In Guanajuato, corn is one of the most important crops from a food, industrial, political and social standpoint. Experience with producers in recent years has shown that fertilizer recommendations based on soil tests fail to meet the nutritional needs of the crop and thus high yields are not achieved. Optimization of nitrogen (N) management in corn requires proper determination of the nitrogen fertilizer dose to apply, specifically in the second fertilization. An alternative is the use of infrared sensors such as the Minolta SPAD 502, which measures the chlorophyll content in leaves; this value has a clear correlation with the amount of nitrogen in the plant, as it allows determining nutritional needs in terms of nitrogen. During the 2010 and 2011 spring-summer cycles, two trials were conducted in the center-south region of the state of Guanajuato; seven treatments, consisting of increasing doses of N (0, 45, 90, 135, 180, 240 and 300 UN), were assessed. SPAD values were obtained when plants presented seven fully-developed leaves (V7), and yield was also determined. Combined analysis of variance and comparison of means (LSD α = 0.05) were performed using the SAS 9.2 statistical package. The maximum grain yield response occurred in the range of 180 to 300 UN, because there were no statistical differences among them. A proportional relationship between the N dose and the SPAD value was observed in the V7 stage of the crop. This information is a basis for generating the nitrogen fertilizer requirement diagnosis in corn cultivation.

Pecan (Carya illinoinensis (Wangenh.) K. Koch) has a genetic distinction due to the formation of annual growth rings, as a result of changes among environmental, management and genetic factors in the productivity of pecan. Such asseverations conducted to carry out the present study with the objective of describing the relationship between water availability corresponding to annual irrigation and annual wood growth (rings) using an image analyzer. Comments and analysis of these images allowed us to distinguish the extent of annual growth in relation to the irrigation. As a result, three groups were identified: wood growth with water stress (0.6mm), without water stress (2.3 to 2.7 mm) and with water excess (4.2 mm).

This paper presents the development of a methodology for calculating return periods of annual rainfall in the windward and leeward regions of the Gulf of Mexico. The data used were daily records of 147 National Weather Service stations that were validated and processed to perform the Kolmogorov-Smirnov nonparametric goodness-of-fit test for the Gumbel distribution. Probabilities and levels of rainfall were calculated at each station, in return periods of 2, 10, 20, 30, 40, 50 and 100 years by the inverse transformation of the Gumbel distribution. Timely information was applied to the spatial interpolation thin plate smoothing spline method to plot isolines. The images showed that the levels of rainfall in different return periods have greater variation in the windward (50-350 mm) area; while in the case of the leeward region, rains are kept between 50 and 100 mm annually. This methodology can be used as a tool in defining and developing contingency plans to provide quick solutions to the population located in vulnerable areas affected by an event of rain.

The drought of the past few years in north-central Mexico underscores the need for extensive hydroclimatic data that can reveal fluctuations and trends over time, in order to establish water resource planning and mitigation measures. Using dendrochronological techniques, an 800-year streamflow reconstruction was developed for the upper Nazas River watershed in Durango. The reconstruction showed high inter-annual and multiannual hydroclimatic variability and decadal droughts were detected in the 1250s, 1320-1340s, 1370-1380s, 1440-1450s, 1460-1470s, 1650-1660s, 1710-1730s, 1790-1810s, 1920-1940s, 1970-1980s, and 1990s. Some of the droughts were longer and of higher intensity than ones observed in climate records. Extreme flow events were detected in the years 1212, 1229, 1242, 1245, 1271, 1313, 1404, 1427, 1451, 1504, 1520, 1563, 1566, 1620,1671, 1681, 1735, 1816, 1833, 1869, 1920, 1956, 1959, and 1992, and they were linked with the El Niño–Southern Oscillation (ENSO) warm phase. Water decision-makers in the Comarca Lagunera region could use this information to establish probabilities of droughts and occurrence of extreme runoff events for management purposes.

In the preservation of the quality of the soil is essential the implementation of natural fertilizers, because all methods used by organic agriculture guarantee the presence of beneficial microorganisms that facilitate the fixing of nutrients and absorption by plants. In arable soils, the addition of organic matters is used among other things, to improve fertility and soil properties, such as aggregation and water holding capacity. The pepper (Capsicum annuum L.) is one of the most important species cultivated in Mexico and other countries. A sustainable and ecological management is the use of organic matter in soil and in the preparation of substrates for the establishment of the crop under controlled conditions of climate, pests and diseases. According to this problem, arose the need for a project using the variety creole of Pepper Pulla in a substrate composed with a mixture of sandy soil and compost, where three doses of compost (10, 25 and 50 t·ha-1) were included as treatments. The objective was to determine the optimal dose of organic fertilization to sustain production and to assess the effect on phenological development and crop production. The statistical analysis showed significant differences between treatments. Short term results showed that treatments of 25 t·ha-1 of compost and the control with chemical fertilization had the highest yields and improved plant phenological behavior. The conclusion was that the optimal dose of compost goes from 10 t·ha-1 to 25 t·ha-1.

During its lifespan, a tree under the pressure of a biotic or abiotic factor may lose some of its foliage. As leaves are the basis of photosynthesis, eventual defoliation has a direct effect on the carbohydrate reserves of the tree. Some species, such as beech (Fagus sylvatica), develop in low light conditions. The white oak (Quercus petraea), on the other hand, grows in direct sunlight conditions. There are marked differences between beech and oak in terms of physiological responses to defoliation. Both species are of great importance in the forests of the Lorrain region in eastern France. It is believed that a better understanding of behavioral response to biotic and abiotic stresses will contribute to better knowledge and design of management plans for forests and thus optimize their yield. The aim of this work was to study the effect of seasonal defoliation and shading on carbohydrate reserves in two-year-old white oak and beech saplings. It was observed that the two species differ in the amount of reserves and storage organs. Throughout the year, carbohydrate reserves stored in winter gradually decrease; some are used for respiration during the winter, and some for growth and sprouting in the spring. In defoliation, carbohydrate reserves are used to replace the leaves, without affecting biomass.