Biomass response of chickpea ( Cicer arietinum L.) to different textured soils and irrigation levels

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INTRODUCTION
Chickpea (Cicer arietinum L.) is the third most important pulse crop in production after dry bean and field pea (Siddique and Krishnamurthy, 2016;Merga and Haji, 2019) and is cultivated all over the world for its seeds (Yegrem 2021).It is grown primarily in developing and underdeveloped countries for household consumption and localized trade (Bell, 2014;Sharma et al., 2020).Chickpea is well known for contributing to soil fertility by fixing atmospheric nitrogen (N 2 ) into ammonia, which can be further transformed into various organic forms (Verma et al., 2015;Abd-Alla et al., 2023;Crop Trust, 2023) and thus minimizes the fertilizer costs for subsequent crops.It is a quality food source rich in protein (McDermott and Wyatt, 2017), minerals (calcium, magnesium, phosphorus and potassium), vitamins (riboflavin, niacin, thiamine, folate, and the vitamin A precursor β-carotene), and carbohydrates (Jukanti et al., 2012;Singh et al., 2021).The protein quality of chickpea seeds is better than that of other pulses (Jukanti et al., 2012).Chickpea seeds contain on average 23% proteins (Verma et al., 2015;Crop Trust, 2023).Chickpeas are reported to contain a low quantity of lipids, but are rich in nutritionally vital unsaturated fatty acids such as linoleic acid and oleic acid (Yegrem, 2021).
Although chickpea has a large economic potential in sub-Saharan Africa (Fikre et al., 2020), there is hardly any commercial production of chickpea in some sub-Saharan African countries such as South Africa (SA).Several research trials aiming to encourage the local production of chickpea have been conducted in the Limpopo and Mpumalanga Provinces of SA (Madzivhandila et al., 2012;Masowa et al., 2012;Ogola, 2015;Lusiba et al., 2017;Makonya, 2019;Leboho, 2020;Moloto et al., 2018;Ogola et al., 2021).Although these studies have demonstrated that chickpea can be grown in those parts of SA, access to irrigation water has been identified as one of the serious challenges that could be faced by South African smallholder crop farmers when cultivating chickpea during the winter season (Mpai and Maseko, 2018;Leboho, 2020).Against the previous context, investigations on appropriate water-saving irrigation management strategies that will ensure higher yields of chickpea with a limited amount of water are crucial.The need to use water efficiently is unquestionable in waterscarce countries such as SA (Stelli et al., 2018;Mahlare et al., 2023).
Chickpea is normally grown in semi-arid or arid tropical regions under rain-fed conditions and the crop can be harmed by a shortage of moisture in the soil (Mohammed et al., 2017).Shortage of soil moisture reduces grain and biological yields of crops (Fahad et al., 2017;Pour-Aboughadareh et al., 2019) through negative impacts on plant growth, physiology, and reproduction (Yordanov et al., 2000;Pour-Aboughadareh et al., 2019;Mustafa et al., 2021).Also, a shortage of moisture in the soil leads to difficulties in crop management with regards to pests and diseases and reduced nutrient availability and assimilation by plants (Al-Kaisi et al., 2013;Yetgin, 2023).Although plants cope with soil moisture shortages by evolving various complex resistance and adaptation mechanisms (Osakabe et al., 2014;Fahad et al., 2017;Seleiman et al., 2021), adding the required amount of water through irrigation may alleviate plant water stress.https://doi.org/10.17159/wsa/2024.v50.i3.4082Supplemental irrigation is used to overcome the reduction of chickpea yield caused by a shortage of soil moisture in some parts of the world (Singh et al., 2016;Zhao et al., 2020).However, the dependence on irrigation to supplement rainfall can be a problem for countries that have limited natural water resources and variable rainfall, such as SA (Stelli et al., 2018).This problem can be exacerbated by inappropriate irrigation management practices that not only waste water resources but also damage crop growth (Zhao et al., 2020).Therefore, studies to determine the amount of water to apply to provide the maximum useable soil moisture in a plant's root zone without inducing harmful stress to the crop are crucial.The use of suitable irrigation levels will ensure better water use efficiency of chickpea and reduced water wastage during irrigation (Zhao et al., 2020).However, such irrigation management trials should also evaluate the effects of soil properties on crop growth because soil properties such as soil texture can affect the soil available water capacity as well as the growth of plant roots, which are the main organs in water uptake (Duo et al., 2016).Hence, the objective of this study was to determine the effects of different irrigation levels and soil texture on dry matter production of chickpea grown under greenhouse conditions.

Study site description, design and treatments
A pot experiment was conducted for 50 days in the greenhouse at the Green Biotechnologies Research Centre of Excellence (GBRCE) of the University of Limpopo (23° 53' 10" S, 29° 44' 15" E; 1327 m) in South Africa between February and March 2021.The ambient day/night greenhouse temperatures averaged 28/21°C, with maximum temperatures controlled using thermostatically activated fans.The experiment was arranged as a 3 × 2 factorial in a completely randomized design, with 3 irrigation levels (25%, 50% and 75% of the water-holding capacity (WHC) of the soil (maximum amount of water a soil can retain)) and 2 different textured soils (greyish-brown sandy loam and reddish-brown loamy sand textured soils), replicated thrice.

