Avaliação da libertação de azoto a partir de correctivos orgânicos utilizando membranas de troca aniónica e um medidor de clorofila SPAD-502

Neste trabalho divulgam-se resultados de experiências em vasos em que membranas de troca aniónica (MTA) foram inseridas directamente no solo para monitorar o teor de nitratos ao longo do tempo, e em que o estado nutritivo das plantas foi avaliado através de um medidor de clorofila SPAD- 502. Na estação quente foi cultivado milho e no período outono-inverno nabiça e centeio. O milho foi semeado a 5 de Junho de 2004 e a nabiça e o centeio a 23 de Setembro de 2004.As plantas foram sujeitas aos seguin- tes tratamentos fertilizantes: Nutrisoil (Nut); Beiraadubo (Bei); Phenix (Phe); e Vege- thumus (Veg), quatro correctivos orgânicos comerciais; estrume de bovino (EB); casca de castanha (CC); nitrato de amónio (NA); e um tratamento sem azoto (T). Os resultados das MTA e os valores SPAD foram relacio- nados com a matéria seca produzida e o N exportado. Em Junho, na primeira amostra- gem, a concentração média de nitratos nos extractos das MTA variou entre 18,3 e 239,4 mg L-1, nos tratamentos CC e NA. Na primeira semana de Agosto, foram regista- dos valores médios de nitratos no solo de 12,9 a 52,3 mg L-1 nos tratamentos CC e Bei. Na última amostragem, em Setembro, os valores médios de nitratos no solo varia- ram entre 9,7 e 67,9 mg L-1 nos tratamentos CC e Nut. As MTA revelaram boa capaci- dade para discriminar a forma como os dife- rentes fertilizantes libertaram o azoto ao longo do tempo e como este aspecto condi- cionou a absorção do nutriente e o desen- volvimento das plantas. Os valores SPAD revelaram-se bons indicadores do estado nutritivo azotado do milho, em condições em que foi possível controlar grande parte da variabilidade experimental. Os valores SPAD estiveram linearmente relacionados com a produção de matéria seca e o N exportado. Nas condições deste ensaio, em que a lixiviação e a desnitrificação foram controladas, as culturas intercalares centeio e nabiça recuperaram o N residual da cultu- ra anterior até próximo do limite da sua senescência por falta de azoto. Results from pot experiments where an- ion exchange membranes (MTA) were inserted into the soil to monitor soil nitrate levels over time, and the plant N nutritional status assessed with a SPAD-502 chloro- phyll meter, are reported in this work. Maize was grown in the summer season and turnip and rye in the winter period. Maize was sown on June 5, 2004, and turnip and rye on September 23, 2004. The plants were subjected to the following treatments: Nu- trisoil (Nut); Beiraadubo (Bei); Phenix (Phe); Vegethumus (Veg); cow manure (EB); chestnut fruit bark (CC); ammonium nitrate (NA); and control treatment, without N fertilization (T). Two weeks after the maize was sown, soil nitrate levels extracted by MTA ranged between 18.9 and 239.0 mg L-1 in the CC and Bei treatments, respec- tively. In the first week of August mean soil nitrate values ranged between 12.9 and 52.3 mg L-1 in the CC and Bei treatments. In September, the last sampling date, mean soil nitrate levels were found to be in the range of 9.7 and 67.9 mg L-1 in the CC and Nut treatments. Relationships between MTA and SPAD results with dry matter yield and N uptake were established. The MTA were able to differentiate well as the organic amendments released their N during the season and this aspect influenced N uptake and plant growth. SPAD readings were also a good index of plant N nutritional status. SPAD values were linearly related with dry matter yield and N uptake. In this study, where the pots were managed to avoid ni- trate leaching and denitrification, winter grown species recovered the residual N of maize fertilization. At the end of experiment the plants showed senescent leaves with deep N deficiency symptoms.http://www.scielo.oces.mctes.pt/scielo.php?script=sci_issues&pid=0871-018X&lng=pt&nrm=is

Seed size effects on above-ground stem number and yield of potato crop

The seed is an important production factor in the potato crop since the seed-tuber has a high price cost in Portugal, where almost the seed is imported. On the other hand, the mean national harvest is low. 15 Mg/ha (FAO, 2005), subjected to adverse environmental conditions, particularly the high temperatures during the cropping season (Rodrigues, 2000)

Biomassa microbiana e respiração do solo em pastagens melhoradas. Resultados preliminares

