Mulching impact of Jatropha curcas L. leaves on soil fertility and yield of wheat under water stress

In present studies we have evaluated mulching impact of Jatropha curcas leaves on soil health and yield of two wheat (Triticum aestivum L.) varieties Wadan-2017 (rainfed) and Pirsabak-2013 (irrigated) under imposed water stress. Mulch of Jatropha leaves was spread on the soil surface at the rate of 0, 1, 3 and 5 Mg ha−1 after seed germination of wheat. Water stress was imposed by skipping irrigations for one month at anthesis stage of wheat maintaining 40% soil field capacity. We found a significant decline in soil microbial biomass carbon (30.27%), total nitrogen (22.28%) and organic matter content (21.73%) due to imposed water stress in non-mulch plots. However, mulch application at 5 Mg ha−1 significantly improved soil organic matter (38.18%), total nitrogen (37.75%), phenolics content (16.95 mg gallic acid equivalents/g) and soil microbial biomass carbon (26.66%) as compared to non-mulch control. Soil health indicators like soil carbonates, bicarbonates, electrical conductivity, chloride ions and total dissolved salts were decreased by 5 Mg ha−1 mulch application. We noted a decline in yield indicators like spike weight (14.74%), grain spike−1 (7.02%), grain length (3.79%), grain width (3.16%), 1000 grains weight (6.10%), Awn length (9.21%), straw weight (23.53%) and total grain yield (5.98%) of wheat due to imposed water stress. Reduction in yield traits of wheat due to water stress was higher in Pirsabak-2013 than Wadan-2017. Jatropha leaves mulch application at 5 Mg ha−1 significantly minimized the loss in yield traits of wheat crop caused by water stress. Jatropha curcas leaves mulch application at 5 Mg ha−1 is recommended for the successful establishment of wheat crop under water deficit conditions.


Materials and methods
Preparation of organic mulch. Fresh leaves of Jatropha curcas were collected from 30 healthy plants (3-5 m tall) and dried in shade. The dried leaves were broken down and then sieved with the help of 2 mm mesh 28 . Assessment of organic mulch potential on yield of wheat. In this study certified grains of two wheat (Triticum aestivum L.) varieties Wadan-2017 (rainfed) and Pirsabak-2013 (irrigated) were used. Details about pedigree and parentage of both the varieties are given in Table 1. Standardized size seeds of wheat were sterilized with 95% ethanol and washed with distilled water. In wheat growing season seeds were sown under natural condition during the years of 2018-2019 and 2019-2020 in District Bannu KP, Pakistan. During wheat growing season of 2018-2019 total rainfall was 284.7 mm while in 2019-2020 it was 227.4 mm. In 2018-2019 minimum and maximum average temperature was 11.02 and 24.07 °C correspondingly. Likewise during wheat growing season of 2019-2020 the average monthly minimum and maximum temperature were 11.19 and 23.29 °C respectively. Before sowing of seeds in the field recommended dose of potassium (50 kg ha −1 ), phosphorus (60 kg ha −1 ) and nitrogen (100 kg ha −1 ) were used. The split plot design was used for this experiment. Main treatments were control (irrigated having 100% soil field capacity) and water stress having (40% soil field capacity). Water stress was imposed by skipping irrigation for one month at anthesis stage of wheat. Application of irrigation during wheat growing season of 2018-2019 are given in Table 2. The plot size was 1 × 1 m 2 , having three replicates per treatment. The seeds were sown 10 cm apart and 5 cm deep in soil. Mulch of Jatropha leaves was spread on the soil surface at the rate of 0, 1, 3 and 5 Mg ha −1 after germination of wheat 29 .
When the seeds of wheat become fully matured and plants turned yellow, then they were harvested and yield parameters were determined. Thousand seed weight, spike weight, straw weight and yield per plot were determined with digital balance. Straw weight and grain yield of wheat was converted into kg/ha. By digital Vernier  Statistical analysis. The data of soil parameters was analyzed by one way ANOVA while the data of yield parameters of wheat was analyzed by two way ANOVA. By LSD test means of control and treatment were compared 36 . Pearson correlation was calculated between soil fertility indicators and grain yield of wheat.

