Residual soil-applied zinc improves grain zinc nutritional quality of maize grown under contrasting soil types in Malawi

Lester Botoman^1*Patson Nalivata²Joseph G Chimungu²Elizabeth Helen Bailey³Moses Munthali⁴E Louise Ander⁵Abdul-Wahab Mossa⁶Murray Lark³Martin Broadley⁷

• ¹International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Lilongwe, Malawi
• ²Lilongwe University of Agriculture and Natural Resources, Lilongwe, Malawi
• ³University of Nottingham School of Biosciences, Sutton Bonington, United Kingdom
• ⁴Ministry of Agriculture and Irrigation Department of Agricultural Research and Technical Services, Lilongwe, Malawi
• ⁵British Geological Survey, Nottingham, United Kingdom
• ⁶ISRIC World Soil Information, Wageningen, Netherlands
• ⁷Rothamsted Research, Harpenden, United Kingdom

A proper understanding of the residual value of zinc (Zn) is essential for the sustainable biofortification of food crops. The study hypothesized that Zn applied at higher rates than the current national recommendation would have significant residual benefits on maize productivity and Zn uptake. The residual effects of soil-applied Zn on grain Zn concentration and uptake were evaluated at Chitedze and Chitala agricultural research stations in Malawi, each featuring two common soil types: Lixisols and Vertisols. The experiment involved three Zn fertilizer rates;1, 30, and 90 kg Zn ha-1 applied as ZnSO4.7H2O in the previous season, arranged in a randomized complete block design (RCBD) with 10 replications per site. At harvest, maize grain yield and Zn concentrations in both grain and stover were measured. Crop yield and Zn uptake were analyzed in relation to residual Zn application and soil type. Results showed that maize grain yield in the second season was 24.6% higher on plots that had received 30 kg Zn ha-1 compared to those with 1 kg Zn ha-1. Similarly, grain Zn concentration and Zn uptake were 12.5% and 29.6% greater, respectively, on plots with the 30 kg Zn ha-1 rate versus the lowest rate. There was no indication that applying 90 kg Zn ha-1 provided additional benefits over 30 kg ha-1 in terms of yield, grain Zn concentration, or Zn uptake in the second season. The magnitude of residual Zn benefits did not vary between soil types. In conclusion, the residual effects of applying 30 kg Zn ha-1 in the previous season significantly improved maize performance compared to the national recommendation of 1 kg Zn ha-1. These findings suggest that higher Zn application rates than currently recommended should be considered in biofortification programs.