Quantifying nutrient recovery efficiency and loss from compost-based urban agriculture

Abstract

The use of compost in urban agriculture offers an opportunity to increase nutrient recycling in urban ecosystems, but recent studies have shown that compost application often results in phosphorus (P) being applied far in excess of crop nutrient demand, creating the potential for P loss through leachate and runoff. Management goals such as maximizing crop yields or maximizing the mass of nutrients recycled from compost may inadvertently result in P loss, creating a potential ecosystem disservice. Here, we report the results from the first two years of an experimental study in which four different crops grown in raised-bed garden plots with high background P and organic matter received one of two types of compost (municipal compost made from urban organics waste, or manure-based compost) at two different levels (applied based on crop N or P demand), while additional treatments received synthetic N and P fertilizer or no soil amendments. Because of the low N:P ratio of compost relative to crop nutrient uptake, compost application based on crop N demand resulted in overapplication of P. Crop yield did not differ among treatments receiving compost inputs, and the mass of P recovered in crops relative to P inputs decreased for treatments with higher compost application rates. Treatments receiving compost targeted to crop N demand had P leachate rates approximately twice as high as other treatments. These results highlight tradeoffs inherent in recycling nutrients through UA, but they also show that targeted compost application rates have the capacity to maintain crop yields while minimizing nutrient loss. UA has the potential to help close the urban nutrient loop, but if UA is to be scaled up in order to maximize potential social, economic, and environmental benefits, it is especially important to carefully manage nutrients to avoid ecosystem disservices from nutrient pollution.

Features and Functions of Multifunctional Urban Agriculture in the Global North: A Review

“…Whenever UA takes place in potentially contaminated sites, the integration of peat or potting soil may also be an option to overtake contamination (Pennisi et al, 2016(Pennisi et al, , 2017, although at the expenses of increased associated environmental impacts (Dahlin et al, 2019), which on a large-scale could pose at risk the overall sustainability of UA (Meharg, 2016). Alternatives to commercial/potting soils should therefore be considered, these including among others composted urban waste (Shrestha et al, 2020), spent coffee grounds (Cervera-Mata et al, 2019) or biochar (Song et al, 2020), assuming they do not contain further contaminants and are suitable for plant cultivation (Beniston and Lal, 2012;Hardgrove and Livesley, 2016).…”

Investigating potential hydrological ecosystem services in urban gardens through soil amendment experiments and hydrologic models

“…Each raised bed was divided into four 1m 2 subplots in which the following crops were planted and rotated annually: 1) carrots (60 seeds planted); 2) bush beans (12 seedlings planted); 3) bell peppers (6 seedlings planted); and 4) cabbage (2017) or collards (2018, 2019) (6 seedlings planted). We randomly assigned each of the experimental plots to one of 6 soil amendment treatments previously described by Shrestha et al (2020). Briefly, soil treatments consisted of a: 1) control treatment in which no compost or fertilizer was added (nofert); 2) synthetic fertilizer to meet crop N demand and P (synthetic); 3) higher application rate of manure compost targeted to meet crop N demand (high manure); 4) lower application rate of manure compost targeted to meet crop P demand, with supplemental N fertilizer to meet crop N demand (low manure); 5) higher application rate of municipal compost targeted to meet crop N demand (high municipal compost); and 6) lower application rate of municipal compost targeted to meet crop P demand, along with supplemental N fertilizer to meet crop N demand (low municipal compost).…”

“…Mean garden soil organic matter (loss on ignition method) ranged from 8% on the no fertilizer treatment to 12.6% in the high municipal compost treatment (Table S3). For more detailed information about the study area and the experimental design see Small et al (2018) and Shrestha et al (2020).…”

High water retention in urban garden soils leads to reduced leachate and elevated evapotranspiration

“…Each raised bed was divided into four subplots in which the following crops were planted and rotated annually: 1) carrots; 2) bush beans; 3) bell peppers; and 4) cabbage (2017) or collards (2018,2019). We randomly assigned each of the experimental plots to one of 6 soil amendment treatments previously described by Shrestha et al (2020). Brie y, soil treatments consisted of a: 1) control treatment in which no compost or fertilizer was added (nofert); 2) synthetic fertilizer to meet crop N demand and P (synthetic); 3) a higher application rate of manure compost targeted to meet crop N demand (high manure); 4) a lower application rate of manure compost targeted to meet crop P demand, with supplemental N fertilizer to meet crop N demand (low manure); 5) a higher application rate of municipal compost targeted to meet crop N demand (high municipal compost); and 6) a lower application rate of municipal compost targeted to meet crop P demand, along with supplemental N fertilizer to meet crop N demand (low municipal compost).…”