Feature-specific nutrient management of onion (Allium cepa) using machine learning and compositional methods.

While onion cultivars, irrigation and soil and crop management have been given much attention in Brazil to boost onion yields, nutrient management at field scale is still challenging due to large dosage uncertainty. Our objective was to develop an accurate feature-based fertilization model for onion crops. We assembled climatic, edaphic, and managerial features as well as tissue tests into a database of 1182 observations from multi-environment fertilizer trials conducted during 13 years in southern Brazil. The complexity of onion cropping systems was captured by machine learning (ML) methods. The RReliefF ranking algorithm showed that the split-N dosage and soil tests for micronutrients and S were the most relevant features to predict bulb yield. The decision-tree random forest and extreme gradient boosting models were accurate to predict bulb yield from the relevant predictors (R2 > 90%). As shown by the gain ratio, foliar nutrient standards for nutritionally balanced and high-yielding specimens producing > 50 Mg bulb ha-1 set apart by the ML classification models differed among cultivars. Cultivar × environment interactions support documenting local nutrient diagnosis. The split-N dosage was the most relevant controllable feature to run future universality tests set to assess models' ability to generalize to growers' fields.

Exploratory and discriminant analysis of plant phenolic profiles obtained by UV-vis scanning spectroscopy.

Some species of cover crops produce phenolic compounds with allelopathic potential. The use of math, statistical and computational tools to analyze data obtained with spectrophotometry can assist in the chemical profile discrimination to choose which species and cultivation are the best for weed management purposes. The aim of this study was to perform exploratory and discriminant analysis using R package specmine on the phenolic profile of Secale cereale L., Avena strigosa L. and Raphanus sativus L. shoots obtained by UV-vis scanning spectrophotometry. Plants were collected at 60, 80 and 100 days after sowing and at 15 and 30 days after rolling in experiment in Brazil. Exploratory and discriminant analysis, namely principal component analysis, hierarchical clustering analysis, t-test, fold-change, analysis of variance and supervised machine learning analysis were performed. Results showed a stronger tendency to cluster phenolic profiles according to plant species rather than crop management system, period of sampling or plant phenologic stage. PCA analysis showed a strong distinction of S. cereale L. and A. strigosa L. 30 days after rolling. Due to the fast analysis and friendly use, the R package specmine can be recommended as a supporting tool to exploratory and discriminatory analysis of multivariate data.

Microbial activity in soil with onion grown in a no-tillage system with single or intercropped cover crops / Atividade microbiana em solo com cebola cultivada em sistema de plantio direto com plantas de cobertura solteiras ou consorciadas

ABSTRACT: Microbial biomass is a driving force in the dynamics of soil organic matter, and microbial activity is an indicator of soil quality in agroecosystems, reflecting changes in management practices and environmental conditions. We evaluated the effect of monoculture and intercropped winter cover crops on soil chemical attributes, microbial biomass carbon (MBC), basal respiration (BR), metabolic quotient (qCO2), urease, β-glucosidase, and fluorescein diacetate (FDA) hydrolysis activity, as well as onion yield in a no-tillage system. Soil is a Typic Humudept, and treatments were control with spontaneous vegetation, barley, rye, oilseed radish (OR), OR + rye, and OR + barley. The soil was sampled (0-10 cm) five times between June and December. There were no differences among treatments for MBC and BR, and the highest values for those attributes occurred in June, when cover plants were in their initial stage. Although, qCO2 was not affected by any treatment, it varied among sampling periods, ranging from 0.62 to 10 µg C-CO2 mg-1 MBC h-1, indicating a low- or no stress environment. Cover crops had little influence on enzyme activity, but FDA was lowered in areas with single crops of barley and rye. Average onion yield in cover crops treatments was 13.01 (Mg ha-1), 30-40% higher than in the control treatment.

