Optimizing nutrient use efficiency, productivity, energetics, and economics of red cabbage following mineral fertilization and biopriming with compatible rhizosphere microbes

Conventional agricultural practices and rising energy crisis create a question about the sustainability of the present-day food production system. Nutrient exhaustive crops can have a severe impact on native soil fertility by causing nutrient mining. In this backdrop, we conducted a comprehensive assessment of bio-priming intervention in red cabbage production considering nutrient uptake, the annual change in soil fertility, nutrient use efficiency, energy budgeting, and economic benefits for its sustainable intensification, among resource-poor farmers of Middle Gangetic Plains. The compatible microbial agents used in the study include Trichoderma harzianum, Pseudomonas fluorescens, and Bacillus subtilis. Field assays (2016–2017 and 2017–2018) of the present study revealed supplementing 75% of recommended NPK fertilizer with dual inoculation of T. harzianum and P. fluorescens increased macronutrient uptake (N, P, and K), root length, heading percentage, head diameter, head weight, and the total weight of red cabbage along with a positive annual change in soil organic carbon. Maximum positive annual change in available N and available P was recorded under 75% RDF + P. fluorescens + B. subtilis and 75% RDF + T. harzianum + B. subtilis, respectively. Bio-primed plants were also higher in terms of growth and nutrient use efficiency (agronomic efficiency, physiological efficiency, apparent recovery efficiency, partial factor productivity). Energy output (26,370 and 26,630 MJ ha−1), energy balance (13,643 and 13,903 MJ ha−1), maximum gross return (US $ 16,030 and 13,877 ha−1), and net return (US $ 15,966 and 13,813 ha−1) were considerably higher in T. harzianum, and P. fluorescens treated plants. The results suggest the significance of the bio-priming approach under existing integrated nutrient management strategies and the role of dual inoculations in producing synergistic effects on plant growth and maintaining the soil, food, and energy nexus.


Results and discussion
Macronutrient uptake. Total uptake of N, P, and K by red cabbage was partitioned into head and stalk. The head's highest N uptake was registered in plots receiving 75% RDF + T. harzianum + P. fluorescens (T 6 ) during both the years (Table S1). It showed 29% (1 st year) and 24% (2 nd year) increments over 100% RDF (T 2 ). Similarly, a significant increase in total uptake of N was also observed in T 6 treatment. The total N uptake varied from 21.53 to 70.21 kg ha −1 in the first year and 19.56-69.96 kg ha −1 in the second year. Compared with single-priming and consortium treatments, N total uptake increased by 12-35% with the co-application of T. harzianum and P. fluorescens. The uptake of the other two dual bio-priming treatments, viz., T 7 (75% RDF + P. fluorescens + B. subtilis) and T 8 (75% RDF + T. harzianum + B. subtilis) were at par with T 2 (100% RDF). Phosphorus uptake by red cabbage was also influenced by 75% RDF + T. harzianum + P. fluorescens (T 6 ), but it was at par with 75% RDF + P. fluorescens + B. subtilis (T 7 ). In the head, P uptake ranged from 1.28 to 7.36 kg ha −1 in the first year and 0.80-7.52 kg ha −1 in the second year (Table S2). During the second year, the head uptake of plants under 75% RDF + P. fluorescens (T 4 ) was higher than 75% RDF + T. harzianum + B. subtilis (T 8 ). The application of fertilizers and biopriming agents did not significantly affect the P uptake by stalk during the study years. The total P uptake varied from 3.69 to 10 www.nature.com/scientificreports/ similar P uptake. Except for control, the uptake was found to increase in all the treatments during the second year over 1 st year. In the case of K, a significant increase in uptake (head and total) was recorded in T 6 treatment (Table S3). The magnitude of the increase due to this treatment over 100% RDF (T 2 ) was 31% (head) and 21% (total). However, applying 100% chemical fertilizers and combined use of chemical fertilizers and bio-agents did not significantly differ in the uptake of macronutrients by the stalk. In general, the K uptake varied from 8.25 to 57.35 kg ha −1 for the head and 16.64-22.15 kg ha −1 for the stalk. Stalk K uptake was highest (22.15 kg ha −1 ) in the first year with 75% RDF + B. subtilis (T 5 ). The total K uptake ranged from 29.03 to 78.20 kg ha −1 in the first year and 26.08-78.51 kg ha −1 in the second year. During the second year, the total K uptake of plants under 100% RDF was par with single-and triple-priming treatments. Among single-and triple-priming treatments, the highest total K uptake was observed with the application of 75% RDF + P. fluorescens (T 4 ) during both years. The lowest N, P, and K uptake were recorded from the control (T 1 ) plots. On average, red cabbage removed macronutrients in the order of K (64.32 kg ha −1 ) > N (55.05 kg ha −1 ) > P (8.91 kg ha −1 ). The higher nutrient uptake in the integrated application of chemical fertilizers and bio-agents is explained by developing proliferous root systems in bio-primed plants and increased microbial activity in the soil, which helped mineralize nutrients maintaining the soil solution greater assimilation in plants. Several workers [25][26][27][28][29][30][31] reported increased nutrient uptake in crops due to the combined application of chemical fertilizers (reduced level) and biofertilizers.
