PERFORMANCE OF GRAPEVINES UNDER IRRIGATION SYSTEMS - Management, Performance, and Applications of Micro Irrigation Systems - page 255

Gerstl and Yaron [31] found that the adsorption and movement of chemicals in the
soil are affected by several factors such as soil texture, type of soil minerals, and organ-
ic matter content. Moderately adsorbed chemicals were found concentrated around the
emitters, and lateral movement of these chemicals was more pronounced than the ver-
tical movement, after several irrigation cycles. Weekly adsorbed chemicals were uni-
formly distributed in the soil and leached out of the wetted zone more readily, although
some retardation was noticed. These results indicate that different fertigation strategies
should be used for different fertilizers and different soil types. Gad [28] reported that
on active surfaces in fi ne textured soils absorb a portion of the fertilizer. On the other
hand, coarse textured soils do not adsorb a large portion of the applied chemicals. This
concludes that any fertilizer that is not absorbed by the plants in irrigation cycle might
be leached out of the root zone during the following irrigation. Therefore, intelligent
management of fertilizer application is a must.
Kovacs et al. [51] used the isotopic technique (N 15 ) to evaluate the effects of irriga-
tion on the nitrogen fertilizer use effi ciency for seven irrigation treatments at two fertil-
izer levels. Irrigations were applied at four different growth stages of maize, soyabean
and potato (vegetative, fl owering, yield formation and ripening) in four replications.
Every irrigation treatment was equipped with neutron access tubes in two replications
at a depth from 10 to 130 cm. The study compared the impact of defi cit irrigation (i.e.,
water stress imposed during one growth stage) with normal and traditional irrigation
practices. The relationships were determined between relative yield decrease and rela-
tive evapotranspiration, and between the crop yield and water use.
Neill et al. [65] reported that drip irrigation allowed the fertilizer application
through the irrigation water, and this process is known as fertigation. Although adding
fertilizers in a drip irrigation system is quite simple several precautions are necessary.
He found also that for a successful fertigation, one should take into consideration sev-
eral factors, namely: the fertilizer must be soluble in water; it does not precipitate or
react to form precipitate with other soluble salts in the irrigation water; the application
should place the fertilizer in the root zone at the right time; and it must be also mobile
into the root zone.
Soil characteristics, moisture status, discharge rate, irrigation interval affect the
status of micro and macronutrients, and type of added fertilizer.
Threadgill [76] reported the application of chemicals through irrigation systems
poses several environmental benefi ts. Four categories of these potential environmental
impacts are: Potential backfl ow of chemicals to the irrigation water supply or to the soil
surface around the chemigation system; Potential positive and negative impacts on no
point source pollutant potential of materials applied by chemigation; Potential positive
and negative impacts on operator safety; and Potential effects on chemical residues in
food and fi ber production. The application of good management techniques by chemi-
gation operators will allow signifi cantly less exposure of operator to chemicals during
application.
Veeranna et al. [79] found that drip fertigation of water soluble fertilizers (WSF) at
80% recommended dose produced signifi cantly higher dry fruit yield of 1268.00 kg.
ha -1 (chili cv. Byadagi Dabba) over all the treatments, but was on par with drip fertiga-