-STICS (Simulateur mulTJdiscplinaire pour les Cultures Standard) is a crop model constructed as a simulation tool capable of working under agricultural conditions. Outputs comprise the production (amount and quality) and the environment. Inputs take into account the climate, the soi1 and the cropping system. STICS is presented as a model exhibiting the following qualities: robustness, an easy access to inputs and an uncomplicated f~~t u r e evolution thanks to a modular (easy adaptation to various types of plant) nature and generic. However, STICS is not an entirely new model since most parts use classic formalisms or stem from existing models. The main simulated processes are the growth, the development of the crop and the water and nitrogenous balance of the soil-crop system. The seven modules of STICSdevelopment, shoot growth, yield components, root growth, water balance, thermal environment and nitrogen balanceare presented in tum with a discussion about the theoretical choices in comparison to other models. These choices should render the model capable of exhibiting the announced qualities in classic environmental contexts. However, because some processes (e.g. ammoniac volatilization, clrought resistance, etc.) are not taken into account, the use of STICS is presently limited to several cropping systems. (
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Phosphorus inputs must be estimated accurately to optimize the economic return to farmers and minimize P loss from soils to surface waters. Currently, P recommendations are based on the diagnosis of field crop responses by chemically extracted soil P. However, the inability of chemical extraction to characterize plant‐available P limits the reliability of these recommendations. Major sources of P mobilized by plant roots include P ions in solution and those from soil constituents, which replenish and buffer solution. A mechanistic evaluation of soil P supply should therefore be based on the description of P ion transfer between soil constituents and solution. Sorption, desorption, electro‐ultrafiltration (EUF), and isotopic exchange studies show that an adequate modeling of this quantity [Q(CP,t)] of P ions must account for both the concentration of P ions in soil solution (Cp) and time (t). In one long‐term field experiment, the Q(CP,t) description was not affected by crop rotation and mineral fertilization histories; therefore, Q(CP,t) changes are fully explained by CP changes. In two field experiments, CP changes were linearly correlated with the cumulative P budget, inputs, and outputs over years. In three field experiments, the soil type effect on the relative maize (Zea mays L.) response curve was taken into account using the ability of soil P to replenish solution P for 1 d. The residual variance of this diagnosis is halved compared to Olsen's extraction. Although more information is necessary, accuracy is improved when soil testing is based on mobility of P ions.
Arboriculture must maintain acceptable fruit production levels while preserving natural resources. This duality can be analyzed with the concept of ecosystem service. We reviewed the literature on orchards to explain how ecological functions modified by agricultural practices provide six ecosystem services-fruit production, climate regulation, soil nitrogen availability, water regulation, pest and disease control, and pollination-and which indicators could describe them. The major points are, first, that orchards have a high potential of multiple services. They can sequester from 2.4 to 12.5 t C/ha/year. Their perennial character and multi-strata habitat, as well as the opportunity of creating diversified hedgerows and cover crops in alleys, may contribute to a high level of biodiversity and related services. Second, every service depends on many functions. Fruit yield, which could reach up to 140 t/ha in apple orchards, is increased by light interception, carbon allocation, and nitrogen and water uptake. Third, agricultural practices in orchards have a strong impact on ecosystem functions and, consequently, on ecosystem services. Overfertilization enhances nitrogen leaching, which reduces soil nitrogen availability for the plant and deteriorates the quality of drained water. Groundcover increases humification and reduces denitrification and runoff, thus enhancing soil nitrogen availability and water regulation. It also enhances biotic interactions responsible for pest control and pollination. Pruning may increase fruit quality trough a better carbon allocation but decreases pest control by fostering the dynamics of aphids. To study multiple ecosystem services in orchards, we suggest using models capable of simulating service profiles and their variation according to management scenarios. We then refer to the available literature to show that conflicts between provisioning and regulating services can be mitigated by agricultural practices. Improved knowledge of soil processes and carbon balance as well as new models that address multiple services are necessary to foster research on ecosystem service relationships in orchards.
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