Complies with international, national and/or institutional guidelines. Experimental research
and field studies on plants (either cultivated or wild), comply with relevant institutional, national, and international guidelines and legislation. Experimental studies were carried out in accordance with relevant institutional, national or international guidelines or regulation.
Permissions or licenses. The experiment was started, after taking permission from University of Science and Technology Bannu, Khyber Pakhtunkhwa, Pakistan.
Identification of the plant material. Before collection, the plant was identified by Dr. Zahid Ullah (Taxonomist), using the standard protocol at the Department of botany, University of Swat, Pakistan.A voucher specimen of this material has been deposited in a publicly available herbarium.
Ethics approval and consent to participate. We all declare that manuscripts reporting studies do not involve any human participants, human data, or human tissue. So, it is not applicable.

Results
Jatropha leaves mulch effect on soil fertility. The effects of Jatropha leaves mulch were investigated on the following indicators of soil fertility status.
Soil organic matter and nitrogen content. Mulch application significantly improved soil organic matter and nitrogen % as compared to non-mulch control (Table 3). Highest content of organic matter and nitrogen % was found in soil of plots applied with mulch at 5 Mg ha −1 . Water stress decreased soil organic matter and nitrogen % as compared to irrigated and non-mulch control. However, mulch treated plots exposed to water stress exhibited higher contents of soil organic matter and nitrogen %.
Soil phenolics content. The plots supplemented with Jatropha mulch showed considerable increase in soil phenolics content as compared to non-mulch control (Table 3). Maximum phenolics content was found in plots applied with Jatropha mulch at 5 Mg ha −1 . We observed that water stress increased soil phenolics content over irrigated and non-mulch control. However, water stress treated plots applied with mulch showed highest www.nature.com/scientificreports/ amount of soil phenolics. We noted that soil phenolics content was improved by mulch both under non-stress and water stress conditions. Soil microbial biomass carbon. Application of mulch improved soil microbial biomass carbon as compared to non-mulch control (Table 3). Plots treated with 5 Mg ha −1 showed highest content of soil microbial biomass carbon. However, water stress significantly decreased soil microbial biomass carbon. The decrease in soil microbial biomass carbon was overcome by application of mulch under water stress conditions. Soil electrical conductivity. We examined that electrical conductivity of soil was decreased in plots supplemented with mulch than non-mulch control (Table 3). Water stress treated plots without mulch has high value of electrical conductivity over irrigated and non-mulch control. The mulch application decreased electrical conductivity of soil in plots exposed to water stress. It is stated that application of mulch completely reversed the increase in soil electrical conductivity both in irrigated and water stress treated plots.

