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Title Carbon and nitrogen stock comparisons of corn monocultures, biodynamic graze land, and permaculture managements, as an indicator of carbon sequestration and nitrogen leaching potential across practices.

Author Michael Howard

Mentors Dr. Sherlynette Perez-Castro Dr. Faming Wang Dr. Jim Tang

Abstract

The spread of industrial agriculture and large monoculture croplands comes with an increased frequency of nitrogen watershed pollutions and greenhouse gas emissions from the agricultural sector. In hopes to mitigate and potentially reverse these ecological damages, it is important to perform comparisons on the nitrogen leaching and carbon storage potentials across soils of differing agricultural managements. In this study, soil depth profiles of 50cm were compared from four sample sites; a conventional corn monoculture, an organic corn monoculture, a biodynamic dairy graze land, and a permaculture site within the town of Hudson, NY. To assess - + nitrogen leaching potential nitrate (NO3 ), ammonium (NH4 ), and total organic nitrogen (TON), were analyzed. While organic matter (OM), ground water content (GWC), and total organic carbon (TOC) were used in comparison of soil carbon stocks. The permaculture and dairy sites + showed the greatest concentrations of NH4 , TON, TOC, and OM, along with a favorable depth + - distribution of NH4 and NO3 with higher concentrations at the surface and decreasing - concentrations with depth. The conventional site showed the greatest concentration of NO3 in an unfavorable depth gradient with the highest concentrations at the deepest depths. The organic + and conventional sites showed a low percent OM and NH4 with slight trends across depth. The collected data indicates a greater carbon stock and favorable nutrient accumulation within the dairy and permaculture sites. The organic and conventional sites show a lower carbon stock and - nutrient accumulation, with the conventional site showing the greatest potential for NO3 leaching. The data from this study will be used to compliment ongoing eddie covariance and nitrogen cycling experiments at the same sites to further compare both carbon sequestration and nitrogen leaching across practices. This study shows the permaculture and biodynamic dairy sites to contribute the most to carbon sequestration, possess the most favorable nutrient profile, and contribute the least to potential nitrogen leaching due to the polyculture diversity of these sites, the lack of tilling, the use of organic fertilizer, and the complex rotations of the permaculture site. More research is suggested to examine these management factors independently.

Introduction

Industrial agriculture is a major contributor to the increase in global greenhouse gas (GHG) emissions (Tilman et al., 2011). The supply of available nitrogen in the form of fertilizer has resulted in a release of nitrous oxide (N2O) gas from the conversion of inorganic nitrogen to 2 organic nitrogen (Mosier et al., 1998). The growing number of ruminant livestock, such as cattle, has lead to an increase in global methane (CH4) release (Johnson & Johnson, 1995). Taking up 40% of terrestrial land use, global agricultural has had a massive impact on carbon (C) sequestration potential through the conversion of natural flora to croplands (Asner et al., 2004) (Vitousek et al., 1986). With such a large percentage of land affected by agricultural disturbance, it is of growing interest to evaluate the carbon sequestration potential of differing agricultural practices. Current findings seem to suggest that no till agriculture sequesters more carbon dioxide (CO2) than tilling practices (Smith et al., 1998). Under till practices more subsurface carbon is exposed to weathering elements increasing carbon decomposition (Blanco-Canqui & Lal, 2007). It is uncertain whether organic or inorganic fertilizer application sequesters more CO2 (Aquino et al., 2017).

The expansion of industrial agriculture has been accompanied with an increased usage of synthesized nitrogen (N) fertilizer. A series of “Green Revolutions” resulted in the global use of nitrogen fertilizer to increase 700% in the last 40 years (Tilman et al., 2001). Anthropogenic synthesized fertilizer has doubled the rate of natural N-fixation on the planet (Kinzig & Socolow, 1994). In rainfall events, the percolation of water through the soil can leach these fixed soluble + - nitrogen ions, ammonium (NH4 ) and nitrate (NO3 ), into the water table. This nutrient addition can have dramatic effects upon respective watersheds; resulting in eutrophication events caused by algal blooms which can lead to anoxic zones that threaten local fisheries (Rabalais et al., 2002). N leaching has been studied to potentially decrease when shifting from synthesized to organic fertilizer, manure and compost (Mäder et al., 2002). N leaching of has been amplified under the agricultural practice of tilling. As the soil is homogenized, it results in less clay structure to bind to the present ions and contain them within the soil profile (Mkhabela et al., 2008).

