Growth parameters
Maximum plant height (52.89 cm) was recorded by F
1 (Table 2) under FST which was 3.7% more than that for F
2. For DVFS the significantly higher plant height (55.12 cm) was noted in treatment T
2- Urea @ 2%. The increase in plant height in T
2 compared to the control was 14.8%. This might be due to the effect of nitrogen, since nitrogen increases cell division and elongation. Mona and Azab (2017) observed that the foliar application of urea increased plant height of soybean. F
1 posed its significant effect on LAI as compared to F
2 by producing index value of 3.00 (Table 2). Foliar spray during the dry spells helps in maintenance of turgor pressure of leaves which might be the resulted higher LAI.
Shabbir et al., (2015) reported that foliar application of NPK during water stress condition increased water relation and maintained higher turgor. While in DVFS, the significantly higher value of LAI (3.18) was obtained for treatment T
4. The order of LAI under various foliar spray treatments was T
4> T
3>T
2> T
1>T
5> T
6>T
7. This result was in line with Ling and Silberbush (2002) who reported that foliar spray of NPK showed tremendous increment in leaf area.
F
1 accumulated significantly higher dry matter (20.08 g plant
-1) over F
2. This indicates that foliar spraying during dry spells enable plants to do their metabolic function normally, resulting in more dry matter production. Amongst DVFS, the highest dry matter (21.94 g plant
-1) was observed in T
4 (Table 2). This finding was supported by
Haq and Mallarino (2000) who concluded that the growth parameters were significantly higher for foliar spray of NPK which results in increased total dry matter in soybean. According to
Leach and Hameleers (2001) zinc is also crucial in the formation of higher dry matter. The relative growth rate (RGR) was not significantly influenced by FST, while DVFS had exerted its significant effect. Significantly superior RGR (0.0147 g g
-1 day
-1) was attained by T
4. The increase in RGR over control was 13.5%, 19.7%, 23.3%, 39.4%, 9.0% and 4.1% for T
1, T
2, T
3, T
4, T
5 and T
6, respectively. This might be due to adequate supply of macro (NPK) and micro (Zn) nutrients via foliar spray which promotes faster crop growth.
Gowthami et al., (2018) observed that application of macro and micronutrient through foliar spray increased relative growth rate as compared to control. The non-significant response of FST to RGR specified that the good rainfall occurred between 60 and 85 DAS has led to sufficient moisture in soil, thus, during these period relative crop growth rate increased at constant rate.
Sharma et al., (2019) also reported non-significant response of foliar spray during and after drought stress.
Photosynthetically active radiation and chlorophyll content
Due to varied LAI, the PAR intercepted also differed significantly. F
1 and T
4 intercepted maximum PAR [995.6 and 1002.8 (µ mol m
-2 s
-1)], respectively (Table 3). The PAR intercepted by DVFS stood in the order of T
4>T
3>T
2>T
1> T
5>T
6>T
7. Significantly more PAR intercepted by F
1 and T
4 resulted from taller plant height and more leaf area index. The photosynthetic rate was significantly higher in soybean sprayed with NPK 19:19:19 @ 1.0% reported by
Anjum et al., (2013). In this study, F
1 recorded significantly higher (37.9) SPAD values than these for F
2. This specifies that foliar application during dry spells provides nutrients quickly and helps in formation of chlorophyll. T4 had significant more SPAD values 40.5 as compared to control.
Amanmmula et al., (2014) observed that water soluble NPK fertilizer significantly increased the PAR interception and net photosynthetic rate because of higher chlorophyll production and leaf area.
Seed yield
Different foliar spray treatments produced varying response on plant height, LAI, dry matter accumulation that may have brought differences in seed yield. F
1 produced maximum seed yield (1075 kg ha
-1) compared to that for F
2. The highest seed yield was reported by T
4 (1193 kg ha
-1) (Fig 2) which was statistically superior to T
1, T
6 and T
7 and was similar to the other remaining treatments.T
4 produced 45% more seed yield compared to the control. F
1 and T
4 also had maximum straw yields of 2650 and 2872 kg ha
-1.
Malik et al., (2015) observed that significant increase in yield was because of application of zinc + urea compared to the control.
Mannan (2014) also stated that highest values for seed and straw yields were recorded for the NPK and Mg sprays during drought.
Choudhary et al., (2014) discovered that foliar Zn spraying increased seed yield.
Protein and oil content
Variation in seed yield under different treatments also produced significant differences in oil and protein content (Table 3). F
1 recorded significantly higher oil and protein content than these for F
2. T
4 yielded significantly more oil as compared to T
6 and T
7. Maximum protein content noticed by T
4 (43.1%) and minimum by T
7. Increase in protein content might be due to zinc which is important structural element of protein synthesizing enzymes
(Ravi et al., 2008). Zambre et al., (2017) found that foliar spray of zinc enhances the level of soluble protein and oil content under water limited conditions and also mitigated adverse effect of dry spell.
Energetics
Maximum energy input was observed in T
2 (6452 MJ ha
-1) because nitrogen production has huge energy requirements, while T
7 (control) recorded the lowest energy input consumption (Table 4) since it does not use any special treatment/input material. All the energetic parameters were significantly influenced by FST and DVFS. The highest output energy was received from T
4 (53440 MJ ha
-1) measure as seed yield. Similarly, maximum net energy was also recorded by T
4 (47272 MJ ha
-1) because it has less input demand and more output energy. Likewise, the energy efficiency, energy productivity and energy intensity in economic terms were significantly higher in T
4, however, the specific energy was significantly higher in T
7 (7.84 MJ kg
-1). Energetics findings of this study are similar to those of
Navaz et al., (2017).
Carbon footprint
Carbon is a main integral part of the agriculture production system. C-budgeting of FST did not differ significantly (Table 5). The maximum and minimum C-inputs were consumed by T
4 (160.9 kg C
e ha
-1) and T
7 (140.6 kg C
e ha
-1). The chemical fertilizers accounted for more amount of C-share
(Jat et al., 2019). It might the reason that T
4 and T
7 have maximum and minimum C-input consumption. Maximum C-output was produced by treatment T
4 (1788.4 kg C
e ha
-1). The trend followed for C-output was T
4>T
3>T
2>T
5>T
1>T
6>T
7.
Kumar et al., (2020) observed that more biomass production was the prime reason for maximum C-output. We also observed similar results in the present study. T
3 had the highest C-efficiency (12.01) followed by T
4. The sustainability of agricultural production systems mainly depends on their C-footprints. The C-footprints of soybean production system is highly dependent on ability of the crop to convert the nutrients into grains. The treatment T
3 recorded high carbon sustainability index value (CSI) (11.01) whereas the lowest CSI was observed in T
7. Similarly, T
3 had more carbon efficiency ratio (CER) compared to other treatments. This might be due to good yield and low C-input consumption under T
3. These results from the present experimentation are in close agreement to those reported by
Rakesh (2020).
Economics
FST were recorded equal cost
i.e. Rs 20218 ha
-1 while in DVFF; the maximum cost (Rs 20782 ha
-1) was recorded by T
4 followed by T
3 (Rs 20625 ha
-1). T
4 achieved maximum gross income (Rs 35790 ha
-1) and net income (Rs 15008 ha
-1) (Table 6).
Singh et al., (2018) reported that foliar application of water soluble fertilizer 19:19:19 (NPK) @ 2% in soybean gain maximum net returns. Table 6 again confirmed that F
1 and
T4 fetched highest values of B:C ratio
i.e. 1.60 and 1.72 respectively.