The effects of nitrogen and light levels on carbohydrate and nitrogen contents in Phaseolus vulgaris

Abstract

The effects of three light levels (30%, 70% and 100% of incident sunlight) combined with three nitrogen doses (0, 30 and 60 kg/ha of N) on total soluble carbohydrate, starch and nitrogen contents were studied in Phaseolus vulgaris L. cv. Negrito 897, grown under field conditions, during the entire cycle of the crop. The carbohydrate and nitrogen contents in the plant parts increased with the increase of the light and nitrogen levels. Maxima values are observed under 70% and 100% of sunlight combined with 30 and 60 kg/ha of N. A sharp reduction on carbohydrate and nitrogen contents was observed in all plant parts, caused by the lowest light level associated with high nitrogen levels (30 and 60 kg/ha of N). Lower carbohydrate and nitrogen contents were obtained by no nitrogen addition, independently of light levels. The total nitrogen contents in the plant organs was proportional to dry matter production. A close correlation between leaf nitrogen content at onset of the flowering stage and number of pods at maturation was found. The high accumulation of carbohydrate and nitrogen in the seeds caused by high nitrogen and light levels was due mainly to photosynthesis and assimilate mobilization of leaf tissues during grain filling, as well as mobilization of assimilate stored in stems and roots during the vegetative phase.