Boron deficiency in cotton in calcareous soils of Pakistan. II. correction and internal boron requirement

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1 Symposium no. 16 Paper no Presentation: poster Boron deficiency in cotton in calcareous soils of Pakistan. II. correction and internal boron requirement RASHID A. and RAFIQUE E. Soil Fertility & Plant Nutrition Program, National Agricultural Research Center, Islamabad 45500, Pakistan Abstract On the revelation of widespread boron (B) deficiency in cotton (Gossypium hirsutum L.), 26 replicated farmers field experiments were conducted over 4 years in soils with <0.6 mg HWE B kg -1. Boron was supplied either through soil surface broadcast or foliar feeding. Soil application rates ranged from 0-3 kg B ha -1 as borax and foliar feeding was done by three sprays of boric acid solution containing 0.1% B (plus 0.05 detergent as a surfactant) 45, 60 and 90 days after crop sowing. Boron application enhanced boll weight from 3.4 to 3.6 g boll -1 and boll bearing from 24 to 27 bolls plant -1. Consequently, B application resulted in 8 to 27% enhanced crop yield generally corresponding to severity of B soil deficiency. Mean yield increase was 13% over control (average ~2000 kg seed cotton ha -1 ). Fertilizer B requirement associated with near-maximum (95%) yield was 1.0 kg B ha -1. Higher dose of soil applied B, upto 3 kg B ha -1, did not prove toxic. Foliar feeding of B proved equally effective, but was more cost-effective compared with soil application: value:cost ratio (VCR) of B use was 16:1 in soil application and 30:1 in foliar feeding. Boron concentration in cotton leaves increased with B application. Contrary to widely reported 20 mg B kg -1 as the critical B level in youngest matured leaf blades at early flowering, our research revealed that B requirement in this plant tissue was much greater, 53 mg B kg -1. Further studies are warranted for determining critical B range in a more sensitive foliar tissue, like youngest leaves of cotton. Keywords: cotton, boron deficiency, foliar analysis, critical level, soil application, foliar feeding Introduction Cotton is categorized as sensitive to soil B deficiency, presumably because of its high B requirement (Shorrocks, 1992). Having identified widespread B deficiency in cotton (Rafique et al., 2001), therefore, the next logical task was to investigate crop response to applied B as well as to determine B fertilizer requirement of the crop. This paper presents results of multi-locatoin, multi-year field experiments on the effect of soil-applied and foliar-fed B on cotton productivity. Fertilizer B requirement and internal B requirement of the crop were also determined. Materials and Methods Twenty six field experiments were carried out during in low B fields (< 0.6 mg B kg -1 soil) in six administrative districts within the cotton belt in Punjab

2 province, Pakistan. Soils of experimental fields belonged to Soil Taxonomy Subgroups Fluventic Haplocambids (97% sites) and Fluventic Camborthids (3% sites). Soil textures were sandy clay loam (48% sites), loam (22% sites), sandy loam (19% sites), clay loam (7% sites), and sandy clay (4% sites). Composite soil samples (0-15 and cm) collected before fertilization were analyzed for selected properties and HWE B (Table 1). Table 1 Soil properties of field experimental sites in Pakistan. Parameter Range Mean ph (1:1) Organic matter (%) CaCO 3 (%) Electrical conductivity (1:1) (ds m -1 ) AB-DTPA extractable (mg kg -1 ) P Zn Hot water extractable (HWE) B (mg kg -1 ) Experimental treatments imposed during a particular year were various combinations of the followings: 1. Control 2. a 1.0 kg B ha kg B ha kg B ha kg B ha b Three foliar sprays of 0.1% B solution (plus 0.05% detergent powder/ surfactant), 45 days, 60 days, and 90 days after sowing. a Nos. 2 5, soil application of B as borax; for uniform field broadcast, small quantity of borax was premixed in a few kg well-pulverized soil. b B source was H 3 BO 3. Basal fertilizers were 150 kg N ha -1 as urea (in 3 split doses), kg P ha -1 as DAP and 5 kg Zn ha -1 as zinc sulfate. All fertilizers were applied by soil surface broadcast, before crop sowing. Experimental design was randomized complete block, with three replications. Cotton (mostly cv. CIM-240) was sown during mid May mid June and the crop received standard irrigations and other production practices of the respective area. Fourth leaf (blade, excluding petiole) from the top on main stem was sampled from ~25 plants within each plot, at flower initiation. Foliar B analysis was carried out by dry ashing and colorimetry as described elsewhere (Rafique et al., 2001). Seed cotton was harvested by two manual pickings, completing the second normally in January of the subsequent year. Boll bearing, boll weight and seed cotton yield were recorded

