The Rain and The Rose
Soil erosion, flooding, and oxygen deficiency,
leaching of nutrient ions
The sky has opened up in Northern
California. Raindrops are falling and
falling since early January, flooding the garden and eroding the soil. The
roses are producing new shoots abundantly.
The roses need plenty of nutrients to support new growth. Unfortunately, nutrient ions leach out both
from the soil and from the leaves.
Adding fertilizers to a soil or foliar -feeding is a simple waste of
time, energy and money, as rains will wash them away. To compound the problem,
low temperatures slow down the uptake of nutrients. Insufficient nutrient
supply will eventually lead to nutrient deficiency that will adversely affect
plant health.
Soil erosion is a major problem in a
sandy soil. In clay soil there is a
danger of flooding. The poor drainage in clay, due to smaller pore size, and
tight binding of water to soil particles, causes waterlogged conditions and
poor ventilation. The lack of oxygen in a waterlogged clay soil, practically
chokes the roots by reducing the root respiration, inhibits the fibrous root
development, and causes root injury.
Because of the reduced root respiration, the root cells cannot generate
adequate high-energy compounds (ATP) that are required for the active transport
of nutrients from the soil to the root hairs.
The active transport process is an uphill movement of nutrient ions from
a site of lower concentration to a site of higher concentration. Such a
condition exists in the cell sap of root hairs where the concentration of
nutrient ions is higher than the concentration of nutrients in the soil
solution and therefore, the root cells need ATP for the uptake of soil
nutrients. An oxygen deficiency also
decreases the root absorption of nutrient ions that are needed for the
synthesis of the green pigment, chlorophyll and causes chlorosis--a symptomatic
yellowing of leaves due to an impaired chlorophyll development. When both conditions, excessive water and
poor aeration occur (especially during heavy rainfall and flooding), the
aerobic microorganisms in the soil are also adversely affected. These microorganisms, which are absolutely
essential for the decomposition of organic matter, cannot survive in the
absence of oxygen. The aerobic microorganisms in their struggle for survival
will compete with the plant roots for the available oxygen, which will
ultimately lead to oxygen-depletion. Waterlogging will eventually result in the
decline of microbial population and thereby, adversely affect soil fertility.
Although roses need plenty of water for good growth, they must be grown in a
soil with good drainage. A loamy
soil--a blend of clay, sand, silt, and organic matter, provides the ideal
growing conditions for plants. By
adding soil amendments, a sandy or a clay soil can be changed to approximate
the beneficial conditions of a loam.
What are these amendments? The
choices include peat moss, aged manure, and compost.
A
root absorbs nutrients mostly as ions. The macronutrients, such as potassium,
magnesium, and calcium are available in soil solutions as positively charged
cations: potassium as K +, magnesium as Mg++,
and calcium as Ca++.
Nitrogen is unusual in that it is available for absorption both as a
cation, ammonium (NH4+,) and as negatively charged
anion, nitrate (NO3-). Plants absorb phosphorus and sulfur as anions--phosphorus as H2
PO4- and PO4=
ions, and sulfur as sulfate, SO4=. The micronutrients that occur predominantly
as cations in the soil solution are iron (Fe+++), copper (Cu++),
manganese (Mn++), and zinc (Zn++).
Molybdenum (MoO4=) and chlorine (Cl-)
occur predominantly as anions. Boron
occurs as the neutral species, borate--H 3BO 3. The anions (negatively charged ions) NO3,
SO4, HCO3, and Cl leach
more easily, as they do not attach to the negatively charged soil particles.
The cations, Ca, and K bind tightly to the negatively charged clay
particles. Calcium binds more tightly
to clay than potassium, as it carries more positive charge than potassium. Cations do not readily leach out from a clay
alkaline soil. However, iron a cation
and boron a neutral species also leach from a soil during heavy rainfalls.
Calcium leaches readily from leaves as well as from soil during heavy rains.
Since magnesium leaches easily from the leaves during rainy seasons, the
addition of Epsom salt after heavy rains is good for the plant. Plants can lose
calcium, magnesium, potassium and nitrogen from leaves, but not iron,
manganese, and zinc. Leaves can lose
almost 12% of minerals after 48 hours of rain.
A nutrient deficiency affects plant
growth in several different ways. The
most commonly recognized symptoms resulting from a nutrient deficiency are
chlorosis (the yellowing of leaves), mottling (spotting), necrosis (the death
of tissues, browning of leaves), etiolation (long spindly wiry thin stems),
stunted growth, reduced and smaller blooms.
A rose garden with such problems would not be beautiful! It would be almost impossible to exhibit
lovely blooms in the rose shows.
What can a gardener do to prevent
nutrient deficiencies that will result from flooding of a soil, soil erosion or
leaching of nutrient ions? As
suggested earlier grow roses in raised beds with right soul composition for a
good drainage of water. A retaining wall with bricks, rocks or redwood boards
will minimize soil erosion as well as leaching of nutrients. Early in November,
add organic fertilizers to rose beds.
Since organic fertilizers release nutrients slowly, one can minimize
leaching of nutrient ions during heavy rains.
Pay attention to weather reports.
If there is no prediction of rains for a couple of days, foliar-feeding
with a diluted liquid fertilizer will compensate for the loss of nutrients from
the leaves.