GSDR 2015 Brief Fertilizer addiction: Implications for Sustainable Agriculture

By Matteo Pedercini, Gunda Zullich and Kaveh Dianati, The Millennium Institute*

To meet increased demand for food Numerous studies have concluded that spurred by a larger and richer population, routine NPK fertilization depletes SOM in FAO projects that global agricultural the long-run (Kotschi 2013). Loss of SOM production in 2050 will be 60 percent decreases soil productivity and the higher than in 2005/07. Most of this agronomic efficiency of fertilizer N, calling increase in production over the next 40 for increasingly intensive practices and years is expected to derive from improved larger amounts of fertilizer (Mulvaney et al. yields (FAO 2012). 2009). This dynamic is the reason some have portrayed excessive fertilizer use as This brief presents a model-based equivalent to an addiction. examination of short and long-term trade- offs between two alternate agricultural Conceptual model of fertilizer addiction paradigms: industrial agriculture dependent on agrochemicals, fuel-based The essence of fertilizer addiction is mechanization and irrigation operations, captured in the causal loop diagram in etc.; and sustainable, low external input Figure 1. Balancing feedback loop B1 agriculture centered on preservation of soil captures the introduction of industrial organic matter (Pedercini, Zullich and agriculture practices as a (short-term) Dianati 2014a, 2014b). The associated solution to low yields, intending to directly policy implications for long-term increase soil nutrients and bring yield closer sustainability in agricultural yields, and to a given target. Reinforcing feedback food security, are huge. loop R1 describes the mechanism where intensified use of industrial practices Industrial agriculture practices are used as a damages SOM, reducing mineralization cost-effective form of insurance against low and available soil nutrients. This leads to yields, without regard to their inherent lower than otherwise yield, intensifying the effect on the ecosystems below the soil’s need for industrial practices. surface. This has led to a net loss of soil organic matter observed in numerous long- The implication of the loss of SOM on yield term studies of chemical-based cropping is not immediately evident, because rapid systems. Soil organic matter (SOM) decomposition of organic matter releases consists of plant residues and animal large amounts of nutrients that boost yield manure at various stages of decomposition, in the short run. The reduction of SOM cells and tissues of soil organisms, and undermines natural mineralization only substances synthesized by soil organisms. after some years. Feedback loop R2 SOM improves water-holding capacity and exacerbates this vicious dynamic by aeration, enhances absorption and release undermining nitrogen use efficiency, of nutrients, and makes soil less susceptible implying the need for larger amounts of to leaching and erosion. fertilizer to maintain high yields.

*The views and opinions expressed are the authors’ and do not represent those of the Secretariat of the United Nations. Online publication or dissemination does not imply endorsement by the United Nations. Corresponding author is Matteo Pedercini, [email protected].

The reinforcing loops R1 and R2 are Industrial vs. sustainable practices eventually stabilized by two distinct mechanisms, not shown in the CLD for To assess industrial vs. sustainable simplicity. In the case of R1, the loss of practices three scenarios are presented: SOM gradually decreases as the more unstable SOM is depleted. In the case of Maize-NIL: intensive practices, including R2, as nitrogen efficiency decreases, a point detrimental practices such as tillage, mono- is reached where further increasing cropping, burning crops residues, etc., nitrogen input does not make economic without external inputs (including sense. fertilizers); Maize-N: industrial practice, as above, but including extensive use of fertilizers; and Maize-S: sustainable

desired yield cultivation, crop rotation, integrated fertilizer and pest management, cover desired increase in yield crops, etc. yield B1 Mineral nitrogen (Figure 2) shows overshoot patterns for all three scenarios. available soil external input and nutrients industrial practices Under intensive practice mineral nitrogen

R1 local input and initially rises while SOM (simulated SOM sustainable practices soil organic not shown here) quickly decomposes, mineralization matter causing rapid nitrogen mineralization.

R2 Following the decline in SOM, and drastic

nitrogen decline in SOM decay due to increasing efficiency chemical stability of remaining organic Figure 1 - Causal Loop Diagram of fertilizer matter, mineral nitrogen availability falls addiction (Pedercini, Zullich and Dianati, rapidly. 2014b). Under industrial agriculture, mineral Formal Model nitrogen initially rises rapidly as To simulate the above-described dynamics decomposition of SOM accelerates. This we have built a stock-and-flow model initial tendency is further strengthened by (Pedercini, Zullich and Dianati, 2014a, usage of N-fertilizer seeking higher yields. 2014b). The model structure reflects how This trend is reversed once the loss of the the stocks of soil carbon (our proxy for less stable SOM reduces mineralization, SOM) and mineral nitrogen interact and and ability of the soil to retain N-fertilizer evolve, and how industrial agriculture decreases. Attempting to counteract this practices moderate this interaction. decline, the farmer applies increasingly larger amounts of fertilizer, up to a point The model is parameterized to represent where it no longer makes economic sense soil characteristics at a location in Kisii to increase fertilizer usage. The continuous District, Kenya. Initial conditions reflect soil use of industrial practices kills even more conditions of natural grasslands. The organic matter, bringing fertilizer efficiency expansion of industrial agriculture in Kenya lower, further exacerbating the problem, in is a highly relevant issue. The formal model, a classic example of policy resistance. however applies equally well to other agroecological zones. 2

