ADDRESSING THE FERTILIZER ADDICTION
14.4.1 Global Food Demand by 2050
The projected increase in global agricultural production of 60% by 2050 compared with that of 2005-07 (FAO 2012) necessitates a closer look at the role of fertilizers in enhancing and sustaining food production. Excessive and indiscriminate use of chemical fertilizers can have severe environmental and sustainability concerns and can also adversely affect soil quality (Kotschi 2013; Mulvaney et al. 2009). Thus, site-specific options need to be considered to minimize dependence on the use of chemical fertilizers. Pedercini et al. (2014,2015) suggested sustainable management of SOM as one of the options because increasing SOM can enhance soil and crop resilience.
14.4.2 Managing Soil Organic Matter and Soil Quality
Restoration of SOM in depleted and degraded soils can improve soil quality and functionality and decrease the rate of fertilizer application. Some of the options for reducing dependence on fertilizers by managing SOM (Figure 14.6) include system-based conservation agriculture (CA) done in conjunction with no-till (NT) residue retention, cover cropping with appropriate legume and grass species or a mixture of species that enhance biodiversity, integrated systems of nutrient and pest management, and a close integration of crops in association with trees and livestock. In-field burning of crop residues must be avoided (Shyamsundar et al. 2019). Use of compost and increasing SOC contents can enhance the disease-suppressive attributes of a soil through
FIGURE 14.6 Strategies to enhance soil organic matter content.
improvements in soil health. Although there are some niches for the establishment of biofuel plantations on degraded and drastically disturbed lands, bioenergy is not always a feasible option (Stokstad 2019).
14.5.1 Meeting Global Food Demand by 2050
Meeting global food demand by 2050 and beyond does not necessarily imply increasing land area under agriculture, fertilizer and pesticide use, water use for irrigation, intensity and frequency of tillage, and other energy-based inputs. Resources used for agriculture are already more than what is needed, and the amount of food already produced is adequate to feed the world population of -10 billion. Thus, the first priority is to reduce food waste, which may be as much as 30% of the total amount produced. The next step is to improve access and distribution by addressing poverty, civil strife, political unrest, and climate/soil refugees. Any justifiable allocation of additional resources (e.g., land water, fertilizers, pesticides, tillage) must be critically considered and objectively assessed. By abridging the yield gap and enhancing the use efficiency of fertilizers, water, and other inputs, some of the hitherto allocated land resources must be returned back to nature (Lai 2016, 2018b). Furthermore, priority must be given to plant-based diet for the growingly and increasingly affluent population (Lai 2017; IPCC 2019).
14.5.2 Way Forward
The answer to the question “Are fertilizers needed?” is not in the form of either/or. With the world population of 7.7 billion in 2019 and expected to reach 8.5 billion by 2030 and 9.7 billion by 2050, all options are on the table. The strategy is for the judicious, discriminate, and targeted use of fertilizers as determined by the desired agronomic yield and the soil test for each specific soil/crop/ecosystem. Poisoning of soil by excessive, over, and indiscriminate use of chemicals is not acceptable and must be avoided. Further, plant nutrients contained in soil may not be adequate to obtain the desired agronomic yield. Thus, the inherent supply must be supplemented with external imports for obtaining the desired agronomic yield. The external input of plant nutrients for improving crop growth and enhancing nutritional quality can come from diverse sources: natural, recycled by-products, microbial inoculants, and synthetic or chemical formulations (solid or liquid). Most sources of plant nutrients can be grouped as biological, organic, and mineral. The strategy of enhancing soil fertility by the use of diverse sources of amendment is called “integrated nutrient management” (INM) or integrated soil fertility management (ISFM). The latter also includes recycling of plant nutrients contained in the remains of plants and animals and by-products of their processing, nitrogen-fixing biofertilizers, mineral materials such as rock phosphate, and Chilean saltpeter or guano.
There is also a wide range of nitrogen-fixing biofertilizers based on a wide range of organisms including bacteria (Rhizobian, Azotobacter, Azospirildum, Acetobacter), algae (Blue Green Algae composed of Nostoc Anabaena, Aulosira, Tolypothrix, and Calothrix used in rice paddies), and a fern (Azolla) (FAO 2006). There are also phosphate-solubilizing biofertilizers including bacteria (.Bacillus megatherium), fungus (Aspergillus sp, Penicillium sp), yeast (Saccharomyces sp) and acti- nomycetes (Streptomyces sp). In addition, there are also nutrient-mobilizing biofertilizers composed of soil fungi mycorrhizal (ecto- and endomycorrhiza). Amendments are used to alleviate soil-related constraints such as low pH by liming, high pH by acidification (CaS04 2H20 or sypsum), coarse texture (by adding clay), fine texture (by adding sand), and soil structure by introducing conditioners (e.g., organic or polymers and inorganic compounds) (FAO 2006). The strategy of INM and ISFM is to minimize dependence on the use of synthetic (mineral) formulations (i.e., ammonium sulfate, muriate of potash, ammonium nitrate, urea). The application of balanced plant nutrients is important because an excess or deficiency of one can impact the availability or efficient use of another.