this is a good summary of the chapter you might find useful;
1. In general, most nutrient solution formulations are not well balanced,
particularly with regard to the major elements, N and K.
2. The total elemental concentration in most nutrient solutions is higher than
can be justified in terms of meeting crop requirements. Most nutrient
element insufficiencies in plants are due to ion imbalances in the applied
nutrient solution rather than due to a deficiency of one or more elements.
3. The atmospheric demand should be a determinant of the total elemental
concentration of a nutrient solution as well as a factor in determining the
frequency of application (the higher the atmospheric demand, the lower
the element ion concentration should be in the nutrient solution with
increased frequency of application).
4. There is justification for designing the nutrient solution delivery system
so that only water can be applied, particularly during periods when the
plant atmospheric demand is high. Also being able to easily change the
dilution ratio during the delivery of a nutrient solution would be a very
useful factor.
5. The concentration of P in most nutrient solution formulations is about
twice that needed and may be the primary cause for some plant nutrient
insufficiencies among the micronutrients Cu, Fe, Mn, and particularly Zn.
6. The concentration of N in a nutrient solution may be the primary factor
determining fruit yield and quality (the higher the N, the lower the fruit
yield and poorer the fruit quality). In general, the N content of a nutrient
solution should be at the lower end of the recommended formulation
amount and should be adjusted based on atmospheric demand — the
higher the demand, the lower the N concentration in the nutrient solution.
7. The ratio between K and Ca in a nutrient solution is probably a major
factor determining fruit yield and quality. That nutrient solution elemental
ratio for most crops should about 1 to 1.
8. The use of chelated micronutrients may be the primary cause for deficiencies
of the micronutrients Cu and particularly Zn in plants.
9. Insufficient Zn in most nutrient solution formulations may be the primary
cause for low Zn levels in the plant. It is recommended that the Zn amount
be double that specified in most nutrient solution formulations. It should
be remembered that high P in a nutrient solution will inhibit Zn uptake
and distribution within the plant. The use of chelated Fe is also a contributor
to lower Zn uptake and distribution within the plant.
10. The inclusion of NH4-N in a nutrient solution formulation can enhance the
uptake of NO3-N, which can be either beneficial or detrimental. The amount
of total N in a nutrient solution formulation can be reduced by 10 to 20%
if 5% of the total N in the nutrient solution is NH4.
The Nutrient Solution 115
11. The adjustment of the pH of a nutrient solution to a particular point is
unjustified unless the pH is outside the desired range between 5.2 and
6.5. It should be remembered that the pH in the immediate area around
plant roots is determined by the roots themselves.
12. The adjustment of a nutrient solution to a particular EC is probably not
justified unless there is a compelling need to restrict water and nutrient
element uptake.
13. The accumulation of elements as precipitates in the rooting medium,
whether the medium is inorganic or organic, can have a significant effect
on the plant’s nutrition with time. Therefore, reducing the concentration
of most elements is justified, particularly Ca, Mg, P, S, and Mn, in the
nutrient solution being applied with time.
14. The requirement for leaching a rooting medium due to the accumulation
of unused elements can be significantly reduced by carefully adjusting the
nutrient solution formulation and frequency of application as well as having
the ability to apply only water for meeting high atmospheric demand.
15. An EC measurement of the solution exiting the growing medium or that
within is used to determine when the rooting medium requires water
leaching. That requirement for leaching should be viewed as a warning
signal that the quality of nutrient elements being applied at greater than
that required by the crop. This leaching requirement can be significantly
reduced if greater care is used in formulating and applying a nutrient
solution — the ideal is that no water leaching is required. An elemental
analysis of exiting or retained nutrient solution will indicate which elements
are accumulating, providing guidance in reformulating the applied nutrient
solution in order to minimize this accumulation.
16. The reuse of a rooting medium can pose a problem since that medium
will start with a significant nutrient element charge from the accumulation
of nutrient elements as precipitates that can not be removed by leaching.
17. In a closed nutrient solution system, the nutrient solution must be filtered
and sterilized between applications.
18. A nutrient solution should be assayed for its elemental content when
initially made to ensure that all the elements are within the specifications
of the formulation. Errors in selecting and weighing ingredients and mixing
when preparing stock solutions can be easily made, and the malfunctioning
of dosers (see Figures 7.4-1 and 7.4-2) is not uncommon