Annual change in organic carbon (OC) and available N, P, and K. A positive annual change in OC ( Fig. 1) was noted for all the treatments (T 2 -T 9 ) except in control plots (T 1 ) which showed a negative change of − 0.22 g kg −1 year −1 . The highest positive change was documented under 75% RDF + T. harzianum + P. fluorescens (T 6 , 0.59 g kg −1 year −1 ) followed by 75% RDF + P. fluorescens + B. subtilis (T 7 , 0.49 g kg −1 year −1 ), and the lowest was recorded under 100% chemical fertilization (T 2 ) being 0.17 g kg −1 year −1 which was at par with 75% RDF + T. harzianum + P. fluorescens + B. subtilis (T 9 , 0.20 g kg −1 year −1 ). In the case of annual change of available N, P, and K, similar trends were noticed as OC (Fig. 1). However, the highest and lowest changes varied. Application of 75% RDF + P. fluorescens + B. subtilis (T 7 ) and 75% RDF + T. harzianum + B. subtilis (T 8 ) demonstrated ( Fig. 1) higher positive changes in available N (11.06 and 10.06 kg ha −1 year −1 , respectively), while 100% RDF (T 2 ) showed the lowest change (4.47 kg ha −1 year −1 ). The control plots (T 1 ) showed a significant negative annual change in available N (− 13.46 kg ha −1 year −1 ) after crop harvest. The T 8 treatment showed the maximum positive annual change (6.70 kg ha −1 year −1 ) followed by T 7 (6.27 kg ha −1 year −1 ) for available P (Fig. 1). However, the least positive change in available P was evident in T 2 (3.10 kg ha −1 year −1 ), which was at par with the treatment T 9 (3.48 kg ha −1 year −1 ). A negative change of − 1.27 kg ha −1 year −1 in available P was observed in T 1 plots. There were no significant positive annual changes observed between the treatments for available K (Fig. 1). However, the T 8 treatment presented the highest positive annual change value of 10.04 kg ha −1 year −1 , followed by T 7 (8.92 kg ha −1 year −1 ); the rest of the treatments (T 2 , T 3 , T 4 , T 5 , T 6 , and T 9 ) documented at par values of the same. The T 1 plots recorded a significant negative annual change in available K (− 11.43 kg ha −1 year −1 ).  www.nature.com/scientificreports/ Conclusively, due to no supplement of fertilizer nutrients and/or biofertilizers, the control plots exhibited a negative annual change in all the studied cases demonstrating the loss/mining of nutrients. However, where both are supplied, a positive change is noticed, indicating annual enrichment of the respected soil attributes over control. In this study, T 8 and T 7 treatments performed better in enhancing available N, P, and K except in OC where T 6 treatment presented a significant positive result over these two, and the rest of the treatments remained at par with positive change. Furthermore, Kaur and Reddy 32 reported improved soil fertility using mineral fertilizer and biofertilizer (Pseudomonas plecoglossicida and Pantoea cypripedii). Similarly, the integrated application of NPK fertilizers and organic amendments (green manure + Pseudomonas putida + Azotobacter chroococcum) recorded a higher OC value and available N and K over only NPK fertilizer application 33 . Nitrogen use efficiency. Optimization of fertilizer for achieving higher input use efficiency without hindering the economic yield is a crucial issue in agriculture. The extent of crop utilization to applied N was analyzed through different parameters of N use efficiency. Agronomic efficiency (AE N ) varied from 9.48 to 19.38 kg of head kg −1 of N applied (Table 1). During the study period of the field experiment, the mean value of AE N increased from 12.95 kg of head kg −1 of N applied in 2016-2017 to 15.50 kg of head kg −1 of N applied in 2017-2018. The application of 75% RDF + T. harzianum + P. fluorescens (T6) increased AEN by 84% and 75% over 100% RDF (T2) during the first and second years. Compared to T 6 , the application of 75% RDF + T. harzianum + P. fluorescens + B. subtilis (T 9 ) significantly reduced the AE N by 59% and 39% in the first and second years respectively. Application of triple consortium also recorded low AE N in comparison to single-species bio-priming and dual microbial consortium treatments. Seedling inoculation with biofertilizers along with 75% RDF + vermicompost demonstrated similar results in cabbage 34 .
