Circular Nutrient Management and Alternative Nutrient Products

Nutrients in Agriculture Overview

• Essential plant nutrients are categorized into:

  • Basic Nutrients: $C$, $H$, $O$.

  • Primary Macronutrients: $N$, $P$, $K$.

  • Secondary Macronutrients: $Ca$, $Mg$, $S$.

  • Micronutrients: $Fe$, $B$, $Mn$, $Cu$, $Zn$, $Mo$, $Cl$, $Ni$.

• Module Aim: To quantify and interpret soil properties related to plant nutrition and nutrient dynamics.

Phosphorus ($P$) Sources and Management

• Historical Sources: Manure, Human Excreta, Guano, and Phosphate rock.

• Primary Resource: Phosphate rock is the main source of $P$ for society, used in fertilizers, animal feed, detergents, food additives, and water treatment.

• Distribution Issues: Global $P$ use is highly concentrated; $45\%$ of phosphorus surpluses relative to crop uptake occur on only $10\%$ of global cropland, while another $10\%$ of cropland faces $65\%$ of the world’s phosphorus deficits.

• Mining and Processing: Phosphate rock is surface-mined using dragline excavators and processed using thermal or wet methods (applying $H_2SO_4$, $HCl$, or $HNO_3$) to create products like Single Superphosphate (SSP), Triple Superphosphate (TSP), Monoammonium Phosphate (MAP), and Diammonium Phosphate (DAP).

Conventional vs. Circular Nutrient Management

• Conventional (Linear) System: Follows a path of Extraction $\rightarrow$ Production $\rightarrow$ Use $\rightarrow$ Loss, leading to resource depletion and environmental degradation (pollution, greenhouse gas emissions).

• Circular System: Focuses on recovering, reusing, and recycling nutrients to "close the nutrient loop."

• Circular Benefits: Waste is viewed as a resource; supports sustainability, climate mitigation, and cost efficiency.

Alternative Nutrient Products and Sources

• Recoverable Sources: Agricultural residues, animal manure, food waste, sewage sludge, and industrial by-products.

• Biofertilizers: Living microbes (e.g., $N$-fixing bacteria, $P$-solubilising bacteria) that energize root-soil interactions.

• Organic Fertilizers: Compost and digestate provide a steady release of nutrients and build soil organic matter.

• Recovered Mineral Products: Nutrients (like struvite) extracted from wastewater.

Nutrient Management Planning

• SFI Guide Recommendations: Plan in late winter or early spring before crop uptake.

• Testing: Sample and test soil for pH, $P$, $K$, and $Mg$ every $3$ to $5$ years.

• Input Strategies: Calculate crop requirements, account for nutrients supplied by organic sources (manure, slurry, or digestate), and determine the necessary amount of artificial fertiliser to fill remaining gaps.

• Influencing Factors: Soil organic matter, parent material, texture, structure, stone content, and rooting depth.

Questions & Discussion

• Class Activity 1: What nutrient wastes exist in your area and how could they be reused?

• Class Activity 2: Can alternative fertilizers replace synthetic ones? What are the risks and what barriers exist regarding scalability and adoption?