Trawling the Ocean of Grass: Soil Nitrogen in Saskatchewan Agriculture, 1916–2001

Using a socioecological metabolism approach to analyze data from the Census of Agriculture, this article examines the underlying soil fertility of two case study areas in the Canadian province of Saskatchewan through the calculation of soil nitrogen balances. The Rural Municipalities of Wise Creek and Livingston are 300 miles apart and therefore have different topography, soil types, and rainfall levels, even though both are within the northern Great Plains. Over 85 years, from first settlement in the 1910s until the beginning of the twenty-first century, Wise Creek agriculture focused increasingly on livestock production while in Livingston farmers began to grow a greater variety of crops, most notably incorporating canola into rotations. Despite the differences between the two case studies, the pattern of soil nitrogen losses was remarkably similar, with biomass yields declining along with soil nitrogen. The addition of chemical nitrogen fertilizers since the 1960s did not produce yields matching historic highs, nor did a renewed focus on livestock. Wise Creek and Livingston showed two different responses to declining yields, but neither one ultimately provided a long-term solution to the problem of soil nutrient depletion and consequent productivity declines.

Co-evolutionary signals from Burkholderia pseudomallei population genomics highlight its survival strategy in a hostile environment

The soil bacterium Burkholderia pseudomallei is the causative agent of melioidosis and a significant cause of human morbidity and mortality in many tropical and sub-tropical countries. The species notoriously survives harsh environmental conditions but the genetic architecture for these adaptations remains unclear. Here we employed a powerful combination of genome-wide epistasis and co-selection studies, gene expression analysis, and gene knockout assays to uncover genetic markers that have been repeatedly selected through B. pseudomallei evolution. These enabled us to identify a large number of mutation pairs under co-selection in distinct genes and non-coding RNA. Genes under co-selection are mostly conditionally expressed with a marked correlation in the expression of gene-gene pairs when grown under physical stress conditions. We discovered a putative adhesin (BPSL1661) as a hub of co-selection signals and experimentally confirmed the essential role of BPSL1661 under nutrient deprivation. The gene co-selection network surrounding BPSL1661 likely offers B. pseudomallei a selective advantage to survive nutrient limited conditions. We propose that anthropogenic activities such as pre- and post-harvest crop residue burning have accelerated soil nutrient depletion and may have directly contributed to the preferential survival of B. pseudomallei over other relatively benign soil microorganisms. This is expected to lead to a consequent increase in the incidence of melioidosis should the “slash-and-burn” practices continue to expand.

Chemical Residues in Food Grains: The Burning Health Issues in Asian Countries

Food security is a high-priority issue for sustainable global development both quantitatively and qualitatively. Once pesticides are applied, residues may be found in soil, on plant, on harvested product, on application equipment, in water and irrigation canals, in pesticide storage area, on cloth of applicant. Short term poisoning effects like nausea, vomiting, headache, chest pain, eye, skin and throat irritation etc. and potential long-term health effect like allergies, cancer, nervous system damage, birth defects, reproductive problem have been reported in recent decades, adverse effects of unexpected contaminants on crop quality have threatened both food security and human health. Heavy metals, metalloids (e.g., Hg, As, Pb, Cd, and Cr) from pesticides and fertilizers can jeopardize human metabolomics, contributing to morbidity and even mortality. Those during crop production include soil nutrient depletion, water depletion, soil and water contamination, and pest resistance/outbreaks and the emergence of new pests and diseases.

Maintaining grain yields of the perennial cereal intermediate wheatgrass in monoculture v. bi-culture with alfalfa in the Upper Midwestern USA

Intermediate wheatgrass (Thinopyrum intermedium; IWG) is a perennial cereal crop undergoing development for grain production; however, grain yield declines of >75% are often observed after year 2 of the perennial stand and may be linked to soil nutrient depletion. Intercropping IWG with a perennial legume such as alfalfa (Medicago sativa) could benefit nutrient cycling while increasing agroecological diversity. Intermediate wheatgrass was established at five environmentally diverse sites in Minnesota, USA in (1) bi-culture with alfalfa, (2) non-fertilized monoculture and (3) monoculture fertilized annually in the spring with 80 kg N/ha. At northern sites where alfalfa growth was favoured, IWG grain yields were reduced in year 2 by growing IWG in bi-culture with alfalfa, relative to the monoculture systems. Across all sites IWG grain yield decreased by 90% in the non-fertilized monoculture, 80% in the fertilized monoculture and 65% in the bi-culture from year 2 to 4 and plant macronutrient concentrations decreased by 25–70%. In year 4, IWG grain yield was similar or greater in the bi-culture than the fertilized monoculture at three of the five sites and alfalfa biomass was correlated positively with grain yield, harvest index and nutrient uptake in the year 4 bi-culture. Chemical-nitrogen fertilization increased grain yields in year 2 but did not mitigate the decline in yields as stands aged. Intermediate wheatgrass in the bi-culture had similar yields and nutrient uptake and lower yield declines than the chemically fertilized stand at sites where alfalfa growth was maintained throughout the life of the stand.

Will forestry follow agriculture toward unsustainable soil depletion?

Human settlement has increased food production by progressively converting complex, self-managing natural ecosystems with tight nutrient cycles into simplified, intensively-managed agricultural ecosystems that are subject to nutrient leaching. Conventional stem wood forest harvesting is now poised to be replaced by intensive harvesting of biomass to substitute for increasingly scarce non renewable fossil fuels. Removal of nutrient-rich forest biomass (harvesting slash) can not be sustained in the long term. Key words: soil nutrient depletion, biomass harvesting, site productivity