COPPER, MANGANESE, AND ZINC FERTILIZATION EFFECTS ON GROWTH OF SOYBEAN ON A CALCAREOUS SOIL

Authors: HEITHOLT, J - TX AGRIC. EXPER. STN.,DAL; SLOAN, J - TX AGRIC. EXPER. STN.,DAL; Mackown, Charles

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2001
Publication Date: 1/15/2002
Citation: HEITHOLT, J.J., SLOAN, J.J., MACKOWN, C.T. 2002. COPPER, MANGANESE, AND ZINC FERTILIZATION EFFECTS ON GROWTH OF SOYBEAN ON A CALCAREOUS SOIL. JOURNAL OF PLANT NUTRITION. v. 25. p. 1727-1740.

Interpretive Summary: In northeast Texas, soybean producers may see an abundance of yellow leaves before and during the early grain development phase when their crops are planted on high pH Blackland soils. This can lead to reduced yield and lower quality of soybean cut for hay. The occurrence of yellow leaves on soybean at this stage of growth is symptomatic of stress and may be associated with low availability of micronutrients that are often associated with high pH soils. Before conducting a field experiment to test the micronutrient hypothesis, soil was collected from a site where soybeans exhibited early leaf yellowing and was used for greenhouse experiments to determine the effects of adding increasing amounts of copper, manganese and zinc fertilizers. The greenhouse experiments revealed that additions of each of these micronutrient resulted in greater leaf greenness as measured with a hand held meter, and by beginning seed fill, leaves of plants not supplied copper were yellow. Total biomass of the soybean plants was enhanced only by copper additions, but each of the micronutrient treatments increased yields of pods. Additions of micronutrients did not reduce growth. It appears that the early season stresses observed for soybean grown on high pH Blackland soils is linked to micronutrient stress. These results will be used to design further experiments for the field to test the effects of individual and combinations of micronutrients on soybean productivity. This information will be useful to agronomist, crop consultants, and producers seeking to understand limits to soybean production on soils similar to the high pH Blackalnd soil of Texas.

Technical Abstract: High pH may limit micronutrient availability for soybean (Glycine max L. Merr.) on Blackland soils found in northeast Texas. In three separate greenhouse studies, a pH 8.3 Houston Black clay (fine, smectitic, thermic Udic Haplusterts), initially containing 0.74 mg Cu kg-1, 3.74 mg Mn kg-1, and 0.47 mg Zn kg-1, was treated with CuSO4 (0, 25, 50, 75, and 100 ppm Cu), MnSO4 (0, 10, 20, 30, and 40 ppm Mn) or ZnSO4 (0, 2, 4, 6, and 8 ppm Zn). Soybean (cv. Hutcheson) seed were planted then thinned to three per pot at the first true leaf stage. One leaf from each plant was harvested at growth stage (GS) R3 for nutrient analysis. Between 20 and 110 days after planting, five to six nondestructive leaf chlorophyll readings were obtained. Plants were destructively harvested at R6 (mid podfill) for nutrient and yield determination. No visible symptoms appeared through early reproductive growth, but by GS R5 (beginning seed), leaves from the 0 ppm Cu treatment were chlorotic. Chlorophyll (SPAD 502) values of the 3rd uppermost leaf between R3 to R5 were greater when Cu, Mn, and Zn were added to the soil than in the 0 ppm treatment. Fruit yield at GS R6 was greater in pots receiving 25 to 100 ppm Cu, 20 to 40 ppm Mn, and 4 to 8 ppm Zn than in the check treatment. Total biomass was increased by 25 to 100 ppm Cu, but there was only a trend for Mn or Zn to increase biomass. Increases in fruit yield by addition of individual micronutrients may increase further with a combination of micronutrients. There was no evidence that the higher rates of Cu, Mn, or Zn caused reduced growth. These greenhouse results indicated that field studies testing the effects of Cu, Mn, and Zn on soybean yield on this calcareous soil are warranted.