https://newgenerationplantations.org/multimedia/file/e20fd847-0511-11e5-91a6-005056986313

Integrating genetic and silvicultural strategies to minimize abiotic and biotic constraints in Brazilian eucalypt plantations

In the context of increasing global food demand, ecological intensification of agroecosystems is required to increase nutrient use efficiency in plants while decreasing fertilizer inputs. Better exploration and exploitation of soil resources is a major issue for phosphorus, given that rock phosphate ores are finite resources, which are going to be exhausted in decades from now on. We review the processes governing the acquisition by plants of poorly mobile nutrients in soils, with a particular focus on processes at the root–soil interface. Rhizosphere processes are poorly accounted for in most plant nutrition models. This lack largely explains why present-day models fail at predicting the actual uptake of poorly mobile nutrients such as phosphorus under low input conditions. A first section is dedicated to biophysical processes and the spatial/temporal development of the rhizosphere. A second section concentrates on biochemical/biogeochemical processes, while a third section addresses biological/ecological processes operating in the rhizosphere. New routes for improving soil nutrient efficiency are addressed, with a particular focus on breeding and ecological engineering options. Better mimicking natural ecosystems and exploiting plant diversity appears as an appealing way forward, on this long and winding road towards ecological intensification of agroecosystems.

Acquisition of phosphorus and other poorly mobile nutrients by roots. Where do plant nutrition models fail

We conducted a 6-year field manipulation drought experiment in an evergreen Quercus ilex forest where we simulated the drought predicted by GCM and ecophysiological models for the coming decades (an average of 15% soil moisture reduction). We thereby tested the hypothesis that enhanced drought will change Ca, Fe, Mg, Mo and S availability, concentrations and accumulation patterns in Mediterranean ecosystems. The strongest effects of drought occurred in the soil. Drought increased the total soil concentrations of S, the soil extract concentrations of Fe, Mg and S, the Mg saturation in the soil exchangeable complex and tended to increase the percentage base saturation of the soil exchangeable complex. These increased soil concentrations were related to a decrease of plant uptake capacity and not to an increase of soil enzyme activity, which in fact decreased under drier conditions. Drought increased leaf Mg concentrations in the three dominant species although only significantly in Quercus ilex and Arbutus unedo (20 and 14%, respectively). In contrast, drought tended to decrease Ca in Phillyrea latifolia (18%) and Ca and Fe concentrations in the wood of all three species. Drought increased Ca and Fe concentrations in the roots of Quercus ilex (26 and 127%). There was a slight general trend to decrease total biomass accumulation of nutrients that depend on water flux such as Mg, Fe and S. This effect was related to a decrease of soil moisture that reduced soil flow, and to a decrease in photosynthetic capacity, sap flow, transpiration and growth, and therefore plant uptake capacity under drought observed in Quercus ilex and Arbutus unedo. On the contrary, drought increased Mo accumulation in aboveground biomass in Phillyrea latifolia and reduced Mo accumulation in Arbutus unedo by reducing growth and wood Mo concentrations (51%). Phillyrea latifolia showed a great capacity to adapt to drier conditions, with no decrease in growth, an increase of Mo uptake capacity and a decrease in leaf Ca concentration, which was related to a decrease in transpiration under drought. The results indicate asymmetrical changes in species capacity to accumulate these elements, which are likely to produce changes in inter-specific competitive relations among dominant plant species and in their nutritional quality as food sources. The results also indicate that drought tended to decrease nutrient content in aboveground biomass, mainly through the decrease in growth and transpiration of the most sensitive species and caused an increase in the availability of these nutrients in soil. Thus, drought decreased the ecosystem’s capacity to retain Mg, Fe and S, facilitating their loss in torrential rainfalls.

Drought’s impact on Ca, Fe, Mg, Mo and S concentration and accumulation patterns in the plants and soil of a Mediterranean evergreen Quercus ilex forest

f In the Netherlands the Pow value, based on an extraction of soil P with water, is used as a basis for P-fertilizer recommendations for arable crops. Using a simple, mechanistic model of P transport in the soil the Pw value required for adequate P uptake by crops can be calcu- lated on the basis of daily uptake requirements, root area index, P-adsorption isotherms and total amount of P taken up during a growing season, Calculated Pw values for adequate up- take are in the same range as the present recommendation scheme based on field experiments. Possible refinements of the model are discussed. For each soil the Pw value can be calculated that corresponds to the P concentrations in the soil solution according to standards set to reduce environmental pollution. Our model predicts that, unless the root area index of non- cereal crops is considerably improved, these standards cannot be met in the plough layer \\ithout affecting crop production levels, Calculations show that the present method of deter- mining the Pw value yields a reasonable compromise between a measurement of intensity and capacity of P supply in the soil. Key~vords: root length density, root area index, phosphorus availability, phosphate adsorp- tion, barley, bean, maize, onion, potato, sugar beet, wheat

.JAOO35-04 A simple model of P uptake by crops as a possible basis for P fertilizer recommendations

Climate change adaptation and mitigation management options: a guide for natural resource managers in southern forest ecosystems.

Models of soil nutrient bioavailability and uptake assist in nutrient management and lead to a better understanding of nutrient dynamics in the soil-plant system. SSAND (Soil Supply and Nutrient Demand) is a steady state, mechanistic nutrient uptake simulation model based on mass flow and diffusive supply of nutrients to roots. It requires user inputs for soil and plant parameters to calculate a nutrient’s concentration at the root surface and the subsequent uptake by a plant root and/or extrametrical mycorrhizal hyphae. It can be considered a sub-model linked to hydrological or plant growth models. SSAND provides a basis for simulating nutrient uptake under different soil-plant scenarios, including multiple soil compartments, net mineralization inputs, changing root growth, changing mycorrhizal hyphae growth, changing soil water content and multiple fertilizer events. It incorporates uptake from roots and mycorrhizal hyphae, including the potential competition between these entities. It should be useful ...

http://www.nutricaodeplantas.agr.br/site/culturas/eucalipto_pinus/eucalipto_cjss86.pdf

P J Smethurst

Papers

Soil supply and nutrient demand (SSAND): A general nutrient uptake model and an example of its application to forest management