Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Fluid Journal 1993-1995
1 Fluid Journal Fall 1995 Table 1. Dry matter production and potassium uptake for cotton, Mullins, et al., Auburn University, 1994. Decatur SiL Lucedle SCL Dry Matter K Uptake Dry Matter K Uptake --------lba/A-------- 0 7,874 71.4 7,074 79.9 Surface 9,200 84.5 7,452 84.1 3 inches 7,580 69.1 7,838 84.3 9 inches 8,096 81.3 9,084 101.9 15 inches 6,920 67.3 8,313 83.1 21 inches 7,596 65.8 7,713 91.7 Surface/3 inches 8,111 80.1 9,437 129.7 Surface/3/9 inches 7,523 81.7 9,357 105.7 Surface/3/9/15 inches 8,396 86.2 9,740 116.9 Surface/3/9/15/21 inches 9,156 101.6 7,155 87.4 Band/Surface 7,257 73.9 7,358 93.2 Band/3 inches 7,558 78.3 8,530 97.0 Band/9 inches 8,423 83.8 7,860 83.1 Foliar/0 soil K 6,803 64.1 7,328 83.4 Foliar/3 inches soil K 7,929 83.1 7,742 95.1 Foliar/9 inches soil K 8,242 80.9 8,359 91.4 Summary: Recent potassium (K) fertilization studies on cotton have concentrated on deep K placement to deter late-season K deficiencies. Little is known, however; about the efficiency of the cotton plant in removing K from various positions in the soil profile. Hence, we initiated a two-year field study at two sites in 1992 to determine the cotton plant 's ability to remove K from different positions in the soil. Potassium as a KCl solution (as well as rubidium as a RbCl solution) was injected to depths of 0, 3, 9, 15, and 21 inches. In 1994, K uptake was maximized on a Decatur soil when the greatest proportion of the soil profile received K. However; no significant differences in uptake were observed between surface- and deep-applied treatments at each location. Root length density measurements were not significantly different for surface-or deep-applied K. K uptake data for both years suggest that surface application of K, or incorporation of applied K into the plow layer; is sufficient for cotton. Cotton is the number one row crop grown in the state of Alabama. Increased reports of late-season potassium (K) deficiencies, and recent surveys revealing low subsoil K for many soils in the Southeast, prompted studies to correct these deficiencies via deep placement of K. Little is known, however, about the cotton plant's ability to exploit K in the subsoil. Since cotton is a tap-rooted plant, the efficiency of roots inhabiting various soil profile depths must be defined before late-season K deficiency can be solved. This study employs K Dr. G.L. Mullins, C.H. Burmester, G.L. Pate How Can Cotton Plants Best Exploit Potassium In Soil? In search of an answer, Alabama researchers vary positioning of K in soil profile to study its effects on crop yield, K uptake, and root length density. uptake, as affected by K fertilizer placement, in its attempt to define the efficiency of cotton root systems in exploiting K in the soil. Rubidium as a RbCl solution was also injected into the soil profile as a tracer for K. Low-K sites Both sites were selected for their low soil test K. Test areas were established in the fall of 1990 by planting wheat. In the summer of l 991, sorghum- sudangrass was planted. Both forages were clipped and the clippings were removed to reduce the amount of available K in the soil. In 1992, the Lucedale soil had a "low" soil test rating in the 0 to 6-inch and 6- to 12- inch depths. The Decatur soil had a "low" soil test rating in the top 0- to 10- inch depth, and a "medium" soil test rating at a depth of 10 to 20 inches. Each treatment area consisted of 39.4-inch rows extending to the inter-row center on either side of the row. Deltapine 5690 was grown in 40- inch rows and treatments were applied the day after planting. A grid was placed over the treatment area and liquid KCl and liquid RbCl were applied in the spring by making 36 injections per plot. The KCl solution was injected at a test rate of 120 lbs/A of K2O. For the 3-inch depth, rates of 0, 0.25, 0.5, 1, and 2 times the test rate were used to define the K response curve. In addition to single injection
Fluid Journal 1996-1998