Summaries of Arkansas Cotton Research 23 CRITICAL PETIOLE POTASSIUM LEVELS AS RELATED TO PHYSIOLOGICAL RESPONSES OF CHAMBER- GROWN COTTON TO POTASSIUM DEFICIENCY D.L. Coker, D.M. Oosterhuis, M. Arevalo, and M. Mozaffari 1 RESEARCH PROBLEM Throughout the growing season, potassium (K) plays a critical role in cotton (Gossypium hirsutum L.) nutrition, yield, and fiber quality. The effect of K deficiency on plant growth and physiological processes during early reproductive growth needs additional investigation in order to develop K fertility management practices for modern fast-fruiting cotton cultivars. Our study objective was to investigate the effect of K deficiency on growth, physiology, and K partitioning to determine the critical K concentration in petioles of uppermost fully expanded main-stem leaves of growth chamber-grown cotton. BACKGROUND INFORMATION The nutritional status of the cotton plant can be determined during the growing season with dependable accuracy by petiole sampling (Robertson et al., 22). Early detection of pending and perhaps sporadic K deficiencies in cotton is crucial to avoid loss of yield and decreased fiber quality (Oosterhuis, 1995). However, a good understanding of when and which physiological processes are first affected by declining K concentrations in petioles during and after the onset of reproductive growth is important for correcting pending K deficiencies. RESEARCH DESCRIPTION Seeds of Suregrow 215BR cotton were planted on 8 August 23 in 5, 4-L pots filled with washed sand. Plants were nurtured with half-strength Hoagland s solution for optimal moisture and nutrients. Growth chamber environmental conditions were adjusted to a 12-hour photoperiod with day/night temperatures of 3/25 C, humidity of 6/8%, and the CO 2 concentration in the growth chamber was kept at ambient levels. To establish treatments, approximately 1 Research specialist, distinguished professor, graduate assistant, Crop, Soil, and Environmental Sciences Department, Fayetteville; research assistant professor, Soil Testing and Research Lab, Marianna, respectively. 81
AAES Research Series 521 21 days after planting, the pots were divided into two groups of 25 each. Half of the pots received half-strength complete Hoagland s solution, which contained 3 mm of K (plus K treatment), and the other half of pots received a K-free, halfstrength Hoagland s solution (minus K treatment). The pots were arranged in a completely randomized block design with five replications of each treatment for each of the planned five weekly harvests. A more complete description of methodology for this type of study was published by Bednarz and Oosterhuis (1999). There were five weekly harvests following the establishment of K treatments. The following were measured at each of the five weekly harvests: photosynthesis, stomatal conductance, chlorophyll, and temperature of uppermost fully expanded main-stem leaves, air temperature, dry-matter partitioning between above-and below-ground organs and nutrient concentration in all harvested organs. RESULTS AND DISCUSSION The earliest indicators of K deficiency stress were observed in lowerstomatal conductance (P#.5) and less leaf cooling (P#.1) in the uppermost unfolded (fourth-node) leaves at 14 days after treatment establishment (DATE) (Fig.1). Stomatal conductance (P#.5) was reduced in K-deficient compared to K-sufficient leaves at 14 DATE while photosynthesis (P#.5) and leaf cooling (P#.1) were reduced in K-deficient compared to K-sufficient leaves at 21 DATE (Fig.1 and 2, respectively). At 28 DATE, photosynthesis (P#.5), chlorophyll a (P#.1), and chlorophyll b (P#.5) were lower in K-deficient compared to K- sufficient leaves (Figs. 1 and 3, respectively). At each harvest interval, we analyzed K in the fourth-node petioles. Beginning at 7 DATE and at each harvest interval thereafter, petiole K concentrations were lower (P#.5) in the minus compared to plus treated plants (Fig. 4). The decreases in petiole nitrate concentration at 14 DATE coincided with significant decreases in plant physiological growth parameters (e.g. gas exchange), which indicated critical concentrations of petiole nitrate. PRACTICAL APPLICATION Decreased stomatal conductance and less leaf cooling were two of the earliest physiological indicators of the onset of K deficiency. The reduction in leaf photosynthesis beginning at 14 DATE corresponded well with reductions in plant growth, i.e., leaf area and biomass accumulation (Oosterhuis et al., 23). By 21 DATE, stomatal conductance and photosynthesis of the fourth-node leaves were significantly lower due to K deficiency; therefore less photoassimilates and energy were available for vegetative and reproductive growth. Based on our physiological measurements, the critical level of K concentration in fourth-node petioles would be between 1.65 to 2.12 %. Verification of the consistency of these results in future field tests will provide valuable information for in-season management of 82
Summaries of Arkansas Cotton Research 23 K nutrition for cotton production in Arkansas. These results will improve our understanding of expected K concentration values in uppermost unfolded leaf petioles for cotton between the onset of the reproductive stage and peak bloom. ACKNOWLEDGMENTS Fees. Support for this research was provided by the Arkansas Fertilizer Tonnage LITERATURE CITED Bednarz, C.W. and D.M. Oosterhuis. 1999. Physiological changes associated with potassium deficiency in cotton. J. of Plant Nutrition. 22:33-313. Robertson, B., L. Espinoza and B. Weatherford. 22. Foliar fertilization of cotton. In: D.M. Oosterhuis (ed.). Summaries of Arkansas Cotton Research 22. Ark. Agri. Exp. Sta., Res. Ser. 57:94-98. Oosterhuis, D.M. 1995. Potassium nutrition of cotton in the USA with particular reference to foliar fertilization. P. 133-146. Proc. of the World Cotton Res. Conf., Brisbane, Australia. Oosterhuis, D.M., D.L. Coker, M. Mozaffari and M. Arevalo. 23. Plant growth, potassium partitioning and physiological response of growth chamber-grown cotton to K deficiency: implications for developing critical K levels for cotton production in Arkansas. In: N.A. Slaton (ed.). Wayne E. Sabbe Arkansas Soil Fertility Studies 23. Ark. Agri. Exp. Sta., Res. Ser. 515:53-57. 83
AAES Research Series 521.8.7 Conductance (mol/m 2 /s).6.5.4.3.2.1 Days After Soil K Treatment Establishment p.1 -.5 Canopy:Air Differential ( C) -1-1.5 p.1-2 -2.5 Days After Soil K Treatm ent Establishm ent Fig. 1. Effect of K deficiency on fourth-node leaf conductance (top) and leaf cooling (bottom) of chamber-grown cotton. 84
Summaries of Arkansas Cotton Research 23 25 Photosynthesis ( mol/m 2 /s) 2 15 p.1 1 Days After Soil K Treatment Establishment 5 Chlorophyll a:b (unitless) 4 3 2 1 35 D a ys A fte r S o il K T re a tm e n t E s ta b lis h m e n t Fig. 2 Effect of K deficiency on photosynthesis of the fourth-node leaf of chamber-grown cotton. 85
AAES Research Series 521 5 4 Chlorophyll b (mg/g dry weight) 3 2 p.5 p.1 1 35 D ays A fter Soil K Treatm ent Establishm ent Fig. 3. Effect of K deficiency on fourth-node leaf chlorophyll a (top) and chlorophyy b (bottom) of chamber-grown cotton. Fayetteville, 23. 6 5 Petiole K (mg/g) 4 3 2 1 Days After Soil K Treatment Establishment Fig. 4. Effect of K deficiency on fourth-node petiole concentration of chamber-grown cotton. Fayetteville, 23. 86