Agriculture Reference
In-Depth Information
foliar sprays, macronutrient concentrations of generally less than 2% are used to avoid leaf burning.
Plant age should also be considered in selecting nutrient concentration. Old plants are more tolerant
of higher concentration of salts compared to young plants. In foliar fertilization, droplet size and
fertilizer solubility should be carefully controlled since it will affect crop response. Foliar fertiliza-
tion in food crops may not increase yield but may increase the protein content of grains, if applied
during anthesis or flowering (Fageria et al., 2009).
Urea is the most popular form of N used for foliar fertilization in crop plants. Yamada (1962)
reported that the greater effectiveness of urea when applied to foliage resided in its nonpolar
organic properties. Urea containing the
15
N label has been used to measure rates of absorption
and translocation of foliar-applied N, because it permits the direct determination of the uptake and
translocation of foliar-applied N (Gerik et al., 1998). Oosterhuis et al. (1989) and Baolong (1989)
reported that the sympodial leaf rapidly took up foliar-applied N. They found that 30% and 47%
of applied N were recovered within 1 and 24 h after application, respectively. Approximately 70%
of the foliar-applied urea N was absorbed by 8 days after application. There have been similar
reports for soybean when urea was sprayed on the foliage of this crop (Vasilas et al., 1980). Foliar-
applied
15
N to cotton was rapidly translocated from the closest treated leaf to the bolls and was first
detected 6 h after application (Baolong, 1989). Baolong (1989) found that about 70% of the total
foliar-applied
15
N urea was found in the cotton bolls, with less than 5% remaining in the leaves,
petioles, bracts, and branches.
Gerik et al. (1998) reviewed the literature on foliar N fertilization and reported that absorption
was more rapid in young leaves than in old leaves on many crops. Bondada et al. (1997) reported the
correlation between increasing leaf cuticle thickness as the leaf aged and decreased absorption of
foliar-applied
15
N in cotton. Many factors can affect the uptake of foliar-applied urea, including the
condition of the leaf and the prevailing environment. It has been reported that the leaf water status
affects the physical structure of the cotton leaf cuticle (Oosterhuis et al., 1991) and consequently
affects the absorption of the foliar-applied nutrients (Kannan, 1986). Baolong (1989) reported that
water deficit stress impeded the absorption of foliar-applied urea N by sympodial leaves, as well
as the subsequent translocation within the branch of cotton. Furthermore, application made either
in the late afternoon or early morning was more effectively absorbed than those made at midday,
and this was more pronounced for water-stressed plants (Gerik et al., 1998). These authors further
reported that this was associated with the crystallization of urea on the leaf surface and also with
changes in the cuticle caused by water stress.
The yield response of field crops to foliar fertilization of N is highly variable. Positive results
with foliar fertilization of N in soybean have been associated with high-yielding environments.
Yield responses to foliar fertilization are generally not positive when yield is low or nutrients are
at an optimum level in the soil. Leaf damage due to higher concentration of foliar fertilization may
be one of the reasons for either yield decreases or the lack of yield increases. Foliar spray of nutri-
ents should be avoided at high temperature during the day to avoid leaf burning. Similarly, windy
days may drift the applied nutrient solution, and rain immediately after application may wash out
the sprayed material and reduce its efficiency. In rice, foliar spray of nutrients should not be done
after flowering because this may cause spikelet discoloration. Foliar fertilization cannot substitute
soil application. It is simply a nutrient corrective technique in crops during the growth cycle when
soil application is ineffective due to immobilization of soil-applied nutrients or the cost or methods
of application are prohibitive (Fageria et al., 2009).
8.4 CROP MANAGEMENT PRACTICES
Crop management practices are defined as the practices adopted during the crop growth cycle to pro-
duce maximum economic yield. There are several crop management practices that can be adopted
during planting and/or the crop growth cycle to improve nitrogen use efficiency. These practices are
adopting conservation tillage, appropriate crop rotation, and water management.
