The Effect of Nitrogen and Phosphorus Biofertilizers on Photosynthetic Pigments, Grain Yield, Yield Components and Grain Protein Content of Two Pea (Pisum sativum L.) Varieties under Different Irrigation Regimes

In order to study the effects of nitrogen and phosphorus biofertilizers on photosynthetic pigments, grain yield, yield components and grain protein content of two pea (Pisum sativum L.) varieties under different irrigation regimes; a split-split plot experiment was conducted based on a randomized complete block design with three replications at a field in Farsan, southwestern Iran, in 2021. The main plots were allocated to irrigation treatments including: irrigation after 50, 75 and 100 mm (I1, I2 and I3, respectively) cumulative evaporation from class A evaporation pan and the sub plots were allocated to different sources of biofertilizers treatments including: control (no biofertilizer application), Azotobarvar-1(nitrogen), Phosphatebarvar-2 (phosphorus) and Azotobarvar-1 + Phosphatebarvar-2 (nitrogen + phosphorus). Sub-sub plots were allocated to two varieties of peas (Majarestani and Wolfholland). Results showed that in Majarestani variety mild drought stress increased chlorophyll a and b contents, but severe drought stress decreased them. In Wolfholland variety, both mild and severe drought stress decreased chlorophyll a and b contents. In both varieties, mild drought stress increased carotenoid contents, but severe drought stress decreased them. Biofertilizers were effective in improving chlorophyll a, b and carotenoid contents, particularly under drought stress conditions. The drought stress reduced the grain yield and yield components of both pea varieties but application of biofertilizers moderated the effects of drought stress. The highest value of grain yield was obtained from the Majarestani variety when grown under full irrigation conditions (I1) and nitrogen biofertilizer application. Under the mild and severe drought stress (I2 and I3), the highest value of grain yield was obtained from Majarestani variety in the presence of phosphorus and nitrogen + phosphorus biofertilizer application, respectively. Majarestani variety outranked the Wolfholland in terms of  pods/plant, grain/pod and grain yield under both stress and normal conditions, but the latter variety indicated a greater 1000-grain weight. Therefore, Majarestani variety is a more suitable cultivar, particularly under drought stress conditions. Grain protein percentage was not affected by variety. The highest percentage of grain protein content was achieved with I2 irrigation and nitrogen + phosphorus biofertilizer treatments, averaged over the examined varieties. To conclude, given the prevalence of water scarcity in the semi-arid regions of Iran’s type, further examinations of more drought resistant varieties such as Majarestani and application of biofertilizers may prove suitable for reducing the adverse effects of drought stress.