3 Results and discussion Cotton responses to B and fertilizer B requirement Boron application through soil surface broadcast as well as through foliar feeding enhanced seed cotton yield appreciably (P < 0.05; Figure 1). In conformity to earlier reports (Rothwell et al., 1967; Honisch, 1975), yield increase was the consequence of enhanced seed setting and boll weight (Table 2). Native HWE B in our experimental fields being mg B kg -1 (Table 1), the soils were deficient or marginally fertile in B (Tiwari et al., 1988; Rashid et al., 1994). Positive crop responses to B at >0.50 mg B kg -1 soil is attributed to greater B requirement (removal in crop harvest) by cotton compared with most other field crops (e.g., wheat and maize; Shorrocks, 1992). Maximum increase in seed cotton yield with soil applied B, ranged from 12% in to 16% in with an average of 14% over control. The magnitude of maximum yield increase generally corresponded well with severity of soil B deficiency, and fertilizer B requirement associated with near-maximum (95% of maximum) yield was 1.0 kg B ha -1 (Figure 1). Foliar feeding was almost equally effective, resulting in 13% mean yield enhancement. The value: cost ratio (VCR) of B use (i.e. ratio between value of additional seed cotton produced and cost of the applied B) was very attractive, 15:1 in soil application and 31:1 in foliar feeding. B Applied (kg ha -1 ) Figure 1 Relationship between B fertilizer rate and seed cotton yield (maximum yield: , 2,970 kg ha -1 ; , 2,706 kg ha -1 ; , 1995 kg ha -1 ). Previously, many studies have reported increase in cotton yield with B For example, Shi and Yu (1987) in China recorded 15% increased yield with B at soil B level of 0.25 mg kg -1 and 6% increase at 0.37 mg B kg -1. Mortvedt and Woodruff (1993) have listed kg B ha -1 as the recommended fertilizer B rates for cotton in various States of US. In our field studies on peanut in a calcareous Typic Hapludalf, 0.5 kg B ha -1 was inadequate for correcting B deficiency and fertilizer B requirement was 1.0 kg ha -1 (Rashid et al., 1997). In consideration of high B fixation in calcareous soils

4 and high B requirement of cotton (Shorrocks, 1992), therefore our cotton field experiments did not include fertilizer application <1.0 B kg ha -1. In our field studies, soil applied and foliar fed B were almost equally effective in enhancing seed cotton yield presumably due to multiple foliar sprays at appropriate crop growth stages. Soil applied B is readily absorbed by plant roots, rapidly translocated to the plant s growing points, and thus is well distributed throughout the plant. Contrarily, foliar sprayed B is believed to remain in the targeted tissues due to its poor mobility within the plant (Shorrocks, 1992). However, even if upto 98% of the foliar-applied B may remain in the target leaves, a small efficient portion of <2% useful fraction is quite mobile and is distributed to different plant parts including the newly formed leaves (Martini and Thellier, 1980). Boron deficiency in cotton is believed to hamper plant growth by decreased photosynthate translocation through vascular bundles of petioles, causing stunted growth and abnormal reproductive development (Liu et al., 1986; Wang and Zhou, 1992). In the present extensive experiments stunted growth was not observed; however, decreased boll weight and/or boll bearing (Table 2) must be the consequence of abnormal reproductive development. Table 2 Boron nutrition and cotton fruit setting. Boll weight (g boll -1 ) Bolls per plant Crop year Control +B Control +B Mean Internal B requirement of cotton Increased soil B rates resulted in progressive increased B concentration in cotton leaves, and overall B concentration in 26 field experiments was mg kg -1. A plot of leaf B concentrations versus percentage relative seed cotton yield revealed that B concentration for near-maximum yield (95% of maximum) was 53 mg kg 1 (Figure 2). However, the generally suggested critical B levels in leaves are very low: 15 mg kg -1 (Shorrocks, 1992) to 20 mg kg -1 (Plank, 1979; Reuter, 1986; Reuter et al., 1997). These low critical levels were not understable, because in our five year extensive nutrient indexing studies B concentrations in cotton leaves were much greater, i.e mg kg -1 (Rafique et al., 2001). To our apprehension, therefore, foliar analysis diagnostic criteria listed for cotton in the literature appear to be an extrapolation of the criteria for other field crops rather than experimental evidence in cotton itself. Conclusion Boron application in the deficient fields enhanced seed cotton yield appreciably, by improving seed setting and boll weight. Soil application and foliar feeding proved equally effective; however, the latter was much most cost-effective