Soil collection, preparation, and characterization
The loamy sand textured soil was obtained from the GBRCE, while the sandy loam textured soil was collected from the University of Limpopo Experimental Farm (ULEF;23° 50' 42.86" S;29° 42' 44.35" E).The ULEF and GBRCE soils were previously classified as Hutton soils following the South African soil classification system (Phefadu and Kutu, 2016;Pofu and Mashela, 2022).For the purposes of this paper, the loamy sand textured soil and sandy loam textured soil will hereafter be referred to as LS soil and SL soil, respectively.Both soils were collected from the surface (0-25 cm), air-dried, homogenized and sieved (4 mm sieve) to remove stones and plant roots.
Selected physico-chemical properties (Table 1) of the soils used in this study were analysed following standard laboratory procedures.Soil particle size was determined using a hydrometer procedure as described by Sheldrick and Wang (1993).Soil pH was measured in a 1:2.5 soil: water extract (Non-Affiliated Soil Analyses Work Committee, 1990) while soil organic carbon (C) was determined using the Walkley-Black method (Walkley and Black, 1934).The contents of nitrate and ammonium in the soil were determined colorimetrically following the extraction with 0.5 M KCl solution (Okalebo et al., 2002).The total mineral N content was calculated as the sum of the contents of ammonium and nitrate.Available phosphorus (P) was determined using the Bray-1 method (Bray and Kurtz, 1945).The WHC of the soil was determined using a method described by Mahajan et al. ( 2018) with slight modifications.Six pots (25 cm diameter and 20 cm height) filled with 6 kg of air-dried soil were saturated with tap water (3 pots for LS soil and 3 pots for SL soil).The surface of the pot was covered with a plastic sheet and then left to drain for 48 h.Following this, a soil sample was taken from the middle of each pot.These samples were weighed (wet weight of soil, A), oven-dried at 105°C for 72 h and re-weighed (dry weight of soil, B).Following this, the WHC was calculated using the following formula (Mahajan et al., 2018) (1)

Crop husbandry
Prior to planting, pots (25 cm diameter and 20 cm height) were filled with 6 kg of air-dried soil.Limestone ammonium nitrate (LAN; 28%) and single superphosphate fertilizers (SSP; 10.5%) were applied before planting to supply N and P at the rates of 20 and 40 kg/ha, respectively.These fertilizers were applied based on the calculated weight of soil used per pot and an assumption of 2 million kg/ha weight of soil from the furrow slice (Masowa et al., 2022).Based on the recommended rates and percentage of N and P content in the fertilizers, the quantities of LAN and SSP fertilizers were 214.28 and 1 142.86 mg/pot, respectively.Three seeds of kabuli-type chickpea were planted in each pot and one seedling was thinned after 2 weeks of planting.Pots were watered to achieve 100% of the WHC of the soil before subjecting the plants to the different irrigation levels 28 days after planting.To subject the plants to water deficit treatments, pots were watered to achieve 25%, 50% and 75% of WHC (Table 2).The amount of water lost from each pot was measured every 7 days by weighing each pot before re-watering to 25%, 50%, 75% and 100% of WHC.The mass of water added was considered to be equal to the volume of water added, assuming that the density of water is 1 g/cm 3 (Mulidzi et al., 2016;Imakumbili et al., 2021).

Data collection
Plants were harvested 50 days after sowing (R 1 : flowering stage) for the determination of shoot biomass (SBM), root biomass (RBM), total plant biomass (TBM; SBM + RBM) and root/shoot ratio (RSR; root dry weight/shoot dry weight).After harvesting the plants, shoots and roots were separated, washed with tap water to remove dirt, placed in separate labelled paper bags, oven-dried to a constant mass at 65°C, and the mass recorded as dry matter (g dry matter/plant).

Statistical analysis
The data collected were subjected to a factorial analysis of variance using SAS software version 9.4.The treatment means were separated using Fisher's protected least significant difference (LSD) test at the 5% level of significance.Regression analysis was performed to establish the relationship between the measured crop parameters and the irrigation levels, regardless of the soil textural class.

