Davie M. Kadyampakeni

Imidacloprid transport and sorption nonequilibrium in single and multilayered columns of Immokalee fine sand

Imidacloprid (IMD) is a neonicotinoid pesticide soil-drenched to many crops to control piercing-sucking insects such as the Asian citrus psyllid (ACP). Neonicotinoids are persistent in the environment and transport analyses are helpful estimate leaching potential from soils that could result in groundwater pollution. The objective of this study was to analyze IMD breakthrough under saturated water flow in soil columns packed with three horizons (A, E, Bh) of Immokalee Fine Sand (IFS). Also, we used the dimensionless form of the convective-dispersive model (CD-Model) to compare the optimized transport parameters from each column experiment (retardation factor, R; fraction of instantaneous-to-total retardation, β; and mass transfer coefficient, ω) with the parameters obtained from sorption batch equilibria and sorption kinetics. The tracer (Cl-) breakthrough curves (BTCs) were symmetrical and properly described by the CD-Model. IMD BTCs from A, Bh, and multilayered [A+E+Bh] soil columns showed steep fronts and tailing that were well described by the one-site nonequilibrium (OSNE) model, which was an evidence of non-ideal transport due to IMD mass transfer into the soil organic matter. In general, IMD was weakly-sorbed in the A and Bh horizons (R values of 3.72 ± 0.04 and 3.08 ± 0.07, respectively), and almost no retardation was observed in the E horizon (R = 1.20 ± 0.02) due to its low organic matter content (0.3%). Using the HYDRUS-1D package, optimized parameters (R, β, ω) from the individual columns successfully simulated IMD transport in a multilayered column mimicking an IFS soil profile. These column studies and corresponding simulations agreed with previous findings from batch sorption equilibria and kinetics experiments, where IMD showed one-site kinetic mass transfer between soil surfaces and soil solution. Ideally, sandy soils should be maintained unsaturated by crop irrigation systems and rainfall monitoring during and after soil-drench application. The unsaturated soil will increase IMD retardation factors and residence time for plant uptake, lowering leaching potential from soil layers with low sorption capacity, such as the E horizon.

Biomass, nutrient accumulation and tree size relationships for drip- and microsprinkler-irrigated orange trees

ABSTRACT A three-year study was conducted at two sites in Florida with Spodosols and Entisols differing in drainage characteristics to: 1) estimate biomass and nutrient accumulation in 1- to 5-year-old citrus and their relationship to tree size; and 2) determine tree size characteristics as a function of time. Nitrogen (N) accumulation with intensive drip- and microsprinkler fertigation increased by 45% over conventional grower practice (Conventional) at the Spodosol site (SS). Phosphorus (P) and potassium (K) accumulation were similar. The results further showed that intensive fertigation increased citrus growth rate (by up to 330%) in 6 months resulting in greater canopy volumes and trunk cross-sectional areas than conventional practices at the Entisol site. Results at SS showed that canopy size and trunk cross-sectional areas for Conventional were similar to drip fertigation probably because it was fertigated. This suggests the possibility of improving nutrient accumulation and tree size with intensive fertigation practices and a modified, fertigated conventional practice.

Nutrient Management Options for Florida Citrus: A Review of NPK Application and Analytical Methods

Citrus production in Florida is ranked first in the United States. Success of the citrus industry in the state relies heavily on sound water and nutrient management practices. Recently, citrus production has been declining due to the escalating prevalence of the citrus greening (Liberibacter asiaticus) and canker (Xanthomonas axonopodis) diseases. One option being explored is the manipulation of nutrient management scenarios to increase and enhance tree productivity. The paper presents a review of the management, analytical and application methods of three major nutrients Nitrogen (N), Phosphorus (P), and Potassium (K) on Floridas sandy soils with low organic matter (OM) and high leaching potential due to heavy annual rains (∼1200 mm). The NPK management options for Florida citrus are compared with those of other citrus producing regions around the world. Also, the critical tissue and soil nutrient concentrations for optimal and high citrus production are discussed. The review paper should provide important nutrient management guidelines to citrus growers in Florida and other regions with similar climatic and soil conditions.

Modeling Water and Nutrient Movement in Sandy Soils Using HYDRUS-2D

Models help to describe and predict complex processes and scenarios that are difficult to understand or measure in environmental management systems. Thus, model simulations were performed (i) to calibrate HYDRUS-2D for water and solute movement as a possible decision support system for Candler and Immokalee fine sand using data from microsprinkler and drip irrigation methods, (ii) to validate the performance of HYDRUS-2D using field data of microsprinkler and drip irrigation methods, and (iii) to investigate Br, NO, and water movement using annual or seasonal weather data and variable fertigation scenarios. The model showed reasonably good agreement between measured and simulated values for soil water content ( = 0.87-1.00), Br ( = 0.63-0.96), NO-N ( = 0.66-0.98), P ( = 0.25-0.78), and K ( = 0.44-0.99) movement. The model could be successfully used for scheduling irrigation and predicting nutrient leaching for both microsprinkler and drip irrigation systems on Floridas sandy soils.

Nutrient Management Strategies for Coping with Climate Change in Irrigated Smallholder Cropping Systems in Southern Africa

Sound management of soil nutrients is critical for optimizing crop vegetative and reproductive development and realizing high yields in irrigated cropping systems. This paper discusses the work done in Africa and presents lessons from other parts of the world for improved nutrient management under irrigation. Considering the rising temperatures and erratic rainfall as a consequence of climatic change and depleted soil nutrients as a result of continuous cropping, this review offers remedial options for managing soil fertility while optimizing water use and crop yields. The paper intends to inform agricultural policy makers and help farmers and organizations in Africa to manage soil nutrient and water resources efficiently and achieve high yields. Importantly, this discussion should stimulate further research in nutrient and water management under varying ecological scenarios of southern Africa to provide a cogent basis for climate change adaptation interventions.