The objectives of this study were to conduct a regional (Hudson Valley, NY) comparison of C and N soil stocks across depths at four differing agricultural land managements; an organic corn monoculture, a conventional corn monoculture, a biodynamic dairy graze land, and a permaculture operation with both perennial and annual crops. The measured variables include; soil organic matter (SOM), gravimetric water content (GWC), total organic carbon (TOC), total + - organic nitrogen (TON), NH4 , and NO3 . These C and N stock variables were used as proxies for soil health, indicators to compare potential carbon sequestration, and indicators of N leaching potential. The goal of this study was to provide preliminary insight into what agricultural managements minimize the negative environmental effects of greenhouse gas emissions and N pollution caused in the agricultural sector, while suggesting what particular practices contributed to a desirable soil profile and should be investigated further.

It was hypothesized that C stocks would be the greatest at the permaculture and dairy sites and the lowest at the organic and conventional sites. This was due to the expected accumulation of soil organic matter within the permaculture and dairy managements indicating a greater sequestration potential. Expected N stocks were hypothesized to indicate a favorable concentration gradient, concentrations decreasing with increasing depth, amongst the permaculture and dairy sites; along with a steady or an unfavorable concentration gradient, increasing with depth highest, at the conventional and organic sites. These expected gradients would indicate the lowest leaching potential at the permaculture and dairy sites and the greatest 3 leaching potential at the conventional and organic sites. Based upon the C and N stock hypotheses it was predicted that the permaculture and dairy sites would indicate the greatest soil health.

The data from this study will be complimentary to ongoing Eddie Covariance gas flux and resin bag N cycling experiments being conducted at the same sites (Tang & Wang, unpublished). Centralized at Stone House Grain Farm, previous research on these sites played a pivotal legislative role in blueprinting the agricultural carbon sequestration study laid out in Bill A11111 of the NYS Senate (NYS Assembly). It is our hope that the complementary data collected in this study will provide a foundation to further agricultural and environmental legislative insight.

Materials and Methods

Site Description:

The four study sites are located within the town of Hudson, NY in Columbia County. They are located within close proximity to one another. The organic farm is located at 42° 9'57.42"N, 73°46'13.39"W, the conventional farm at 42° 6'59.51"N, 73°48'34.48"W, and the dairy and permaculture at 42°10'28.49"N, 73°43'42.80"W. The dairy and permaculture sites are located on the same property adjacent to one another.

The conventional farm is a monoculture operation producing corn, soybean, and wheat crops in a three-year rotation. This past year a corn monoculture was grown. This farm does not have a USDA organic certification. The owners typically operate under a no till practice but the land was tilled in the Fall of 2017. Synthesized inorganic N fertilizer is applied to the crops each year.

The organic farm operates under a no till (NT) practice. The farm produces corn and soybeans in a biannual rotation. This past year a corn monoculture was grown. The owners plant cover crops each growing season throughout the rows. Organic fertilizer is used as the only source of added fertilizer to the system.

The dairy graze land is used as pasture for dairy cows. This farm is under a biodynamic land management (Kennedy & Reganold, 2000). The grasses contain a diverse arrange of regional grazing strains that make up the entirety of the ground cover The cattle eat the grasses growing in the pasture, disturb the vegetation through movement, and input nutrients into the soil through the excretion of their own waste. No anthropogenic organic or inorganic fertilizer is added to this land besides the excretions from the cows. Some of the manure produced from the cows each year is exported off the graze land and used as fertilizer on the permaculture beds. At a depth of roughly 20cm the soil is composed significantly of rocks.

