Using green seaweed (Ulva spp.) as a soil amendment: Effects on soil quality and yield of sweet corn (Zea mays L.)

Using green seaweed (Ulva spp.) as a soil amendment: Effects on soil quality and yield of sweet corn (Zea mays L.)

Summary

Application of seaweed as a soil fertility management strategy is a traditional practice in many coastal regions, utilizing an inexpensive, abundant, nutrient-rich resource, and often supporting diversified, sustainable agriculture. In this study, I will investigate the application of this practice in coastal New England. The use of excessive beach-cast green seaweed biomass may address the problems of reliance on increasingly expensive inorganic fertilization, accumulation of problematic seaweed biomass, and maintenance of soil fertility and quality. I will evaluate the effects of seaweed biomass application on diverse soil physical, biological, and chemical parameters important for agricultural productivity, maintenance of soil quality, and associated conservation of soil resources. In fall 2011, seaweed biomass was applied to field sites, and soil quality analyses following application were completed. Initial results suggest that seaweed amendment reduces soil pH and increases electrical conductivity, and analysis of other soil quality parameters is ongoing. To assess the production result obtained by initiating seaweed amendment as a soil fertility management practice, I will compare the yield of sweet corn (Zea mays L.) in response to soil amendment with either inorganic fertilizer or seaweed biomass. Additionally, documentation of persistent soil quality changes and effects developing over time will continue to explore the feasibility and viability of adopting seaweed use in agriculture, a practice that may allow farmers to reduce costs, improve soil fertility, enhance environmental stewardship efforts, and increase sustainable use of local resources.

Objectives/Performance Targets

In order to evaluate the application of seaweed biomass as a soil fertility management strategy, the overall objective of this study is to determine the effects of seaweed amendment on soil quality parameters and the yield of sweet corn (Zea mays L.) in a field experiment. The specific objectives and progress steps associated with each objective are listed below.

1) Characterize and prepare suitable amendment material from raw green seaweed biomass for field application

Complete: Fall seaweed biomass collection, species identification, and field application
Ongoing: Seaweed composition analysis and possible supplementary application of green seaweed material

2) Evaluate the effect of seaweed amendment on the yield (bushel/acre and biomass/cob) and quality of sweet corn, an economically important crop for local agricultural production, in comparison to a conventional inorganic fertilization treatment

Complete: Fall tillage for sweet corn plot preparation; weed management (herbicide spraying in November 2011)
Ongoing: Sweet corn will be planted in spring 2012

3) Evaluate seaweed amendment effects on physical, chemical and biological soil quality parameters in comparison to a conventional inorganic fertilization treatment

Complete:
Initial (pre-seaweed application) sampling – Aggregate stability, bulk density, infiltration, earthworms abundance
Initial and post-seaweed application sampling – In-field tests for soil respiration, soil temperature and moisture; insect collection; analysis of soil pH and electrical conductivity (EC); soil extraction for nitrate (NO3-), ammonium (NH4+), phosphate (HnPO4n-3), potentially mineralizable nitrogen (N), microbial biomass N, and nematodes
Ongoing: Extract analysis; soil analysis for micronutrients and heavy metals; insect and nematode identification and counting; data analysis

4) Assess the economic and practical feasibility of seaweed amendment for sustainable agriculture in coastal New England through synthesis of experimental findings, both from this and previous studies, and through discussions with local agriculturalists, Extension agents and agricultural economists

Complete: Documentation of time and cost requirements for seaweed location, collection, preparation and application
Ongoing: Continued determination of benefits and limitations of seaweed application

Accomplishments/Milestones

Field treatment plots (7.6 x 7.6 m) were established at the University of Rhode Island Greene H. Gardner Crops Research Center (Kingston, RI). The field was previously planted with winter squash (2011 season) and disc harrowed prior to initial soil sampling. In October 2011, initial soil sampling for physical, chemical and biological quality before application of seaweed amendment treatments was completed. Sampling procedure and analysis methods are summarized in Table 1. Preliminary results do not indicate substantial differences in physical, chemical, and biological soil quality parameters across plots prior to seaweed amendment. Plots were rototilled to an approximate depth of 25 cm after initial sampling but before seaweed application.

