Evaluating the effects of Grassland Set Asides on soil nutrient availability and crop yields in Delta, British Columbia

Project Lead: Khalil Walji
Project Type: Graduate Thesis

Supervisor: Dr. Sean Smukler
Project Partner: Delta Farmland and Wildlife Trust


The Delta Farmland and Wildlife Trust initiated The Grassland Set Aside (GLSA) stewardship program in 1994. Enrolling farmers planted a mixture of grasses and legumes and allow fields to lay in fallow for up to four years in exchange for a cost share. These set asides provide a vegetative cover, protecting the soil surface from erosion while building up soil organic matter and creating prime bird habitat.

No research to date has evaluated set asides beyond a two year period for the effects on soil quality. Long-Term evaluations proposed by this project have been requested by growers enrolled in the GLSA program for well over a decade, however the interest has heightened among the Delta farming community after the results of the pilot study of UBC masters student (Yates,2014) were made available to producers in 2013. The work proposed in this project looks to build off this foundation and aims to assist farmers in tailoring the management of their set asides to meet the needs of their farming operations sustaining agriculture as a viable industry in delta for the foreseeable future.

IMG_0244 (1)

Bean field & paired Grassland Set Aside, Delta, BC


The overarching goal of this project is to provide farmers with detailed information about the effects of integrating short to medium term recurrent GLSA’s into their crop rotations. We will look to evaluate the effectiveness of the GLSA in enhancing long term soil quality and productivity.

Specific research questions to be addressed by this project are:

a) How does the incorporation of GLSA into crop rotation affect soil nutrient cycling and subsequently crop yield?

b) How do differences in soil nutrient cycling and yield vary with duration of set aside?

c) How does GLSA incorporation change the microbial communities following 3-year GLSA cessation?

Experimental design

  1. Grassland set aside treatment
  2. Control (no treatment)

Sub-objective 1. Evaluate nitrogen availability following 4-year GLSAs

Four 4-year GLSA fields were  selected as study sites. Each production field following GLSA incorporation was paired with a nearby production field of the same crop that had not previously had GLSA treatment (control).

Immediately following the incorporation of the GLSAs, soil samples were collected from GLSA fields and control and analysed for a suite of baseline properties at 0-15 and 15-30 cm depth, including: bulk density, total C, total N, nitrate (NO3), ammonium (NH4), soil pH, and electrical conductivity (EC).

Starting summer 2015, every two weeks throughout the crop growing season and then immediately after harvest, soils in each of the production fields following GLSA and control fields were sampled at 0-15 cm and 15-30 cm depth and analyzed for available nitrogen (NO3 and NH4).  Anion and cation exchange resin strips were deployed at each sampling time to assess cumulative release of NO3 and NH4. Soils and resin strips were extracted using potassium chloride and then analyzed cholormetrically 

Sub-objective 2. Quantify differences in crop yields and quality following 4-year GLSAs

Crops in each of the GLSA and control fields were sampled at harvest to determine yield and quality. Crop nutrient content was also assessed using Inductively coupled plasma atomic emission spectroscopy 

Sub-objective 3.  Assess changes in microbial communities following 4-year GLSAs

At the beginning and at the end of the growing season soil (0-15 cm) was sampled and kept frozen. Samples will be later thawed and extracted to run phospholipid fatty acids (PLFA) on a gas chromatograph.


Bean field 1 x 1 (m) sample harvest, Delta BC

Exchange probes inserted to capture cumulative nitrogen availability in the rhizosphere, Dleta BC

Exchange probes inserted to capture cumulative nitrogen availability in the rhizosphere, Delta BC













Research Assistants

The following students (listed alphabetically) have assisted with this project:

  • Alfred Koentjoro
  • Marie Nosten
  • Nicole Read
  • Pariya Torkaman
  • Sarah Wong