I talked to a MD organic vegetable farmer today that in the past has
relied nearly entirely on heavy applications of compost to meet his
As a result his soils test very high in P... As mandatory P based nutrient
management looms over his head, (mandatory in MD as of 2004) he is in
somewhat of a quandry as to how he will meet future crop N needs if he
greatly reduces his reliance on compost (which has a ~1:1 N:P ratio).
We discussed the possibility of meeting most of his crop N need
using legumes cover crops... he thinks this is feasible for supplying
N to his summer crops (e.g. tomatoes, squash...) but he is
concerned about supplying N to his spring and fall crops... especially the
fall crops that follow a summer crop...
All of the above is a lead-in to an off-the-wall idea that I pondered as I
drove home from the organic growers meeting.
In MD, several golfcourses are using a biological control system called
Bioject... this system cultures an isolated strain of microbes in a tank
and periodically injects them into the golf courses irrigation system. The
goal is to biologically control fungal pathogens such as dollar spot.
(the efficacy of this system is being evaluated by a PhD student at the U
The farmer (mentioned above) told me that he had recently constructed a
new irrigation pond and that he was developing
enhanced irrigation capacity.
As I drove home a bevy of possibilities for using irrigation water
to enhance biologically mediated soil N fertility flashed through my
1) inject irrigation water with free living N fixers, photoautotrophs or
heterotrophs depending on the irrigation system...
2) culture N fixing blue green algae in the irrigation pond and then
deliver the N enriched pond water to crops
3) inject irrigation water with a culture of aquatic microbial grazers
such as protoza (or nematodes) to stimulate a timely flush of microbial
turnover/mineralization of nutrients immobilized in soil bacteria
The last idea is the most intriguing to me...
It is well estabilished that while protozoa and nematodes are only a
small fraction of soil microbial biomass, their feeding on bacteria/fungi
is a very important feature of nutrient cycling in soils.
Many studies have found that soil microcosms with bacteria but with and
without the addition of protoza have very different levels of N
I am wondering whether anyone has ever heard of field
applications of protozoa (via irrigation water) to stimulate a timely
Looking forward to any comments on this scheme or any other use of
microbial cultures applied to fields via irrigation water ?
Comments on how to use P-based nutrient managment for
intensive organic vegetable production would also be appreciated...
U of MD
Soil Quality Research
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