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ScienceDaily (Dec. 29, 2010) — Most agricultural crops require large quantities of nitrate-rich fertilizer to realize optimal yields. The dilemma for growers is finding ways to balance the amount of nitrogen needed for production while minimizing potentially harmful nitrates that can leach into ground and surface waters. Increased interest in environmentally beneficial "low-input" approaches is challenging researchers to identify genotypes that have a characteristic called "high nutrient use efficiency," or NUE.
Using vegetable types with high NUE could help growers lessen environmental impacts while maintaining high crop yields. A new study reported on improved NUE traits that resulted from grafting melon plants onto commercial rootstocks.
Scientist Giuseppe Colla from the University of Tuscia and colleagues published the research in HortScience.The researchers evaluated a "rapid and economical" methodology for screening melon rootstocks for NUE using two experiments. In the first experiment melon plants, either ungrafted or grafted onto four commercial rootstocks grown in hydroponics, were compared. The second experiment was designed to confirm whether the use of a selected rootstock with high NUE could improve crop performance and NUE of grafted melon plants under field conditions.
The researchers observed that NUE traits were improved by grafting melon plants onto commercial rootstocks; grafted plants needed less nitrate in the nutrient solution to reach half maximum shoot dry weight. "In addition, the higher nitrate reductase activity of grafted plants under low nitrate conditions confirms that certain rootstocks have the potential to improve the NUE of grafted plants," they noted. In the second experiment, carried out under open field conditions, increasing the fertilization rates increased the total and marketable yields of melon plants, while decreasing NUE. When averaged over nitrogen levels, the marketable yield, NUE, and N uptake efficiency were higher by 9%, 11.8%, and 16.3%, respectively, in grafted plants than in ungrafted plants.
"We found that the use of melon grafted on selected rootstock represents a potential strategy for increasing yield and NUE and coping with soil fertility problems under low-input conditions," the authors concluded.
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Society for Horticultural Science, via EurekAlert!, a service of AAAS.
Friday 06 August 2010 11:15
Growing a cover crop or green manure is mainly associated with building fertility in organic systems, but the rise in fertiliser prices means that conventional growers could benefit, too.
Anton Rosenfeld, a research officer at Garden Organic, highlighted at a recent Garden Organic green manures workshop in Warwickshire that from 2003 to 2009, fertiliser prices rose by 51% in the UK. In contrast, the cost of growing green manures had risen by just 7% in the same period.
While not a new concept, conventional growers are being urged to look again at green manures as the change in economics will mean greater savings in fertiliser inputs.
The amount of nitrogen contributed by green manures depends on several factors, including weather, management, and availability of nutrients and the correct rhizobacteria in soil.
Francis Rayns, a research manager at Garden Organic, highlighted one ADAS project on a clover crop that fixed 500kg N/ha per year, but 100-300kg N/ha is more typical.
Dr Rosenfeld highlighted the potential savings in nitrogen fertiliser use, by using green manures, assuming a typical 150kg of N/ha is fixed. At 2010 prices (£220/t) this is a cost saving of £98/ha, he said. In 2009 when fertiliser prices were much higher (£368/t = £1.08 kg/N), this is a saving of £162/ha.
• Reduces nitrate leaching
• Fixes nitrogen and saves fertiliser costs
• Build up organic matter
• Help with disease and weed control
• Generate points for agri-environment schemes
• Time and money spent on crops
• May delay drilling of spring crop
• Not a priority in conventional cropping
On top of the fertiliser saving, green manures bring a number of other benefits. They can improve soil fertility, structure and water-holding capacity, suppress weeds, stimulate microbiological life in the soil and help the environment by reducing leaching risk in winter.
The result is an improved performance in the subsequent crop and often beyond. Dr Rosenfeld pointed to one case where there was a 0.8t/ha improvement in barley yield. With potatoes, there was an extra 7.7t/ha [£121/t 2009 conventional maincrop potatoes] - a cost benefit of £932/ha.
Green manures can be grown as annual crops or just for overwintering areas or even undersown in cereal crops. But the key one highlighted by Mr Briggs is the winter crop which is incorporated prior to spring drilling, releasing the fixed nitrogen and other nutrients to the following crop.
So what green manure options are there? There are a number of crops, the key ones being black medick, white or red clover and lucerne.
However, it is important to choose the right species for the right task. Although red clover is a popular option, it can be disease prone when grown too often, so ideally a five-year break should be left between crops.
Therefore, growers should look at other species, too. To prevent overwinter leaching, grazing rye is by far the best. It establishes rapidly producing lush leaf growth and work by Garden Organic has shown that it will typically reduce leaching of nitrogen by 90% over the winter period. But it must be established early in September to be effective.
