It was not clear why there is too much emphasize on overuse of fertilizers, but little attention has been paid to adverse consequences of poor nutrition of crop plants with mineral fertilizers. The imbalance between low and overuse of fertilizers should be avoided. Below a few examples are given about the adverse consequences associated with inadequate mineral nutrition of crop plants.
An adequate mineral nutrition is required for better tolerance (resistance) of crop plants to pathogen and pest attack: Crop plants are facing diverse of threats if the mineral fertilizers are applied at low doses. Besides well-known decreases in productivity, a poor mineral nutrition increases high risk of pathogenic infection and pest pressure (see Lawrence et al., 2007 in Mineral Nutrition and Diseases, American Phytopathological Society; Dordas, 2008; Agron. Sustain. Dev. 28: 33–46). A suboptimal application of fertilizers raises a high risk for the use of pesticides and fungicides. There are many published scientific evidence demonstrating why a poor mineral nutrition makes the crop plants highly susceptible to pest and pathogenic attack (see Marschner, 2012; Relationship between Nutrition, Plant Diseases and Pests. In Marschner’s Mineral Nutrition of Higher Plants, Elsevier).
Fighting human malnutrition with better plant nutrition: An optimal mineral fertilization of plants is also required to produce more nutritious food for human populations, especially with micronutrients and protein. In recent years, a biofortification concept has emerged and developed as a novel strategy to improve nutritional value of staple food crops in order to combat hidden hunger (i.e., micronutrient deficiency) problem, especially in children and women living in developing world (Cakmak et al., 2010, Cereal Chem. 87:10-20; Bouis and Saltzman, 2017, Global Food Security, 12: 49-58). Hidden hunger refers to deficiencies of micronutrients including zinc, iron, selenium and iodine that affects about 2 billion people worldwide and causes serious health complications such as impairments in immune system, mental functions, and physical development. Agronomic biofortification, involving application of micronutrient-containing fertilizers, has been shown to be highly impactful and cost effective strategy for improving nutritional value of staple food crops with micronutrients and contributing to human nutrition (Valenca et al., 2017, Global Food Security, 12:8-114; Cakmak and Kutman, 2018, Eur. J. Soil Sci. 69: 172-180; Olum et al., 2018, Nutrients 10: 4/407, DOI: 10.3390/nu10040407 and www.harvestzinc.org).
Hidden hunger problem has also adverse impacts on economic development and causes losses up to 5 % of gross domestic product in a given country having high incidence of micronutrient deficiencies (Stein, 2007, Food Nutrition Bull. 28: 125-134; Harding et al., 2018, Public Health Nutr. 21: 785-795).
The points raised above suggest that this Fertilizer Code of Conduct should emphasize the adverse consequences of low use of mineral fertilizers, at least regarding the increase in susceptibility of crop plants to pathogen and pest attack (otherwise it may lead farmers to apply more pesticides and fungicides). The zero draft document should also highlight the well-known potential and positive impacts of fertilizer strategy (agronomic biofortification) to reduce hidden hunger problem in children.
Science is missed in the document: Surprisingly, many sections of this “FAO report” are superficial and provide too much generic statements. I strongly suggest to avoid those generic formulations and statements. The document should be based on published, peer-reviewed scientific data/evidence (with a proper citation). I believe, this document can benefit significantly from a scientific panel consisting of experienced and well-recognized scientists and stakeholders in the field. Source of information given in the (revised) Code of Conduct should be provided by paying attention to authority, accuracy and currency of the corresponding information.
“The dose makes the poison”: As indicated above, the document focused mainly on overuse-related problems and concerns, and highlighted “responsible use” of fertilizers. These terminologies need a clarification and discussion to avoid misconceptions about mineral fertilization of crop plants. Science-based definitions and discussions are required. When this issue is discussed, it is important to remember the well-known fundamental statement on poisons made about 500 years ago by Paracelsus (the father of toxicology): The dose makes the poison. It is obvious: too much of anything is toxic. This FAO document should therefore give priority to optimal (or proper) use of fertilizers, while discussing the adverse consequences of both low use and overuse of fertilizers. Increasing awareness of the importance of the optimal use of fertilizers would be a useful and important message of this document.
Listen to plants: There is too much emphasize on soil test, soil maps and other geospatial methods for efficient and effective use of fertilizers and identification of suitable fertilizer formulations. These are fine and correct; but almost no attention is paid to leaf tissue analyses for effective use of fertilizers. Soil and leaf tests need to be combined for development proper fertilizer application rates. There are many situations where soil analysis results for mineral nutrients does not correlate with mineral nutritional status of plants or leaf tissue concentrations of the nutrients. In most cases, agricultural soils have many physical and chemical problems which restrict the nutrient acquisition capacity of roots, leading to poor correlation between leaf and soil analysis results. This document should also highlight importance of leaf tissue analysis (besides soil tests) in better and reliable fertilizer recommendations.
Prof. Ismail Cakmak