Soil carbonates and bicarbonates.
Our results showed that application of mulch significantly decreased soil carbonates and bicarbonates contents as compared to non-mulch control ( Table 4). The lowest content of carbonates and bicarbonates was found in plots applied with mulch at 5 Mg ha −1 . Interestingly water stress treated plots showed significantly higher content of carbonates and bicarbonates as compared to non-mulch and irrigated control. We concluded that Jatropha mulch decreased soil carbonates and bicarbonates content both under normal and water stress conditions. Soil calcium and magnesium. We observed that soil calcium and magnesium content was increased by mulch application as compared to non-mulch control (Table 4). Highest value of calcium and magnesium content was found in plots applied with mulch at 5 Mg ha −1 . Water stress decreases the content of calcium and magnesium in soil as compared to irrigated and non-mulch control. The decrease in calcium and magnesium content was reversed by mulch application under water stress. Most effective dose of mulch was 5 Mg ha −1 .
Soil chloride ions and total dissolved salts. We found that the content of chloride ions and total dissolved salts were lower in plots supplemented with mulch as compared to non-mulch control ( Table 4). The plots exposed to water stress and not applied with mulch had higher content of chloride ions and total dissolved salts over irrigated control. The mulch application decreased chloride ions and total dissolved salts in plots exposed to water stress. It is worthy to mention that mulch application at 5 Mg ha −1 completely reversed increase in the content of chloride ions and total dissolved salts of water stress treated plots as compared to non-mulch and irrigated control.
Jatropha leaves mulch effect on wheat yield. Grain spike −1 . Data of treatment means in Table 5 showed useful effect of Jatropha mulch on grain spike −1 of wheat. Highest number of grain (16.25%) was recorded for plants supplemented with 5 Mg ha −1 of mulch. We noted severe decrease (7.02%) in grain number due to water stress, however, percent decrease in grain number was higher in Pirsabak-2013 (9.77%) than Wadan-2017 www.nature.com/scientificreports/ (4.81%). It is noted that decreasing effect of water stress on grain number was decreased by Jatropha mulch particularly at 5 Mg ha −1 mulch.
Thousand grains weight. Jatropha mulch at 5 Mg ha −1 considerably increased thousand grains weight by 4.13% as compared to well irrigated and non-mulch control (Table 5). Thousand grains weight was decreased (6.10%) by water stress as compared to well irrigated and non-mulch control. On the other hand, use of mulch at 3 and 5 Mg ha −1 significantly reversed decrease in thousand grain weights caused by skipped irrigations. Treatment × variety interaction showed that in sensitive variety Pirsabak-2013 percent decrease in thousand grain weights was higher than tolerant Wadan-2017. Both the varieties have better reaction to mulch at 5 Mg ha −1 .
Grain length. Treatment means indicated that under well watered conditions Jatropha mulch at 5 Mg ha −1 considerably increased grain length by 7.47% over well irrigated and unmulched control ( Table 6). As compared to well irrigated and unmulched control skipped irrigation decreased grain length by 3.79%. However, decrease in    www.nature.com/scientificreports/ seed length was significantly overcome by application of mulch at 3 and 5 Mg ha −1 . Treatment × variety interaction showed that skipped irrigation highly decreased grain length of sensitive variety Pirssbak-2013 (4.36%) than tolerant Wadan-2017 (3.28%). It is noted that Wadan-2017 had taller seed length (7.31%) than Pirsabak-2013. Both varieties showed good response to mulch at 5 Mg ha −1 .
Grain width. Treatment means data in Table 6 indicated that Jatropha mulch has favorable effect on grain width of wheat. Highest seed width (3.56 mm) was noted for plants treated with 5 Mg ha −1 of mulch over irrigated and unmulched control (3.32 mm). Grain width was significantly decreased (3.16%) by skipped irrigation. However, as compare to Wadan-2017 skipped irrigation highly decreased grain width in Pirsabak-2013. It is noted that skipped irrigation effects was minimized by Jatropha mulch. As compared to other mulch treatments 5 Mg ha −1 mulch was more effective.
Spike weight. Application of mulch at 3 and 5 Mg ha −1 considerably increased spike weight (13.36% and 17.33%) respectively (Table 7). Major reduction (14.74%) occurred in spike weight due to skipped irrigation. Percent decrease in spike weight was higher in Pirsabak-2013 (17.53%) as compared to Wadan-2017 (12.42%) due to skipped irrigation. However, skipped irrigation does not significantly effects the spike weight of plants treated with Jatropha mulch. It is noted that application of mulch at 5 Mg ha −1 significantly increase spike weight of wheat both under skipped irrigated and well irrigated conditions. Table 7 showed that as compared to well irrigated and unmulched control awn length of wheat spike was significantly increased (8.43%) by Jatropha mulch at 5 Mg ha −1 under well irrigated conditions. Awn length was decreased (9.21%) by skipped irrigation than unmulched control and well irrigated. Moreover, decrease in awn length was significantly overcome by 3 and 5 Mg ha −1 mulch. Decrease in awn length was higher in sensitive variety Pirssbak-2013 (13.15%) than tolerant Wadan-2017 (5.26%) due to skipped irrigation. It is noted that variety Wadan-2017 has higher awn length than Pirsabak-2013.

Awn length. Data of treatment means in
Straw weight. Treatment means data showed that mulch at 3 and 5 Mg ha −1 respectively increase straw weight (35.01% and 45.79%) in non stressed groups (Table 8). Skipped irrigation significantly decrease (23.53%) straw weight. Straw weight was considerably decreased in Pirsabak-2013 (29.29%) as compared to Wadan-2017 (18.89%) by skipped irrigation. Moreover, straw weight treated with Jatropha mulch was not affected by skipped irrigation. It is examined that both under skipped irrigated and well irrigated conditions straw weight of wheat was increased by application of mulch at 5 Mg ha −1 . Wadan-2017 had high straw weight (20.05%) than Pirsabak-2013.
Grain yield. Table 8 indicated that 5 Mg ha −1 Jatropha mulch significantly increased (24.48%) grain yield of wheat as compared to unmulched and irrigated control. Skipped irrigation considerably decreased (5.98%) grain yield of wheat as compared to unmulched and irrigated control. The percent decrease due to skipped irrigation in grain yield of wheat was higher in Pirsabak-2013 (7.30%) compared to Wadan-2017 (4.7%). However, the   www.nature.com/scientificreports/ decrease in grain yield of wheat was overcome by leaves mulch of Jatropha. Comparably Wadan-2017 had high grain yield (10.01%) than Pirsabak-2013.

Discussion
Jatropha mulch showed positive effects on soil organic matter content. A soil organic matter contains organic compounds released from dead and decaying of living organisms 37 and improves soil health 38 . Soil organic matter improves water holding capacity of soil and this is the major reason that organic mulches minimize water stress effects on the establishment of crops 39 . Organic matter resulting from microbial degradation of mulch releases nutrients to the soil and thus improving soil fertility 40 . We recorded improvements in soil total nitrogen (%) due to Jatropha mulch application. Mulching improves nutrients cycle in cultivated lands 41 leading to better establishment of crops 42 . Nitrogen content was high in the plots supplemented with maize straw mulch 43 . Studies have shown impact of mulches on soil N and C pools 44 . Organic mulching materials of oak (Quercus fabri), cogon grass (Imperata cylindrica), bracken fern (Pteridium aquilinum) and Chinese coriaria (Coriaria nepalensis) increased soil nitrogen content which was directly proportional to the decaying rate and nutrients content of the mulching material 45 .
We reported that water stress decreased soil microbial biomass in non-mulch plots; however, Jatropha mulch improved soil microbial biomass both under non-stress and water stress conditions. Microbial biomass shows considerable response to the climatic conditions and soil micro environment. Changing pattern of rainfall and global warming effects the reproduction and growth of soil microbes [46][47][48] . Therefore, in soil ecosystem degradation, microbial biomass carbon content acts as an early warning indicators 49 . Many researchers have reported that with the increase of drought stress soil microbial activity becomes damaged [50][51][52] and decreased up to 39% 53 . Our studies indicated that Jatropha leaves mulch improved soil microbial biomass which assisted in better establishment of wheat crop under low soil moisture availability.
Phenolics concentration was higher in plots supplemented with Jatropha mulch. Studies of Stoklosa et al. 54 showed that phenolics concentration was higher in soil provided with rye and oat mulch. Higher content of phenolics in plots applied with mulch may be because that Jatropha leaves contained a reasonable amount of phenolics. Although phenolics are highly reactive having phytotoxicity yet they are degraded either by soil microbes or by oxidation limiting their allelopathic potential in mulching trials 55 .
We noted a severe decrease in yield related traits of wheat due to imposed water stress. Water stress considerably minimized the yield of wheat 56 . This reduction in grain yield of wheat under water stress may be due to leaf senescence acceleration, degeneration of photosynthesis and sink restrictions 56 . In our studies Jatropha mulch minimized water stress negative impact on grain yield of wheat. Furthermore, decrease in grain number per spike was due to reduction in spikelets number per spike of wheat 57 . Studies have shown that black plastic mulch and rice straw mulch significantly increased straw yield, thousand seed weight and seed yield of wheat respectively 29 . Deng et al. 58 have also described the benefits of mulching on yield of wheat. Water stress reduced the grain and straw yield as compared to well watered treatments. Application of Jatropha mulch on grain yield may be majorly due to its improving effects on soil organic matter and soil nitrogen content as reported earlier 59 . Our results are also in confirmation with those of 60 that dual transparent plastic film + straw mulching and dual black plastic film + straw mulching considerably improved soil temperature, biomass, soil water storage potential, total nitrogen, soil organic carbon and grain yield of wheat. Arbuscular mycorrhizal fungi significantly increased water use efficiency, soil microbial biomass carbon/nitrogen ratio and crop productivity of non-irrigated wheat 61 .

Conclusion
Application of Jatropha mulch improved soil microbial activity, total N, organic matter and phenolics content as compared to non-mulch and irrigated control. Water stress restricted microbial biomass production, decreased soil nitrogen content and grain yield of wheat. The application of Jatropha curcas leaves mulch reversed negative effects of water stress on grain yield and soil fertility status. Findings of our research are novel in the sense that Jatropha leaves mulch was beneficial on soil microbial biomass and soil phenolics which might contribute in the reduction of disease attacks on wheat crop. Moreover, phenolics present in mulch have made a way of diffusion into the soil which might have assisted in the water stress resistance of wheat varieties. It was found that both the wheat varieties showed similar response to Jatropha mulch application irrespective of their tolerance level to water deficit stress.

Data availability
The datasets generated and/or analysed during the current study are not publicly available, but are available from the corresponding author on reasonable request. www.nature.com/scientificreports/