RESULTS AND DISCUSSION
The assessment of SBM and plant weight is of primary importance when quantifying the accumulation of biomass (Souza et al., 2016), which is used when evaluating the crop performance (Ogola et al., 2021;Wang et al., 2021;Meiyan et al., 2022).In this study, the performance of chickpea subjected to different irrigation levels and soils with different textures was assessed by measuring the crop's dry biomass.Shoot biomass and the TBM were significantly influenced by the soil texture, irrigation level and their interaction, while RSR was significantly affected by the soil texture and irrigation level (Table 3).The 25% WHC treatment reduced SBM by up to 60% and TBM by up to 56% as compared to the 50% and 75% WHC treatments, which were statistically on par with each other (Figs 1A and 1C).Previous studies also reported a decrease in the SBM of various plants under reduced irrigation (Moosavi et al., 2015;Imakumbili et al., 2021;Mehak et al., 2021).The non-significant effect of irrigation level on RBM (Fig. 1C) indicated that subjecting chickpea plants to reduced irrigation (25% and 50% WHC) does not compromise chickpea root growth.Root biomass adjustment is one of the strategies that plants use to avoid and tolerate water deficit (Brunner et al., 2015).The 50% and 75% WHC treatments gave significantly lower RSR values as compared to the 25% WHC treatment (Fig. 1D), indicating that the 25% WHC reduced the growth of shoots more than that of roots.A study by Saidi et al. (2010) also showed a decrease in RSR under reduced irrigation treatment as compared to that observed under full irrigation.This finding confirms that the reduction of root growth in response to low water availability due to a decreased amount of irrigation  is lower than the accompanying reduction in shoot growth (Hsiao and Liu-Kang, 2000;Saidi et al., 2010).
Although RBM was not significantly increased by an increase in the amount of irrigation water applied, a linear (R 2 = 0.81) effect on RBM was observed, regardless of soil texture (Fig. 2A).
Shoot biomass and TBM were significantly higher in SL with high clay content (16.67% clay) and high WHC than in LS soil with low clay content (8.83% clay) and low WHC (Table 4).The greater SBM and TBM observed in SL soil than in LS soil may be ascribed to the higher WHC of this soil (Souza et al., 2016).This finding is in line with that of Ogola et al. (2021), who reported that the above-ground biomass and grain yield of chickpea were quantitatively higher in high clay content soil (clay-textured soil) than in soil with low clay content (loamy sand-textured soil).On the contrary, Moloto et al. ( 2018) found that 4 out of 5 desi-type chickpea genotypes had greater plant growth in sandy loam-textured soil than in the clay-textured soil.High values of SBM and TBM in SL soil may be attributed to the sandy loam soil's good water retention capacity (Purushothaman et al., 2017), nutrient retention and permeability, as well as its higher clay content, which provide good soil structure and fertility (Molepo et al., 2017).Conversely, the dry roots of plants from pots with LS soil were generally (24.24%) heavier than the dry roots of plants from pots with SL soil (Table 4).A study by Ahmadi et al. (2011) also showed a significantly higher potato root dry matter in loamy sand soil compared to sandy loam soil.Significantly higher RSR (Table 4) in the LS soil than in the SL soil indicated that the conditions of LS soil allowed plants to allocate higher proportions of biomass into roots, possibly due to increased competition for soil resources (Qi et al., 2019).Soils with high clay content, such as the SL-textured soil used in this study, may also have a temporary mechanical impedance that limits root growth when the soil dries out (Cairns et al., 2004;Whitmore and Whalley, 2009;Ahmadi et al., 2011;Bengough et al., 2011).The loamy sand-textured soil on the other hand has a high permeability due to its coarser texture (Molepo et al., 2017), which has been shown to promote root growth (Ahmadi et al., 2011).
The 25% WHC treatment reduced SBM by up to 68% as compared to the 50% and 75% WHC treatments in SL soil (Fig. 3A).Even though the differences in RBM amongst the different irrigation levels were insignificant, the RBM increased correspondingly with the irrigation level in SL soil (Fig. 3B).The TBM obtained from the 25% WHC treatment was 65% lower than that recorded from the 75% WHC treatment in SL soil (Fig. 3C).The RSRs obtained from the irrigation treatments in LS soil were significantly higher than those from irrigation treatments in SL soil (Fig. 3D), indicating that irrigation treatments favoured root growth over shoot growth more under LS soil than SL soil.This result is different from that reported by Souza et al. ( 2016), who showed that irrigation promotes greater growth of plants in soils of a medium texture with high clay content compared to sandy soils with low clay content.

Figure 1 .
Figure 1.Effect of irrigation level on (A) shoot biomass, (B) root biomass (C) total plant biomass, and (D) root/shoot ratio of chickpea.Means with the same letter are not significantly different at the 5% probability level.WHC = water-holding capacity of soil.

Figure 2 .
Figure 2. Linear regression of (A) root biomass, (B) shoot biomass, (C) total plant biomass and (D) root/shoot ratio for different irrigation levels across the different soils.

Table 1 .
Physico-chemical properties of soils used in this study

Table 3 .
Results of analysis of variance conducted to determine the effects of soil texture, irrigation level and their interaction on shoot biomass, root biomass, root/shoot ratio and total plant biomass of chickpea

Table 4 .
Effect of soil texture on root biomass, shoot biomass, root/shoot ratio and total plant biomass Soil texture Root biomass (g/plant) Shoot biomass (g/plant) Root/shoot ratio Total plant biomass (g/plant)Means with the same letter in each column are not significantly different at the 5% probability level