On heavy soils, Stephen Briggs, director of Abacus Organic Associates, recommended mustard or grazing rye mixed with some black medick (yellow trefoil). They are better suited to overwintered cold conditions.
Over a longer period, white clover or lucerne are the best bets. Although slower to establish, they show better persistence over a longer period than the other species. Lucerne also shows good drought tolerance on light soils.
Vetch is suited to both light and heavy soils and it fixes nitrogen well, but seed rates may need to be increased for heavier soils.
For a quick flush of nitrogen in the spring, Mr Briggs recommends red clover or black medick, because they decompose rapidly and release nitrogen quickly. Mustard, however, has a woody stem and a high carbon/nitrogen ratio and releases nitrogen later.
For autumn drilling, seeds should be sown into a good, firm seed-bed, and be rolled down well, Mr Briggs advises.
Green manures can be either drilled or broadcast. Any drill that can drill close to the surface and handle small seeds is suitable.
The depth is particularly important for clovers which are small seed and should be drilled no deeper than 1cm or emergence will be poor. Seed costs for clover, sown at a rate of 10kg/ha are typically £60/ha. Generally, green manure seeds cost £2-6/kg. Seed rates for leguminous green manures are typically 10-15kg/ha.
Green manures should be topped before incorporation then they can be ploughed or rotavated in. Spraying with a herbicide is an option for conventional farms. He also stresses that for cereal crops, it is important that they are sown soon afterwards to make use of the nitrogen released.
Looking at this season, Mr Briggs says growing manures was "challenging", due to dry conditions. But growing mustard with legumes worked particularly well, as a protection against flea beetle.
"The mustard grows faster than the legumes, and the flea beetle preferentially attacks the mustard, leaving the clover to grow underneath. "When you top the mustard off, the clover is fine below."
Green manures can be used to build fertility on fallow land, thereby helping growers gain extra points under agri-environment schemes, says Mr Briggs.
Alternatively, growers with severe blackgrass problems looking to fallow badly affected areas could put some overwintered green manure in to protect the soil and provide some nitrogen.
Undersowing a standing crop and keeping it in over winter can be an even better option, says Mr Briggs. "It will help with your blackgrass problem, reduce your fertiliser bill and improve soil structure."
There is now a small window for early buyers to complete their purchases before the market lull over harvest and holidays.
Livestock producers are chasing grass after the driest period for the northwest since 1929. Even so, sales of NPK have only seen a minor downturn.
Sulphur grades are selling at a small premium of £5/t over their straight nitrogen equivalents so there is no reason not to use this cheap, but immensely valuable nutrient.
Imported AN is not widely available at present, but prices are about £5/t below the UK equivalent. Around 100,000 tonnes of urea has been traded (40,000 believed to be ex-store from last season), but prices have been quite volatile, between £215/t and £240/t.
The market for phosphate and potash has been very quiet. Prices have dropped a little with both triple superphosphate and muriate trading between £305/t and £320/t.
However, the global forecast for these nutrients is one of reinvestment by farmers and growth in sales of the nutrients. Prices will not be stable for long, although after three or four years the supply of potash should be capable of exceeding demand.
As for the future supply balance of nitrogen, excessive imbalances either way are not immediately anticipated.
New capacity is planned, notably in the Middle East and China, but seemingly endless delays prevent the market from being currently swamped with product.
By 2014, supply is predicted to exceed demand by some 10%, but history teaches us that, should this be the case, it will lead to the removal of older, less-efficient plants from manufacturing.
July 2010 (£/t delivered)*
UK 34.5% N
NK Silage grades
£5 below domestic
*All illustrated prices are based upon 24t loads for cash payment the month following. Prices for smaller loads and 50kg bags will vary considerably.
ScienceDaily (June 23, 2010) — Chicken litter is much more valuable as a fertilizer than previously thought, according to an Agricultural Research Service (ARS) study showing its newfound advantages over conventional fertilizers.
Litter is a mixture of chicken manure and sawdust or other bedding material. Some cotton farmers in the Mississippi area are switching to chicken litter and away from standard inorganic, synthetic fertilizers. Many other farmers are interested in the possible economic benefits of using chicken litter, but are reluctant to switch without the numbers to back up their decision.
Now a study by ARS agronomist Haile Tewolde at the agency's Genetics and Precision Agriculture Research Unit (GPARU) at Mississippi State, Miss., and cooperators has provided those numbers. Tewolde did the research with GPARU soil scientist Ardeshir Adeli, two Mississippi State University colleagues, and Karamat Sistani, research leader at the ARS Animal Waste Management Research Unit in Bowling Green, Ky.
Previous studies only considered the economic value of the nitrogen, phosphorus and potassium in chicken litter, compared to that in synthetic fertilizers. Farmers know that chicken litter, an organic fertilizer, is a better soil conditioner than synthetic fertilizers, but have never had a way to assign a number to the value of that benefit.
