La Paradoja del fósforo: De su necesidad en la producción agraria, escasez de reservas mundiales y la contaminación de aguas

fosforo-en-suelos

El fosforo en los suelos Fuente: Google imágenes

Si garantizar la soberanía alimentaria a nivel global resulta ser un reto difícil de afrontar, la ciencia y tecnología actual parecen agravar alarmantemente el problema, en lugar de resolverlo. Al parecer somos incapaces de utilizar el sentido común, poniendo en riesgo nuestros objetivos del milenio. ¡Sí, esos que nunca se cumplen! Nadie duda de las bondades de la ciencia y la tecnología, pero usando la razón como punto de partida, don que al parecer vamos perdiendo, o dejamos en mano de científicos y tecnólogos cortos de vista, así como en las procelosas fauces de multinacionales a las que no les importa la salud de la biosfera, el hambre en el mundo, ni la salud humana. En un post precedente (El Futuro de la Agricultura tropical y el problema del fósforo en sus suelos: El Hambre de Fósforo y la Tasa del Fósforo), ya constamos que una de las mayores amenazas para garantizar la producción y soberanía alimentaria mundial resulta ser las escasas reservas que alberga la geosfera de un elemento imprescindible para nuestro futuro. Hoy os  mostramos dos noticias paradójicas que publicó simultáneamente el boletín de Noticias TerraDaily.  En la primera se nos informa de que el exceso de abonados fosfatados contamina las aguas (como por ejemplo, vía floraciones algales) creando, numerosos problemas ambientales. Por el contrario, en la segunda, nos alerta de que hay que comenzar ya a generar una nueva perspectiva con vistas a ahorrar este apreciado y escaso elemento químico. En otras palabras, mientras que los países ricos inducen severos problemas de degradación ambiental por sobre-fertilización con enmiendas fosfatadas, la última nos advierte de que, si no intervenimos ¡ya!, reduciendo las cantidades que se añaden,  el futuro de la agricultura mundial se enfrenta a un panorama tenebroso por la escasez del mentado elemento. ¿Dónde veis vosotros la racionalidad científica?. Desde luego dudo mucho que los “tocagenes” y su biotecnología sean la solución (hablan mucho pero no resuelven los principales problemas de la agrosfera). Más bien nos hace falta un cambio de paradigma agronómico que catapulte hacia actividades sustentables, algo difícil de lograr bajo el imperio de una política comandada por los que tan solo buscan amasar dinero a corto plazo, sin pensar en el futuro. Como podréis leer abajo, en USA se ha demostrado que las prácticas agrarias más eficientes logran reducir la polución de fósforo en las cuencas de drenaje y sus cuerpos de agua intercalados (lagos), no resultan eficaces como para poder paliar el problema.   Y así los investigadores concluyen que:

 

Los esfuerzos convencionales, como la siembra directa y los cultivos de cobertura, han tratado de abordar el escurrimiento de nutrientes al reducir su movimiento de los suelos hacia los cursos de agua. Sin embargo, nuestro estudio demuestra que la simple prevención de la escorrentía y la erosión no resuelven el problema principal del exceso de fósforo del suelo por producido por los fertilizantes, mientras que tal sobreabundancia podría anular cualquier esfuerzo de conservación. Las soluciones deben centrarse en evitar que el fósforo entre en el paisaje o en extraer el exceso que ya se está acumulado”, dice el co-autor Christopher Kucharik, profesor de agronomía y estudios ambientales en UW-Madison”.

 Personalmente considero que el principal objetivo del milenio estribaría en disminuir la estupidez humana hasta límites sostenibles para el propio hombre y la biosfera, algo que se me antoja cada día más difícil, lejano, o simplemente imposible de alcanzar.  Tan solo un cambio de modelo económico y agrario, simultáneamente, podrán hacer frente al exponencial incremento de cretinismo del que hace gala la especie humana.

Juan José Ibáñez

Seguidamente exponemos ambas notas de prensa……..

Study quantifies effect of legacy phosphorus in reduced water quality
by Staff Writers
Madison WI (SPX) Mar 17, 2017

For decades, phosphorous has accumulated in Wisconsin soils. Though farmers have taken steps to reduce the quantity of the agricultural nutrient applied to and running off their fields, a new study from the University of Wisconsin-Madison reveals that a “legacy” of abundant soil phosphorus in the Yahara watershed of Southern Wisconsin has a large, direct and long-lasting impact on water quality.

Published March 13 in the journal Ecosystems, the study may be the first to provide quantifiable evidence that eliminating the overabundance of phosphorus will be critical for improving the quality of Wisconsin’s lakes and rivers.

For example, the results indicate that a 50 percent reduction in soil phosphorus in the Yahara watershed’s croplands would improve water quality by reducing the summertime concentration of phosphorus in Lake Mendota, the region’s flagship lake, by 25 percent.