As pastagens melhoradas (pastagens permanentes semeadas biodiversas ricas em leguminosas) constituem um sistema de pastagens inovador que contribui para o aumento de matéria orgânica no solo. Os microrganismos do solo são considerados bioindicadores sensíveis de mudança na qualidade do solo, pelo que as alterações na população microbiana poderão ter consequências positivas ou negativas nas propriedades do solo. Este trabalho pretende avaliar alterações na biomassa microbiana e na respiração do solo ao longo de um gradiente topográfico (cimo da encosta – CE; meio da encosta – ME e fundo encosta – FE) em pastagens melhoradas, instaladas na Quinta de França (Covilhã), no Outono de 2007. A recolha de amostras de solo para a determinação dos parâmetros microbianos foi realizada em finais de Outubro de 2008, na profundidade de 0-10 cm. A avaliação do C da biomassa microbiana (CBM) foi efectuada pelo método de fumigação-extracção. A respiração do solo foi avaliada pela produção de CO2 em sistema fechado. O carbono orgânico total (CT) foi determinado por incineração. Os primeiros resultados de CBM não revelaram diferenças significativas (p>0,05) no gradiente topográfico estudado. Os valores médios variaram entre 225,5 µg g-1 solo na parcela FE e 385,7 µg g-1 solo na parcela ME. No que respeita à respiração do solo registaram-se valores de 62,1 µg C-CO2 g-1 solo dia-1 na parcela FE, 50,6 µg C-CO2 g-1 solo dia-1 na parcela CE e 44,8 µg C-CO2 g-1 solo dia-1 na parcela ME. Apesar dos valores mais elevados registados no fundo da encosta as diferenças não foram estatisticamente significativas (p>0,05). A razão CBM/CT, considerada como um indicador fiável da dinâmica de C nos solos em sistemas agrícolas a curto e médio prazo, foi de 15,3, 24,7 e 10,9, respectivamente nas parcelas CE, ME e FE. Os valores sugerem um balanço positivo de C na parcela ME.As pastagens melhoradas (pastagens permanentes semeadas biodiversas ricas em leguminosas) constituem um sistema de pastagens inovador que contribui para o aumento de matéria orgânica no solo. Os microrganismos do solo são considerados bioindicadores sensíveis de mudança na qualidade do solo, pelo que as alterações na população microbiana poderão ter consequências positivas ou negativas nas propriedades do solo

Large chestnut trees (Castanea sativa) respond poorly to liming and fertilizer application

Establishing a fertilization plan for large trees is particularly difficult due to the high soil volume that the roots exploit and the buffer effect of the perennial woody structure on the concentration of nutrients in the leaves. This work evaluates the response of chestnut, a very large tree, to different fertilizer solutions. The study was conducted in two chestnut orchards planted in acid soils that were subjected to the application of lime plus phosphorus (Lime+P), lime plus a compound NPK fertilizer (Lime+NPK), and an unfertilized control (Control). The effects of the treatments on soil properties, nutritional status and photosynthetic performance of the trees, and nut production, were assessed from field and laboratory analyses. Liming significantly increased soil pH and exchangeable calcium (Ca). Treatments did not significantly influence leaf P and K levels, although leaf N concentrations were significantly higher in the Lime+NPK treatment on two of the three sampling dates. In one of the trials, the average accumulated nut yield was higher in the Lime+NPK (71.7 kg tree−1) treatment compared with the control (59.6 kg tree−1) and the Lime+P (51.7 kg tree−1) treatments, although without significant differences at P < 0.05. Overall, the results show the chestnut tree to be a species tolerant of soil acidity. The results also show that the buffer capacity of the plant in regulating the nutrient concentration in the leaves seems to be higher for P than for N, and therefore, concentrations of N in the leaves require the regular application of the nutrient as a fertilizer.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2015) and FEADER (The European Agricultural Fund for Rural Development) through the project CMP122 - PDR2020-101-030981 – EGIS, Estratégias para uma Gestão Integrada do Solo e da Água em Espécies Produtoras de Frutos Secos. We also thank João Paulo Roxo and Carlos Lopes for allowing the experiments to be conducted on their farms.info:eu-repo/semantics/publishedVersio

Recycling nutrient-rich hop leaves by composting with wheat straw and farmyard manure in suitable mixtures

The harvesting of hops (Humulus lupulus L.) generates large amounts of nutrient-rich leaves that can be used in composting mixtures to add value to other organic resources on the farm. In this study, hop leaves were mixed with cow manure and wheat straw in several combinations with the aim of establishing guidelines on how farmers can manage the raw materials and better use these valuable organic resources. The composting process was monitored and the quality of the composts evaluated in relation to the effects on lettuce (Lactuca sativa L.) grown in pots over two consecutive cycles. The mixture of hop leaves with cow manure produced a stable compost after nine months of composting which may be used in horticultural crops, irrespective of the proportion of raw materials, due to their low and similar C/N ratios. However, when using mixtures of leaves and straw in proportions of less than 2:1, the composts did not mature properly, showing high C/N ratios. Their application to the soil led to a strong reduction in plant tissue N concentrations, due to biological N immobilization, which significantly reduced lettuce dry matter yield. Thus, to reduce composting time and increase the quality of the compost, the ratio leaves/straw should be as high as possible, at least 2:1. Alternatively, either the composting process should take longer, or the poorly-matured compost be applied far in advance of sowing a crop so that complementary biological processes can take place in the soil, as recorded in the second cycle of lettuce. Ash from hop stems did not benefit the composting process and proved itself not to be worth using in mixtures.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and European Regional Development Fund (ERDF) under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2015) and also the scholarship grant of Sandra Afonso (number BD/116593/2016) under the Programme PT2020 (UID/AGR/00690/2019).info:eu-repo/semantics/publishedVersio

Ising model with spins S=1/2 and 1 on directed and undirected Erd\"os-R\'enyi random graphs

Using Monte Carlo simulations we study the Ising model with spin S=1/2 and 1 on {\it directed} and {\it undirected} Erd\"os-R\'enyi (ER) random graphs, with $z$ neighbors for each spin. In the case with spin S=1/2, the {\it undirected} and {\it directed} ER graphs present a spontaneous magnetization in the universality class of mean field theory, where in both {\it directed} and {\it undirected} ER graphs the model presents a spontaneous magnetization at $p = z/N$ ($z=2, 3, ...,N$), but no spontaneous magnetization at $p = 1/N$ which is the percolation threshold. For both {\it directed} and {\it undirected} ER graphs with spin S=1 we find a first-order phase transition for z=4 and 9 neighbors.Comment: 11 pages, 8 figure