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The objectives of this study were to examine soil organic matter (SOM) functional group composition and its relationship to labile SOM fractions with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). We analyzed soils from 13 organically managed tomato (Solanum lycopersicum) fields in northern California for labile organic C, N, and P fractions and by DRIFTS for bands representing organic functional groups, including aliphatic C‐H (2924, 2850, 1470, 1405, 1390 cm‐1), aromatic C=C (1650 cm‐1) and C‐H (920, 840 cm‐1), polysaccharide and phenol C‐O (1270, 1110, 1080 cm‐1), and amine and amide N‐H (3400, 1575 cm‐1). Significant differences in relative band intensities occurred among the 13 organic tomato fields, in particular a relative increase in absorbance of bands representing aliphatic C‐H positively associated with soil organic carbon (SOC), as well as permanganate‐oxidizable carbon (POXC), extractable organic carbon (EOC) and nitrogen (EON), and potentially mineralizable N (PMN). In comparison, organic P fractions like sodium bicarbonate extractable (NaHCO3–Po) and sodium hydroxide extractable organic P (NaOH‐Po) were poorly associated with SOC and functional groups represented by bands, including aliphatic C‐H. This could reflect limitations of DRIFTS, but is consistent with hypotheses of greater decoupling of C and P vs. C and N in soils. This study implicates relative differences in organic functional groups with differences in SOC and labile SOM fractions, and in agreement with previous studies, identifies absorbance of infrared bands representing aliphatic C‐H functional groups in these systems as a potential indicator of SOM transformations related to changes in its labile fractions.

The low water solubility of struvite is thought to limit its agronomic utility as a phosphorus (P) fertilizer compared with highly soluble P fertilizers. Furthermore, struvite's fertilizer potential is complicated by its hypothesized soil pH‐dependent solubility, crop‐specific interactions, and limited availability of struvite‐derived N, which may explain conflicting reports of crop responses to struvite compared with conventional P fertilizers. A systematic literature review and meta‐analysis was conducted to evaluate the effects of soil pH, soil test P (STP), P rate, struvite particle size, and struvite‐derived N on crop aboveground biomass, P concentration, P uptake, and N uptake. Struvite‐fertilized plants yielded higher biomass, P concentration, and P uptake compared with ammonium phosphates, and superphosphates in soils with pH < 6 and crop responses decreased with increasing pH. Crop responses to struvite were inversely related to experiment duration to soil mass ratios (d kg−1) used in greenhouse studies, opposite to the hypothesized benefit of more roots per unit soil on struvite dissolution. The proportion of total N applied derived from struvite increased with increasing struvite‐P application rate and was inversely related to total N uptake, likely due to the increased crop reliance on slowly available struvite‐N. Crop responses were potentially overestimated by high STP and/or P rates and underestimated due to N limitation from large proportions of total N applied derived from struvite. Evaluations of struvite collectively indicate its efficacy as a P fertilizer is affected by soil pH and its contribution to total N application.

Sanitation remains a global challenge, both in terms of access to toilet facilities and resource intensity (e.g., energy consumption) of waste treatment. Overcoming barriers to universal sanitation coverage and sustainable resource management requires approaches that manage bodily excreta within coupled human and natural systems. In recent years, numerous analytical methods have been developed to understand cross-disciplinary constraints, opportunities, and trade-offs around sanitation and resource recovery. However, without a shared language or conceptual framework, efforts from individual disciplines or geographic contexts may remain isolated, preventing the accumulation of generalized knowledge. Here, we develop a version of the social-ecological systems framework modified for the specific characteristics of bodily excreta. This framework offers a shared vision for sanitation as a human-derived resource system, where people are part of the resource cycle. Through sanitation technologies and management strategies, resources including water, organics, and nutrients accumulate, transform, and impact human experiences and natural environments. Within the framework, we establish a multitiered lexicon of variables, characterized by breadth and depth, to support harmonized understanding and development of models and analytical approaches. This framework’s refinement and use will guide interdisciplinary study around sanitation to identify guiding principles for sanitation that advance sustainable development at the nature-society interface.

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Recovering human-derived nutrients from sanitation systems can offset inorganic fertilizer use and improve access to agricultural nutrients in resource-limited settings, but the agronomic value of recovered products depends upon product chemistry and soil context. Products may exacerbate already-compromised soil conditions, offer benefits beyond nutrients, or have reduced efficacy depending on soil characteristics. Using global spatial modeling, we evaluate the soil suitability of seven products (wastewater, sludge, compost, urine, ammonium sulfate, ammonium struvite, potassium struvite) and integrate this information with local recovery potential of each product from sanitation systems that will need to be installed to achieve universal coverage (referred to here as “newly-installed sanitation”). If product recovery and reuse are colocated, the quantity and suitability of nutrient reuse was variable across countries. For example, alkaline products (e.g., struvite) may be particularly beneficial when applied to acidic soils in Uganda but potentially detrimental in the southwestern United States. Further, we illustrate discrepancies across soil data sets and highlight the need for locally accurate data, knowledge, and interpretation. Overall, this study demonstrates soil context is critical to comprehensively characterize the value proposition of nutrient recovery, and it provides a foundation for incorporating soil suitability into local and global sanitation decision-making.

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