Soil and Plant Nutrition in Asparagus

By Donald E. Brock  

    I have put together information about soil fertility and
plant nutrition from several sources, including a leading university professor
and recognized expert from California, an agronomist/fertilizer expert from
southern California, and a soils specialist and agronomist from Latin America. Being
a third generation asparagus farmer in California and Mexico, and after
observing asparagus being grown around the world, it has become obvious that
genetics alone will not answer all the problems encountered with asparagus.
However, there are some issues that remain constant no matter what geographical
area is involved.

 Interestingly enough, there are not that many
professors or agronomists in the field today that are current in their
information when discussing soil and plant nutrition as it relates to asparagus. We
all know about basic fertilization practices for a variety of crops, but there
are too many nuances and subtleties that need to be addressed. By reading
thoroughly and understanding the information in this paper, an asparagus farmer
will increase yield and improve quality significantly.

 The
basic approach to soils is to balance them so that no harm is done when
fertilizing. The basic idea is to apply what is needed and that when
the fertilizer is applied, the reaction is a positive one, not a negative one,
thus increasing yields and improving quality.

 Asparagus and sugar cane are
the only two crops that come to mind that we don’t want fruit nor flower, as it
decreases production of shoots, which are harvested in both cases.

 One agronomist that we have
worked with has many years of experience in agriculture in Brazil, Nicaragua,
Honduras, Peru and Costa Rica, dealing with asparagus, sugar cane, and other
high value crops. The nutritional math becomes quite apparent after just a
brief study. The math varies depending on the soil and what is known as
the CEC or Cation Exchange Capacity. When the CEC is a low number, say
below 7, we know that the soil is a sandy soil without much retention capacity,
whereas a drip irrigation droplet will go straight down, versus opening up a
bulb like that of a loamy soil.

 A loamy soil has a CEC from 8
to 15 or so. Above 14 or 15 we tend to see clays, with charges up to 50 or
60. The higher the charge, generally the more clay you will see.

 The Albrecht method, which is
the balancing concept of what progressive agronomists practice on the bases
(potassium, magnesium, calcium, sodium, hydrogen and aluminum), shows us that
once potassium and sodium get above 8 or 10% of the soil, we have salt
problems. A sandy soil should have 16 to 18% magnesium (versus a clay
soil, which should have much less, say 10%).  Magnesium is responsible for
the tightness in the soil, and therefore there is a tendency for the soil to
crack down to 4 inches or more when saturated with water. In sand, we want
this tightness to open up the drip bulb,
but in clay, it makes for anaerobic conditions, where the result is a greatly
reduced root system and poor yields/quality.

Calcium is the element that is
almost always the problem. It is the most ignored as well. Most likely
because it is so cheap. At $40 per ton, no one is interested in selling it
as they don’t make any money. Calcium in a clay soil needs to be up in the
high 70’s to 80% range. In sand we want upwards of 60-70%
calcium. Calcium also goes by the name of Gypsum, which is Calcium
Sulfate. This is not to be confused with Lime, which is Calcium Carbonate, and
much slower acting.

 In Mexico, the whole country
seems to experience a dramatic excess of magnesium. This means that a farmer is
greatly restricted to when they can mature a plant. This is what magnesium
does when in great excess in a soil. In asparagus the plant stays
greener longer than it should, or until cold and lack of moisture induce some
dormancy. In a mango tree, the tree won’t flower for anything as it is
unable to translocate carbohydrates until the tree is super affected by
cold. 

 This is the same phenomenon
that takes place in Caborca. They can’t get the fern to mature until a
heavy cold comes. As well, there is only one peak in the harvest of
asparagus, and then the plant tapers off. This is a clear lack of
carbohydrates. 

If one looks at what is happening,
the soils are full of magnesium (upwards of 25-30%), their calcium is in the
high 40’s to 50% and potassium and sodium are over 12%. There is a fair amount
of salt damage in that area. According to one analysis from a soil lab in
Hermosillo, there is also a very large amount of magnesium in the water,
which obviously compounds the problem.

 There is only one solution
here, which is calcium. In Caborca, some of the growers are using a high
priced type of calcium, by purchasing a product out of the US to run through
their drip system. However, that is a very costly method with only limited
results. In the U.S., a product known as “Hi-Cal” fits this description. 

 Diagnosing calcium problems in
alkaline soils is quite interesting as one always runs up against the U.S.
mentality, saying that if the soil is alkaline, that there is plenty of
calcium. However, that rule of soil science came from Kansas and
Iowa. The fact of the matter is that potassium, sodium and magnesium are
all more alkaline than calcium.

 That is only the problem with
the bases. On top of the base issues, there is a phosphorus issue, using
material prima that does not work on those type soils. Then there is the whole
micronutrient problem. Micronutrients are not being properly used, or else
not used at all. Low boron will hold back calcium uptake (foliar boron doesn’t
work well either), and then there are the zinc, manganese, iron, copper and
sulfur requirements, which all need to be balanced.

 Sometimes growers tend to
plant too shallow, resulting in all kinds of problems as well.

 One agronomist has taken
asparagus farms that produced 12 tons to the hectare in Peru to 22 tons
(exportable) per hectare.  In a test field in these calcium experiments,
32 tons to the hectare on one field were produced.  This same agronomist
has taken an asparagus farm of 13 years of age, producing 4.5 tons/hectare and
taken it to 14 tons/hectare in two years.

 Another agronomist in Honduras
had excellent results using calcium with sweet potatoes and other
crops. Yields went from 8 tons/hectare to more that 40 tons/hectare
exportable. Their cucumber yields have also gone through the roof, and their
eggplant is excellent. They are achieving excellent yields in organic
pineapples as well.   

 It
is recommended that soil samples be taken on a regular basis to determine the
exact content of the various elements discussed in this paper. Once the soil is
in balance, the farmer should have lower unit costs of production, better quality and
higher yields.