In their study, Tewolde and colleagues figured the litter's value as a soil conditioner as an extra $17 per ton of litter. They calculated this by balancing the price tag of the nutrients in litter with its resulting higher yields, a reflection of its soil conditioning benefits.
They found that cotton yields peaked 12 percent higher with organic fertilizers, compared to peak yields with synthetic fertilizers. With all benefits factored in, they found that chicken litter has a value of about $78 a ton, compared to $61 a ton when figured by the traditional method.
The economic analyses also showed that farmers could further increase their profits by using less of either fertilizer than currently used for maximum yields--which is also good news for the environment.
This research was published in the Agronomy Journal.
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by USDA/Agricultural Research Service. The original article was written by Don Co
Lameiro de regadio (Rio de Onor, Bragança)
Catão o Censor [234-149 a.C.], diz-nos Columella [Res Rusticae II, 16, 2], enumerava numa passagem hoje perdida dos seus escritos, as seguintes vantagens para os prados: 1) o mau tempo afecta-os menos do que a outras partes do campo, 2) necessitam de um investimento [de manutenção] mínimo, 3) produzem ganhos todos os anos. Columella refere ainda que a palavra prado significa sempre pronto, e que os prados eram mais considerados do que a terra arável no modelo de exploração agrícola pugnado por Catão, há mais de 2000 anos! Os Scriptores Rei Rusticae desconheciam a lei da conservação das massas de Lavoisier ou os princípios de nutrição de plantas formulados nos meados séc. XIX por von Liebig. Catão valorizava os prados porque estes, além de serem uma fonte fiável da energia que põe em marcha o carro e o arado, eram uma peça determinante nos sistemas de restituição da fertilidade dos solos agrícolas. O mecanismo da restituição da fertilidade dos solos agrícolas é conceptualmente muito simples. A manutenção da produtividade dos sistemas agrícolas depende da reposição dos nutrientes – por exemplo o azoto e o fósforo – consumidos pelas plantas cultivadas, e exportados dos solos agrícolas no interior dos grãos de cereal ou na carne animal. Sem nutrientes as plantas não crescem, e não produzem; se as perdas de nutrientes são maiores do que os ganhos o solo esgota-se e a produção de alimentos desaba. Os nutrientes eram um recurso escassíssimo nas sociedades orgânicas (muitos serviços pagavam-se com carros de estrume ou com direitos de pasto). Consequentemente, a restituição da fertilidade do solo era (e será sempre) a chave da produtividade dos sistemas orgânicos de agricultura.
Antes da generalização do uso de adubos químicos, a reposição dos nutrientes fazia-se recorrendo aos resíduos das culturas (quanto mais resíduos permanecessem no solo melhor), a estrumes (mais ou menos enriquecidos com resíduos de origem diversa) e ao enterramento em verde (sideração) de leguminosas. Os estrumes eram um produto animal tão importante como a carne, o leite, a lã, o couro ou a tracção. A produção de estrumes depende do consumo de erva. Quanto mais erva, maior o número de herbívoros domésticos e maior a produção de estrumes. Nos sistemas tradicionais de agricultura da montanha nordestina uma vaca produzia ca. de 15 t estrume/ano e 1 ha de centeio consumia ca. 15 t de estrume, que por sua vez sustentava ca. de 1,5 pessoas. Por conseguinte, quanto maior a área de pasto, e a sua produtividade, maior era a produção de alimentos vegetais, e maior densidade populacional de humanos. A criação de animais, e o consumo de carne, não são uma invenção moderna. A componente animal (e implicitamente o consumo de carne) é indispensável no desenho de sistemas sustentáveis de agricultura. As leguminosas pratenses e forrageiras foram tão importantes como o carvão na génese da revolução industrial em Inglaterra, no séc. XVIII. A incorporação de trevos nas rotações trienais herdadas da Idade Média aumentou os imputs de azoto no solo, a produção de pasto e fenos e a produção de estrumes. Por esta via (mas não só) os trevos incrementaram a produtividade do trabalho agrícola e a disponibilidade de trabalho para a industria. "Carvão, trevos e proletários", poderia ser este o título de um livro sobre a revolução industrial. Os serviço de regulação do ciclo de nutrientes prestado pelo tandem pastagem-animal é pouco valorizado nas sociedades industrializadas. Para além de sustentarem a produção animal, e de servirem de refúgio a plantas e animais de elevado valor conservacionista, a restauração da fertilidade química e física dos solos degradados pela cerealicultura, e a sequestração de carbono são os serviços ecossistémicos prestados pelos prados de maior valor social na actualidade. No entanto, estou seguro que a função de colector de nutrientes no passado desempenhada pelas pastagens será, mais tarde ou mais cedo, recuperada. A escassez energética, e a depleção das reservas globais de fósforo a isso obrigarão.
