[Behaviour of the principal climatological variables affecting some crops in Chapingo, Mexico influence area]

English. An agroclimatical methodology is presented to determine the best time to plan maize, wheat and dry beans in the Chapingo area. It is based on the thermal and hydrological evaluation, through the generation of two agroclimatic indexes and their comparison with the thermic and hydric requirements that should satisfy the crops, within the corresponding Effective Growing Season EGS. The indexes were generated from existing climatological information with daily maximun and minimum air temperature, precipitation and evaporation. The (EGS) determination envolves the previous determination of the Freeze Free FFS and the Moisture Available Season MAS. The dates for the first and last frost determinated the FFS. The time-space patterns of earlier parameters were evaluated and their effect on different planting dates. Computer programs were used to group the information every 5 days and realize a water balance, calculate the normal distribution of frost dates and determine the potential thermal and hydric indexes in the area. Thermal Efficiency (TE), and Total Hydric Index (IT) respectively. The results shows that TE was for maize with 79.6 % 85.5 % for dry beans, and 94.4 for wheat. Concerning to HI for the planting date 80 % of probability, the results show that maize crop had 57 % wheat 68.4 and dry beans 72.9. The year's period with maximum TE were from May to September for wheat; April to July for dry beans and June to October for maize.

Spanish; Castilian. Se presenta una metodologia para determinar la mejor epoca de siembra para maiz, trigo y frijol en Chapingo. Se basa en la evaluacion termica e hidrica del area, con la generacion de 2 indices agroclimaticos y su comparacion con los requerimientos termicos e hidricos de los cultivos dentro del periodo de crecimiento efectivo (PCE). Indices generados con informacion climatologica diaria del area, temperaturas maxima y minima del aire, precipitacion y evaporacion. El PCE involucra el periodo libre de heladas (PLH) y el periodo por disponibilidad de humedad (PCH). Las fechas de primeras y ultimas heladas de 12 estaciones determinaron el PLH. Estos parametros agroclimaticos se estudiaron en su efecto en las fechas de siembra. Con programas de ordenador se agrupo la informacion cada 5 dias, calculo el balance hidrico, la distribucion de las fechas de heladas y los indices termico e hidrico potenciales del area, [Eficiencia Termica (ET) e Indice Hidrico Total (IT) respectivamente]. El maiz satisfizo en sus necesidades con 57 y 79.6 %; el trigo, con 68.4 y 94.4 y el frijol con 72.9 y 85.5. Los meses con la mayor ET fueron de mayo a septiembre (trigo), abril a julio (frijol) y junio a octubre (maiz).