Plant-Available Phosphorus in Highly Concentrated Fertilizer Bands: Effects of Soil Type, Phosphorus Form, and Coapplied Potassium.

Phosphorus (P) is increasingly being applied in concentrated bands to satisfy plant nutrient requirements. To quantify changes in plant-available P in the fertosphere of highly concentrated fertilizer bands, we conducted a soil-fertilizer incubation experiment using seven soil types, three highly water-soluble P sources [monocalcium phosphate (MCP), monoammonium phosphate (MAP), and diammonium phosphate (DAP)], and coapplication of potassium chloride (KCl). First, we found that soil properties were important in influencing P availability. For a calcareous soil, availability was generally low irrespective of treatment, presumably due to precipitation of the fertilizer as Ca-P minerals. For all six noncalcareous soils, fertosphere pH was critical in determining potential P availability, with decreasing pH values decreasing availability, presumably due to precipitation of Al- and Fe-P minerals. Second, given the importance of pH, we also found that the form of P supplied (MCP, MAP, or DAP) had a pronounced effect on P availability due to associated changes in fertosphere pH. Finally, we also found that the coapplication of K also decreased P availability in some soils. We conclude that the selection of the P source is of utmost importance when fertilizers are placed as highly concentrated bands and that soil properties also need to be considered.

Speciation and accumulation of Zn in sweetcorn kernels for genetic and agronomic biofortification programs.

MAIN CONCLUSION: In sweetcorn (Zea mays L.), embryo Zn is accumulated mainly as Zn-phytate, whereas endosperm Zn is complexed with a N- or S-containing ligand. Understanding the speciation of Zn in crop plants helps improve the effectiveness of biofortification efforts. Kernels of four sweetcorn (Zea mays L.) varieties were analysed for Zn concentration and content. We also assessed the speciation of the Zn in the embryo, endosperm, and pericarp in situ using synchrotron-based X-ray absorption spectroscopy. The majority of the Zn was in the endosperm and pericarp (72%), with the embryo contributing 28%. Approximately 79% of the Zn in the embryo accumulated as Zn-phytate, whereas in the endosperm most of the Zn was complexed with a N- or S-containing ligand, possibly as Zn-histidine and Zn-cysteine. This suggests that whilst the Zn in the endosperm and pericarp is likely to be bioavailable for humans, the Zn in the embryo is of low bioavailability. This study highlights the importance of targeting the endosperm of sweetcorn kernels as the tissue for increasing bioavailable Zn concentration.