If we continue to apply phosphorus at a greater rate than we remove it, then phosphorus accumulates over time and that’s what’s been happening over many decades in the Yahara watershed,” says Melissa Motew, the study’s lead author and a Ph.D. candidate in the UW-Madison Nelson Institute for Environmental Studies.

Phosphorus seeps into soils primarily by way of fertilizer and manure, and what crops and other plants don’t use to grow then leaks into waterways with rain and snowmelt runoff. Scientists have long believed that excess soil phosphorus is a culprit behind the murky waters and smelly algal blooms in some of Wisconsin’s lakes and rivers.

Conventional efforts, like no-till farming and cover crops, have tried to address nutrient runoff by slowing its movement from soils to waterways. However, the study shows that simply preventing runoff and erosion does not address the core problem of abundant soil phosphorus, and this overabundance could override conservation efforts.

Solutions should be focused on stopping phosphorus from going onto the landscape or mining the excess amount that is already built up,” says co-author Christopher Kucharik, a professor of agronomy and environmental studies at UW-Madison.

Increasing plant yield in wake of looming phosphate supply limits
by Staff Writers
Chapel Hill NC (SPX) Mar 17, 2017

Scientists at the University of North Carolina at Chapel Hill have pinpointed a key genetic switch that helps soil bacteria living on and inside a plant’s roots harvest a vital nutrient with limited global supply. The nutrient, phosphate, makes it to the plant’s roots, helping the plant increase its yield.

The work, published in Nature, raises the possibility of probiotic, microbe treatments for plants to increase their efficient use of phosphate. The form of phosphate plants can use is in danger of reaching its peak – when supply fails to keep up with demand – in just 30 years, potentially decreasing the rate of crop yield as the as the world population continues to climb and global warming stresses crop yields, which could have damaging effects on the global food supply.

“We show precisely how a key ‘switch protein’,PHR1, controls the response to low levels of phosphate, a big stress for the plant, and also controls the plant immune system,” said Jeff Dangl, John N.

Couch Distinguished Professor and Howard Hughes Medical Institute Investigator. “When the plant is stressed for this important nutrient, it turns down its immune system so it can focus on harvesting phosphate from the soil. Essentially, the plant sets its priorities on the cellular level.”

Dangl, who worked with lead authors, postdoctoral researchers Gabriel Castrillo and Paulo Jose Pereira Lima Teixeira, graduate student Sur Herrera Paredes and research analyst Theresa F. Law, found evidence that soil bacteria can make use of this tradeoff between nutrient-seeking and immune defense, potentially to help establish symbiotic relationships with plants. Bacteria seem to enhance this phosphate stress response, in part simply by competing for phosphate but also by actively ‘telling’ the plant to turn on its phosphate stress response.

In recent plant biology studies, there have been hints of a relationship between plant phosphate levels and immune system activity – a relationship that some microbes can manipulate. In the new study, Dangl and colleagues delved more deeply into this relationship, using mutant versions of Arabidopsis thaliana, a weed that has long been the standard “lab rat” of plant biology research.

In one experiment, Dangl’s team found that Arabidopsis plants with mutant versions of the PHR1 gene not only had impaired phosphate stress responses, but also developed different communities of microbes in and around their roots when grown in a local native North Carolina soil.

This was the case even in an environment of plentiful phosphate – where phosphate competition wouldn’t have been a factor – hinting that something else was happening in the plants to trigger the growth of different microbial communities. The researchers found similar results studying PHL1, a protein closely related to PHR1 with similar but weaker functions.

In another experiment, in lab-dish conditions, the researchers colonized roots of sterile-grown normal Arabidopsis plants with a set of 35 bacterial species isolated from roots of plants grown previously in the same native soil. In these re-colonized plants, the phosphate stress response increased when exposed to a low-phosphate condition.

Investigating further, the team showed that PHR1 – and probably to a lesser extent PHL1 – not only activates the phosphate stress response but also triggers a pattern of gene expression that reduces immune activity, and thus makes it easier for resident microbes to survive.

The findings suggest that soil-dwelling microbes have figured out how to get along with their plant hosts, at least in part by activating PHR1/PHL1 to suppress immune responses to them. Dangl’s team also thinks these microbes may even be necessary for plants to respond normally to low-phosphate conditions. It could be possible, then, to harness this relationship – via probiotic or related crop treatments – to enable plants to make do with less phosphate.

Phosphate is a limited resource and we don’t use it very efficiently,” said Dangl, who is also an adjunct professor of microbiology and immunology at the UNC School of Medicine.

As part of fertilizer, phosphate runs off into waterways where it can adversely affect river and marine ecosystems. It would be better if we could use phosphate in a way that’s more efficient.”

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