Browsing by Author "Stewart, Ryan E."

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    Physical and Chemical Parameters of Common Soils in the Central Plateau Region of Haiti
    Stewart, Ryan E. (Virginia Tech, 2012-04-20)
    Soil degradation is a common occurrence in Haiti that is mainly caused by the cultivation of marginal lands and deforestation, which both contribute to the excessive erosion rate seen in the country today. The Central Plateau of Haiti is a mountainous region in which a majority of the population is rural and practices subsistence agriculture on hillsides and steeply-sloping land. Essential plant nutrients, such as nitrogen (N) and phosphorus (P), are commonly a limiting factor in crop production, yet fertilizer is unavailable or is too expensive for smallholder farmers to purchase. This study was conducted to a) evaluate organic matter and nutrient stocks of various soils in the Central Plateau region, along with other chemical and physical characteristics and b) to evaluate the phosphorus-scavenging ability of commonly-grown crops to isolate those that may benefit subsequent smallholder yields. Soils from four locations in the Central Plateau were assessed for organic matter in labile and non-labile fractions as well as for cation exchange capacity (CEC), total organic carbon (C) and N, pH, texture, and other characteristics. Results indicated that most of the soil (92%) was contained within aggregates, and organic matter was mainly present in stable, slowly-decomposing fractions. Seven species were evaluated in a controlled-environment pot experiment for bulk and rhizosphere soil P and pH, plant dry weight, and above- and below-ground P tissue content as indicators of the species' ability to solubilize P from the soil. Velvet bean (Mucuna pruriens (L.) DC) produced the most biomass and was able to take up the most P, though lablab (Lablab purpureous (L.) Sweet), took up comparable amounts of P.
  • Rhizosphere phosphorus solubility and plant uptake as affected by crop in a clay soil from the Central Plateau Region of Haiti
    Stewart, Ryan E.; Hodges, Steven C.; Mulvaney, Michael J.; Pavuluri, K.; Thomason, Wade E. (Taylor & Francis, 2014)
    The nutrient Phosphorous (P) can be available in forms not available for plant uptake, and it is often a limiting factor in tropical crop production. However, certain plants are particularly efficient at extracting phosphorous. These plants can be effective cover crops because they improve phosphorous availability and uptake for the subsequent crop. This study examines the ability of seven different crops to improve phosphorous availability for farmers in Haiti’s Central Plateau. Surface soil from the Central Plateau was air dried and shipped to researchers in the US, where treatments of black bean (Phaseolus sp.), chickpea (Cicer arietinum L.), cowpea (Vigna unguiculata [L.] Walp.), grain sorghum (Sorghum bicolor [L.] Moench), lablab, pigeon pea, and velvet bean were applied in a controlled-environment chamber. After forty-nine days the plants were uprooted and samples of rhizosphere and bulk soil were analyzed. Phosphorous uptake did not differ among the seven species studied. However, researchers found that P uptake positively correlated with rhizosphere P and dry weight. Velvet bean was found to have the high quantity of dry mass, a positive characteristic for a cover crop.