Machine Learning, Compositional and Fractal Models to Diagnose Soil Quality and Plant Nutrition

Soils, nutrients and other factors support human food production. The loss of high-quality soils and readily minable nutrient sources pose a great challenge to present-day agriculture. A comprehensive scheme is required to make wise decisions on system’s sustainability and minimize the risk of crop failure. Soil quality provides useful indicators of its chemical, physical and biological status. Tools of precision agriculture and high-throughput technologies allow acquiring numerous soil and plant data at affordable costs in the perspective of customizing recommendations. Large and diversified datasets must be acquired uniformly among stakeholders to diagnose soil quality and plant nutrition at local scale, compare side-by-side defective and successful cases, implement trustful practices and reach high resource-use efficiency. Machine learning methods can combine numerous edaphic, managerial and climatic yield-impacting factors to conduct nutrient diagnosis and manage nutrients at local scale where factors interact. Compositional data analysis are tools to run numerical analyses on interacting components. Fractal models can describe aggregate stability tied to soil conservation practices and return site-specific indicators for decomposition rates of organic matter in relation to soil tillage and management. This chapter reports on machine learning, compositional and fractal models to support wise decisions on crop fertilization and soil conservation practices

Conditioning machine learning models to adjust lowbush blueberry crop management to the local agroecosystem

Agroecosystem conditions limit the productivity of lowbush blueberry. Our objectives were to investigate the effects on berry yield of agroecosystem and crop management variables, then to develop a recommendation system to adjust nutrient and soil management of lowbush blueberry to given local meteorological conditions. We collected 1504 observations from N-P-K fertilizer trials conducted in Quebec, Canada. The data set, that comprised soil, tissue, and meteorological data, was processed by Bayesian mixed models, machine learning, compositional data analysis, and Markov chains. Our investigative statistical models showed that meteorological indices had the greatest impact on yield. High mean temperature at flower bud opening and after fruit maturation, and total precipitation at flowering stage showed positive effects. Low mean temperature and low total precipitation before bud opening, at flowering, and by fruit maturity, as well as number of freezing days (<−5 °C) before flower bud opening, showed negative effects. Soil and tissue tests, and N-P-K fertilization showed smaller effects. Gaussian processes predicted yields from historical weather data, soil test, fertilizer dosage, and tissue test with a root-mean-square-error of 1447 kg ha−1. An in-house Markov chain algorithm optimized yields modelled by Gaussian processes from tissue test, soil test, and fertilizer dosage as conditioned to specified historical meteorological features, potentially increasing yield by a median factor of 1.5. Machine learning, compositional data analysis, and Markov chains allowed customizing nutrient management of lowbush blueberry at local scale

Vegetable Response to Added Nitrogen and Phosphorus Using Machine Learning Decryption and the N/P Ratio

The current N and P fertilization practices for vegetable crops grown in organic soils are inaccurate and and may potentially damage the environment. New fertilization models are needed. Machine learning (ML) methods can combine numerous features to predict crop response to N and P fertilization. Our objective was to evaluate machine learning predictions for marketable yields, N and P offtakes, and the N/P ratio of vegetable crops. We assembled 157 multi-environmental fertilizer trials on lettuce (Lactuca sativa), celery (Apium graveolens), onion (Allium cepa), and potato (Solanum tuberosum) and documented 22 easy-to-collect soil, managerial, and meteorological features. The random forest models returned moderate to substantial strength (R2 = 0.73–0.80). Soil and managerial features were the most important. There was no response to added P and null to moderate response to added N in independent universality tests. The N and P offtakes were most impacted by P-related features, indicating N–P interactions. The N/P mass ratios of harvested products were generally lower than 10, suggesting P excess that would trigger plant N acquisition and possibly alter soil N and C cycles through microbial processes. Crop response prediction by ML models and ex post N/P ratio diagnosis and N and P offtakes proved to be useful tools to guide N and P management decisions in organic soils

Retention, hydrolysis and plant availability of pyrophosphate applied to organic soil material

Pyrophosphate retention and half-life values, and pyrophosphatase activity, were determined in 24 organic soil materials containing < 20% ash. Pyrophosphate retention was correlated with ash content (r = 0,876**) but still was weak. Pyrophosphatase activity (11,6 to 148,1 mmol.kg('-1).2h('-1)) was higher in virgin than in cultivated materials and was promoted apparently by nonspecific acid phosphatases. The interaction between water-soluble pyrophosphate and pyrophosphatase activity explained 77% of the variation in log-transformed half-life values ranging from 0,1 to 3,7 days. Copper decreased significantly pyrophosphatase activity. However, pyrophosphate hydrolysis rate was not affected significantly by Cu contents up to 1177 mg.kg('-1) in humic materials. Because of rapid rates of pyrophosphate hydrolysis in humic and mesic materials compared with rate of P uptake by onions, no significant difference in bulb yield and P uptake were obtained at harvest between pyrophosphate and orthophosphate fertilizers

Cost analysis of two community-based HIV testing service modalities led by a Non-Governmental Organization in Cape Town, South Africa

