Foliar Silicon Alleviates Water Deficit in Cowpea by Enhancing Nutrient Uptake, Proline Accumulation, and Antioxidant Activity

Abstract

Silicon has emerged as a beneficial element in mitigating water deficit in various crops, although the underlying mechanisms still require further investigation. This study evaluated the foliar content of nutrients (N, P, K, and Ca) and proline, antioxidant activity, growth, water use efficiency, and yield of cowpea cultivars subjected to two irrigation depths (50% and 100% of crop evapotranspiration) and a foliar application of silicon (orthosilicic acid). A field experiment was conducted in a split-plot scheme using the randomized block design with four replications in a semi-arid region of northeastern Brazil. Silicon supplementation increased the foliar contents of N, P, and Ca; stimulated proline synthesis; and enhanced the activity of the SOD, CAT, and APX enzymes. These changes promoted growth, improved water use efficiency, and increased crop yield. The results indicate that foliar silicon application mitigates the effects of water deficit in cowpea plants while enhancing crop performance under full irrigation (100% of crop evapotranspiration), leading to higher yields even under favorable water conditions.

Keywords: Vigna unguiculata; abiotic stress; orthosilicic acid; water use efficiency; yield.

Figure 1

Foliar contents of N (a,d), P (b,e), Ca (c,f), and K (g) in cowpea cultivars subjected to different irrigation depths and foliar silicon applications. ** and * indicate significance at p < 0.01 and p < 0.05, respectively, according to F-test. Lowercase letters indicate differences among cultivars, and uppercase letters indicate differences among irrigation depths, according to Tukey’s test. Bars represent standard error of mean.

Figure 2

Effect of silicon × cowpea cultivar interaction on free proline content in leaves. Lowercase letters indicate differences among cultivars, and uppercase letters indicate differences between presence and absence of foliar silicon application, according to Tukey’s test. Bars represent standard error of mean.

Figure 3

Activities of enzymes superoxide dismutase (SOD) (a,b), catalase (CAT) (c,d), and ascorbate peroxidase (APX) (e) in cowpea cultivars subjected to different irrigation depths and foliar silicon applications. ** and * indicate significance at p < 0.01 and p < 0.05, respectively, according to F-test. Lowercase letters indicate differences among cultivars; uppercase letters indicate differences among irrigation depths; and Greek letters indicate differences between presence and absence of foliar silicon application, according to Tukey’s test. Bars represent standard error of mean.

Figure 4

Main branch length (MBL) (a,b) and shoot dry mass (SDM) (c) of cowpea cultivars subjected to different irrigation depths and foliar silicon application. ** indicates significance at p < 0.01 according to F-test. Lowercase letters indicate differences among cultivars; uppercase letters indicate differences among irrigation depths; and Greek letters indicate differences between presence and absence of foliar silicon application according to Tukey’s test. Bars represent standard error of mean.

Figure 5

(a) Effect of irrigation depths × silicon interaction and (b) effect of silicon × cultivar interaction on yield. Lowercase letters indicate differences among cultivars; uppercase letters indicate differences among irrigation depths; and Greek letters indicate differences between presence and absence of foliar silicon application according to Tukey’s test. Bars represent standard error of mean.

Figure 6

Effect of irrigation × silicon × cultivar interaction on number of pods per plant (NPP) in cowpea. Lowercase letters indicate differences among cultivars; uppercase letters indicate differences among irrigation depths; and Greek letters indicate differences between presence and absence of foliar silicon application according to Tukey’s test. Bars represent standard error of mean.

Figure 7

(a) Grain yield of cowpea cultivars subjected to different irrigation depths and (b) effect of silicon × cultivar interaction on yield. ** indicates significance at p < 0.01 according to F-test. Lowercase letters indicate differences among cultivars, and Greek letters indicate differences between presence and absence of foliar silicon application according to Tukey’s test. Bars represent standard error of mean.

Figure 8

A graphical representation of the weather conditions recorded in the experimental area during the experiment and the time representation of the main experimental events.