The simulated increase in dry matter or growth is allocated to different plant organs by following a set of rules for partitioning that change with development and sometimes also with different stress levels. In early vegetative growth, priority often goes to leaf growth, with an additional portion for stems to ensure that there is supporting structure for the leaves. Root growth is adjusted to ensure that enough roots are formed to satisfy demand for water or specific nutrients. As the plant grows, it may produce more assimilates than are required to sustain the estimated maximum possible growth rate of organs. This excess may be stored in roots or shoots, or it may be allocated to a pool of remobilizable reserves. As the plant transitions to reproductive growth, partitioning to reproductive structures begins. The details of how partitioning to reproductive growth is simulated vary with the morphology of the crop and the physiological complexity of the model. Simple models apportion assimilate to reproductive organs by assuming a linear increase in harvest index over the grain-filling phase (Spaeth and Sinclair 1985). Alternately, growth of individual fruits or cohorts of fruits is simulated, allowing for competition among the fruits to senesce the least competitive fruits (Boote et al. 2002). Further complications arise in attempting to simulate growth of individual seeds, especially if protein or oil contents are considered. The final seed yield is variously determined at physiological maturity, which is estimated from routines for development, or at the harvest date, which may be estimated or provided as an input.

Partitioning rules for tuber and root crops are similar except that in place of flowering or onset of grain filling, a stage of onset of tuber or storage root growth demarcates major changes in partitioning rules (Singh et al. 1998). In such models, growth of storage organs is described separately from fibrous root growth.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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