CITATION: Meehan, Sue-A., Beyers, N. & Burger, R. 2017. Cost analysis of two community-based HIV testing service modalities led by a Non-Governmental Organization in Cape Town, South Africa. BMC Health Services Research, 17:801, doi:10.1186/s12913-017-2760-8.The original publication is available at https://bmchealthservres.biomedcentral.comPublication of this article was funded by the Stellenbosch University Open Access Fund.Background: In South Africa, the financing and sustainability of HIV services is a priority. Community-based HIV testing services (CB-HTS) play a vital role in diagnosis and linkage to HIV care for those least likely to utilise government health services. With insufficient estimates of the costs associated with CB-HTS provided by NGOs in South Africa, this cost analysis explored the cost to implement and provide services at two NGO-led CB-HTS modalities and calculated the costs associated with realizing key HIV outputs for each CB-HTS modality. Methods: The study took place in a peri-urban area where CB-HTS were provided from a stand-alone centre and mobile service. Using a service provider (NGO) perspective, all inputs were allocated by HTS modality with shared costs apportioned according to client volume or personnel time. We calculated the total cost of each HTS modality and the cost categories (personnel, capital and recurring goods/services) across each HTS modality. Costs were divided into seven pre-determined project components, used to examine cost drivers. HIV outputs were analysed for each HTS modality and the mean cost for each HIV output was calculated per HTS modality. Results: The annual cost of the stand-alone and mobile modalities was $96,616 and$77,764 respectively, with personnel costs accounting for 54% of the total costs at the stand-alone. For project components, overheads and service provision made up the majority of the costs. The mean cost per person tested at stand-alone ($51) was higher than at the mobile ($25). Linkage to care cost at the stand-alone ($1039) was lower than the mobile ($2102). Conclusions: This study provides insight into the cost of an NGO led CB-HTS project providing HIV testing and linkage to care through two CB-HIV testing modalities. The study highlights; (1) the importance of including all applicable costs (including overheads) to ensure an accurate cost estimate that is representative of the full service implementation cost, (2) the direct link between test uptake and mean cost per person tested, and (3) the need for effective linkage to care strategies to increase linkage and thereby reduce the mean cost per person linked to HIV care.https://bmchealthservres.biomedcentral.com/articles/10.1186/s12913-017-2760-8Publisher's versio

Acidez do solo e calagem em pomares de frutíferas tropicais Soil acidity and liming in tropical fruit orchards

A produtividade agrícola nos trópicos é afetada, principalmente, pelos fatores ligados à acidez do solo (pH, saturação por bases, acidez potencial, disponibilidade de nutrientes). A calagem é uma prática bem conhecida para corrigir a acidez do solo em culturas anuais, ainda que não seja praticada com a regularidade necessária. Entretanto, em culturas perenes, a incorporação de corretivos é mais complexa, devido às características desse grupo de plantas e à carência de informações científicas sobre o assunto. Em condições de acidez, a calagem promove a neutralização do Al3+, a elevação do pH e o fornecimento de Ca e Mg, possibilitando a proliferação de raízes, com reflexos positivos no crescimento da parte aérea das plantas. Contudo, devido à baixa solubilidade e à lenta movimentação do calcário ao longo do perfil do solo, há obrigatoriedade de se fazer distribuição uniforme e incorporação profunda, antecedendo a implantação do pomar, a fim de garantir o eficiente aproveitamento de água e de nutrientes contidos nessas camadas. A calagem deve ser considerada um investimento, pois seus benefícios perduram além de um ano ou de uma safra agrícola. Isso se deve ao efeito residual dos corretivos de acidez do solo, sendo o tempo de duração desse efeito dependente de vários fatores, entre os quais: condições edafoclimáticas, cultura, manejo da área e tipo de corretivo empregado. Em geral, partículas maiores de calcário têm efeito residual mais prolongado, sendo empregadas na implantação dos pomares. No entanto, a relação entre o tamanho da partícula e o efeito residual tem sido pouco pesquisada, devido à necessidade de estudos de longa duração. Em função das elevadas doses de adubos nitrogenados utilizadas nos pomares de altos rendimentos, a acidez do solo aumenta, como resultado do processo de nitrificação. Em pomares já implantados, o procedimento atualmente utilizado pelos produtores é a incorporação superficial do calcário na área. As recomendações talvez fossem outras, caso houvesse maior subsídio da pesquisa, tendo em vista os diversos problemas fitossanitários que podem ocorrer, direta ou indiretamente da prática da incorporação do corretivo, tais como redução do sistema radicular, ferimento das raízes e consequente risco de infecções, com disseminação de pragas e doenças no pomar. O objetivo desta revisão é apresentar os principais resultados de pesquisas sobre o assunto, mostrando os efeitos da calagem sobre a fertilidade do solo, a nutrição e a produtividade de frutíferas de grande importância econômica para o Brasil, bem como discutir a duração do efeito residual dos corretivos e a dose mais ecônomica a ser aplicada nos pomares de frutas em implantação e em produção.Agricultural productivity in the tropics is affected first by soil acidity and related factors (pH, base saturation, potential acidity, nutrient availability). Liming is a well-known but irregularly used beneficial practice to correct soil acidity in annual cropping systems. For perennial crops such as fruit orchards, lime incorporation is more difficult to implement as a result of length of the rotation and lack of scientific support. The lime neutralizes exchangeable aluminum, increases pH and supplies Ca and Mg to the growing roots. Because lime moves slowly in the soil, it must be incorporated deeply and uniformly before establishing the orchard to enhance soil exploration by the root system. Compared to fertilizers and pesticides liming can impact soil properties during several consecutive seasons and its effect depends on soil type, contact with the soil as lime is incorporated, fruit species and liming material. In general, the effect of larger lime particles is long-lasting. In orchards, lime is applied before establishment using lime materials of varying grain sizes. However, the relationship between grain size and long-time effect has been little studied because long-time research is expensive. With increasing application of ammonium-based N fertilizers in high-yielding orchards, soil acidity increases as a result of nitrification. Farmers presently apply lime superficially to established orchards in absence of sufficient experimentation on possible damage to the root system, root infection, pest blooms and soil compaction. The aim of this chapter is to quantify the effect of liming experiments on soil fertility, mineral nutrition and yield of tropical orchards in Brazil during establishment and full production cycles and determine the economic lime rate optimum for a long-term effect

