Impact of phosphorus drip fertigation practices on chickpea physiology, yield, and nutrient dynamics in soil-plant continuum under Mediterranean climate

Activiteit: OverigeAndere soorten (prijzen, externe en andere activiteiten) - (Co)promotor doctoraatsthesis

Beschrijving

The agricultural sector in the Mediterranean basin faces many challenges
related to the use of water and mineral resources for crop production and food
security for an exponentially growing population. Most countries in arid and
semi-arid areas suffer from water scarcity and soil nutrient depletion which
severely impact the productivity of different cropping systems currently
challenged by climate change and the high pressure on natural resources. Given
its role in several plant biophysiological processes, such as plant photosynthesis,
carbon fixation, energy transfer and allocation, and plant growth and
development, phosphorus (P) nutrition take increasing attention in the last
decades. The limited resources of rock phosphate as well as the low use
efficiency of phosphorus fertilizers push the scientific community to urgently
rethink the strategies of P fertilizer management at different scales.
In this dissertation, we focus on the study of the impact of P agricultural
management practices on P availability and mobility under drip fertigation
systems and the consequent effects on plant photosynthesis, nutrient uptake,
plant growth and productivity, and nutrient use efficiency. A series of
agronomic pot experiments were conducted under controlled conditions to
investigate the impact of various P drip fertigation practices on phosphorus
availability in Moroccan alkaline soils, on chickpea physiology, productivity,
and nutrient uptake. The objective of the first trials was to study the potential
use of inorganic soluble polyphosphates (Poly-P) as slow-release fertilizer under
drip fertigation. The impact of the chemical properties of polyphosphate and
orthophosphate (Ortho-P) fertilizers (polymerization degree, solubility, and
interactions with other nutrients), as well as P application frequency on the
availability of phosphorus in soil (Olsen-P) and its relocation into deeper soil
layers, were investigated. The second pot trials were conducted in controlled
conditions to evaluate the interactive effect of P fertilizer form (Ortho-P vs PolyP) and soil moisture conditions on chickpea photosynthetic activity, water and
nutrient uptake, and their consequent effects on biomass accumulation and
nutrient use efficiency. The mechanisms underlying phosphorus nutrition
impacts on chickpea photosynthesis efficiency, grain yield, and nutrient uptake
and use efficiency were explored using different plant sensors and analytical
methods like chlorophyll fluorescence, plant phenotyping, and plant nutrient
analysis. Based on the results of pot trials, two-years field experiments were
conducted in a 2.5 ha plot. The objective of these field experiments was to
evaluate the potential use of electromagnetic induction as a fast and reliable
technique to characterize soil properties. Soil electrical conductivity (ECa), crop
yield data, and soil chemical properties were used as input data to delineate chickpea fertigation management zones using unsupervised clustering analysis.
The variable rate P application strategy was evaluated as an efficient agricultural
practice to increase the chickpea grain yield and quality and to improve
phosphorus use efficiency at the field scale in Moroccan semi-arid conditions.
The results from pot experiments showed that soil phosphorus availability
varied significantly between fertilizer forms and fertigation frequencies. As
compared to the Ortho-P fertilizer, P becomes less mobile in soils fertigated with
Poly-P forms (Poly-100 and Poly-53) and its availability is maintained until
harvest. The analysis of Olsen-P at the harvest stage showed that the higher P
availability in soil was obtained with Poly-P forms with higher values in the 0-
5 and 5-10 cm soil layers than in the 10-20 cm. Moreover, weekly fertigation
(Fweek) revealed the best results in terms of P availability compared to fertigation
at sowing (Fsow) or 3-day frequency (F3days) and all P fertilizers significantly
improved chickpea grain yield, seed quality, and water productivity, compared
to the unfertilized control. In addition, our findings showed that the
photosynthesis efficiency was significantly improved in fertigated chickpea
plants compared to the control treatment as revealed by the electron transport
chain between photosystem II and I, which was significantly enhanced. The
polyphosphate fertilizer (Poly-A: Poly-53) increased the number of electron
acceptors of the photosynthetic linear electron transport chain compared to the
other P fertilizer forms. Furthermore, the interactive effect between P fertilizer
forms and soil moisture conditions resulted in several significant changes in
chickpea phenotypic and physiological traits. The stomata density and
conductance, chlorophyll content, photosynthesis efficiency, biomass
accumulation, and plant nutrient uptake were significantly improved under P
drip fertigation with varied values depending on P fertilizer form and irrigation
regime. Our results suggested that the P fertilizer form and irrigation regime
providing chickpea plants with enough P and water, at the early growth stage,
increased the stomatal density and conductance, which significantly improved
the photosynthetic performance index (PIABS) and P use efficiency (PUE), and
consequently biomass accumulation and nutrient uptake. The significant
correlations established between leaf stomatal density, PIABS, and PUE
supported the above hypothesis. Based on these results from the pots
experiments we can conclude that Poly-P fertilizers can be recommended as an
effective source of phosphorus for plants, due to their slow-release properties
and the frequency of P application through the drip fertigation system which can
be reduced while ensuring high crop yields. However, the effectiveness of PolyP fertilizers was greatly reduced under water stress conditions, unlike the OrthoP form which kept stable positive effects on the chickpea's physiological traits.
On other hand, the field experiment showed that the soil spatial variability can
be properly assessed by the electromagnetic induction sensor (CMD MiniExplorer), which represents basic information to conduct an oriented soil
sampling design. Moreover, the statistical correlation analysis as well as the
multiple regression model used for the prediction of chickpea yield greatly
contributed to identifying the main soil properties influencing chickpea grain
yield in the studied site. The combination of soil and plant sensing data (ECa,
Ca, P, and GY) and their processing by geostatistical tools (semi-variograms,
interpolation by ordinary kriging and IDW methods, and fuzzy c-means
clustering algorithm) were very useful to delineate chickpea drip fertigation
management zones (MZs). The application of variable rate P fertilizers through
a drip fertigation system in the identified MZs increased the chickpea grain
yield, seed size, and phosphorus use efficiency by 12%, 9%, and 18%
respectively.
Based on these results, we can conclude that the optimization of P fertigation
practices, especially the choice of adequate P fertilizer form and application
frequency, considering the availability of irrigation water and soil properties,
can greatly contribute to improving crop yield and phosphorus use efficiency at
field scale. Moreover, the integration of precision agricultural practices like
variable rate application could be of great interest to farmers in semi-arid regions
like Morocco to enhance water and mineral resource use efficiency which in
return contributes to improving farmers' income, preserving the ecosystem, and
ensuring sustainable agricultural production systems
Periode22-mei-2023
Gehouden opULiège, België
Mate van erkenningInternationaal