Evaluation the effects of different sources of nitrogen on agro-meteorological indices and sources use efficiency in potato Abstract

Background and objective: Growing degree days (GDD) and helio thermal units (HTU) are the temperature based agro-meteorological indices that play important role in predicting crop growth and yield. The efficiency of conversion of heat and radiation energy to dry matter depends on genetics factors, planting date and crop. Heat summation units (HSU), that mainly called growing degree days, and its derivations such as helio thermal units, heat use efficiency and helio thermal units use efficiency are the most necessary to determine phenological stages and the suitable planting dates for cultivars of different crops. There is little information concerning the effects of different sources of nitrogen on agro-metorological indices and sources use efficiency for potato in the sub-tropic regions. This experiment was undertaken to define the effects of different sources of nitrogen on agro-meteorological indices in phonological stages and sources use efficiency in two potato cultivars (Sante and Savalan).

Material and method This study was conducted in a factorial arrangement as two factors in a randomized complete block design with three replications at Behbahan Agriculture Research Stations. Factor (A) was nitrogen sources: nitrogen fertilizer lack, plots that received 50% nitrogen from mineral fertilizer Plus 50% nitrogen from vermicompost (50% M+50%V), plots that received 75% nitrogen from mineral fertilizer Plus 25% nitrogen from vermicompost (75% M+25%V), and plots that obtained 100% nitrogen from mineral fertilizer (100% M). Factor (B) was potato cultivars (Sante and Savalan). Sprouted seed tubers were planted at early January. One week before harvesting haulms were defoliated and tubers harvested at mid -May. Growing degree days, helio thermal untis were calculated in all phonological stages, and after harvesting thermal use efficiency and helio thermal unit use efficiency determined. Data were statistically analyzed by SPSS software. Significant differences among treatments means were determined at P≤0.05 by Duncan’s multiple test range.

Results: The duration, growing degree days and helio thermal units of sprout development stage were significantly lower in Savalan than Sante cultivar. The effects of different sources of nitrogen on duration, growing degree days and helio thermal units in sprout development stage were not significant. The duration of vegetative stage was 15 days in all studied treatmrnts. Early exposure of plants to favorable climatic conditions for tuber initiation, short day and cool night temperature, caused the duration of vegetative growth, growing degree days and helio thermal units were low in this phonological stage. Due to high temperature at late April and early May growing degree days and helio thermal units in tuber bulking stage were considerable higher than previous stages. Maturation was not observed in this research. Yield, thermal use efficiency, helio thermal units use efficiency and nitrogen use efficiency were significant higher in Savalan cultivar as compared with Sante. Application of vermicompost in 50% M+%50V and 75% M+25%V lead to increase yield, thermal use efficiency, helio thermal units use efficiency and nitrogen use efficiency in these treatments in comparison with application of only mineral fertilizer (100% M).

Conclusion: 75% M+25%V treatment is recommended for cultivation of Savalan and Sante cultivars.