10Boron Is Mobile in Cowpea Plants

Cowpea [Vigna unguiculata (L.) Walp] is cultivated in tropical and subtropical regions worldwide, but its production is usually limited by boron (B) deficiency, which can be mitigated by applying B via foliar spraying. In plants with nutrient mobility, the residual effect of foliar fertilization increases, which might improve its efficiency. An experiment was carried out to evaluate the concentration and mobility of the B isotopic tracer (10B) in different organs of cowpea plants, after the application of this micronutrient in the growing media and also to leaves. Treatments were designed based on B fertilization as follows: without B in the growth media, with 10B applied via foliar spraying (10B-L), with B in the growth media (substrate) and 10B via foliar spraying (10B-L + B-S), and with 10B in the growth media (substrate) without foliar spraying (10B-S), and a control without fertilization. A redistribution of 10B was observed in new leaves when the element was supplied via foliar spraying, resulting in greater leaf area, dry mass and dry matter production of aerial parts, and also the whole plant. 10Boron was redistributed when applied via foliar spraying in cowpea plants, regardless of the plant's nutritional status, which in turn might increase internal B cycling.

Distribution of Metals along Simiyu Wetland of Lake Victoria Basin and its Impact on Agriculture

More than 70% of communities living along Simiyu wetland area are agriculturalists and pastoralists. Physical land degradation and poor nutrient mobility within the soil-plant system have shown a notable impact on agricultural production. Cycling of selected and their impact on agriculture were investigated along Simiyu wetland. Cation Exchange Capacity (CEC) of the soil was studied with respect to soluble cations and selected trace metals. To study the longitudinal and spatial distribution of the selected metals along Simiyu wetland, samples (water, sediments and soil) were taken in three stations along the river namely Bariadi Bridge, Simiyu Bridge and the Simiyu River mouth. Sampling of soil was done at different distances from the river so as to study the flow pattern of the metals and hence to explain the direction of cycling. Sampling was done both inn wet and dry seasons to study the seasonal variation of the metals. Geographical Position System was used to locate the sampling points for soil and water/sediment. Metals Chromium (Cr), Lead (Pb), Zinc (Zn), Coper (Cu), Cadmium (Cd) and Manganese (Mn) analyses were analyzed by atomic absorption spectrophotometer (AAS). High levels of Manganese and Zinc were detected in most samples with different distribution behavior between water and sediments that may reflect difference in solubility of metals in water or possible complex formation of the metals resulting to potentially less solubility of metals, hence retarding their bioavailability to plants low cation exchange capacity. Retarded nutrient mobility in clay soils was observed facilitated by the formation of hard pans resulting to less availability of the nutrients to plants. The study suggests some ways in which farmers can improve soil cation exchange capacity and hence improve agricultural productivity. DOI: http://dx.doi.org/10.3126/jowe.v6i0.5967 J Wet Eco 2012 (6): 31-43

Leaf Litter Decomposition and Nutrient Dynamics in Woodland and Wetland Conditions along a Forest to Wetland Hillslope

Leaf litters of jarrah (Eucalyptus marginata Donn ex Sm.) and banksia (Banksia menziesii R. Br.) were decomposed at woodland and wetland conditions for two years to test site influence on the rates of decomposition. Weight loss was rapid in early rains but slowed substantially in the following months, resulting in 2/3 to 1/2 weights remaining after two years of field exposure. Litter weight loss was well described by a two-substrate quality decay model (R2=0.97−0.99), and the half-lives were 2.6–3.2 weeks (labile fraction) and 6.4–6.9 years (recalcitrant fraction) for jarrah, and 1.0–1.7 weeks (labile) and 6.6–9.9 years (recalcitrant) for banksia. The nutrient mobility was K≈Mg≈S>Ca>P, and the losses of K, Mg and S were correlated with the weight loss of litter (R2=0.77−0.94, P<0.03). P mass increased by 129% in jarrah litter and 174% in banksia litter in the woodland site, suggesting woodland with tree cover provided a better habitat for microbial biomass than non-inundated wetland, hence a notable P conservation in the decomposing litter.