Background and Aims Understanding the spatial distribution of inorganic nutrients within edible parts of plant products helps biofortification efforts to identify and focus on specific uptake pathways and storage mechanisms. • Methods Kernels of sweetcorn (Zea mays) variety 'High zeaxanthin 103146' and maize inbred line 'Thai Floury 2' were harvested at two different maturity stages, and the distributions of K, P, S, Ca, Zn, Fe and Mn were examined in situ using synchrotron-based X-ray fluorescence microscopy. • Key Results The distribution of inorganic nutrients was largely similar between maize and sweetcorn, but differed markedly depending upon the maturity stage after further embryonic development. The micronutrients Zn, Fe and Mn accumulated primarily in the scutellum of the embryo during early kernel development, while trace amounts of these were found in the aleurone layer at the mature stage. Although P accumulated in the scutellum, there was no direct relationship between the concentrations of P and those of the micronutrients, compared with the linear trend between Zn and Fe concentrations. • Conclusions This study highlights the important role of the embryo as a micronutrient reserve for sweetcorn and maize kernels, and the need to understand how biofortification efforts can further increase the inorganic nutrient concentration of the embryo for human consumption.

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The greenhouse gas fluxes and effective mitigation strategies in subtropical vegetable cropping systems remain unclear. In this field experiment, nitrous oxide (N2O) and methane (CH4) fluxes from an irrigated lettuce cropping system in subtropical Queensland, Australia, were measured using manual sampling chambers. Four treatments were included: Control (no fertiliser), U100 (100 kg N ha–1 as urea), U200 (200 kg N ha–1 as urea) and N100 (100 kg N ha–1 as nitrate-based fertilisers). The N fertilisers were applied in three splits and irrigation was delivered sparingly and frequently to keep soil moisture around the field capacity. The cumulative N2O emissions from the control, U100, U200 and N100 treatments over the 68-day cropping season were 30, 151, 206 and 68 g N2O-N ha–1, respectively. Methane emission and uptake were negligible. Using N2O emission from the Control treatment as the background emission, direct emission factors for U100, U200 and N100 treatments were 0.12%, 0.09% and 0.04% of applied fertiliser N, respectively. Soil ammonium (NH4+) concentration, instead of nitrate (NO3–) concentration, exhibited a significant correlation with N2O emissions at the site where the soil moisture was controlled within 50%–64% water-filled pore space. Furthermore, soil temperature rather than water content was the main regulating factor of N2O fluxes in the fertilised treatments. Fertiliser type and application rates had no significant effects on yield parameters. Partial N balance analysis indicated that approximately 80% and 52% of fertiliser N was recovered in plants and soil in the treatments receiving 100 kg N ha–1 and 200 kg N ha–1, respectively. Therefore, in combination with frequent and low-intensity irrigation and split application of fertiliser N, substitution of NO3–-based fertilisers for urea and reduction in fertiliser N application rates were considered promising mitigation strategies to maintain yield and minimise N2O emissions during the low rainfall season.

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Effects of varying lanthanum (La) or aluminium (Al) concentrations (0-30 µM) on corn (Zea mays L.) root elongation were examined in the presence and absence of (i) humic acid (HA) at 35 mg carbon (C)/L, or (ii) fulvic acid (FA) at 15 mg C/L, using dilute nutrient solutions. The organic acids were extracted from a mixture of decomposed grass (Sorghum halepense) and lucerne (Medicago sativa) hay. In the absence of added HA or FA, the addition of La at ≥5 µM and Al at 30 µM was toxic to the root growth of corn. The rhizotoxic effects of La at 5 and 10 µM were negated by HA. The ability of FA to overcome La rhizotoxicity was much less, significantly ameliorating the toxic effects of 5 µM La but not those of 10 or 30 µM La. HA and FA did not precipitate La from solution. Both organic acids ameliorated Al toxicity by complexing Al and reducing monomeric Al in solution. It is concluded that concentrations of HA and FA, commonly present in soil solutions, are capable of forming non-rhizotoxic complexes with La, hence plant tolerance to La in the soil solution may be appreciably higher than would be indicated by results of solution culture experiments in which these ligands are not present.