PDF《Iowa》

3 CHAPTER 2. PLANT TISSUE ANALYSIS TO ASSESS PHOSPHORUS AND POTASSIUM NUTRITIONAL STATUS OF CORN AND SOYBEAN IN IOWA A paper to be submitted to the Soil Science Society of America Journal Andrew J. Stammer and Antonio P. Mallarino ABSTRACT Interest in re-evaluating the value of tissue testing to assess P and K status in corn (Zea mays L.) and soybean (Glycine max L. Merr.) is increasing. The objective of this research was to study relationships between grain yield response to P and K and the concentration of these nutrients in plant tissue. Single-year and multi-year response trials were conducted in Iowa at

30 sites for P (32 sites-years with corn and

34 with soybean) and at

53 for K (67 sites years with corn and

52 with soybean) that encompassed

17 soil series. We sampled above-ground plant parts at the V5-V6 growth stage, corn ear-leaf blades at the R1 stage, and uppermost trifoliolate soybean leaves at R2-R3 stage. Critical concentration ranges were defined using linear-plateau and quadratic-plateau models. All models fit significantly (P ≤ 0.01) and R2 values were 0.31-0.45 for corn plants P, soybean plants and leaf P, and soybean plant K;

0.51-0.53 for K in corn plants and leaves and soybean leaves K;

and 0.62-64 for corn leaf P. Critical concentration ranges were 4.8-5.5 and 2.5-3.1 g P kg-1 and 18.8-25.4 and 10.6-14.2 g K kg-1 for corn plants and leaves;

and 3.3-4.1 and 3.5-4.7 g P kg-1 and 18.9-22.7 and 15.6-19.9 g K kg-1 for soybean plants and leaves. We conclude that P testing of corn ear-leaves at R1 was better than of young plants at V5-V6 but either tissue provided similar K assessments. Testing soybean

4 plants for P at V5-V6 was better than testing leaves at the R2-R3 stage but K testing of leaves was better than K testing of plants. Abbreviations: LP, linear-plateau;

OM, organic matter;

QP, quadratic-plateau;

STP, soil- test P by the Bray-1 method;

STK, soil-test K by the NH4OAc method. INTRODUCTION Plant-tissue analysis directly assesses crop nutrient status. Tissue testing could identify symptomless or developing deficiencies, evaluate effects of nutrient management practices on plant nutrient uptake, help understand the physiology of nutrient utilization by plants, guide complementary fertilization for the current or future crops, and to recommend additional diagnostic procedures (Aldrich, 1973). The majority of P and K fertilization guidelines for row crops and forages are based on soil testing, but tissue testing is used in some regions as a complement of soil testing, and there is renewed interest in using tissue testing to guide nutrient management from agribusinesses, farmers, and crop consultants. Appropriate interpretation of tissue testing to guide fertilization requires correlation research to interpret test results. Early research summarized in thorough reviews and recent research has shown that the nutrient concentrations reported with plant analysis vary greatly not only with ........