Physiological efficiency (PE N ) reflects better accumulation and conversion of N from source to sink. The highest PE N (34.06 and 39.27 kg kg −1 ) was observed with the application of 75% RDF + P. fluorescens + B. subtilis (T 7 ) during both the years of study (Table 1). Low PE N of crops was recorded under 75% RDF + T. harzianum + P. fluorescens (T 6 ). Plants under 75% RDF + B. subtilis (T 5 ) registered 4% higher PE N compared to that under 75% RDF + T. harzianum + P. fluorescens + B. subtilis (T 9 ). Among the single-species bio-priming agents, B. subtilis resulted in maximum PE N (33.74 and 37.49 kg kg −1 ) during both years. Individual application of T. harzianum and co-application of T. harzianum and P. fluorescens showed an equivalent effect on PE N .
Nitrogen use efficiency in apparent recovery efficiency (ARE N ) varied from 32.73 to 55.99% ( Table 1). The highest N use efficiency of 54.10% and 55.99% in 2016-2017 and 2017-2018, respectively, was observed under 75% RDF + T. harzianum + P. fluorescens (T 6 ). Among the bio-priming treatments, the lowest ARE N was obtained under triple consortium treatment (T 9 ). In the first year, ARE N in P. fluorescens bio-primed plants was greater than other individual bio-priming agents. However, in the second year, single bio-priming of T. harzianum and P. fluorescens recorded similar N use efficiency. In addition, improved ARE N was reported in lettuce plants treated with Trichoderma-based biostimulants 35 .
Regarding partial factor productivity (PFP N ), the results showed similar trends to that of ARE N . The response ranged between 13.97 and 23.44 kg of head kg −1 of N applied ( Table 1). Application of 75% RDF + T. harzianum + P. fluorescens (T 6 ) and 75% RDF + T. harzianum + P. fluorescens + B. subtilis (T 9 ) registered highest and Table 1. Nitrogen use efficiency of red cabbage as influenced by bio-priming and fertilisation. Different letters indicate significant differences at P ≤ 0.05 among the treatments as per DMRT.  www.nature.com/scientificreports/ lowest N use efficiency, respectively. About 68% increase in PFP N was found in T 6 compared to 100% RDF (T 2 ). The effect of P. fluorescens on PFP N was higher than other single-species bio-priming agents. The results revealed that dual consortium treatments were more competent in converting the applied N into marketable yield. Our result was consistent with the observation of Chatterjee et al. 34 .
The effect of fertilization and bio-priming on apparent recovery efficiency (ARE P ) is presented in Table 2. The ARE P was found to be maximum (16.23%) under 75% RDF + P. fluorescens + B. subtilis (T 7 ) during the first year, but during the second year, maximum (17.45%) ARE P was noted under 75% RDF + T. harzianum + P. fluorescens (T 6 ). Among the three bio-agents, P use efficiency was in P. fluorescens > B. subtilis > T. harzianum. The present study results revealed that bio-priming with P. fluorescens demonstrated the highest increment (18%) in AREP compared to the first year. Application of triple consortium and single bio-priming with T. harzianum resulted in a similar ARE P . Increased P use efficiency due to co-inoculation of rhizospheric bacterial (endophytic) agents was reported by Emami et al. 37 .
Partial factor productivity (PFP P ) ranged from 27.94 to 46.87 kg of head kg −1 of P applied with an average value of 37.51 kg of head kg −1 of P applied during the first year and 38.69 kg of head kg −1 of P applied during the second year (Table 2). Among the bio-priming treatments, the application of 75% RDF + T. harzianum + P. fluorescens (T 6 ) and 75% RDF + T. harzianum + P. fluorescens + B. subtilis (T 9 ) recorded the highest and lowest PFP P , respectively. Compared with 100% RDF (T 2 ), T 6 increased the P use efficiency by 67%. P. fluorescens exhibited the highest P use efficiency regarding individual bio-priming agents, followed by T. harzianum and B. subtilis. However, compared with the first year, bio-priming with B. subtilis showed a 6% increment in PFP P during the second year. The results of PFP P followed the order: dual-species bio-priming > single-species biopriming > triple-species bio-priming.   www.nature.com/scientificreports/ Potassium use efficiency. The results of K use efficiency in the form of agronomic efficiency (AE K ), and partial factor productivity (PFP K ) was similar to that of P use efficiency (AE P and PFP P ) because the amount of nutrient applied for P and K was the same, i.e., 60 kg as RDF. The maximum and minimum K use efficiency (AE K and PFP K ) were obtained from 75% RDF + T. harzianum + P. fluorescens (T 6 ) and 100% RDF (T 2 ), respectively ( Table 3). The performance of the triple consortium was lowest among the bio-primed treatments. Application of P. fluorescens resulted in higher AE K in terms of single-species bio-priming. Physiological efficiency (PE K ) varied from 29.18 to 34.33 kg of head kg −1 of K applied ( Table 3). The highest PE K of 32.31 kg of head kg −1 of K applied was recorded with 75% RDF + T. harzianum (T 3 ) in 2016-2017, while application of 100% RDF (T 2 ) registered the highest PE K of 34.33 kg of head kg −1 of K applied in 2017-2018. Results of PE K further indicated that microbial consortium treatments gave an equivalent effect to that of singlespecies bio-priming treatments. Sole application of T. harzianum resulted in higher PE K than other bio-primed treatments including dual and triple consortiums.
In the present study, apparent recovery efficiency (ARE K ) ranged from 59.13 to 116.49%, with a mean value of 89.34% (Table 3). The maximum ARE K was achieved under 75% RDF + T. harzianum + P. fluorescens (T 6 ), which increased from 109.26% in the first year to 116.49% in the second year. Among single bio-priming agents, P. fluorescens showed the highest ARE K . This microbe recorded a 13% increment in ARE K as compared to the first year. Results followed the trend of 75% RDF + dual consortium > 75% RDF + single bio-priming agents > 75% RDF + triple consortium > 100% RDF. Application of triple consortium reduced the ARE K by 45% (average of two years) compared to that of dual consortium (T. harzianum + P. fluorescens). Enhanced K uses efficiency in AE K , PE K , and ARE K due to bacterial inoculations and reduced chemical fertilizer quantity reported by Khanghah et al. 38 .
Yield attributes. The observation on heading percentage and head diameter indicated that the sole application of mineral fertilizers and integrated application along with bio-agents did not bring any significant variation among the treated plants (Fig. 2). Heading percentage (72.92), as well as head diameter (13.85), was recorded to be maximum in 75% RDF + T. harzianum + P. fluorescens (T 6 ). The lowest heading percentage was noticed in absolute control (29.17) followed by a triple consortium (64.06). The average diameter of marketable heads was 13.35 cm. Head weight varied from 371.63 to 736.29 g (Fig. 2).