RESUMO: A biomassa microbiana é determinante na dinâmica da matéria orgânica do solo e sua atividade é um indicador de qualidade do solo em agroecossistemas, refletindo mudanças em práticas de manejo e em condições ambientais. Avaliou-se o efeito de culturas de cobertura de inverno, solteiras ou consorciadas, sobre atributos químicos do solo, carbono da biomassa microbiana (CBM), respiração basal (RB), quociente metabólico (qCO2) e atividade das enzimas urease, β-glucosidase e FDA, bem como o rendimento da cebola em um sistema de plantio direto. O solo é um Cambissolo Húmico alumínico, os tratamentos foram testemunha com vegetação espontânea, cevada, centeio, nabo forrageiro (NF), NF + centeio e NF + cevada. Realizaram-se cinco coletas de amostras de solo (0-10 cm) entre junho a dezembro. Não houve diferenças entre os tratamentos para CBM e RB, e os maiores valores para esses atributos ocorreram em junho, quando as plantas de cobertura estavam em seu estágio inicial. Embora o qCO2 não tenha sido afetado por nenhum tratamento, ele variou entre os períodos de amostragem, com valores entre 0,62 e 10 µg de C-CO2 mg-1 MBC h-1, indicando um ambiente de baixo ou nenhum estresse. As culturas de cobertura tiveram pouca influência na atividade enzimática, mas o FDA foi reduzido em áreas com cultivos solteiros de cevada ou centeio. O rendimento médio de cebola nos tratamentos com culturas de cobertura foi de 13,01 (Mg ha-1), mais alto que no tratamento controle.

Matéria seca de plantas de cobertura, produção de cebola e atributos químicos do solo em sistema plantio direto agroecológico / Dry matter of cover crops, onion yield and soil chemical attributes in agroecological no-tillage system

O cultivo e a deposição de resíduos de plantas de cobertura em sistema plantio direto podem afetar os atributos químicos do solo e a produção de cebola. O trabalho objetivou avaliar a interferência do cultivo de plantas de cobertura sobre a produção de cebola e sobre os atributos químicos do solo em sistema plantio direto (SPD) agroecológico. O experimento foi conduzido na EPAGRI, em Ituporanga (SC), em um Cambissolo Húmico, nas safras de 2010 e 2011. Em abril, foram implantados os tratamentos: testemunha com vegetação espontânea (T1); cevada (2010)/aveia-preta (2011) (T2); centeio (T3); nabo-forrageiro (T4); centeio + nabo-forrageiro (T5); e cevada (2010)/aveia-preta (2011) + nabo-forrageiro (T6). Aos 60, 80 e 95 dias após a semeadura (DAS) das espécies de inverno, coletou-se a parte aérea das plantas e determinou-se a produção de matéria seca por hectare. Em julho, foram transplantadas mudas de cebola e, em novembro, avaliou-se a produção. Após o acamamento das plantas de cobertura de inverno e a colheita da cebola, foi coletado solo na camada de 0-10 cm e submetido à análise de atributos químicos. O cultivo e a deposição dos resíduos de matéria seca das espécies de plantas de cobertura em SPD contribuíram para o aumento e a manutenção da produção total de cebola ao longo dos anos. Os atributos químicos do solo, com exceção do K trocável, P disponível e valores de saturação da CTCpH7,0 por bases não foram afetados pelo cultivo de plantas de cobertura.

The cultivation and deposition of waste from cover crops in no-tillage can affect soil chemical attributes and onion yield. The aim of this study was to evaluate the dry matter yield of plant species from winter cover crops, onion yield and chemical attributes of soil in agroecological no-tillage system. The experiment was carried out at EPAGRI Experimental Station in Ituporanga (SC) under Humic Haplumbrept in the agricultural years of 2010 and 2011. The following treatments was implanted in April: weed vegetation (T1), Hordeum vulgare L. (2010)/Avena strigosa L. (2011) (T2), Secale cereale L. (T3), Raphanus sativus L. (T4), Secale cereale L + Raphanus sativus L. (T5) e Hordeum vulgare L. (2010)/Avena strigosa L. (2011) + Raphanus sativus L. (T6). At 60, 80 and 95 days after sowing (DAS) of winter species, the cover crops were collected to determine the dry matter yield. In July the onion seedlings were transplanted and in November the yield was evaluated. After the rolling of winter cover crops and after onion harvest, soil was collected at 0-10cm for the evaluation of chemical attributes. The cultivation and deposition of waste from cover crops in no-tillage contributed to the growth and maintenance of the total production of onion over the years. The soil chemical attributes in 0-10cm layer, with the exception of exchangeable K, available P and CTCpH7,0 saturation values for bases, were not affected by cover crops cultivation and deposition of waste.