The permaculture operation consists of a variety of perennial and annual raised beds growing primarily herbs and berries. This site had the shortest history of land management, with permaculture operations beginning 4 years prior, 2014. The beds contain more than one species often adjacent to two or three differing species in a polyculture like manner. The annual crops undergo a diverse rotation each growing season often in an attempt to utilize excess soil nutrient remnants from the following year. The annual beds are fertilized with the input of the dairy cow 4 manure, and covered with hay each year. Cover crop natural grasses are grown between the beds. There is no tilling on this land.

Soil Sampling and Analysis

At the organic, conventional, and dairy sites 3 plots were selected randomly to obtain samples. The three plots were taken to be replicates of one another. At each plot one soil core was taken to a depth of 50cm. For each core, 5 depth samples were taken at 10cm increments; 0-10, 10-20, 20-30, 30-40, and 40-50cm. Ideally each core would yield 5 samples with three replicate plots, containing 45 samples total. It should be noted, due to a rocky subsurface, no samples were taken below a depth of 30cm at the dairy site, thus dairy measurements are based upon fewer samples. Each soil sample was roughly 100g, which was then stored in a cooler until analyses. The samples at these three sites were taken on 11/7/18, after the corn had been harvested from both monocultures.

At the permaculture site, due to the landscape variability, 5 cores were taken. 2 were taken within annual beds, and 3 were taken in perennial beds. This yielded 25 total samples at this site. All the cores were treated as “replicates” with depth values being averaged together within the analysis. The permaculture samples were collected on 11/28/18, after the harvest date of the annual beds.

Upon returning the soils to the lab, the wet soils were place in a drying oven at 100oC overnight to remove any moisture. Weight measurements were taken before and after drying to determine GWC. SOM was measured using the loss of ignition (LOI) method, placing the samples in a muffled furnace for 5 hours at 450oC (Davies, 1974).

+ - Nitrogen stocks were analyzed through the colorimetric assays of both NH4 and NO3 . 15g of soil were weighed and extracted with 100mL of 1M KCl. The extracted and filtered KCl was run - through a Lachat FIA 8500 in order to determine the NO3 concentrations of each sample. The result was a detectable magenta like color from a methodology derived from Wood et al. (1967). The ammonium absorbances were hand written off a Cary 50 spectrophotometer. The procedure used a modification of the phenolhypochlorite method using indophenol blue published by Solarzano, L. (1969).

TOC and TON of soils were measured within a C/N Elemental Analyzer. The soils were dried, ground with a mortar and pestle, and folded inside tin bags with weights of roughly 20mg (Bisutti et al., 2004).

Results

Carbon Stocks

The SOM showed a higher percent OM across the dairy and permaculture samples (Figure 1). The data showed a significant difference, with the dairy and permaculture sites containing greater percent OM than the organic and conventional sites (Table 1). Across the depth profile of each site there was a general trend of decreasing SOM with increasing depth, in particular within 5 the subsurface depths of the permaculture site (Figure 2). The 0-10, and 10-20cm permaculture depth samples contained a larger variability due to the values measured in plot 4, -8.71% (0- 10cm) and 22.0% (10-20cm).

The GWC data showed a lower soil moisture trend within the conventional site when compared to the other three sites (Figure 3). The dairy and permaculture sites contained significantly more moisture content than the conventional site. There was no significant difference between the conventional and organic sites. The dairy site held significantly more moisture than the permaculture site (Table 1).

The TOC data depicted the highest carbon content to be in the dairy site, the second highest in the permaculture site, and the lowest in the organic and conventional sites (Figure 8). The data showed the dairy soil with significantly more TOC than the permaculture soil, and the permaculture soil with significantly more TOC than the conventional soil. The permaculture TOC was not significantly greater than the TOC of the organic soil, with both sites containing large variability; permaculture 0.0002–0.0363 gC/gSoil, organic 0.1490–2.192 gC/gSoil (Table 1). In summation the TOC means across sites mimicked the trends seen in percent OM (Figure 1).

