Biosolids stabilized with lime (calcium hydroxide) can cause calcium/magnesium imbalances in the soil.
These imbalances can lead to grass tetany (magnesium deficiency) in livestock, especially lactating
cows. This imbalance is more likely to occur on sites with sandy soils that are already low in magnesium
and have higher pH levels (6.2 or above). Therefore, lime-stabilized biosolids should not be applied on
any soil with a pH greater than 6.2. The higher pH can also lead to a reduction in the availability of other
nutrients such as manganese, iron, copper, and zinc because the solubility of these trace elements goes
down as the pH goes up.
Recent changes to Virginia regulations prohibit the application of lime-stabilized biosolids on Coastal
Plains soils with pH levels greater than 6.3 and on non-Coastal Plains soils with pH levels greater than
6.5. Thus, nutrients and lime content are both limiting factors that determine the quantity and type of
biosolids that can be applied on a given site.
Biosolids are delivered in large dump trucks, usually with a 20-ton capacity. Delivery truck traffic at off-
loading areas when the biosolids are dumped and windrowed can cause compaction, as can tractors
being repeatedly loaded to spread the material. Occasionally, some of the off-loading areas in grass
fields may need reseeding or cultivation to breakup compaction. Farmers report that approximately 5 to
10 percent of a given field is compacted. Compaction adds the cost of extra land preparation. Further,
these off-loading areas tend to receive more biosolids and nutrients than the rest of the field. Farmers
report that windrow areas suffer a yield decrease in the first season after application, but typically
experience a yield enhancement the following season. Very little nutrient-laden water is actually lost
under the windrowed piles in off-loading areas in spite of the high liquid content (typically 75 to 85
percent). The material does not readily lose water due to its high organic matter.
Poor coordination between the farmer and supplier can result in disruptions to production plans, operational
conflicts, increased farm costs, and suboptimal use of the biosolids. The economic and environmental
success of biosolids use depend on the competence and professionalism of the service providers and
farmers’ knowledge of their soils and crop requirements.
PRODUCTION CONSIDERATIONS
Because biosolids applications work better with some crops and in some crop rotations than others,
farmers need to be sure that the applications will fit their crop rotations. Some crops, such as green leafy
vegetables and tobacco, tend to accumulate higher concentrations of metals than grain crops. As a
result, the application of biosolids on leafy vegetables and tobacco is not recommended.
The timing of biosolids application is very important. Applications made too early in the growing season
could result in added weed competition. Late applications can interfere with seedbed preparation and
planting. Poor coordination between the farmer and supplier can result in operational delays, poor use of
farm labor, inconveniences, and failure to maximize plant growth and yield.
Biosolids applications generally work well on cropland in the Piedmont and Coastal Plains of Virginia if
applied in the spring before planting corn or full-season soybeans or if applied in the fall after corn harvest
and before planting small grains. Spring applications to corn and full-season soybeans provide the best
results.