Impact of urbanization trends on production of key staple crops.

Urbanization has appropriated millions of hectares of cropland, and this trend will persist as cities continue to expand. We estimate the impact of this conversion as the amount of land needed elsewhere to give the same yield potential as determined by differences in climate and soil properties. Robust spatial upscaling techniques, well-validated crop simulation models, and soil, climate, and cropping system databases are employed with a focus on populous countries with high rates of land conversion. We find that converted cropland is 30-40% more productive than new cropland, which means that projection of food production potential must account for expected cropland loss to urbanization. Policies that protect existing farmland from urbanization would help relieve pressure on expansion of agriculture into natural ecosystems.

Microwave assisted biocidal extraction is an alternative method to measure microbial biomass of carbon from cultivated and non-cultivated soils.

Developing simple and cost-effective methods for soil microbial biomass carbon (MBC) measurement eases routine laboratory analysis and enables large numbers of soil samples to be measured in a relatively short period of time. Thus, the objective of this study was to develop a microwave-assisted biocidal-extraction (MWE) method which does not employ CHCl3 as biocide and K2SO4 as C-extractor, to estimate MBC. First, the microorganisms of soil samples are killed using microwave (MW) irradiation at energy level of 800 J g-1 soil as biocide followed by microwave irradiation extraction (MWE) at 562 W (120 J g-1 soil for 1 min), using deionized water as solvent. Microbial biomass of carbon from two contrasting soils microwaved with 80, 100, and 140 J g-1 soil did not differ from those obtained by using the chloroform fumigation-extraction (CFE) method with 0.5 mol L-1 K2SO4 as extractant. To evaluate the robustness of the MWE method, twenty-six soil samples, from cultivated and non-cultivated areas, with clay contents from 70-690 g kg-1, organic carbon from 5.52 to 50.82 g C kg-1 and pH values from 3.9 to 6.8 were analyzed for MBC using MWE and CFE methods. There was a linear regression (MW = - 17.87 + 0.92*K2SO4; R2 = 0.705; p < 0.001) between MWE and CFE. The biocidal microwave-assisted extraction method using 120 J g-1 soil for 1 min is a cleaner method for evaluating MBC, because it does not require chloroform, potassium sulfate salt and takes a shorter time to extract a set of soil samples.

Can sub-Saharan Africa feed itself?

Although global food demand is expected to increase 60% by 2050 compared with 2005/2007, the rise will be much greater in sub-Saharan Africa (SSA). Indeed, SSA is the region at greatest food security risk because by 2050 its population will increase 2.5-fold and demand for cereals approximately triple, whereas current levels of cereal consumption already depend on substantial imports. At issue is whether SSA can meet this vast increase in cereal demand without greater reliance on cereal imports or major expansion of agricultural area and associated biodiversity loss and greenhouse gas emissions. Recent studies indicate that the global increase in food demand by 2050 can be met through closing the gap between current farm yield and yield potential on existing cropland. Here, however, we estimate it will not be feasible to meet future SSA cereal demand on existing production area by yield gap closure alone. Our agronomically robust yield gap analysis for 10 countries in SSA using location-specific data and a spatial upscaling approach reveals that, in addition to yield gap closure, other more complex and uncertain components of intensification are also needed, i.e., increasing cropping intensity (the number of crops grown per 12 mo on the same field) and sustainable expansion of irrigated production area. If intensification is not successful and massive cropland land expansion is to be avoided, SSA will depend much more on imports of cereals than it does today.

Symbiotic specificity of tropical tree rhizobia for host legumes.

• The host range and specificity is reported of a genetically diverse group of rhizobia isolated from nodules of Calliandra calothyrsus, Gliricidia sepium, Leucaena leucocephala and Sesbania sesban. • Nodule number and nitrogen content was measured in seedlings of herbaceous and woody legume species after inoculation with rhizobial strains isolated from tropical soils, to establish symbiotic effectiveness groups for rhizobial strains and their hosts. • Specificity for nodulation and N2 fixation varied greatly among the legumes. Symbionts of all four legumes exhibited a wide range of promiscuity and symbiotic effectiveness with isolates of S. sesban having the narrowest host range. N2 fixation varied greatly; although some strains fixed large amounts of N2 with more than one host, none was effective with all hosts. Rhizobial isolates of C. calothyrsus, G. sepium and L. leucocephala were able to effectively cross-nodulate each others' hosts as well as a number of other species. • The complex nature of cross-nodulation relationships between diverse rhizobial strains and legume hosts is highlighted. Host plants inoculated with effective rhizobial strains showed better nitrogen use efficiency than plants supplied solely with mineral nitrogen.