On a pooled basis, a significantly higher head weight (725.51 g) was detected with T 6 compared to the rest of the treatments. It registered 12% and 83% increments over 100% RDF (T 2 ) and absolute control (T 1 ), respectively. Bio-priming with triple consortium recorded 17% lower head weight than dual consortium (T. harzianum + P. fluorescens). Results on head weight followed the order of 75% RDF + T. harzianum + P. fluorescens (T 6 ) > 75% RDF + P. fluorescens + B. subtilis (T 7 ) > 75% RDF + T. harzianum + B. subtilis (T 8 ) > 100% RDF (T 2 ) > 75% RDF + P. fluorescens (T 4 ) > 75% RDF + T. harzianum (T 3 ) > 75% RDF + B. subtilis (T 5 ) > 75% RDF + T. harzianum + P. Table 3. Potassium use efficiency of red cabbage as influenced by bio-priming and fertilisation. Different letters indicate significant differences at P ≤ 0.05 among the treatments as per DMRT.  www.nature.com/scientificreports/ fluorescens + B. subtilis (T 9 ) > absolute control (T 1 ). A perusal of pooled data presented in Fig. 2 revealed that the total weight varied from 693.33 to 1030.49 g. In total weight, T 6 was 8% and 49% higher than T 2 and T 1 , respectively. The total weight of plants under T 6 was at par with T 7 . P. fluorescens combined with 75% RDF resulted in an equivalent total weight to that of 100% RDF. The direct impact of bio-priming on plant growth promotion was reported in earlier studies 5,8 . However, these studies were conducted in pot conditions. The current study focuses on the practical utility of such technology under field conditions. Higher yield attributes in bio-primed treatments could alter cellular mechanisms in these plants and regulated nutrient supply from the soil. Integrated application of inorganic fertilizers (75% RDF) and organics (biofertilizer + vermicompost) yielded the highest marketable head percentage and a head weight of cabbage 39 . Application of organics (poultry manure) alone showed greater head weight (17%) and head length (8%) of cabbage over NPK fertilizers 40 . Energy budgeting. Efficient use of energy inputs in a production system must lessen our dependence on non-renewable energy and maintain sustainability. The magnitude of energy input ranged from 6323 to 14,663 MJ ha −1 (Table 4). Bio-priming intervention in red cabbage cultivation saved 1906 to 1965 MJ ha −1 energy requirement. As expected, the energy consumed under 100% RDF (T 2 ) was ~ 15% higher than bio-priming treatments. Energy output (26,370 and 26,630 MJ ha −1 ) and energy balance (13,643 and 13,903 MJ ha −1 ) were considerably higher in T 6 treatment (75% RDF + T. harzianum + P. fluorescens) during both the years of study. Compared to the first year, energy balance declined (2%) in T 2 treatment. Among the treatments with amendments, T 6 showed the highest energy use efficiency (2.09). The triple consortium treatment (T 6 ) recorded the lowest energy balance (9799 MJ ha −1 ) and energy use efficiency (1.77) compared to other bio-priming treatments. However, the bio-priming treatments were greater in energy balance and energy use efficiency than sole use of chemical fertilization. It shows that fertilizer inputs consume the highest energy. In cabbage production, the consumption of energy by mineral fertilizers may be as high as 77% 20 . It is of great concern, and the nonrenewable sources of plant nutrients must be substituted with renewable sources. Mihov et al. 41 reported that cabbage's organic production could save 31.23% energy unit area −1 than its conventional production system. Application of biofertilizers and reduced dose of fertilizers enhance energy balance and energy use efficiency of a cropping system 42-48 . Economic analysis. Farmers will adopt any technology when it is economically feasible. Different economic indicators, such as gross return, the net return, and benefit:cost (B:C) ratio showed wide variations among the treatments (Table 5). Maximum gross return (US $ 16,030 and 15,966 ha −1 ) and net return (US $ 13,877 and 13,813 ha −1 ) were recorded with the application of T 6 treatment (75% RDF + T. harzianum + P. fluorescens) during both the years of study. The treatment also achieved the highest B:C ratio of 6.45 and 6.42. Lowest returns and B:C ratio were observed in control. Our results showed that the application of microbial consortium and 75% RDF could be profitable than 100% RDF by providing about US $ 3222.5 higher net return on a hectare  www.nature.com/scientificreports/ basis. The integrated approach's performance was better in a dual consortium in most cases, while in singlespecies bio-priming, application of P. fluorescence yields a higher B:C ratio than 100% RDF. The high profitability of a system is related to higher productivity and lowering of production cost. Thakur et al. 49 noted the highest net return and B:C ratio with the conjoint application of 75% NPK and organics (organic manures + biofertilizers) in cauliflower. Another study by Kamal et al. 50 reported a significant effect on B:C ratio of hybrid cabbage production due to the combined application of bio-agents and chemical fertilizers.

Conclusion
We have evaluated different performance indicators, each depicting new viewpoints on biotechnological intervention in integrated nutrient management. Our results generated from field experiments indicated bio-priming in combination with mineral fertilization augmented the productivity, nutrient use efficiency, and profitability of red cabbage cultivation while minimizing the energy requirements. The strategy was more effective under Table 4. Energetics of red cabbage production as influenced by bio-priming and mineral fertilization. Different letters indicate significant differences at P ≤ 0.05 among the treatments as per DMRT.    www.nature.com/scientificreports/ dual inoculation treatments over control. Bio-priming with T. harzianum and P. fluorescens emerged out to be the most suitable treatment over control for red cabbage production, followed by bacterial co-inoculations of P. fluorescens and B. subtilis. Development of low-cost technology with a high B:C ratio has prime importance for resource-poor farmers. Our investigation also has great relevance to the United Nations Sustainable Development Goals' targets by adopting cleaner and cost-effective crop production practices to ensure food security and resource use efficiency in developing countries like India.

