Combined Effects of Legumes with Phosphorus Fertilizer on Nutrient Balances and Gross Margins in Maize (Zea mays L.) systems of Kabete sub-County, Kenya

Calculation of soil nutrient balances and gross margins (GM) is imperative in ascertaining effect of innovative technologies on soil fertility and farm profitability. A field experiment to evaluate effect of combined legumes and phosphorus fertilizer on soil N, P and K balances and crop GM in maize (Zea mays L.) systems was set up in Kabete Division, Kenya, in the long and short rainy seasons of 2012. The experimental set up was a randomized complete block design (RCBD) with a split plot arrangement. The main plots comprised cropping systems; (i) monocropping (sole maize), (ii) intercropping [white lupin (Lupinus albus L.)/maize (L/M) and chickpea (Cicer arietinum L.)/maize (CP/M)], and (iii) rotation [white lupin-maize (L-M) and chickpea-maize (CP-M)]. The split plots were phosphorus (P) fertilizers; Minjingu phosphate rock (MPR) and triple superphosphate (TSP), and (iii) no P fertilizer applied (CTRL). Soil N, P and K balances and gross margins were analyzed at plot level using NUTrient MONitoring (NUTMON - now known as MonQi) Tool box. Nutrient balances were negative across cropping systems and P sources except for K in M/CP (CTRL and TSP) intercrop. Significantly less negative N balances were obtained in maize monocrop (MPR), CP/M (CTRL) intercrop, CP-M (TSP) rotation, and L/M (MPR) intercrop. L/M (CTRL and TSP) intercrop and L-M (CTRL and TSP) rotation recorded more negative (highest losses) N balances. Across P sources, the maize monocrop, M/L intercrop and L-M rotation had significantly more negative P balances, than CP-M rotation and M/CP intercrop. P balances, across P fertilizers, were significantly less negative in M/CP compared to M/L intercrop. Less negative P balances were recorded in CTRL treatment compared to TSP and MPR across cropping systems. M/L (CTRL and TSP) intercrop system had pronounced negative K balances. In the rotation systems, significantly less negative balances were observed when maize was rotated with chickpea compared to lupin across all P sources. Pronounced GMs were realized in M/L intercrop (TSP) followed by L-M (TSP) and lowest in M/L (TSP and CTRL). The N, P and K nutrient balances in response to P sources and cropping systems exhibited a negative relationship with crop GM. The positive GMs obtained were thus at the expense of soil nutrient mining as treatments with high nutrient losses, case for N and P, had the highest GMs. Considering nutrient balance studies alongside economic analysis has thus demonstrated the hidden environmental costs in the positive crop GMs and by extension the efficiency of such production systems. As a result, increased GMs under introduced technologies are not sustainable unless the same is matched with adequate nutrient replenishments to balance those lost through harvested products and other nutrient loss pathways. Farmers would, actually, go for those technologies that not only maximize yields but also accrue high profits. In the context of this study, and in order of GM (from highest) analysis, M/L intercrop, maize monocrop and L-M rotation with application of TSP are such technologies. In the long-run however these technologies will prove untenable due to nutrient mining. Nonetheless to guarantee efficient production and sustainable maize systems, following application of P fertilizer and legume integration, it is important that profits accrued from farm sales be used to purchase fertilizers and/or support practices geared towards replenishing mined soil nutrients. This way farm profits realized will not be at the expense of nutrient mining. Keywords: Cropping systems; gross margins; Kabete sub-County; MonQi; Nutrient Balances; Rock phosphates

Generalized Centrifugal Force Model for Pedestrian Dynamics

A spatially continuous force-based model for simulating pedestrian dynamics is introduced which includes an elliptical volume exclusion of pedestrians. We discuss the phenomena of oscillations and overlapping which occur for certain choices of the forces. The main intention of this work is the quantitative description of pedestrian movement in several geometries. Measurements of the fundamental diagram in narrow and wide corridors are performed. The results of the proposed model show good agreement with empirical data obtained in controlled experiments.Comment: 10 pages, 14 figures, accepted for publication as a Regular Article in Physical Review E. This version contains minor change

The minimum energy expenditure shortest path method

This article discusses the addition of an energy parameter to the shortest path execution process; namely, the energy expenditure by a character during execution of the path. Given a simple environment in which a character has the ability to perform actions related to locomotion, such as walking and stair stepping, current techniques execute the shortest path based on the length of the extracted root trajectory. However, actual humans acting in constrained environments do not plan only according to shortest path criterion, they conceptually measure the path that minimizes the amount of energy expenditure. On this basis, it seems that virtual characters should also execute their paths according to the minimization of actual energy expenditure as well. In this article, a simple method that uses a formula for computing vanadium dioxide ($VO_2$) levels, which is a proxy for the energy expenditure by humans during various activities, is presented. The presented solution could be beneficial in any situation requiring a sophisticated perspective of the path-execution process. Moreover, it can be implemented in almost every path-planning method that has the ability to measure stepping actions or other actions of a virtual character

The promise and peril of intensive-site-based ecological research: insights from the Hubbard Brook ecosystem study

Abstract. Ecological research is increasingly concentrated at particular locations or sites. This trend reflects a variety of advantages of intensive, site-based research, but also raises important questions about the nature of such spatially delimited research: how well does site based research represent broader areas, and does it constrain scientific discovery?We provide an overview of these issues with a particular focus on one prominent intensive research site: the Hubbard Brook Experimental Forest (HBEF), New Hampshire, USA. Among the key features of intensive sites are: long-term, archived data sets that provide a context for new discoveries and the elucidation of ecological mechanisms; the capacity to constrain inputs and parameters, and to validate models of complex ecological processes; and the intellectual cross-fertilization among disciplines in ecological and environmental sciences. The feasibility of scaling up ecological observations from intensive sites depends upon both the phenomenon of interest and the characteristics of the site. An evaluation of deviation metrics for the HBEF illustrates that, in some respects, including sensitivity and recovery of streams and trees from acid deposition, this site is representative of the Northern Forest region, of which HBEF is a part. However, the mountainous terrain and lack of significant agricultural legacy make the HBEF among the least disturbed sites in the Northern Forest region. Its relatively cool, wet climate contributes to high stream flow compared to other sites. These similarities and differences between the HBEF and the region can profoundly influence ecological patterns and processes and potentially limit the generality of observations at this and other intensive sites. Indeed, the difficulty of scaling up may be greatest for ecological phenomena that are sensitive to historical disturbance and that exhibit the greatest spatiotemporal variation, such as denitrification in soils and the dynamics of bird communities. Our research shows that end member sites for some processes often provide important insights into the behavior of inherently heterogeneous ecological processes. In the current era of rapid environmental and biological change, key ecological responses at intensive sites will reflect both specific local drivers and regional trends

Thermoluminescence of zircon: a kinetic model

The mineral zircon, ZrSiO4, belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such amodel. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time annealing at a given temperature. (iv) Heating of the irradiated sample to simulate TL experiments both after laboratory and natural irradiation. The input parameters of the model, such as the types and concentrations of the TL centres and the energy distributions of the hole and electron traps, were obtained by analysing the experimental data on fading of the TL-emission spectra of samples from different geological locations. Electron paramagnetic resonance (EPR) data were used to establish the nature of the TL centres. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. The saturation and annealing behaviour of filled trap concentrations has been considered in the framework of the proposed kinetic model and comparedwith the EPR data associated with the rare-earth ions Tb3+ and Dy3+, which play a crucial role as hole traps and recombination centres. Inaddition, the behaviour of some of the SiOmn− centres has been compared with simulation results.