Esta semana decorreu entre Miranda do Douro e Zamora, o IV Reunião Ibérica de Pastagens e Forragens. Para quem gosta, pratica e/ou estuda a agricultura foi um momento fantástico de convívio e aprendizagem, fundamental num tema tão complexo, tão interessante, tão importante como são as comunidades herbáceas, indígenas ou semeadas, sujeitas a pastoreio, ou as culturas forrageiras. Senti uma angústia crescente nos quatro dias que durou o encontro. Um tema crucial como este reuniu muito menos interessados do que um qualquer encontro nacional dedicado à conservação da natureza, ou a um pequeno grupo de vertebrados. Já nem falo na correria que são os congressos de energias renováveis, de planeamento e gestão do território, de economia regional ou de segurança alimentar, quatro temas de discussão recorrentes na lista AMBIO. Alguma coisa não está bem!
ScienceDaily (Dec. 21, 2009) — Human activity is increasing the supply of nutrients, such as nitrogen and phosphorus, to stream systems all over the world. The conventional wisdom -- bolstered by earlier research -- has held that these additional nutrients cause an increase in production all along the food chain, from the tiniest organisms up to the largest predators. A long-term, ecosystem-scale study by a team of University of Georgia researchers, however, has thrown this assumption into question.
The researchers -- a team from the UGA Odum School of Ecology and department of entomology in the College of Agricultural and Environmental Sciences -- found, unexpectedly, that while nutrient enrichment did indeed cause a steady increase in the production of organisms lower on the food chain, organisms at the top of the food chain did not benefit.
Their study, published in Proceedings of the National Academy of Sciences, was funded by the National Science Foundation. It documents the effects of long-term nutrient enrichment of a headwater stream in a forested area at the Coweeta Hydrologic Laboratory in North Carolina. For the first two years of the study, the results were as expected: the production of both prey (the organisms low on the food chain) and predators (in this case salamanders and macroinvertebrates) increased. But with continued addition of nutrients, things began to change. While the prey continued to increase at the same rate, the production of predators leveled off, signifying a 'decoupling' of the typical relationship between predators and prey.
Maintaining patterns of energy flow between predators and prey is a critical aspect of healthy ecosystems. "What we found was a dead end in the food chain," said Amy Rosemond, assistant professor at the Odum School, and one of the lead researchers. "This is the first time we've seen this kind of trophic decoupling, or break in the food chain, between the levels of prey and predator on this scale. This kind of disruption of the food web wasn't on anyone's radar screen before now. "
In this instance, Rosemond explained, the break was driven by the traits of the various prey species that inhabit the stream system. Some of these species were better able to take advantage of the extra nutrition than were others. After the first two years, the nutrient enrichment began to favor the growth of large-bodied prey, such as the caddisfly, Pycnopsyche spp., over smaller organisms. These large-bodied prey were simply too big for the stream's predators to consume; hence, they were unable to capitalize on the increase in available food.
John Davis, who conducted the research as part of his Ph. D. dissertation, said that the work has global implications. "Nutrient enrichment is a global threat to the health of freshwater ecosystems," he explained. "However, our understanding of its effects is limited. Our experimental results varied substantially from the few other large-scale experiments, which suggests that ecosystem-level responses to nutrient enrichment are largely context-dependent. This is important because humans are increasing nutrient loading rates to a diversity of ecosystems, but our understanding of their effects is based on only a small number of ecosystem types. "
Rosemond said that their results point to the need for more research, especially large-scale, long-term studies in a variety of ecosystems. Davis agrees. "It took over four years for nutrient enrichment to decouple predator and prey production within these headwater streams," he said. "But most ecological experiments are limited to time scales of weeks to months. "
And the need to understand the effects of nutrient enrichment continues to grow more important. According the Environmental Protection Agency, the health of 47 percent of lakes and 45 percent of streams in the U. S. is impaired, with excessive nutrients a significant source of that impairment. Nutrient inputs to lakes and streams are likely to continue to increase globally from fertilized agricultural and suburban lands and from human and animal wastes that enter aquatic systems from treated sewage, septic tanks, or run-off from land. Furthermore, headwater streams, like the study stream in Coweeta, may account for as much as 73% of all stream miles. These headwater streams are the 'feeders' of larger rivers, so their response to nutrient enrichment likely affects downstream systems as well. But long-term effects of nutrients have not been previously tested in these systems.
"Without more accurately assessing the long-term effects of nutrients on a diversity of ecosystem types," Davis concluded, "we won't be able to adequately predict how global ecosystems are going to respond to chronic nutrient enrichment. "