Adequate and Toxic Levels of Copper and Manganese in Upland Rice, Common Bean, Corn, Soybean, and Wheat Grown on an Oxisol

Copper (Cu) and manganese (Mn) play an important role in many biochemical functions of plants. Knowing their adequate and toxic levels in soil and crop plants can be helpful in better fertilizer management and improving crop yields. Ten greenhouse experiments were conducted to determine adequate and toxic levels of Cu and Mn in upland rice (Oryza sative L.), common bean (Phaseolus vulgaris L.), corn (Zea mays L.), soybean (Glycine max L.), and wheat (Triticum aestivum L.) grown on an Oxisol. The Cu levels used were 0, 2, 4, 8, 16, 32, 64, and 96 mg kg−1 of soil applied through Cu sulfate. Similarly, the Mn levels used were 0, 10, 20, 40, 80, 160, and 320 mg kg−1 of soil. Ninety percent maximum relative dry matter yield of shoot was used to determine adequate level and decrease in 10% dry matter yield after achieving maximum value was used to determine toxic level. Adequate Cu application rate was 3 mg kg−1 for upland rice, 2 mg kg−1 for common bean, 3 mg kg−1 for corn, and 12 mg kg−1 for wheat. For soybean, there was no necessity to apply Cu to achieve 90% of maximum yield. Copper toxicity was observed when rice received 51 mg Cu kg1, common bean 37 mg Cu kg1, corn 48 mg Cu kg1, soybean 15 mg Cu kg1, and wheat 51 Cu kg1 of soil. Adequate soil test level of Cu was 2 mg kg−1 for upland rice, 1.5 mg kg−1 for common bean, 2.5 mg kg−1 for corn, 1 mg kg−1 for soybean, and 10 mg kg−1 for wheat, when Mehlich-1 extracting solution was used. Toxic level for the same extractor was 48 mg kg−1 for upland rice, 35 mg kg−1 for common bean, 45 mg kg−1 for corn, 10 mg kg−1 for soybean and 52 mg kg−1 for wheat. When DTPA extracting solution was used, the adequate soil test level was 1 mg kg−1 for upland rice, 0.5 mg kg−1 for common bean, 1.5 mg kg−1 for corn 0.5 mg kg−1 for soybean, and 8.5 mg kg−1 for wheat. For the same extractant, the toxic level was 28 mg kg−1 for upland rice, 18 mg kg−1 for common bean. 32 mg kg−1 for corn, 6 mg kg−1 for soybean, and 28 mg kg−1 for wheat. Adequate plant tissue level was 15 mg kg−1 for upland rice, 6 mg kg−1 for common bean, 7 mg kg−1 for corn and soybean, and 14 mg kg−1 for wheat. Toxic level in plant tissue was 26 mg kg−1 for upland rice, 10 mg kg−1 for common bean, 11 mg kg−1 for corn, 10 mg kg−1 for soybean, and 17 mg kg−1 for wheat. These results suggest that crop species differ in adequate and toxic levels of Cu in soil and plant tissue for maximum yield. Adequate Mn application rate was 2 mg kg−1 for upland rice, 12 mg kg−1 for common bean and corn. For wheat and soybean, there was no necessity to apply Mn to achieve 90% of maximum yield. Manganese toxicity was observed, when rice received 560 mg Mn kg1, wheat 10 mg Mn kg1, common bean 112 mg Mn kg1, corn 400 mg Mn kg1, and soybean 72 mg Mn kg1 of soil. Adequate soil test level of Mn was 8 mg kg−1 for all the five crop species, when Mehlich-1 extracting solution was used. Toxic level for the same extractor was 168 mg kg−1 for upland rice, 44 mg kg−1 for wheat, 128 mg kg−1 for common bean, 400 mg kg−1 for corn, and 92 mg kg−1 for soybean. When DTPA extracting solution was used, the adequate soil test level was 4 mg kg−1 for upland rice, 3 mg kg−1 for wheat, 6 mg kg−1 for common bean, 4 mg kg−1 for corn and soybean. For the same extractant, the toxic level was 80 mg kg−1 for upland rice, 40 mg kg−1 for wheat, 88 mg kg−1 for common bean, 336 mg kg−1 for corn and 56 mg kg−1 for soybean. Adequate plant tissue level was 520 mg kg−1 for upland rice, 173 mg kg−1 for wheat, 400 mg kg−1 for common bean, 60 mg kg−1 for corn and 67 mg kg−1 for soybean. Toxic level in plant tissue was 4560 mg kg−1 for upland rice, 720 mg kg−1 for wheat, 1640 mg kg−1 for common bean, 2480 mg kg−1 for corn, and 720 mg kg−1 for soybean. These results suggest that crop species differ in adequate and toxic levels of Mn in soil and plant tissue for maximum yield.