Response of a sandy soil and maize plants to zinc fertilizers

[摘要] English: Maize in Southern Africa is the most important crop for animal and human nutrition. Soil fertility, its management and understanding have an unmistakable role to play in modern agriculture. Maize is prone to zinc deficiency and is known to decrease yield as well as lowering nutritional value. Zinc is reported to be one of the most important micronutrients for the growth and development of maize.An incubation and glasshouse experiment was conducted to evaluate the response of plant available zinc in sandy soil when fertilized with ZnSO4, ZnO and ZnEDTA at different rates. For this purpose a range of extractants were used: HCl, Mehlich I, DTPA, EDTA and Ambic II. In the incubation experiment, two almost similar sandy soils differing only in acidity were treated with the three zinc fertilizers to increase the zinc content with 0 mg kg-1, 1 mg kg-1, 2 mg kg-1, 3 mg kg-1 and 4 mg kg-1. Each treatment was repeated five times. Fertilizers were applied as a solution, and after application soil went through three wetting and drying cycles before plant available zinc was determined in them.In the mentioned glasshouse experiment maize was planted in 40.5 L pots using a complete randomized block design. The same zinc fertilizers were used as for the incubation experiment but application rates differed. One of the soils used for the incubation experiment was selected and treated to increase its zinc content with 0 mg kg-1, 0.5 mg kg-1, 1 mg kg-1, 2 mg kg-1 and 4 mg kg-1. Phosphorus and nitrogen were added to the soil at a constant rate. Fertilizers were dissolved in water and applied as a solution on soil before thoroughly mixed. Maize were planted 50 mm deep and soil was maintained at drained upper limit during the growing period. During the five week growing period stem thickness, plant height and number of leaves were measured weekly while leaf area, root length, root mass and plant available zinc were measured at the end of the growing period. The experiment was repeated at two planting dates. After the growing period soil was sampled for zinc and phosphorus analysis.Concerning zinc source used, ZnSO4 was superior followed by ZnEDTA and ZnO in most of the measured plant parameters as well as plant available zinc content. Plant available zinc content at the end of the incubation experiment differed between the two soils. Extraction methods used to determine plant available zinc content led to different values. For both soils used in the incubation experiment Ambic II, DTPA and EDTA tend to extract more zinc than HCl and Mehlich I.Zinc fertilizers and application rates had a significant effect on plant parameters in the glasshouse experiment. The two plantings differed from each other. The effect of ZnO and ZnEDTA on aerial and subsoil growth parameters was not consistent throughout the glasshouse experiment. Most of the plant parameters showed an impaired development at increasing application rates. This phenomenon however did not occur in the plant available zinc content at the end of the growing period. Extraction method used to determine plant available zinc content at the end of the glasshouse experiment differed. However, the order differs from the results obtained in the incubation experiment. For both experiments the Ambic II and EDTA methods tend to extract the highest amount of zinc from the soil. Zinc source and application rate had a significant effect on both the concentration and uptake of zinc in/by maize. Again ZnSO4 was superior in increasing uptake and concentration of zinc by/in maize, with ZnO and ZnEDTA being inconsistent.Considering the reasons for this study it is clear that ZnSO4 was superior over ZnO and ZnEDTA. This could be attributed that with ZnEDTA and ZnO there were no compensation for the S in ZnSO4. Furthermore the ZnEDTA used was synthetically prepared and may be less effective than natural products. Zinc fertilizer and application rate also proved to have an effect on plant available zinc content and maize growth response.

[发布机构] University of the Free State