Nitrogen Stocks

Average nitrate data showed the conventional site to contain the highest concentration across the four sites (Figure 4). There was no significant nitrate concentration relationship between any of the sites (Table 1). When analyzed by depth, a trend of decline in nitrate concentrations can be seen within the dairy site and even more so within the permaculture site; both having the largest concentrations in the surface layer. The opposite trend is true for the conventional site, showing the greatest nitrate concentrations within the three deepest depths of the soil (Figure 5). There was a large variability at the two lowest depths of the conventional site, with plot 3 containing concentrations an order of magnitude greater than the other two replicate plots.

Ammonium data showed a lower average concentration for both the organic and conventional sites (Figure 6). The data showed a significant relationship between all of the sites excluding the dairy and permaculture comparison. The dairy and permaculture sites contained a significantly higher concentration of ammonium than the organic and conventional sites. The organic site contained a significantly higher concentration than the conventional site (Table 1). There is a general trend of decline across ammonium concentrations within the dairy and permaculture sites. The permaculture soil showed the highest surface concentration, decreasing to a mean value of -0.171 gN/gSoil at the 40-50cm depth. The organic and conventional soils showed no clear trend with depth (Figure 7).

+ The collected TON data represented the trends seen within the TOC, and NH4 data, with the dairy and permaculture sites being the greatest (Figure 9). The significant relationships between sites were the same within the TOC variable analysis; dairy greater than permaculture, permaculture greater than conventional, no significance between permaculture and organic (Table 1).

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Discussion

+ The analyzed results show similar mean concentrations across the SOM, TOC, TON, and NH4 variables, with the dairy and permaculture sites containing greater values than the organic and conventional sites. The GWC results show the conventional site with the lowest average water - content. As the opposite is true for the NO3 variable, in which the conventional site contains the - greatest concentration. As depth increases, NO3 increases in the conventional site and decreases + within the permaculture and dairy sites. NH4 also decreases with increasing depth in both the dairy and permaculture sites.

Carbon Sequestration Potential

The percent OM and TOC can be used as comparative indicators for the carbon stock and sequestration potential across the sites. OM is the total percentage of soil mass existing as molecules bound to carbon within the sample (Westermann D., 1996). The OM data represents the highest carbon storage between the dairy and permaculture sites with the lowest in the conventional and organic sites. The decrease in organic matter with depth validates the data, as a decreasing OM is expected with depth (Foth D., 1990). In addition to increasing carbon sequestration potential, OM is also used as a proxy for soil health as higher OM indicates a higher presence of nutrients, water retention, and clay structure to bind to ions () (Six et al., 2000). Under this frame, the dairy and permaculture sites show the greatest soil health as indicated by OM.

TOC represents all of the present carbon within the soil sample (Bernard et al. 1994). The TOC data trends mimic those of the percent OM further validating the data. The TOC within the soil shows the greatest C stock within the dairy plots followed by the permaculture plots. It is expected that if soil samples were taken from the 30-40 and 40-50cm depths at the dairy plots, the mean TOC of the dairy site would be closer to that of the permaculture site. It is also expected that a greater number of analyzed samples would result in the TOC of the permaculture site being significantly larger than the organic site. In any case, the greater TOC values within the permaculture and dairy sites indicate a higher potential for carbon storage and sequestration within the soils.

The higher levels of OM and TOC within the dairy and permaculture operations could be due to both the diversity and permanence of the present flora. The grasses within the graze land and the perennial beds within the permaculture operation are never completely removed from the ground. We expect this absence of annual disturbance to accumulate greater amounts of carbon than the uprooting of annuals or the tilling of the soil. The annual permaculture beds still show a greater TOC and OM, potentially due to the diverse crop rotation and overall floral diversity of the operation. It could be that the crops grown at the permaculture site tend to result in more surrounding OM than corn results in. The complete groundcover of the graze land grasses most likely results in more OM within the soil. The monoculture approach within the organic and conventional sites seems to limit the amount of carbon storage within both soils. The cover crops and no till practice within the organic site show no significant increase in soil carbon storage when compared to the conventional site. It should be noted that this may differ significantly based upon the type of crop being grown and region in which the sites are located. 7

