1. Soil N dynamics, chlorophyll content, and leaf nitrate reductase activity influenced by seed priming, mulching, and nitrogen application in grain barley
Tassadduq Rasool1,3*, Muhammad Farooq1, 2, Riaz Ahmad1
3 Visiting scholar, Department of plants soils and climate, Utah State University, USA *
1Department of Agronomy, University of Agriculture, Faisalabad-Pakistan
2The UWA Institute of Agriculture, The University of Western Australia, Crawley WA 6009, Australia
Results
Introduction
Soil dynamics show that mulch application resulted in higher ammonium and less nitrate contents as compared to un-mulched plots ammonium and nitrate contents.
This suggests the potential use of mulch for controlled release of N during crop production and for making N available for longer period.
A balance between maximizing N availability for plant uptake and minimizing the risk of nitrate leaching can be achieved.
Mulch has not affected plant growth and yield, when supplied with fertilizer.
NRA activity was lower in N-stressed (N0) plants, indicating that N-uptake and assimilation was greater at higher levels of nitrogen. Nitrate reductase activity was (55%) higher in N50 and (84%) in N100 as compared to control.
Leaf color was also used as an assessment tool for estimation of N status or photosynthetic activity.
Chlorophyll content increased with increasing levels of N and in combination with mulch.
Plants supplied with N resulted in an increase of (19%) in chlorophyll-a content over plants without nitrogen (No).
Nitrogen is usually the most limiting nutrient in agricultural soils.
Its mobility in soil, availability, and interaction with other crop production practices are in continuous study by the agriculture scientific communities.
The lack of N can hamper the chlorophyll biosynthesis and N content in plant tissues.
We hypothesized that its availability and other plant growth characteristics would be significantly affected by various nitrogen (N) regimes in interaction with mulch (M) and seed priming (P) treatments, aiming to provide guidelines for nitrogen management.
We also predicted that application of M would alter the soil dynamics of N, studied at short-term intervals, and might have an impact on its mineralization, availability, and uptake by the plant.
Nitrate is the predominant source of nitrogen in fertilized soils (Marschner, 2012).
Nitrate reductase activity can be used as a biochemical tool for predicting grain yield and N supply to plant.
The assimilation of N involves the nitrate reductase (NR) enzyme, and its activity seems to be dependent on N supply.
Nitrate reductase activity (NRA) is proportional to nitrate uptake by the plant and growth (Chen, 2004).
Jabran et al., 2013
Methods
Experimental treatments and details
The experiment was conducted at greenhouse experimental facility of Department of Agronomy, University of Agriculture, Faisalabad. Barley (Hordeum vulgare L. var. H-93) seeds were planted deep in 2 cm fine soil of earthen pots (45 cm circumference × 30 cm high). Initially, 15 seeds per pot were sown and thinned to 10 after complete emergence. Sorghum was used as mulch material in chopped form ( cm pieces).
Barley seed osmopriming and hydropriming were carried out by saturating the seeds in aerated solutions of CaCl2 (1.25%) and distilled water, respectively, for a time period of 12 h at 25±2 ºC (Farooq et al., 2008). Seed weight to soaking solution volume (w/v) was being kept 1:5. One third of the seeds were kept untreated (dry seeds) to use that portion as a control.
Plant and soil traits determination
Nitrate reductase activity was measured by the method of Sym (1984). Soil available or absorbed N (i.e., NH+4-N and NO-3-N) were extracted by KCl solution (Keeney and Nelson method). Quantification of ammonium was done by indophenol blue method and for nitrate phenoldisulphonic acid method was used.
Treatments and Experimental Design
The experiment was arranged in a factorial arrangement with three replicates.
A: Seed priming
Dry seed
Hydropriming
Osmopriming
B: Sorghum mulching
No mulch
Mulch
C: Nitrogen levels (mg/kg soil)
0 mg/kg
20 mg/kg
40 mg/kg
D0= Before fertilizer application; and subsequent D denotes to the respective date of sampling after nitrogen addition
References
Farooq M., Basra S M A., Rehman H., Saleem B A Seed priming enhances the performance of late sown wheat by improving the chilling tolerance. Journal of Agronomy and Crop Sciences, 194:
Sym G J Optimization of the in vivo assay conditions for nitrate reductase in barley (Hordeum vulgare L.CV. irgri). J. Sci. Food Agric. 35:
Chen, Bao-Ming, Z.H. Wang, S.X. Li, G.X. Wang, H.X. Song and X.N. Wang Effects of nitrate supply on plant growth, nitrate accumulation, metabolic nitrate concentration and nitrate reductase activity in three leafy vegetables. Plant Science. 167:
Marschner, Petra. Ed Marschner's mineral nutrition of higher plants (3rd ed.). Amsterdam: Elsevier/Academic Press. p. 135. ISBN 
Jabran, K., M. Farooq, T. Aziz and K.H.M. Siddique Allelopathy and crop nutrition. p In Z.A. Cheema, M. Farooq and A. Wahid (eds.). Allelopathy: Current Trends and Future Applications. Springer: Verlag Berlin Heidelberg, Germany.
Source of variation DF
Chlorophyll-a
(mg/g f. wt.)
Seed Priming (P) 2 * * *
Mulching (M) 1 * ** ns
Nitrogen (N) ** ** **
Seed Priming × Mulching (P× M) ns ns ns
Seed Priming × Nitrogen (P× N) 4 ** * **
Mulching × Nitrogen (M×N) ** ** **
Seed Priming × Mulching × Nitrogen * ** *
Error 36
Total 53
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Acknowledgment
Department, of plants, soils and climate, Utah State University.
Professor, David Hole
Conclusion
Thus, barley grown through primed seed perform better, and application of mulch is a potentially useful practice for effective utilization of nitrogen for a longer period of time during crop growth.
UC Davis Plant Sciences Symposium- April, 24, 2017