Phosphorus is often the second most limiting nutrient for plant and therefore, P fertilization
is required to maintain high productivity. Phosphate fertilizers are typically applied through
the soil and react with clay minerals, metal oxides or Ca near the point of fertilizer
placement. Consequently, a substantial fraction of the applied P may be adsorbed, fixed or
precipitate as insoluble complexes. Due to its slow mobility and high fixation, P fertilizer-
utilization efficiency (PUE) is typically low.
The Israeli agricultural sector is characterized by: (i) low arable lands and highly dense
population, (ii) high evaporative demand and low, infrequent, precipitation and, (iii)
demand for premium products. These unique circumstances were the drive for highly
intensive and water efficient agro-system using drip irrigation with marginal water as the
main practice (“necessity is the mother of invention”). Utilization of the irrigation system for
fertilizer application (i.e. fertigation) affecting water and solutes distribution, root system,
microbial activity which expected to have implication on PUE. Solid P fertilizer is commonly
applied once, before sowing. In such case, P is destined to undergo fixation before being
took up by plants and therefore farmers increases application rates. Fertigation enables
application of low P dose at high frequency, occasionally at daily basis. Increasing
application frequency was shown to accelerate P mobility and elevate its availability.
Furthermore, under fertigation, the limited soil volume is allowing to maintain higher soil
moisture level (in the root zoon) and therefore P mobility is increases. Yet, at P fixing soils,
P mobility is still limited to the upper soil layer while root length density tends to be higher
in deeper moist layers. We therefore speculate that subsurface fertigation will ensure that
P is supplied at the right time and the right place.
To overcome the severe water deficient, Israeli agro-system vastly utilizes treated
wastewater (TWW) which are roughly 50% of the available irrigation water. TWW may
contain considerable amounts of valuable nutrients including P (average of 4-5 mg l -1 ).
These “recycled” nutrients often have large annual variations depending on the source of
sewage water, treatment and precipitation. Therefore continuous monitoring of P level is
needed for accurate P management. In some cases, all of the crop requirement can be
supply from the TWW only. Numerous recent studies on fruit trees demonstrated that P
fertilization is sometimes underestimated since P deficiency symptoms are rare and
develop long after productivity was impaired.
The modern Israeli agro-system, designed to save water, was shown to increase PUE
mainly due to: (i) application of P through fertigation, (ii) high application frequency at the
time and place P is needed and (iii) recycling P in the TWW and manure.