GWC was not used to directly examine soil C or N stocks, but was instead used as a general proxy of soil health. The dairy site contains the highest soil moisture, but it is possible that if samples were taken for the lower soil depths that the permaculture, organic, and dairy moisture may be similar. The conventional soil shows a trend of lower moisture than the three other sites. This is expected to be due primarily due to tilling. The homogenizing of the soil through tilling further breaks down soil carbon structure (Six et al., 2000). We suspect that this lack of structured carbon decreases the water holding capacity of the soil. It is also noted that the planting of cover crops within the organic site may have been a factor in increasing soil moisture content, but we expect this to be minimal.

Nitrogen Leaching Potential

- + The average mean concentrations of NO3 , NH4 , and TON provide insight into the nutrient - accessibility, application efficiency, and leaching potential across the sites. The NO3 data shows the greatest concentration within the conventional site most likely due to the application of synthesized fertilizer in the form of urea. It is a potential indicator that the conventional monoculture is being over fertilized, that at the end of the growing season there is still ample - NO3 within the soil. The other three sites, which receive no synthesized fertilizer, suggest a - slower release of accessible NO3 from organic fertilizer into the soil.

- The depth concentrations profiles provide a more complete picture of how NO3 moves through - each soil system. At the conventional site, the increasing amount of NO3 with depth indicates - potential NO3 leaching through the soil system. While corn crops contain a deeper rooting - profile than most commodity crops, this increase of NO3 with depth is typical for systems - - leaching NO3 ions. We suspect there is not enough floral or microbial uptake of NO3 within the surface depths of the conventional soil to keep the nutrient from percolating deeper into the soil - depths. Perhaps NO3 is applied to the system in such high concentrations that the microbes do - not allocate energy for its uptake. In events of rainfall these NO3 molecules will likely continue to sink deeper into the soil, passing beneath the rooting zone, and potentially entering the - respective watershed if not attenuated. This unfavorable NO3 gradient is likely due to a combination of over-fertilization, tilling practice, and the presence of a monoculture rooting system. The similar rooting profiles of the entire present flora make the efficiency of available nutrient uptake much lower than natural systems (Brussard et al. 2007). The homogenized soil structure decreases clay particle binding to present ions (Six et al., 2000). Each of these factors leads to a potential increase in nutrient leaching and water pollution within the conventional site. - It should be noted that the large variability in the deeper conventional NO3 concentrations indicates some discrepancy within the data. Excluding plot 3, with the elevated values, the concentrations remain more stable with depth.

- The permaculture site shows a decreasing NO3 concentration with increasing depth. In these - soils the greatest NO3 concentrations were measured at the surface, indicating an accessibility of - NO3 to the location of most rooting profiles. The concentration decreases drastically by the final - measured depth, indicating a low potential for NO3 leaching through the system. We expect that the absence of tilling, the application of organic fertilizer, the polyculture characteristics, and the - diverse rotation of crops led to this favorable NO3 gradient. 8

It is expected that if lower depth samples were taken at the diary site, a more definitive trend of - NO3 decline would be observed with depth. The initial trend of observed decline is likely due to the absence of fertilizer application or tilling.

+ - The NH4 and TON data complement the observed NO3 data. The greatest concentrations of + NH4 and TON are both observed at the permaculture and dairy sites further validating the data. + The depth profile of NH4 shows a similarly observed decrease in concentration with depth + among the permaculture and dairy sites. The greater amounts of NH4 in the depths of the + highest rooting activity suggest that the presence of NH4 in these two sites is due to N cycling + within the soils. This suggested N cycling and NH4 turnover is a proxy for soil health and could be due to the diversity and permanence of the flora at the permaculture and dairy sites.

+ - The decreasing NH4 concentrations with depth, as with the NO3 concentrations, suggest limited nutrient leaching potential through the permaculture soils. We suspect that this is due to an effective uptake and recycling of N within the rooting zone, the application of organic fertilizer, and a greater soil structure due to the absence of tilling. Once again it is expected that the concentrations would continue to decline into the deeper depths of the dairy site if samples were obtainable.

