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Summer 2021 Garden Research Updates

Small and Zeiner labs

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Part 1: Project background (Chip)

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Burger et al. (2012)

Urban ecosystems:

Lots of imported materials, lots of waste produced

Can/should cities be more self-sufficient?

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Food waste

Organics waste collection

Regional composting facility

Compost sold through distributors

Compost applied to gardens

Locally-grown produce

Composting and Urban Agriculture

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Urban agriculture

Cleveland could provide 46-100% of its fresh produce, 94% of its poultry and eggs, and 100% of its honey.

Grewal & Grewal (2012)

Twin Cities currently produces 1.3% of its food using reused urban P. Could be as high as 47%

Baker (2011)

Cities feeding themselves…

Urban Agriculture could produce 100-180 million tonnes of food per year globally, and provide ecosystem services worth $80-160 billion.

Clinton et al. (2018)

…and closing the nutrient loop

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If compost is applied based on crop N-demand, soils receive excess P.

Klienman et al. (2011)

Challenges of Nutrient Recycling from Composting + Urban Agriculture

1. Organics wastes typically have low N:P ratios.

2. Lack of economic/regulatory disincentives for overapplication of nutrients, plus perception of sustainability.

Taylor and Taylor Lovell (2014)

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Compost P

Compost inputs

Uptake by crops

Mineralization

Plant-available P

Loss through leachate

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Previous results from Minneapolis-Saint Paul:

40x more P applied as compost compared to harvested P

Garden soils have mean Bray P of 80 ppm, correlated with garden age

Gardens make up 0.1% of total watershed area, but constitutes one of the largest urban P fluxes (~35 kg P/km²/y).

Our data

From Hobbie et al. 2017

G. Small, P. Shrestha, G. Metson, K. Connelly, I. Jimenez, A.D. Kay (2019). Excess phosphorus from compost applications in urban gardens creates potential pollution hotspots. Env. Res. Comm. 1: 091007

Survey-> Participants were also asked to identify the size of their garden/farm, length of operation, land history, physical address, the list of individual crops grown and their respective yields in the survey

http://www.capitolregionwd.org/watershed-information/what-is-crwd/

Estimate UA associated nutrient fluxes at the watershed scale in CRWD, Minnesota

Low P efficiencies – inefficient conversion of P into crops

Median garden P inputs (0.03 kg P/m²) were approximately 30x greater than mean P application rates in U.S. conventional agriculture

Because UA yields were similar to yields from conventional agriculture (Swaney et al. 2018), nutrient use efficiencies from UA (2.5% for P, 5.0% for N) were much lower than corresponding efficiencies from conventional agriculture (89% PUE (IPNI 2010); 31% NUE (Swaney et al. 2018)).

Estimated N inputs from UA amendments , by contrast, are a minor component of the watershed N budget, making up approximately 3% of total N inputs (Hobbie et al. 2017 ). I don’t mind too much moving between soil amendments and ferltizers, but it might make sense to go through the whole thing and chose one or state in the methods that some things are used interchangeably or chose one terms but define it to encompass a wide range of things

Note that Hobbie et al. did include county compost in their P budget (based on county data—what volume of compost the county distributed each spring), and that is similar to our calculated P inputs. However, this may go to landscaping and other uses, and much of garden soil inputs was from sources other than county compost—so I don’t know if/how we need to address this

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Previous results from Minneapolis-Saint Paul:

Excess P from compost builds up in garden soil and in leaches into native soil below garden.

Low P-use efficiency (<5%)

P loss from leachate can equal uptake from crops

G.. Small, P. Shrestha, A. Kay. The fate of compost derived P in urban gardens. International Journal of Design & Nature and Ecodynamics 4: 415-422.

