Control the Leachate from Silage with a Vegetated Treatment Area
Silage leachate from bunk silos is an environmental problem and should be addressed on all farms. The silage effluent, or juice, can have a very low pH, high biochemical oxygen demand (BOD), and a high level of ammonia. These high concentrations in the juice cause septic odors, vegetation burn, and if allowed to enter directly into a low flowing stream, the damage to aquatic life can be severe. Fish kills have occurred when high strength silage juice enters a stream. Putrid, biologically dead watercourses can be the result of continued leachate flows.
The effluent can have high levels of nutrients such as nitrogen and phosphorus. These too, can become pollutants when they cause excessive algae growth with subsequent oxygen depletion that kills aquatic organisms.
The Vegetated Treatment Area (VTA) system of managing silage leachate from bunk silos has been installed on many farms in New York state as they voluntarily comply with their developed Comprehensive Nutrient Management Plan (CNMP). Concentrated Animal Feeding Operations (CAFO) permitted farms often require a VTA.
The most practical way to deal with silage leachate is to collect and then store the low volume flows of highly concentrated pollutants, while sending the higher volume flows, but lower concentration of contaminants mixed with rainwater, to a VTA.
A Vegetated Treatment Area system typically consists of grading the land to capture all of the leachate, while preventing any clean water from entering the area. The leachate is concentrated to one (or more) point(s) to force the highly concentrated low flows into a waste storage facility, or pumped into a tank. The system uses a series of screens for solids separation and sediment settling pools and piping to direct flows to the proper part of the system. High flows which contain a lesser concentration of pollutants, are directed to a spreading device that creates a shallow sheet flow to spread across a well vegetated area dedicated to the system. Allowing higher flows to bypass the leachate collection and storage system makes storage of the higher concentrated pollutants more affordable to the producer since its size, cost to build, and cost to maintain will be much less than trying to manage all of the effluent coming from the bunk silo.
Sending the low flows of highly concentrated effluent to a storage facility for future land spreading while allowing the less concentrated high flows from runoff events to be treated and assimilated into the environment from a VTA has the potential to significantly reduce pollution, when managed correctly.
Management starts in the bunk. The amount of juice from haylage and silage that is harvested when too wet, peaks quickly after harvest and then decreases to a trickle over time. The amount and concentration of the effluent can be variable from season to season and from day to day depending on crop maturity and harvest conditions. Harvesting crops at more than 30 percent solids will greatly reduce the amount of leachate. Good management such as maintaining a clean bunk floor, and removing spoiled silage piles from flow paths, will reduce the amount of contaminated flows as well.
The low flow collection and separation area needs to be maintained to capture enough of the low flows volume so the vegetation downstream in the system is healthy with no kill zones. The solid separation screens and settling pools also need to be maintained. Developing a standard operating procedure for the feed manager on the farm is needed to keep up with the maintenance. The spreader and the vegetated area require maintenance also. They should be checked regularly to be sure the high flows are moving through the VTA as sheet flow, and are not concentrated to one area. Additional spreaders (gravel trenches) may be needed at intervals along the length of the VTA.
Vegetated Treatment Area - Conservation Practice web page
NRCS-NY Vegetated Treatment Area Standard (Ac) (635), dated 04/2009
For more information, contact your local Soil and Water Conservation District (SWCD), NRCS, or Agricultural Engineer.
Find your local USDA Service Center.