Conclusion

From this study we conclude that the agricultural practices at the permaculture and dairy sites are contributing to greater soil health, increased carbon sequestration potential, and a desirable N gradient that minimizes N leaching potential. From the compared practices, it is suggested that polyculture cropping, minimal soil disturbance, nutrient based rotations, and crop type contribute greatly to increased sequestration and decreased leaching potential; while organic fertilizer contributes to decreased leaching potential alone. More research is needed in examining the specific effects of each agricultural management practice in isolation, along with more sampling both prior to and during the growing season. There is little observed difference between the carbon sequestration potentials of the organic and corn monocultures based upon soil stocks. The - variability in the conventional NO3 data makes it uncertain, but it seems as though the conventional site has a greater N leaching potential than the organic site. This would most likely be due to recent tilling. That said both corn monocultures possess unfavorable or low N profiles in comparison to the permaculture and dairy sites. The analyzed data shows that the organic practice, along with the lack of tilling and the addition of cover crops, do not greatly improve soil health, sequestration, or leaching potential according to C and N soil stocks. From these findings we suggest that, while some progress is made, a significant improvement of these qualities cannot be achieved by meeting USDA organic standards, and that an overhauling of management practices focused upon the conversion of monoculture to polyculture perennial crops is necessary. It should be recalled that this study is based upon a low amount of replicates, all data is analyzed based upon soil collected at one time point, and that results will vary regionally and seasonally. That said this study is meant to be a general foundation of exploring the potential environmental benefits and stressors across differing agricultural managements, and a stepping-stone to examine what particular practices have the greatest impact. It is our hope that this study will further open and legitimize research at Stone House Grain Farm and elsewhere 9 into the environmental effects of diverse perennial and annual polyculture cropping that incorporates biodiversity, utilizes organic fertilizer, and minimizes tilling. Framing these environmentally friendly agricultural practices into conversations upon food production, economic incentives, legislative reform, and consumer awareness can progress New York State as a national leader in sustainable agriculture.

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Tables and Figures

Figure 1: Average Organic Matter % across Sites

Figure 1 showed the percent OM across each site’s replicates. The data showed a trend of a higher concentration within the permaculture and dairy sites.

Figure 2: Average Organic Matter % by Depth across Sites

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Figure 2 represented the percent OM across depths. There is a general trend of decline across organic matter percentages within all four sites.

Figure 3: Average Gravimetric Water Content across Sites

Figure 3 showed the GWC across each site’s replicates. The data showed the largest concentration within the dairy site and the lowest at the conventional site.

Figure 4: Average Nitrate across Sites

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- Figure 4 showed the NO3 across each site’s replicates. The data showed a higher concentration within the conventional site than the remaining three sites.

Figure 5: Average Nitrate by Depth across Sites

- Figure 5 represented the NO3 concentrations across depths. The increased concentration with depth in the conventional site displayed the opposite trend of the permaculture site.

Figure 6: Average Ammonium across Sites 13

+ Figure 6 showed the NH4 across each site’s replicates. The data showed the trend of a higher concentration within the permaculture and dairy sites.

Figure 7: Average Ammonium by Depth across Sites

+ Figure 7 represented the NH4 concentrations across depths. The permaculture and dairy sites showed a decreased concentration with depth.

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Figure 8: Average Total Organic Carbon across Sites

Figure 8 showed the TOC across each site’s replicates. The data showed the trend of a higher concentration within the permaculture and dairy sites.

Figure 9: Average Total Organic Nitrogen across Sites

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Figure 9 showed the TON across each site’s replicates. The data showed the trend of a higher concentration within the permaculture and dairy sites.

Table 1: p-values across Measured Variables and Sites

Computed with a pairwise t test comparison the p-value table showed the significance of data across each of the six measured variables. The variables are represented in green while the p- values showing significance are represented in blue. There was the highest frequency of significant data across the ammonium data, and the least across the nitrate data.

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