5 Contrary to the values listed in the literature, critical level of B in diagnostic cotton leaves is much greater, i.e. 53 mg B kg -1. RELATIVE SEED COTTON YIELD (%) B CONCN. IN LEAVES (mg kg -1 ) Figure 2 Relationship between B concentration in leaf blades and seed cotton yield. Acknowledgements This research was funded in part by Ministry of Food, Agriculture, and Livestock (through Cotton Leaf Curl Virus Project) and Ministry of Science and Technology, Government of Pakistan (through Pak-Kazakh Joint Research Fund). The authors thank Dr. Zahoor Ahmad, Director, Central Cotton Research Institute, Multan, and technical staff of Engro Chemical Pakistan Ltd. for support in field experimentation, Dr. M. Inayat Khan for statistical analysis, and Mr. M. Atif for word processing. References Honisch, O Boron nutrition of cotton in Zambia. Cotton Growing Review 52: Liu, W.D., M.M. Pi and Y.H. Wang Diagnosis of boron deficiency in cotton plant. J. Soil Sci. 17: (China). Martini, F. and M. Thellier Use of an (n,) nuclear reaction to study the long distance transport of boron in Trifolium repens L. after foliar application. Planta 150: Mortvedt, J.J. and J.R. Woodruff Technology and application of boron fertilizer for crops, pp In U.C. Gupta (ed.). Boron and Its Role in Crop Production. CRC Press, Boca Raton, Florida, USA. Plank, C.O Plant Analysis Handbook for Georgia, Univ. of Georgia Coop. Ext. Bull. 739 p

6 Rafique, E., A. Rashid, A.U. Bhatti, G. Rasool and N. Bughio Boron Deficiency in Cotton Grown in Calcareous Soils of Pakistan: I. Boron Fertility Mapping and Convenient Soil Test. Kluwer Academic Publisher, Dordrecht, The Netherlands. Rashid, A., E. Rafique and N. Bughio Diagnosing boron deficiency in rapeseed and mustard by plant analysis and soil testing. Commun. Soil Sci. Plant Anal. 25: Rashid, A., E. Rafique and N. Bughio Micronutrient deficiencies in rainfed calcareous soils of Pakistan: II. boron nutrition of the peanut plant. Commun. Soil Sci. Plant Anal. 28: Reuter, D.J Temperature and sub-tropical crops, pp In D.J. Reuter and J.B. Robinson (eds.). Plant Analysis An Interpretatiosn Manual. Inkata Press, Sydney, Australia. Reuter, D.J., D.G. Edwards and N.S. Wilhelm Temperate and tropical crops, pp In D.J. Reuter and J.B. Robinson (eds.). Plant Analysis An Interpretation Manual. 2 nd ed. CSIRO Publishing, Australia. Rothwell, A.J., W. Bryden, H. Kinght and B.J. Coxe Boron deficiency of cotton in Zambia. Cotton Growing Review 44: Shi, M.T. and G.Z. Yu The available boron content in soils and the effect of boron applied to cotton. China Cottons 3: Shorrocks, V.M Boron a global appraisal of the occurrence, diagnosis and correction of boron deficiency, pp In S. Portch (ed.). Proc. Intl. Symp. on the Role of Sulphur, Magnesium and Micronutrients in Balanced Plant Nutrition. The Sulphur Institute, Washington, DC. Tiwari, R.J., A.K. Tiwari and R.A. Sharma Status of available boron in soils of Rajghat command area in Madhya Pardesh. J. Indian Soc. Sci. 36: Wang, Y.H. and X.F. Zhou The effects of boron on the anatomical structures of cotton petioles, pp In S. Portch (ed.). Proc. Intl. Symp. on the Role of Sulphur, Magnesium and Micronutrients in Balanced Plant Nutrition. The Sulphur Institute, Washington, DC