In Rhode Island bays or estuaries (e.g., Warwick Bay), seaweed biomass accumulating on beaches is generally dominated by green seaweed species (e.g., Ulva spp.), and removal is often required. Consequently, the original study proposed use of green seaweed biomass. However, the abundance of beach-cast seaweed biomass, particularly in estuarine environments, is often affected by variation in factors such as temperature, wave activity, and wind strength (1). Due to seasonal variability, beach-cast green seaweed from bays or estuarine sites in Rhode Island was limited during September and October 2011. In contrast, seaweed proliferation closer to the open ocean is generally less dependent on seasonal variability. Consequently, seaweed biomass for fall application was collected by hand from Watch Hill, Westerly, RI, on November 2, 2011. This seaweed biomass was largely composed of brown and red seaweed species, including Ascophyllum nodosum (12.5% DW), Laminaria digitata (2% DW), Chondrus crispus (15.2% DW), Fucus vesiculus (8.2% DW), assorted filamentous red algae (10.5% DW), and mixed non-algal plant material (e.g., eelgrass, 51.5% DW). Analysis of seaweed material C and N content is ongoing. Seaweed biomass was applied by hand to treatment plots in quadruplicate (4 plots/treatment) at low-dose (0.7 kg wet weight/m2) and high-dose (1.4 kg wet weight/m2) levels. Control plots were not amended.

After 2 weeks of seaweed decomposition, soil sampling for biological and chemical parameters was completed as described in Table 1. Preliminary statistical analyses (ANOVA Single Factor, Microsoft Excel) indicate that soil pH in seaweed-amended plots was significantly reduced compared to control plots (p<0.001). Additionally, soil EC was significantly increased in seaweed-amended plots (p<0.001). However, the average soil EC value of high-dose seaweed amendment (70 ± 9.5 µS/cm), though twice that of control plots, is well below the lower limit for use limitation (750 µS/cm) (2). Soil total carbon (C), nitrogen (N), NO3-, NH4+, HnPO4n-3, potassium (K), sulfate (SO3-), trace mineral, and heavy metal analysis is ongoing. Soil respiration did not differ significantly among plots (One-way ANOVA p=0.64). Analysis of preserved collected insects, nematodes, microbial biomass N, potentially mineralizable N (PMN), ergosterol concentration, and active C is ongoing.

Analysis of soil samples/extracts collected during October and November 2011 is ongoing through January 2012. Additionally, a supplementary method of nematode diversity analysis using molecular techniques (funded by the URI Enhancement of Graduate Research program) will be used for analysis of stored extracted nematodes in early spring 2012. In April 2012, sampling for soil quality will begin and continue through the sweet corn growing season. Sweet corn plot preparation, seeding, and maintenance will begin in May 2012.

In summary, seaweed collection, application, and pre-/post-seaweed application soil sampling was completed as expected, except for variation in the seaweed species composition due to seasonal variability. Initially, soil pH was reduced and EC increased in seaweed-amended plots. Further analysis in spring 2012 and during/after sweet corn culture will add information regarding the persistence of changes or development of effects during seaweed decomposition.

• Table 1. Summary of soil quality analysis sampling procedures, schedules, and methods

Impacts and Contributions/Outcomes

Planned outreach for this project includes participation in URI Cooperative Extension “Twilight Talks,” publication of findings on the Extension website. Additionally, opportunities to share findings with local and regional agricultural organizations (e.g., the Northeast Organic Farming Association and Southeast MA/RI young farmer groups) will expand on Extension-related outreach. Based on the limited findings at this point in the research process, outreach has been focused on informal discussions of the project rationale and goals with interested individuals, including local farmers (in particular, Kettle Pond Farm in Berkley, MA, and Brix Bounty Farm in Dartmouth, MA), high-school environmental science students, and even visitors to the beach where seaweed biomass was collected. Seaweed amendment may initially lower soil pH and increase electrical conductivity, which may have implications for soil fertility; however, further analysis of other physical, biological, and chemical quality characteristics and implementation of upcoming research steps is needed to assess the applicability of findings to farm management practices.

Literature Cited
1. Merceron, M., Antoine, V., Auby, I., and Morand, P. In situ growth potential of the subtidal part of green tide forming Ulva spp. stocks. Sci. Tot. Env. 384 (1-3), 293–305 (2007).
2. Bauder, T.A., Waskom, R.M., Sutherland, P.L., and Davis, J.G. Irrigation water quality criteria. Colorado State University Fact Sheet No. 0.506. http://www.ext.colostate.edu/pubs/crops/00506.pdf (2011).

Collaborators: