Potential Application of Hügelkultur to Increase Water Holding Capacity of Central Missouri Farmland

Commodities

Practices

While many climate models have
predicted a continued increase in spring precipitation for
central Missouri, that forecast is tempered with the accompanying
prediction of hotter, drier summers. Farmers in this area have
experienced the impact of such summers, as many counties are
frequently determined to be in moderate, severe, and occasionally
extreme drought. 

The use of hügelkultur, a
horticultural technique in which a mound constructed from
decaying wood debris and other compostable biomass plant
materials is planted as a raised bed, may help alleviate drought
induced difficulties by more effectively retaining water from
rainfall and irrigation. In a region where 40% of the entire
annual rainfall occurs on the ten wettest days of the year and
the four wettest days have experienced a 35% increase in
precipitation over the past 50 years, a passive water collection
system that can absorb, hold, and gradually release the water
produced in a substantial precipitation event will be beneficial
in both alleviating drought pressure and preventing a large
portion of this region's rainfall being lost as run off.

Solution:

Two types of hugelkultur will be
tested in this experiment; above ground and
inground. 

The above ground test sites will
each consist of two beds (44’x3.5’ upslope and 26’x3.25’
downslope; both placed perpendicular to the slope of the field
(X% slope) and curved towards upslope). These beds will be
constructed with a 22” deep base layer of logs, branches, and
manure, a 8” deep layer of leaf/grass mulch, a 10” deep layer of
compost, and finally a layer of soil roughly 3” deep. The two
inground test sites will be placed and constructed exactly the
same except that the base layer will be placed in a 9” deep
trench.

In addition, two control sites
will be made to the same dimensions and placement but only raised
6” and containing only soil. All six sites will be covered with
3” of leaf/wood chip mulch.

Hugelkultur requires the
saturation of its multiple layers as they are assembled to
promote the breakdown of the internal biomass. The water used in
this step will be documented via a water flow meter. 

Two test sites and one control
site will be irrigated regularly to maintain field capacity. This
will be accomplished with existing gravity fed drip irrigation
systems. All test site and control site reservoirs will be
independent of each other to aid in accurate recording of water
usage. These sites will
provide data indicating if the overall gallons of water used in
irrigation is affected by the presence of either type of
hugelkultur. 

Two test sites and one control
site will be left unirrigated. These sites will provide data
indicating the extent to which either type of hugelculture aids
in water retention in relation to rainfall alone. Rainfall will
be recorded daily from the time all sites are completed until the
end of the experiment using a rain gauge.

All sites will be planted with an
identical row footage of peas (to be replaced with beans later in
the season), kale, beets, leeks, and winter squash. These plants
will help to more accurately represent the evapotranspiration
occurring in an active farm plot. 

Two types of measurements will be
used over the course of this experiment to help quantify the
amount of water in the soil; gravimetric water content and soil
water tension.

The gravimetric water content
will be determined biweekly by collecting soil samples with a
soil probe, weighing those samples, heating the samples to remove
any moisture, and reweighing the samples. This data will be used
to ascertain what percentage of the soil mass is water.

The soil water tension will be
measured by tensiometers. Readings will be taken daily from 3
tensiometers per site. This data will demonstrate how much energy
is required to pull water from the soil (which will roughly
indicate the difficulty plants have in acquiring that
water).

Objectives:

1. Determine if hugelkultur facilitates a significant reduction
   in the need for irrigation compared to traditional raised beds.
2. Determine the quantity of water hugelculture can store from
   sizable precipitation events and for what length of time that
   water is retained.
3. If the first two objectives are met positively, demonstrate
   the construction and uses of hugelkultur through an on-farm
   presentation, website and social media, and direct outreach to
   local farmers and consumers through Known and Grown STL.