Introduction

Cactus pear or Indian fig opuntia (Opuntia ficus-indica L., Family: Cactaceae) is a cactus species that is a domestic crop produced throughout arid and semiarid regions of the globe. The cactus pear is the most commercially important cactus. It is grown chiefly as a fruit crop and for other purposes, including food and medicinal industries, cosmetics, fodder, and soil erosion prevention. Cacti are suitable crops for dry zones because they convert water into biomass efficiently. The fruits are commercialized in many parts of the world and consumed raw. They have one of the highest concentrations of vitamin C. As fruits have vitamin C, they were once utilized to mitigate scurvy. Jams are made from fruits. The red color of the fruits and juice is owed to betalains; the fruits also contain flavonoids and are very nutritious. They have 14% fructose, 1% protein, 20% solids, glucose, ascorbic acid, fatty oil, and a resinous substance. The fruits are used to treat diarrhea (Kuti 2004; Neffar et al. 2013; Zimmer 2013; Miller 2015; Badr et al. 2019; Fattah et al. 2020; Ueckert 2020).

Until now, the cactus pear farms did not receive enough attention in the fertilization programs, like other fruit plants in desert areas. The shortage in mineral nutrients influences cactus pear plant metabolism, negatively impacting fruit yield and quality. Cactus pear plants differ physiologically and morphologically from most other crop plants. For this reason, fertilizer recommendations applied to other crops are unsuitable. The mineral nutrition studies on cactus pears show that chemical fertilizer application is generally valuable for fruit production. Nutrient elements influence the cactus pear's fruit yield and quality. Macroelements have the most significant impact on fruit production. N, P, and K are the most limiting nutrients in cacti and affect their yield (Claassens and Wessels 1997; Dubeux et al. 2006; Zegbe et al. 2014, 2015; Silva et al. 2016; Souza et al. 2017; Food and Agriculture Organization of the United Nations 2018; Neto et al. 2020).

Cultivating the cactus pear crop is profitable for local farms in the desert due to its low production costs, high-added value crop, and tolerance to environmental conditions such as high temperatures, drought, and poor soils (Mason 2015). Concerning the agriculture processes, many farmers still depend on organic fertilizers only in production without chemical fertilizers, which leads to a decrease in the yield and quality attributes. Other farmers add very high nitrogen fertilizers, resulting in excessive vegetative growth and reduced fruit yield.

Calcareous soils possess high levels of calcium carbonate (CaCO₃) that affect soil properties related to plant development. Cultivating calcareous soils presents numerous difficulties, such as low water holding capacity, high infiltration levels, shoddy construction, low organic matter, and clay content. Moreover, low cation exchange capacity (CEC), loss of fertilizers via leaching, texture crusting and cracking, increased pH, losing nitrogen fertilizers, and low availability of nutrients (Elgabaly 1973; El-Hady and Abo-Sedera 2006; FAO 2016; Aboukila et al. 2018). Therefore, the crops that can resist such poor soil conditions are like the cactus pear. So, calcareous soils are suitable for the cultivation of this plant.

Farmers overlook the importance of chemical fertilization for cactus pear farms, despite its importance in improving fruit crop characteristics such as quantity and quality. This study investigates this topic under calcareous soil conditions in newly reclaimed desert lands in Egypt, as this topic has not previously been studied.

The objective of our research was to investigate the effect of different nitrogen, phosphorous, and potassium fertilizers on the yield and quality of plants cultivated in calcareous soil to improve the characteristics of the fruits by knowing the appropriate fertilizer rates. As a result, the area of this crop on those lands has grown.

Materials and Methods

Experimental details and treatments

Experimental details: The experiment was set up in the cactus pear farm in the El-Hammam region (30° 50′ N and 29° 23′ E), Matrouh Governorate, Egypt, over two seasons in 2020 and 2021. Five-year-old cactus pear plants (Opuntia ficus-indica L.) grown in sandy soil and spaced 2 × 5 m apart are subjected to a drip irrigation system. The experimental soil's physical and chemical analyses are shown in Table 1. The chemical analysis of the used water for irrigation is recorded in Table 1. The parameters of compost manure added to the farm are presented in Table 2.

Treatments: This work aimed to determine plants' best-added nitrogen, phosphorus, and potassium levels. Healthy vegetation, nearly in shape and size and productivity were chosen for this experiment. The experiment was designed as a randomized complete block design with four replicates for each treatment. The applied nine fertilization treatments were as the following:

