Date of Graduation


Document Type


Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level



Crop, Soil & Environmental Sciences


Nathan A. Slaton

Committee Member

Trenton L. Roberts

Second Committee Member

Edward E. Gbur, Jr.

Third Committee Member

Jarrod T. Hardke


Potassium, Rice, sap, Y-leaf


Rice (Oryza sativa L.) grain yield can be limited by potassium (K) deficiency on soils low in exchangeable K. Visually diagnosing K deficiency during early reproductive growth is not easily done and the interpretation of traditional tissue analysis is limited to select growth-stages. Our primary focus was to define continuous critical Y-leaf-K concentrations during reproductive growth for the production of maximal grain yield. A secondary objective was to examine Y-leaf sap-K concentration, measured using a handheld device, as a rapid in-field method of monitoring rice plant K nutrition. The Y-leaf is defined as the uppermost fully extended leaf with a visible collar. During reproductive growth, 20 Y-leaves were collected weekly from selected fertilizer-K rates (0 to 150 kg K ha-1) in 13 trials that had suboptimal Mehlich-3 extractable soil-test K and were seeded with either a pure-line or hybrid rice cultivar. For each sample, ten Y-leaves were dried, digested, and K concentration determined using inductively coupled plasma atomic emission spectroscopy. The sap was extracted from ten Y-leaves and the sap-K concentration determined on a handheld Horiba LAQUAtwin B-731 K+ meter (HMIK, Kyoto, Japan). Rice development was assessed weekly and expressed as growing degree days after R1 stage (DD10R1). The Y-leaf-K concentration increased with increasing fertilizer-K rate and, when evaluated across time, declined for K-sufficient rice, but remained relatively constant for rice that was marginally sufficient or deficient in K. The sap-K concentration trend across time differed among trials, sample times and fertilizer-K rates. The sap-K and leaf-K concentrations were linearly related but the relationship was relatively weak (R2 = 0.39). The five trials seeded with a hybrid cultivar showed no benefit from fertilizer-K producing mean relative grain yields from 96 to 99%. The relative grain yield of pure-line cultivars ranged from 66 to 99% with significant yield differences measured in five of eight trials. The inconsistency in sap-K prevented the development of critical sap-K concentrations. The critical Y-leaf-K concentration of pure-line cultivars predicted to produce greater than 95% of maximum yield between the R1 and R2 stage was 16.0 g K kg-1. After the R2 stage, the critical Y-leaf-K concentration gradually declined to 13.7 g K kg-1 by the R3 stage but the accuracy of the prediction also declined. The Y-leaf can be used to assess the K nutritional status of pure-line rice cultivars between the R1 and R2 growth stages.