Mitigating fertility effects of flooding with variable rate amendment

View the project final report

• 2012 annual report
• 2013 annual report

Commodities

• Agronomic: potatoes

Practices

• Crop Production: application rate management
• Education and Training: on-farm/ranch research, workshop
• Soil Management: soil analysis, nutrient mineralization, soil quality/health

With more frequent and intense rainfalls predicted for the North-eastern US as a result of climate change, flood-related fertility problems may occur more often. Flood-prone area are often good farmland and fertility management that considers flooding may help organic farms become more sustainable. Researchers from the University of Vermont and farmers from the Intervale farming community (Burlington, Vermont) will investigate how small farmers can use the concept of variable rate amendments to mitigate flood related patterns of soil fertility deficiencies. Because variable rate agriculture relies on either expensive equipment or extensive soil sampling our team will seek inexpensive proxies for soil fertility testing by correlating topographic factors and soil nutrient concentrations. Our first objective is to find fertility indicators in flood-prone agro-ecosystems. We are also interested testing how crops grown under recommendations that consider spatial variations due to flooding compare to those grown under the more conventional uniform recommendations. Our second objective is to evaluate the spatial distribution of fertility with the goal to identify zones of fertility related to water tables/topography so that amendments can be applied at variable rates to counterbalance the effect of flooding. We will conduct a workshop on the effects of flooding on soil fertility and how to mitigate fertility problems in flood –prone fields. We will also publish a “Farmer’s Guide to Fertility Patterns in Flood Prone Field”.

Goal 1: Correlate spatially referenced soil fertility tests (soil tests) with

a. electrical conductivity measurements as a potential, more affordable fertility assessment tool.
b. elevation and seasonal high water table as a proxy for flooding likelihood.
c. nutrient deficiency symptoms as a biological indicator of fertility needs.

Goal 2: Explore spatially referenced fertility data by combining the data to give averages for

a. an entire depression
b. elevation referenced zones, such as bottom, mid-slope and top of depression
c. by contour intervals

Goal 3: Identify spatial patterns of nutrient needs. Specifically, we will address the question whether proxies for soil tests (Goal 1) can guide fertility recommendations.

Goal 4: Prescribe and apply amendments in accordance with the spatially distributed nutrient needs.

Methods

At each farm we will target one surface depression (at least 50 feet in diameter and 3 ft deep). Each depression will be mapped employing topographic survey techniques with a construction level. At least 50 points will be surveyed in each depression.The map will be referenced to two arbitrary reference points unlikely to change in the near future. The coordinates for these points will be measured using GPS. A topographic map will be generated with GS+ using kriging.

Objective I: Find fertility indicators in flood-prone agro-ecosystems In each depression we will take 25 samples for soil fertility testing three times during the duration of the grant (May 2012, September 2012 and April 2013). At these locations, the location of the seasonal high water table will be determined by determining the depth of redoximorphic features with an auger.The holes will be filled and restored with the excavated material. The sampling scheme will be a stratified random scheme with 6 samples taken at the bottom of the depression, 8 on the mid-slope and 11 in the top tier of the depression. In total there will be 150 soil samples taken for fertility testing from May 2012 to April 2013. The sampling locations will be surveyed using a construction level and referenced to the two reference points used for the maps. This will ensure that the locations on all sampling events can be located on the same topo- graphic map. Soil samples will be sent to UVMs Agricultural and Environmental Testing lab for processing and subsequent dispatch to the University of Maine for standard soil tests and recommendations. Soil nitrogen, organic matter by loss on ignition and active carbon by oxidation with permanganate will be conducted in Dr. Görres’ lab. For each nutrient, data will be correlated to elevation and mapped by co-kriging using GS+. More exhaustive spatial measurements of electric conductivity and soil moisture will be conducted using a W.E.T. sensor (Delta T devices, Cambridge, UK). In order to accomplish accurate soil moisture reading with W.E.T. the sensor will be calibrate for the soils of each depression. In order to do so, 5 large-diameter, undisturbed cores (10 cm in diameter and depth) will be taken from each location and wetted to different degrees on sand tables held at matric potentials of 0 (saturation), 3, 5, 20, 50 kPa of tension. Calibration coefficients will be determined from this set of cores and the W.E.T. programmed to recognize these soils.

For each depression electrical conductivity and moisture will be measured at 100 points in May 2012, after harvest in September 2012 and prior to planting in April 2013. Each point will be surveyed and tied into the reference points.

Multivariate regression will be conducted with measured nutrient concentrations as the dependent variable, and pH, organic matter, active carbon, electrical conductivity, moisture, depth to seasonal high water table and elevation as independent variables. We will eliminate any variables that explain less than 10% of fertility and assess whether the remaining variables can be used to recommend variable rate applications.

Objective II: evaluate the spatial distribution of fertility with the goal to identify zones of fertility related to water tables /topography so that amendments can be applied at variable rates to counterbalance the effect of flooding Each depression is going to be divided into two halves along a North-South line to ensure that both halves get similar light conditions. For one half, nutrients will be applied based on variable rate recommendations and the other will receive amendments according to a uniform recommendation. The uniform recommendation will be based on the average soil test results for the depression area. The variable rate recommendations will be based on nutrient concentrations that exist for each elevation level in the depressions (bottom, mid-slope and top). A uniform crop of vegetables will be grown in the depression. In each half nine plots 6 ft by 6 ft in dimension will be established, 3 per elevation level, giving 6 treatments: Uniform application at bottom (UB), mid-slope (UM)and top (UT), as well as variable applications at bottom (VB), mid-slope (VM), and top (VT. Plant nutrient deficiencies will be assessed by inspection of the crop in each plot and the fraction of plants deficient in any nutrient will be noted. The yield in each plot will be measured.