Under sustainable practices, mineral adaptation starting at year 20 (Maize-N- nitrogen follows a much smoother Shock-PreAdaptation). trajectory. The initial rise in this case is less steep because sustainable practices are less Mineral Nitrogen demanding on SOM, with decomposition 2 and mineralization happening at slower rates, and also due to absence of mineral 1.5 Maize-N-Shock- fertilization application. Consequently, the PreAdaptation Maize-N- ensuing fall is much less precipitous as a 1 result of better conserved soil organic Shock - matter. However, without the introduction (Ton/Ha) 0.5 of any mineral fertilizer or N-fixating crops, Maize-S-Shock nitrogen in the Maize-S scenario tends to Maize -N-Shock be lower than in the Maize-N scenario, 0 although by a decreasing margin. 0 10 20 30 40 50 60 70 80 90 100 Time (Year)

Figure 3 - Mineral nitrogen in soil under 2 Mineral Nitrogen fertilizer scarcity shock (Pedercini, Zullich and Dianati 2014a). 1.5 Maize -N In Figure 3, following the fertilizer scarcity 1 Maize-S shock, mineral nitrogen falls by > 40 % in the Maize-N-Shock scenario. The shock

(Ton/Ha) does not affect mineral nitrogen in the 0.5 Maize-S-Shock scenario, where mineral N Maize -NIL is provided by SOM decomposition only. In 0 the Maize-N-Shock scenario, nitrogen 0 10 20 30 40 50 60 70 80 90 100 availability is permanently damaged and Time (Year) declines continuously.

Figure 2 - Mineral Nitrogen in Soil: Industrial without Fertilizer (Maize-NIL), Industrial with Such trend can be avoided through Fertilizer (Maize-N), Sustainable Practices adaptation measures (Maize-N-Shock- (Maize-S) (Pedercini, Zullich and Dianati Adaptation), i.e., conversion to sustainable 2014a). practices. Assuming an immediate shift to sustainable practices, it takes about 25 Fertilizer scarcity shock scenarios years for SOM and mineral nitrogen levels to return to those of sustainable practices, To mimic the effect of a fertilizer scarcity in line with empirical research findings shock we assume a gradual five-year (Derpsch 1997). reduction of fertilizer use to zero, starting at year 30. We compare the impact of the Transitioning to sustainable practices is shock on four types of agriculture practices: time and resource demanding. The sustainable practices (Maize-S-Shock); observed trends suggest that about two industrial practices (Maize-N-Shock); decades of good yields can be lost in the industrial practices followed by post-shock transition. We also analyze a scenario in adaptation (Maize-N-Shock-Adaptation); which a likely future scarcity in synthetic and industrial practices with pre-emptive fertilizer is anticipated and the same 3

adaptation measures start earlier to avoid References unaffordable costs and loss of crop production (Maize-N-Shock- Derpsch, Rolf. 1997. “Importancia de la PreAdaptation). siembra directa para obtener la sustentabilidad de la producción agrícola.” In the Maize-N-Shock-PreAdaptation CONGRESSO NACIONAL DE AAPRESID 5: scenario soil mineral nitrogen falls slightly 153-176. below the business-as-usual scenario, an example of a worse-before-better FAO. 2012. Current world fertilizer trends outcome, while SOM is restored. This is and outlook to 2016. Rome: FAO. because policies to preserve SOM imply an initial reduction of SOM decomposition and Kotschi, Johannes. 2013. A Soiled nitrogen mineralization. After Reputation: Adverse impacts of mineral approximately six years, the pre-adaptation fertilizers in tropical agriculture. AGRECOL – scenario overtakes business-as-usual in Association for AgriCulture and Ecology, terms of soil N content while the two non- Heinrich Böll Stiftung, WWF Germany. proactive scenarios suffer significant decline in soil N. With pre-adaptation Mulvaney, R. L., S. A. Khan, and T. R. measures soil N does not fall below the Ellsworth. 2009. “Synthetic Nitrogen originally sustainable scenario, converging Fertilizers Deplete Soil Nitrogen: A Global with it around 20 years after the shock. Dilemma for Sustainable Cereal Production.” J. of Environmental Quality 38: 2295–2314. Issues for further consideration Pedercini, M., Gunda Zullich and Kaveh • Policies for long-term agricultural Dianati. 2014a. Addicted to fertilizer – How sustainability and food security soil mismanagement makes our soils must address preservation and increasingly vulnerable. (Submitted for restoration of SOM. review). • Agricultural systems that nurture SOM are more resilient than Pedercini, M., Gunda Zullich and Kaveh industrial agriculture to shocks such Dianati. 2014b. Addicted to fertilizer – How soil mismanagement makes our soils as fertilizer price hikes. increasingly vulnerable. Proceedings of the • Large time lags are involved when International System Dynamics Society, transitioning from industrial to Delft, The Netherlands. sustainable agriculture. Transitioning pre-emptively to anticipated shocks is much less costly than after the fact. • Simulation models that consider feedback loops and stock-flow structure can help us understand the dynamics of coupled human- natural systems and design more effective policies for sustainability.

4