SUMMARYIdentifying and applying the optimum fertilizer nitrogen (N) rate is a permanent challenge for farmers. Prediction of fertilizer N requirement, based on crop chlorophyll measurements (CMs), relies on a strong relationship between fertilizer N supply and leaf chlorophyll concentration at a given crop growth stage. A methodological approach is described, aiming to develop an algorithm that uses CM inputs to derive the economically optimum fertilizer N rate for top-dressing, without using a reference plot for data normalization. The method was tested on maize (Zea mays L. cvar Jabali) at experimental and farmer sites in the central (‘Bajío’) region of Mexico over 3 years (2010–12). Increasing fertilizer N supply at planting significantly influenced chlorophyll concentration at the seventh unfolded maize leaf stage (GS 17 on the Zadoks scale). Maize grain yields increased with increasing total fertilizer N supply and fitted quadratic models, which allowed economically optimum fertilizer N rates (Nopt) to be calculated. The Nopt ranged from 160 to 300 kg N/ha and corresponding grain yields ranged from 7·7 to 14 t/ha. Grouped data analysis (sites–years) confirmed a highly significant relationship between the Nopt and the chlorophyll concentration at GS 17, which could be described by a linear model: Nopt = 513·3–0·58 × CM. This model predicted the top-dressing Nopt within a fertilizer N management regime adapted to local maize cropping systems and led to similar grain yields across test sites compared with the same parameters calculated based on grain yield response trials. The current approach is variety-specific, so development of so-called correction factors accounting for variety-related differences in chlorophyll concentration is described. The results demonstrated the feasibility of the proposed algorithms to support decision-making on the optimum fertilizer N rate to apply in maize production systems with one top-dressing application.

La zeolita y la micorriza son productos naturales que se distinguen por su utilidad en la agricultura, debido a que el primero al entrar en contacto con el amonio lo retienen en su estructura interna y externa, funcionando entonces como un fertilizante nitrogenado de lenta liberación y, el segundo su simbiosis mutualista entre hongos endófitos y las raíces de las plantas cultivadas beneficia la absorción del fósforo a la planta. El presente trabajo se realizó con el objetivo de evaluar la eficiencia de utilización de la urea combinada con zeolita y asociada con micorriza, en el cultivo de trigo bajo riego. El estudio se realizó en Pabellón, Aguascalientes, durante el ciclo otoño-invierno. Se evaluaron seis tratamientos: dos concentraciones de zeolita (0 y 25%), tres dosis de urea (0, 75 y 100%) y un tratamiento adicional preparado sólo con micorriza. Todos ellos conformaron un arreglo factorial. La distribución de tratamientos fue en franjas sin repeticiones, en una superficie de una hectárea. El tamaño de las franjas (16.67 m de ancho x 100 m de largo) fue de 1 667 m2 por tratamiento. Las variables evaluadas fueron rendimiento de grano, contenido de nitrógeno en la hoja bandera en la etapa de grano lechoso y algunas variables de suelo. Los resultados obtenidos demostraron que la urea mezclada con zeolita al 25% permitió sustituir 25% de la fertilización nitrogenada para el cultivo con y sin micorriza, incrementando significativamente el rendimiento del mismo.

Biofertilizers are considered as potential supplements or alternatives to fertilizers. The objective of the present study is to evaluate different biofertilizers in combination with synthetic fertilizers on the yields of maize and wheat in several states in Mexico. Fourteen biofertilizer treatments plus a treatment with 100% the locally recommended fertilizer rate (RFR), another with 50% RFR (the control treatment), and one without any fertilizer (for a total of 17 treatments) were tested on maize and wheat in five states across Mexico. Field experiments were established in five states and several years for a total of 14 experiments in Mexico. In general, except for the experiments conducted in moderately low soil P conditions, Chiapas and Sonora (maize), no response to biofertilizers was observed in the remaining locations, through the years in wheat and maize. We conclude that in high input production systems, the biofertilizer response is more an exception than a rule with only 21% of the experiments showing a significant difference in favor of biofertilizers and only 4 of 15 products tested produced a yield response in more nitrogen deficient environments. Some products containing AMF may be beneficial in maize production systems with phosphorus deficient environments.

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