
This article articulates a presumed “nitrogen dilemma,” as described above, that, on the one hand, agriculture requires increasing amounts of nitrogen and phosphorus fertilizer, especially as the population surges toward 10 billion. On the other hand, ongoing fertilizer application will lead to increasingly polluted and impaired fresh waters around the world, increased greenhouse gas emissions, and over-reliance on limited supplies of mined phosphorus.
The difficulty of reducing nitrogen inputs is twofold according to the article: First, farmers cannot know exactly how much nitrogen their crops will need because yield depends on water supply and respiration rates, and only indirectly on nitrogen availability. Therefore, farmers are reluctant to limit fertilizer input for fear it could in turn limit water utilization. “Because N is usually the first limiting factor other than water, most farmers want to make sure they have enough N available to fully utilize the water” [p.126A]. Second, nutrient-polluted waters is a local problem, and therefore most likely requires a local political solution, rather than being manageable through national regulations. Local policy solutions will happen only when enough people feel the direct effects of the problem locally and demand action.
Curiously, the article fails to mention the farming practices that reduce the need for fertilizers, maximize the soil’s water-holding capacity, and cool the soil through continuous vegetative cover. Practices designed to enhance soil organic matter, such as cover-cropping and replacing synthetic fertilizer input with compost, manure and crop residues, can achieve the same goals that nitrogen fertilizer is supposed to address.
…it is water that determines yield, and the amount of water available for a crop is beyond control of the farmer, even if the crop is irrigated. This is because it is only the amount of water transpired by the growing crop that determines the amount of biomass produced by photosynthesis, and this is affected not only by the amount of water available but on other climatic factors such as temperature, radiation, humidity, and wind [Steward & Lal 2017: 126A].
We argue that there is no nitrogen dilemma unless we cling to the idea that industrial agriculture is the only way forward despite its increasingly apparent fragility, while rejecting the potential of multifunctional, regenerative agriculture to broadly achieve our production and environmental goals.
Stewart, B.A. & Rattan Lal, 2017, The nitrogen dilemma: Food or the environment, Journal of Soil and Water Conservation 72(6): 124A-128A, http://www.jswconline.org/content/72/6/124A.full.pdf+html?sid=ae515a44-e34a-4fa6-b549-06ebcc815d76