Dry matter yield, carbon isotope discrimination and nitrogen uptake in silicon and/ or potassium fed chickpea and barley plants grown under water and non-water stress conditions

A pot experiment was conducted to study the effects of silicon (Si) and/or potassium (K) on dry matter yield, nitrogen uptake and carbon isotope discrimination Δ 13C in water stressed (FC1) and well watered (FC2) chickpea plants using 15N and 13C isotopes. Three fertilizer rates of Si (Si50, Si100 and Si200) and one fertilizer rate of K were used. The results showed that: In chickpeas, it was found, for most of the growth parameters, that Si either alone or in combination with K was more effective to alleviate water stress than K alone. Increasing soil water level from FC1 to FC2 often had a positive impact on values of most studied parameters. The Si100K+ (FC1) and Si50K+ (FC2) treatments gave high enough amounts of N2-fixation, higher dry matter production and greater nitrogen yield. The percent increments of total N2-fixed in the above mentioned treatments were 51 and 47% over their controls, respectively. On the other hand, increasing leaves dry matter in response to the solely added Si (Si50K- and Si100K-) is associated with lower Δ13C under both watering regimes. This may indicate that Si fertilization had a beneficial effect on water use efficiency (WUE). Hence, Δ13C could be an adequate indicator of WUE in response to the exogenous supply of silicon to chickpea plants. Our results highlight that Si is not only involved in amelioration of growth and in maintaining of water status but it can be considered as an important element for the symbiotic performance of chickpea plants. It can be concluded that synergistic effect of silicon and potassium fertilization with adequate irrigation improves growth and nitrogen fixation in chickpea plants.In barley plants, solely added K or in combination with adequate rate of Si (Si100) were more effective in alleviating water stress and producing higher yield in barley plants than solely added Si. However, the latter nutrient was found to be more effective than the former in producing higher spike's N yield. Solely added Si or in combination with K significantly reduced leave's Δ13C reflecting their bifacial effects on water use efficiency (WUE), particularly in plants grown under well watering regime. This result indicated that Si might be involved in saving water loss through reducing transpiration rate and facilitating water uptake; consequently, increasing its use efficiency. Although the rising of soil humidity generally increased fertilizer nitrogen uptake (Ndff) and its use efficiency (%NUE) in barley plants, applications of K or Si fertilizers to water stressed plants resulted in significant increments of these parameters as compared with the control. Our results highlight that Si or K is not only involved in amelioration of growth of barley plants, but can also improve nitrogen uptake and fertilizer nitrogen use efficiency particularly under water deficit conditions. (authors)