Rafael Ángel Parra-Quezada

Intensidad de raleo y calidad de fruto en durazno cv Baby Gold 8

In 2010 this field experiment was conducted in a peach orchard of 5 years, with the variety Baby Gold 8 grafted in Nemaguard where a load of 1-7 fruits per cm 2 of the branch cross-sectional area (BCSA) was adjusted by manual fruit thinning. Thinning was done 45 days after full bloom. Results indicate that higher fruit loading increases yield and decreases the fruit size. The load adjustment in peach fruit allows to program the final size. The highest production value is obtained by leaving 4 to 5 fruits per BCSA. Fruit firmness is not affected by its load, while total soluble solids showed significant differences. The highest vegetative growth occurred in the upper branch and in the lower part, by the effect of shade, growth is lower.

Comparison of three systems of decomposition of agricultural residues for the production of organic fertilizers

Organic wastes (OW) of diverse nature must be subjected to controlled decomposition processes to avoid risks of contamination and obtain products useful for agriculture. The objective of the present study was to compare over time physical, chemical and enzymatic parameters of OW transformed as vermicomposting (VC), semicomposting (SC) and composting (CP) for elaboration of organic fertilizers. A mixture of bovine manure and sawdust was subjected to each of three systems for 183 d. Temperature, total N (Nt), organic C (OC), C/N ratio, pH, enzymatic urease activity (EUA), germination index (GI) and electrical conductivity (EC) were measured throughout the time of study. The variables evaluated showed significant differences between time and treatment. The temperature ranged between 20 and 34 °C in VC and SC, while in CP between 20 and 61 °C. All three systems reduced the C/N ratio to less than 15/1. The CP product had higher pH, EC, and EUA values than both VC and SC. The VC product had the highest GI values. All the products obtained at 183 d were within the parameters to be considered as organic fertilizers, but the SC product transformed into an organic fertilizer fastest and had least water usage.

Urease and nickel in plant physiology

En la presente revision se compila y discute la informacion cientifica actual referente a la funcion de la ureasa en las plantas; ademas, se aborda su funcion catalitica, distribucion, influencia del pH en la hidrolisis de la urea y Ni como cofactor en su activacion. Esta enzima es de vital importancia en el metabolismo nitrogenado. Para ser activada, la ureasa requiere unirse con dos atomos de niquel (Ni), y en las celulas vegetales participa en el metabolismo de los compuestos que contienen nitrogeno (N). La activacion de la ureasa parece ser, hasta la fecha, la unica funcion enzimatica del Ni en las plantas superiores. Asimismo, se plantea la importancia del Ni en los procesos fisiologicos y bioquimicos de la planta, se incluyen las respuestas tipicas frente a la presencia del Ni en el suelo y planta, y se evidencia una estrecha relacion entre la ureasa y el Ni en la fisiologia vegetal de algunas plantas, por lo tanto, su actividad podria ser considerada como un indicador bioquimico de deficiencia de Ni antes de que se presente la sintomatologia de manera visible