Total soil moisture status in the soil column at different growth stages of Lathyrus
Overall soil moisture reserve was gradually decreased throughout the growing season of grass pea irrespective of seed priming and foliar spray levels as the crop was solely dependent on the residual soil moisture. Fig 1 and Fig 2 revealed that total soil moisture content in the soil column was maximum at the branching period. However, the moisture content of the soil column was higher during the 1
st year due to the higher amount of rainfall received as compared to the 2
nd year. Seed priming with Ammonium molybdate @ 0.5 g kg
-1 seed following 0.5% NPK (19:19:19) spray at pre-flowering and 15 days after 1
st spray
i.e., S
2F
5 recorded minimum total soil moisture content at flowering (47.16 and 48.30 mm), pod development stage (31.93 and 19.46 mm) and at harvest (15.19 and 9.26 mm) during both the years respectively (Table 1) implying maximum water uptake. However, the treatment without seed priming and foliar fertilization
i.e., S
1F
1 recorded maximum moisture content in the soil in those mentioned stages.
The treatment S
2F
5 was found with the lowest amount of moisture reserve possibly due to higher water uptake by the plants. Phosphorous augmented deeper root proliferation that helped in better water uptake than the other treatments. Potassium has been reported to reduce the negative effects of soil moisture stress in crop plants (
Sadaf and Tahir, 2017;
Chaudhari et al., 2018). More specifically, the presence of potassium in the foliar sprays prevented excess moisture loss through transpiration by the closure of stomata
(Subbaramma et al., 2017) along coupled with greater uptake of soil moisture
(Zain et al., 2014) under deficit moisture conditions.
Dry aerial biomass and leaf area index are important parameters indicating the moisture uptake pattern of a crop (Table 2). Advancement in these parameters implies improved water uptake and consumption in plants. Total soil moisture content was found to be an exponential function of dry aerial biomass in both years (Fig 3). On the other hand, leaf area index of grass pea was found to be polynomially correlated with total soil moisture content (Fig 4).
Profile water contribution of Lathyrus
Distinctive profile water contribution from soil reserve was recognized in different soil layers with respect to Lathyrus cultivation during
rabi seasons of 2017-18 and 2018-19 in new alluvial soils of West Bengal (Fig 5 and Fig 6). Among the different treatment combinations, S
2F
5 received the highest-profile contribution during both the experimental years (Table 3).
Seasonal consumptive use of water
The seasonal consumptive use of water by grass pea was influenced by only profile contribution and precipitation in the form of rainfall as no external irrigation was provided. Due to high rainfall during 1
st year, the seasonal consumptive use of water was higher as compared to the subsequent year. The maximum seasonal consumptive use was recorded with the S
2F
5 (117.83 mm and 112.63 mm) during 2017-18 and 2018-19 respectively (Table 4).
Water use efficiency (WUE) of Lathyrus
Highest water use efficiency was achieved with S
2F
5 treatment (16.65 and 14.80 kg ha
-1 mm
-1) during 2017-18 and 2018-19 respectively (Table 4). Performance of grass pea in terms of yield under S
2F
5 treatment was best among all the treatment combinations due to maximum utilization of residual soil moisture during all phenological stages. Maximum improvement in WUE under treatment S
2F
5 maybe because of the higher yield as a result of the balanced nutrition combined with reduced loss of water due to the stomatal closure and falling rate of transpiration as supported by the work of
Fahad et al., (2017).
Water use efficiency was polynomially correlated with seed yield and stover yield of grass pea in both the years (Fig 7 and 8). About 96.11 and 91.44% variations in seed yield could be contributed to the variation in WUE of grass pea in the respective years. Likewise, variations in stover yield were 91.19 and 91.13% which could be attributed to the variation in WUE during the two years.
Many researchers have reported that fertilization with K had a significant role in plants to alleviate the effect of the moisture shortage through improved WUE along with lower leaf ET
(Sardans et al., 2012; Grzebisz et al., 2013 and
Hasanuzzaman et al., 2018). K broadly maintains cellular osmo-regulation, which helps in balancing the turgor and expansion of cells
(Yadav et al., 2021). This whole process is required for root and shoot expansion. Kinds of literature has established the role of K in regulating the water economy of plants and thus optimizing WUE
(Egilla et al., 2005; Kanai et al., 2011; Majeed et al., 2016). However, poor seed yield owing to moisture deficit could be overcome through increment of K supply
(Danial et al., 2010; Taia et al., 2016).