Soil phosphorus availability in no-till versus conventional tillage following freezing and thawing cycles

International audienceSoil phosphorus availability in no-till versus conventional tillage following freezing and thawing cycles. Can. J. Soil Sci. 90: 419-428. Projected global warming may result in colder soil temperatures and a greater number of soil freezing and thawing cycles (FTC) during the winter in cool temperate and high-latitude regions. We evaluated the effects of seasons and repeated FTC on soil P availability in the topsoil of no-till (NT) and conventional tillage (CT) systems. In order to determine P availability during fall 2007 and spring 2008, soil samples (0-15 cm) were collected in both seasons from a long-term corn-soybean rotation experiment in plots that received 0, 17.5 and 35 kg P ha(-1) and 160 kg N ha(-1) every 2 yr since 1992. In addition, soil cores (0-5 cm) were collected in fall 2007 in plots that received 35 kg P ha(-1) and 160 kg N ha(-1) every 2 yr and were enriched or not with 2 g of soybean residues. Under controlled conditions, the cores were subjected to various FTC treatments, with each cycle consisting of 5 d of freezing and 5 d of thawing. The water-extractable P (Pw) and Mehlich-3 extractable P (P-M3) contents were higher in soil samples collected in the spring compared with those collected the previous fall. After one and three FTC, Pw values averaged 17.4 mg kg(-1) in NT and 7.5 mg kg(-1) in CT and were not influenced by the addition of soybean residues. At the end of the sixth FTC, the Pw content of soil cores collected in NT increased up to 25.9 mg kg(-1) with the addition of residues but decreased in the absence of residues. The effects of freezing and thawing on soil cores with crop residues occurred at the end of the sixth FTC, where P-M3 in the NT + residues treatment increased twofold, reaching 100 mg P kg(-1). These results confirm that both Pw and P-M3 in NT can be enhanced by increasing the number of FTC

Soil phosphorus availability in no-till versus conventional tillage following freezing and thawing cycles

International audienceSoil phosphorus availability in no-till versus conventional tillage following freezing and thawing cycles. Can. J. Soil Sci. 90: 419-428. Projected global warming may result in colder soil temperatures and a greater number of soil freezing and thawing cycles (FTC) during the winter in cool temperate and high-latitude regions. We evaluated the effects of seasons and repeated FTC on soil P availability in the topsoil of no-till (NT) and conventional tillage (CT) systems. In order to determine P availability during fall 2007 and spring 2008, soil samples (0-15 cm) were collected in both seasons from a long-term corn-soybean rotation experiment in plots that received 0, 17.5 and 35 kg P ha(-1) and 160 kg N ha(-1) every 2 yr since 1992. In addition, soil cores (0-5 cm) were collected in fall 2007 in plots that received 35 kg P ha(-1) and 160 kg N ha(-1) every 2 yr and were enriched or not with 2 g of soybean residues. Under controlled conditions, the cores were subjected to various FTC treatments, with each cycle consisting of 5 d of freezing and 5 d of thawing. The water-extractable P (Pw) and Mehlich-3 extractable P (P-M3) contents were higher in soil samples collected in the spring compared with those collected the previous fall. After one and three FTC, Pw values averaged 17.4 mg kg(-1) in NT and 7.5 mg kg(-1) in CT and were not influenced by the addition of soybean residues. At the end of the sixth FTC, the Pw content of soil cores collected in NT increased up to 25.9 mg kg(-1) with the addition of residues but decreased in the absence of residues. The effects of freezing and thawing on soil cores with crop residues occurred at the end of the sixth FTC, where P-M3 in the NT + residues treatment increased twofold, reaching 100 mg P kg(-1). These results confirm that both Pw and P-M3 in NT can be enhanced by increasing the number of FTC