RT Dissertation/Thesis
T1 Boron foliar fertilization: impacts on absorption and subsequent translocation of foliar applied Boron 
A1 Will,Silke
WP 2012/08/09
AB Foliar fertilization is an agricultural practice to supply plants with a specific nutrient in times of low soil availability of the nutrient or low root activity, e.g. during generative growth. The focus of this study was placed on Boron (B). Boron is an essential micronutrient for higher plants and deficiency appears in many countries on numerous crops throughout the world. B fertilization is often applied as foliar fertilizer, but the efficiency is inconsistent. 
The possible physiological function of B in plants is described in Chapter 1 within the general introduction. The experiments were conducted on two disparate crop species (soybean and lychee) and the impact of different parameters on foliar B absorption and subsequent translocation was studied.
The first study (Chapter 2) shows the impact of plant B status on foliar B absorption and subsequent translocation in soybean. The limited absorption of foliar applied B in B deficient plants was observed in soybean and in lychee. The physiological study was developed for soybean plants pre-treated with different B root supply, ranging from deficient to B intoxicated plants. In addition, different formulations were tested in order to increase the subsequent B translocation after foliar B absorption. For this reason polyols (mannitol, sorbitol) were added to the foliar formulations, as they form stable polyol borate ester with B and these compounds enable phloem mobility in some species. 
Lowest absorption was observed in plants with B deficiency and B intoxication, whereas the share of subsequent B basi translocation was highest. Results correlated with measurements on stomata opening and water potential. The interruption of the transpiration stream, indicated by high water potentials in B deficient and intoxicated plants, might facilitate B phloem translocation, as it was shown in recent publications.
Absorption rates were increased in treatments with polyol supplementation, probably due to a humectants effect (lowering the DRH). Subsequent translocation could not be improved by the addition of polyols. 
In Chapter 3 the impact of leaf side of application and adjuvant supplementation on foliar B absorption and subsequent translocation was studied on lychee and soybean. 
The effect of the adjuvants CaCl2 and sorbitol as humectant adjuvants and mannitol and sorbitol as B-binding adjuvants were investigated. 
Both plant species differed greatly in total absorption rates. Boron absorption through the abaxial leaf side was more than three-fold (soybean) or seven-fold (lychee) higher than through the adaxial side 
The addition of adjuvants significantly enhanced the rate of B absorption in soybean, but had no effect on B absorption in lychee. The positive results of adjuvant supplementation in soybean might be attributed to the humectants effect. Subsequent translocation could not be increased in neither of the treatments. 
The results on foliar B absorption via the abaxial leaf surface in both species suggest a high demand for future research, e.g. techniques to spray the abaxial leaf surface. 
In Chapter 4 the focus was to assess the impact of different parameters on foliar B absorption and subsequent translocation in lychee. B solutions were applied on the adaxial versus the abaxial leaf surface of mature or immature leaves. In addition, nocturnal versus diurnal application was studied. 
Absorption was significantly increased after application to the abaxial leaf surface. The parameters leaf age and time of application did not affect absorption. 
Subsequent translocation of foliar absorbed B increased significantly after foliar application of B to mature in comparison to immature leaves. 
Nocturnal application of B resulted in significantly enhanced basipetal B translocation. 
The efficacy of foliar B fertilization can be limited in lychee, especially if only the adaxial leaf surface is targeted as it commonly occurs with the spraying techniques available in many lychee orchards. The practical implications of our results clearly show that B foliar sprays should be applied nocturnally to the abaxial leaf surface. 
In conclusion, absorption and subsequent translocation of foliar applied B can be increased by different parameters in lychee and soybean. Plant B status and leafside of application showed a strong impact on foliar B absorption. All results are discussed in Chapter 5.

K1 Bor
K1 Borisotop
K1 Bormangel
K1 Blattdüngung
K1 Pflanzenernährung
PP Hohenheim
PB Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
UL http://opus.uni-hohenheim.de/volltexte/2012/745