>Last night, I was browsing an old issue of the Journal of
>Agronomic Education (~ 1991, so it may have been the newly named
>incarnation) and read a case study article titled "Dick and Sharon
>Thompson's problem child".
>The case study presented that
>after ~20 years of organic integrated livestock and row crop
>production, the Thompsons decided that they had to start banding muriate
>of potash (KCl) to alleviate K deficiency. Tissue tests of their corn
>indicated a serious K deficiency but soil tests indicated K levels that were
>more than adequate.
>Since adopting organic management practices in 1969, the Thompsons had
>not applied any salt fertilizers but had ammended all fields with
>manure from their integrated cattle operation. For a number of years, they
>composted the manure prior to field application but eventually decided
>to abandon composting. Despite the fact that their soil test K levels had
>increased during their 20 years of organic management, something was
>causing their crops to become increasing K deficient.
>Sooo... ~ 7 years have gone by since this article was written... I am
>wondering whether the Thompsons have resolved or continued to struggle
>with their "K problem child" and/or what mechanisms were underlying the
>problem... Can anyone enlighten me ?
i think, that's an old problem with grassland. most of the
nutrients (esp. nitrogen in up to 10% organic matter in the
grasslayer) is found in the upper 10 cm of the field. the soil
below gets deficient or the nutrients are fixated. so nutrient
analysis usually is also restricted to a sample of these 10-15 cm,
while in ploughed land you take 30-35 cm.
then you plow the grassland and in the first and also in the
2nd (and most probably also in the 3rd) year you have:
a) a deficiency of K (that's the usual result of our analyses and
it results from the deficiency of the deeper soil layers,
although the upper 10 cm are sufficiently or even high in potash
content). things are getting better with the years, but you will
have a deficiency for about 3 or 4 years. then orthoclas and
caolinit will start to set free more K (but as a rule of thumb :
always add K when switching from grassland to tillage.) and mostly
K isn't the only deficiency to show up, it's only the most evident
b) high leaching of nitrogen, because the usually compact 10 cm
upper soil (with the grassroots) becomes more aerated, drier and
warmer, the OM is rapidly destroyed and cannot be absorbed in the
now 30 cm of plowed soil. there's nowhere so much nitrogen leaching
than in just ploughed grasslands..
Landwirtschaftl. Untersuchungs- u. Forschungsanstalt (LUFA)
(Governm. Inst. for Agricult. & Environm. Res.)
67346 Speyer, Obere Langgasse 40 (GERMANY)
Dept. of Seed Sci., Microscop. Analysis & Plant Pathol.
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