Interpretation of electrical conductivity measurements from ceramic suction cups, wetting front detectors and ECH2O-TE sensors

Electrical conductivity (EC) measurements are often used to identify and address soil salinity issues in irrigated cropping systems. In this study, measurements of soil solution EC (EC-sol) collected in ceramic suction cups (SCs), wetting front EC (EC-wf) collected in Fullstop wetting front detectors (WFDs) and soil bulk EC (EC-bulk) measurements made using ECH2O-TE sensors and converted to EC-sol, were compared. As a result of different methods of measurement and different components of soil waterflow being sampled, variations in EC measurement between SCs and WFDs were observed. EC-sol was usually higher than EC-wf, as expected for this system, due to incomplete mixing between the draining and resident soil water during infiltration. For periods of high solute leaching, however, the opposite can occur, indicating that WFDs are sampling when solutes are first mobilised at the beginning of the leaching event. The ECH2O-TE sensors were less effective in measuring the short-term EC dynamics but were able to detect general changes in soil salinity. This could reflect difficulties estimating soil EC-sol from measured EC-bulk, especially at low soil water contents. Each of these instruments show good potential for application to guide salinity management practices, but a more detailed study on a range of soils subjected to different watering regimes is needed to further improve interpretation of EC measurements and their application.The Water Research Commission (Project 1574), the National Research Foundation, the Cooperative Research Centre for Irrigation Futures and CSIRO.http://www.plantandsoil.co.zanf201

Modelling nitrogen leaching : are we getting the right answer for the right reason?

The complexities and challenges in quantifying N leaching have led to development of a range of measurement and modelling techniques, but none are widely applied. Observations that N moves more slowly than water through the soil profile has resulted in different approaches being used to simulate impeded N movement in crop models: (i) by accounting for nitrate NO−3 adsorption to the soil, (ii) by considering incomplete mixing between resident and draining soil water fractions or (iii) a combination of both.We compare and discuss strengths and weaknesses of these approaches. Our inability to directly measure model parameters (especially with regards to simulating N dynamics), and the risk of compensating errors during model testing and calibration, often results in low confidence in simulated N leaching. We caution that our current ability to simulate N leaching is in most cases not yet well enough developed for reliable and accurate predictions. We recommend a more strategic approach involving better linking measurement and modelling to improve understanding of the critical soil processes that control N leaching as one way of further improving our understanding and quantification of N leaching.http://www.elsevier.com/locate/agwathb201

Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.

BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362

Farmers perceptions of precision agriculture and the role of agricultural extension: a case study of crop farming in the Schweizer-Reneke Region, South Africa

The profit of crop production in South Africa is under pressure due to unreliable rainfall associated with climate change and severe competition in a highly subsidized global food market. Such constraints lead to food insecurity and could be dealt with by adopting inter alia precision agriculture. This study aimed to gain insights into crop farmers’ perceptions of precision agriculture in the Schweizer-Reneke region. For this purpose, both qualitative and quantitative methods were applied by requesting 36 farmers to complete questionnaires; 18 who practice precision agriculture and 18 who do not. The results showed that economic considerations are the most important determinant whether precision agriculture is adopted or not by the crop farmers. Surprisingly, neither the age nor the education of farmers played a major role in the practicing or not of precision agriculture. Farmers who practice precision agriculture said that the most beneficial outcome is the costs saved through variable fertilizer application.Keywords: Economic benefit, Fertilizer application, Food security, Management strategy, Sustainable agricultur

Ecological and agro-economic study of small farms in sub-Saharan Africa

Land degradation, rising population and poverty in sub-Saharan Africa threatens the agricultural sustainability and productivity, quality of the environment and socio-economic wellbeing of rural populations. We studied farm ecological, economic and social sustainability, productivity and production risks in the Mbeere District of Eastern Kenya. We used a soil nutrient monitoring methodology to collect data from 30 households. Ecological sustainability was threatened by soil nutrient decline at rates of 1.7 kg P and 5.4 kg K ha$^{-1}$ half year$^{-1}$ while N was nearly balanced in soils. Soil phosphorus and potassium stocks, in the cultivated soils, declined at rates of 0.3% and 0.1% half year$^{-1}$, respectively. Farm economic returns were positive, albeit low, and could not sustain the livelihoods of the households. All the 30 households were living below the poverty line of 1 US dollar a day. Farm productivity was low, with livestock and yields of major staple food crops below on-farm target yields. To spread out the risks of production, farming households were cultivating an average of 4.7 crop fields, keeping more than two types of livestock and practising intercropping systems. Intercropping maize-beans reduced nutrient decline and raised household incomes compared with monocropping of either of the two crops. Despite the low rates of nutrient decline, high risks of production and the low crop yields, the livestock productivity and farm economic performance put the sustainability of these farming systems into question. The low levels of nutrient decline in small farms averaging at 1.7 kg P and 5.4 kg K ha$^{-1}$ half year$^{-1}$ contrasts with the high nutrient depletion rates on macro-scale levels, e.g. 20–40 N, 3.5–6.6 kg P and 20–40 kg K ha$^{-1}$ year$^{-1}$ for Eastern African countries and 22 kg N, 2.5 kg P and 15 kg K ha$^{-1}$ year$^{-1}$ for sub-Saharan Africa. These findings indicate that the extent of nutrient decline and conservation differs across sub-Saharan Africa. The positive contribution of intercropping to nutrient balances suggests the need to encourage farmers to adopt such systems rather than monocropping

