Reaping what we sow

Screening and optimization of starch from marine microalgae isolated from Penang sea water Malaysia

Livestock manure is not only a major global source of greenhouse gases from agriculture but also an important source of nutrients for crop production. Judicious management of livestock manure should deliver an effective way to both promote crop growth and mitigate greenhouse gas emissions. Here, we show using the global change analysis model (GCAM) integrated assessment model augmented with a pyrolysis module (GCAM-pyrolysis) that biochar production from global livestock manure may intensify agricultural systems through a 10% (median, 3-27% CE) increase in crop yields. GCAM-pyrolysis estimates that in 2050 widespread pyrolysis of livestock manures will cause an expansion of 415,000 km2 of cropland for food production (median, 376,000-473,000 km2 CE) compared to the reference scenario, at the expense of forests, pastures, and crops purposely grown to produce bioenergy (corn, sugar, palm fruit, oil crops), to produce an additional 5.1 Pcal (median, 3.2-6.7 Pcal CE) of food. Biochar presents significant opportunities in allowing productive land use change and increased crop production while increasing carbon dioxide removal and reducing greenhouse gas emissions. However, widespread adoption of pyrolysis may require food equity and land conservation regulations to mitigate its undesirable effects, such as an estimated increase in staple food prices in certain regions.

Rice is the staple food crop for about 50% of the world's population. It is grown mainly under two ecosystems, known as upland and lowland. Lowland rice contributes about 76% of the global rice production. The anaerobic soil environment created by flood irrigation of lowland rice brings several chemical changes in the rice rhizosphere that may influence growth and development and consequently yield. The main changes that occur in flooded or waterlogged rice soils are decreases in oxidation–reduction or redox potential and increases in iron (Fe2+) and manganese (Mn2+) concentrations because of the reductions of Fe3+ to Fe2+ and Mn4+ to Mn2+. The pH of acidic soils increased and alkaline soils decreased because of flooding. Other results are the reduction of nitrate (NO3 −) and nitrogen dioxide (NO2 −) to dinitrogen (N2) and nitrous oxide (N2O); reduction of sulfate (SO4 2−) to sulfide (S2−); reduction of carbon dioxide (CO2) to methane (CH4); improvement in the concentration and availability of phosphorus (P), calcium (Ca), magnesium (Mg), Fe, Mn, molybdenum (Mo), and silicon (Si); and decrease in concentration and availability of zinc (Zn), copper (Cu), and sulfur (S). Uptake of nitrogen (N) may increase if properly managed or applied in the reduced soil layer. The chemical changes occur because of physical reactions between the soil and water and also because of biological activities of anaerobic microorganisms. The magnitude of these chemical changes is determined by soil type, soil organic-matter content, soil fertility, cultivars, and microbial activities. The exclusion of oxygen (O2) from the flooded soils is accompanied by an increase of other gases (CO2, CH4, and H2), produced largely through processes of microbial respiration. The knowledge of the chemistry of lowland rice soils is important for fertility management and maximizing rice yield. This review discusses physical, biological, and chemical changes in flooded or lowland rice soils.

Earth's global climate system is vast, complex, and intricately interrelated. Many areas are influenced by global-scale phenomena, including the "triple dip" La Niña conditions that