Survey-> Participants were also asked to identify the size of their garden/farm, length of operation, land history, physical address, the list of individual crops grown and their respective yields in the survey

http://www.capitolregionwd.org/watershed-information/what-is-crwd/

Estimate UA associated nutrient fluxes at the watershed scale in CRWD, Minnesota

Low P efficiencies – inefficient conversion of P into crops

Median garden P inputs (0.03 kg P/m²) were approximately 30x greater than mean P application rates in U.S. conventional agriculture

Because UA yields were similar to yields from conventional agriculture (Swaney et al. 2018), nutrient use efficiencies from UA (2.5% for P, 5.0% for N) were much lower than corresponding efficiencies from conventional agriculture (89% PUE (IPNI 2010); 31% NUE (Swaney et al. 2018)).

Estimated N inputs from UA amendments , by contrast, are a minor component of the watershed N budget, making up approximately 3% of total N inputs (Hobbie et al. 2017 ). I don’t mind too much moving between soil amendments and ferltizers, but it might make sense to go through the whole thing and chose one or state in the methods that some things are used interchangeably or chose one terms but define it to encompass a wide range of things

Note that Hobbie et al. did include county compost in their P budget (based on county data—what volume of compost the county distributed each spring), and that is similar to our calculated P inputs. However, this may go to landscaping and other uses, and much of garden soil inputs was from sources other than county compost—so I don’t know if/how we need to address this

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Bush beans

(Fabaceae)

Cabbage/Collards

(Brassicaceae)

Carrots

(Apiaceae)

Green Peppers

(Solanaceae)

Crops

Municipal compost

(N demand)

Municipal compost

(P demand)

Manure compost

(N demand)

Manure compost

(P demand)

Synthetic fertilizer

No soil amendment

(Control)

Soil treatments

Can we maintain yields, increase P Use Efficiency, and minimize P leachate, with targeted compost applications?

5-year study: 2017-2021

+N

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Response Variables

Soil Chemistry

LOI OM
pH
Bray P
NH₄⁺
NO₃^-

Leachate

Soil moisture
Volume
PO₄^3-
NH₄⁺
NO₃^-

Microbial activity

Soil CO₂ flux
Teabag decomposition
Microbial abundance

Plant Biomass

Crop yield
Plant C/N/P

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Part 2: Soil moisture (Frank)

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Plot 22A (Manure N)

Plot 21A (Municipal P)

Plot 17A (No fertilizer)

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Part 3: Leachate Volume

Average leachate volume in ml for each treatment through 7/20.

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Leachate Volume: Value W

Value W = Total leachate from weeks 2-8/total leachate from all weeks. Measure of how much the averages are influenced by week 1. Value of 1 means no leachate was recorded in week 1, lower values indicate that a lot of the total leachate for a particular lysimeter came from week 1. Average value for all treatments: 0.4798

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Value W

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Outlier/Broken Lysimeters

Lysimeters 12C and 18A have never had any water pulled from them this year.

3B, 7C, 17B, 20A, 27B, and 31C have only had water pulled from them during week 1.

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Nitrate Leachate

Average nitrate concentration in mg/L for leachate from each treatment (through 7/20).

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Ammonium Leachate

Average ammonium concentration in mg/L for leachate from each treatment (through 7/20).

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Phosphate Leachate

Average phosphate concentration in mg/L for leachate from each treatment (through 7/20).

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Part 4: Crop harvest and Chlorophyll �(Megan and Mary)

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Leaf Chlorophyll Data

Amount of Chlorophyll

Amount of nitrogen

Question: Does the chlorophyll levels differ between each treatment?

Stats data:

Treatment
Manure (N)	<0.0001
Manure (P)	0.0299
Municipal (N)	0.2082
Municipal (P)	<0.0001
No Fertilizer	<0.0001
Synthetic fertilizer	zeroed out

Manure P is statistically significant
Manure N and no fertilizer are not significant.

Crops & Treatment:

we only found that Manure N (collard greens) and Manure P (beans) were significant. Meaning higher chlorophyll response.

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Part 6: Soil nutrients, CO2 flux, teabag decomposition, and mineralization (Chip)

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Soil Organic Matter

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Plant-available phosphorus

Study year

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2021 data

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Soil CO2 flux

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Teabag Decomposition

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this seems weird

this makes sense