Exploring options for integrated nutrient management in semi-arid tropics using farmer field schools: a case study in Mbeere District, eastern Kenya

The farmer field school (FFS) approach was used in semi-arid eastern Kenya in the period 2002–2003 to explore technology options for addressing declining soil fertility and to institute learning processes on integrated nutrient management (INM).The farmer field school (FFS) approach was used in semi-arid eastern Kenya in the period 2002-2003 to explore technology options for addressing declining soil fertility and to institute learning processes on integrated nutrient management (INM). Participatory diagnosis of soil fertility constraints and experimental design workshops led to the formulation of the INM-FFS learning curriculum and choice of INM technologies for testing in the central learning plot. INM technologies jointly chosen for testing included farmyard manure (FYM = T-1), diammonium phosphate (DAP = T-2), combined application of FYM and DAP (T-3); and T-3 combined with Tithonia diversifolia applied as green manure (T-4). Maize was used as a test crop. The treatments were replicated twice using a pair-wise design and data collected, bi-weekly, using the agroecosystem analysis (AESA) framework to aid learning and data analysis with farmers. Farmers' evaluation of the trials was conducted at the end of the study period using matrix scoring and ranking. Treatments with combined application of organic and inorganic materials had better agro-economic performance than sole application of either FYM or DAP (T-4 > T-3 > T-2 and T-1) and they had a high value cost ratio (VCR > 2). The technologies of T, to T-3 did not have a positive impact on either nitrogen or phosphorus balances. However, T-4 resulted in a positive partial N balance. Farmers' evaluation corresponded well with the majority of the quantitative agro-economic analysis. The study showed that there is a potential to use FFS for INM technology development and testing by stimulating interactions, farmer learning and closer working relationships between farmers, research scientists, extension and the institutions that they represent

Salinity guidelines for irrigation: Case studies from Water Research Commission projects along the Lower Vaal, Riet, Berg and Breede Rivers

A vast number of projects on salinity in irrigated agriculture were funded by the Water Research Commission (WRC) during the past 40 years. However, due to the diversity of the projects it is virtually impossible to cover all aspects thoroughly in a paper of limited length. Thus this review focuses mainly on projects along the Lower Vaal, Riet, Berg and Breede Rivers in South Africa. The results on the water quality of these rivers indicate that irrigation has led to the deterioration of water sources. There is a direct relationship between river water quality and soils irrigated. Fortunately, effective land-suitability guidelines were developed and applied during the establishment of the major irrigation schemes. This facilitated the management of soils under irrigation. The results from long-term irrigation case studies along the Lower Vaal River and Breede River show that the quality of soils can be improved. The opposite is also true where mismanagement occurred. Research on the salinity threshold of major crops (grapevines, wheat, maize, groundnuts, etc.) confirmed the empiric nature of the guidelines. It is suggested that a more dynamic approach be used for managing salinity under irrigation at farm level, i.e. the use of models. Amongst others, future research should focus on determining the spatial and temporal distribution of salt in irrigated soils

Monitoring and modelling draining and resident soil water nitrate concentrations to estimate leaching losses

Quantifying nitrogen (N) losses below the root zone is highly challenging due to uncertainties associated with estimating drainage fluxes and solute concentrations in the leachate. Active and passive soil water samplers provide solute concentrations but give limited information on water fluxes. Mechanistic models are used to estimate leaching, but require calibration with measured data to ensure their reliability. Data from a drainage lysimeter trial under irrigation in which soil profile nitrate (NO3-) concentrations were monitored using wetting front detectors (passive sampler) and ceramic suction cups (active sampler) were compared to NO3- concentrations in draining and resident soil water as simulated by the research version of the Soil Water Balance model (SWB-Sci). SWB-Sci is a daily time-step, cascading soil water and solute balance model that provides draining NO3- concentrations by accounting for incomplete solute mixing. As hypothesized, suction cup concentrations aligned closely with resident soil water concentrations, while wetting front detector concentrations aligned closely with draining soil water NO3- concentrations. These results demonstrate the power of combining monitoring and modelling to estimate NO3- leaching losses. Access to measured draining and resident NO3- concentrations, especially when complemented with modelled fluxes, can contribute greatly to achieving improved production and environmental objectives.Nitrate leaching Monitoring Modelling Draining and resident soil water SWB-Sci

Obtaining the parameters required to model labile phosphorus for South African soils

Modelling phosphorus (P) in the environment can increase our understanding of potential transfer pathways into receiving water bodies as well as the plant availability of this nutrient in soil. Many current models make use of algorithms originally developed for the EPIC model over two decades ago. These algorithms were developed primarily using continental USA soils. Obtaining the required input parameters can therefore be challenging when applying this approach to soils not classified according to the USA system, and for soils for which similar parameters are not available. In this paper, new equations for the estimation of labile P from Ambic P, Bray 2 P and the modified ISFEI method are proposed. Guidelines for the classification of South African soils as calcareous, slightly weathered and highly weathered are further suggested, and we propose that only topsoil properties be used for this purpose. Depending on the amount of soil information available, this classification can be achieved using the clay fraction SiO2:Al2O3 molecular ratio, the sum of exchangeable Ca, Mg, K and Na, or a newly proposed categorization system for South African soil forms. It is clear that the above approaches should be thoroughly tested and relevant local research carried out to improve our ability to model P in South African soils