Materials and methods
Study site.   Bio-priming. Preparation of inoculum. Bacterial (B. subtilis and P. fluorescens) culture was inoculated in 250 mL flasks containing 100 mL nutrient broth and kept in a shaking incubator (150 rpm; 28 ± 2 °C) for 48 h. Bacterial pellets were obtained by centrifugation (7000 rpm; 4 °C) for 10 min. Discarding the supernatant, the cell pellets were soon washed with sterile distilled water. An adjustment of final cell density to 4 × 10 8 CFU mL −1 was done using optical density (< 1) at 600 nm 63 . In T. harzianum, spore suspension was prepared from 1 week of culture grown (28 ± 2 °C) on potato dextrose agar by harvesting the spores in sterilized 0.85% sodium chloride (NaCl) 5 . The spore concentration was adjusted to 2 × 10 7 CFU mL −1 by measuring the optical density in a spectrophotometer. Cell suspensions and/or spore suspension were mixed in equal ratios for the dual consortium (1:1) and triple consortium (1:1:1).
Seedling bio-priming. Red cabbage seeds were washed with tap water and surface sterilized with 0.1% mercuric chloride (HgCl 2 ) solution for 2 min. After sterilization, the seeds were immediately washed with autoclaved distilled water three times. Next, the seeds were soaked in sterile distilled water for 2 h. After the hydration treatment, the seeds were sown in the nursery. Seedlings were picked when there were 5-6 leaves. Soil attached with the roots was washed carefully, followed by root dipping in liquid culture containing 2% carboxymethyl cellulose (CMC) as an adhesive agent. The bio-priming process was followed for 5 h under incubated conditions (28 ± 2 °C; > 90% relative humidity) 5,36,62 .
Experimental design and crop management. The field setup was laid out in a randomized block design with nine treatments and three replications. Red cabbage seeds were sown in raised bed nursery about 1 month before transplanting. The field was twice ploughed by a tractor and planked 15 days before the implementation of the experiment. Crop residues, stones, pebbles, or weeds were removed manually from the field. Five weeks of healthy and uniform-sized red cabbage seedlings were transplanted in 4 × 2 m 2 plots with a spacing of 50 cm × 50 cm on 5 th December 2016 and 2017. Four rows in a plot accommodated 32 plants. The crop was irrigated for 2 weeks with a watering can just after transplanting. After that, it received four irrigations at 7-10 days intervals as per the requirement. A full dose of diammonium phosphate (DAP) and muriate of potash (MOP) was applied as basal at the time of final land preparation. The urea dose was given in three splits, including basal application and top dressing, at 30 and 45 days (head initiation) after transplanting plant seedlings. Other intercultural operations like gap filling and weeding (3 times) were also carried. In general, the pest and disease incidence was not observed during both crop seasons. The treatments comprised nine combinations of mineral fertilizers and bio-agents, including one absolute control outlined in Table 7. The recommended dose of fertilizer (RDF) was applied @ 120:60:60 kg ha −1 (N:P 2 O 5 :K 2 O) through urea, DAP, and MOP, respectively. The fertilizer dose was reduced to 25% when the priming agents were used (Table 7). www.nature.com/scientificreports/ Biometric observations. Data related to yield attributing parameters such as heading percentage, head diameter (cm), head weight (g), and total weight (g) were collected at harvest.
Computation of nutrient uptake and nutrient use efficiency. Nutrient uptake and nutrient use efficiency were calculated using the following equations.

Nutrient uptake.
Nitrogen content was determined by the micro Kjeldahl method after pre-digestion with concentrated sulphuric acid (H 2 SO 4 ) followed by catalyst mixture 64 . Phosphorus content was determined by vanadomolybdophosphoric yellow color method after pre-digestion with diacid (HNO 3 :HClO 4 ) 65 . The acid-digest prepared for P was used to assess potassium (K) in a flame photometer 66 .
Partial factor productivity.
Energy analysis. The energy input-output relationship was determined based on the energy equivalent of inputs and output (Table 8). Solar energy was not included in the calculation. Energy analysis involved the following equations. Partial factor productivity kg kg −1 = Head yield kg ha −1 Quantity kg ha −1 of nutrient applied