1- Control

2- 100 g N + 40 g P + 70 g K / plant

3- 100 g N + 40 g P + 90 g K / plant

4- 100 g N + 60 g P + 70 g K / plant

5- 100 g N + 60 g P + 90 g K / plant

6- 120 g N + 40 g P + 70 g K / plant

7- 120 g N + 40 g P + 90 g K / plant

8- 120 g N + 60 g P + 70 g K / plant

9- 120 g N + 60 g P + 90 g K / plant

The used chemical fertilizers sources were ammonium nitrate (33% N), calcium superphosphate (15.5% P₂O₅) and potassium sulphate (48% K₂O). Nitrogen fertilizer was divided into two equal doses, the first 50% of nitrogen fertilizer was added at the end of February and the second 50% of nitrogen fertilizer was added after three weeks of full bloom, at the beginning of May, in both seasons. Potassium fertilizer was divided into two equal doses and added as a soil application while adding nitrogen fertilizer. Nitrogen and potassium fertilizers were added as soil applications at a depth of 15 cm and 1 m from the trunk. The ordinary organic fertilization program was 15 kg/plant of compost manure with phosphate added to a trench in the first week of January. Fruits were taken from each treated plant at harvest time to determine the quantity and physical and chemical aspects. The response of cactus pear plants to fertilization treatments was evaluated through the following determinations:

I) Vegetative growth and pigment measurements: Number of cladodes, cladodes length (cm), cladodes width (cm), cladodes area (cm²), chlorophyll a (mg/g), chlorophyll b (mg/g), total chlorophyll and carotenoids (mg/g).

II) Fruiting measurements: Fruit set%, number of fruits/plant, fruit yield (kg)/plant, fruit weight (g), fruit length (cm), fruit width (cm), fruit volume (cm³), juice weight (g), peel weight (g), peel thikness (cm), pulp weight/fruit (g), number of seeds/fruit, seeds weight/fruit (g), fruit TSS (%), total acidity content (%), fruit TSS / acid ratio, and ascorbic acid (mg/100 mL juice) according to the methods described by (AOAC 1995; Barros et al. 2016).

Statistical analysis

The obtained data were subjected to an analysis of variance according to Clarke and Kempson (1997). The means were differentiated using the range test at the 0.05 level (Duncan 1955).

Results

I- Vegetative growth and pigment measurements: Data in Table 3 showed the effect of mineral fertilization on vegetative growth parameters in both seasons. Generally, NPK nutrient addition significantly enhanced growth Table 1: The soil and irrigation water analyses

Characteristics	Values
Soil physical properties
Sand	93.10%
Silt	1.04%
Clay	5.86%
Soil texture	Sandy
Soil chemical properties
Organic matter	0.10%
pH	8.30
Electrical conductivity	294.40 mg.kg^-1
HCO₃^-	0.02 meq/100 g soil
Cl^-	0.05 meq/100 g soil
SO₄^{2 -}	0.35 meq/100 g soil
Ca²⁺	0.06 meq/100 g soil
Mg²⁺	0.05 meq/100 g soil
Na⁺	0.3 meq/100 g soil
K⁺	0.01 meq/100 g soil
CaCO₃	39%
Irrigation water chemical properties
pH	7.45
Electrical conductivity	485.00 mg.kg^-1
HCO₃^-	4.83 meq/L
Cl^-	1.73 meq/L
SO₄^{2 -}	1.04 meq/L
Ca²⁺	2.04 meq/L
Mg²⁺	1.38 meq/L
Na⁺	2.41 meq/L
K⁺	1.78 meq/L

Table 2: The compost manure physico-chemical analysis

Characteristics	Values
Weight of m³	625 kg
pH	7.85
Electrical conductivity	1760.00 mg.kg^-1
N	1.60%
C/N ratio	17:1
P	0.70%
K	1.25%
Fe²⁺	1587.50 mg.kg^-1
Mn²⁺	162.50 mg.kg^-1
Cu²⁺	65.00 mg.kg^-1
Zn²⁺	21.50 mg.kg^-1

Table 3: Effect of fertilization treatments (g/plant) on number of cladodes, cladodes length, cladodes width, and cladodes area of cactus pear during the two successive seasons

Treatments			Number of cladodes		Cladodes length (cm)		Cladodes width (cm)		Cladodes area (cm²)
N	P	K	2020	2021	2020	2021	2020	2021	2020	2021
0	0	0	5.70 f	6.70 i	24.76 e	24.51 f	16.10 e	17.57 d	273.62 e	300.14 g
100	40	70	7.00 ef	8.00 h	32.60 d	31.27 e	17.35 d	19.50 cd	388.28 d	417.41 f
100	40	90	9.00 de	11.00 f	35.35 c	33.46 d	19.35 c	19.49 bc	370.21 c	475.94 de
100	60	70	7.70 ef	9.00 g	34.85 c	35.25 cd	17.85 d	18.46 cd	427.42 d	444.55 ef
100	60	90	10.70 cd	13.00 d	35.85 c	35.75 c	19.35 d	19.83 b	476.83 c	491.53 cd
120	40	70	12.30 cd	14.70 c	38.85 b	38.75 b	19.60 bc	19.59 b	524.00 b	526.31 bc
120	40	90	18.70 a	19.70 a	40.60 b	42.25 a	20.10 bc	20.11 b	561.91 b	565.16 b
120	60	70	11.00 cd	11.70 e	38.60 b	38.75 b	20.60 ab	19.62 b	547.30 b	523.64 bc
120	60	90	16.00 b	17.00 b	43.60 a	41.25 a	21.35 a	21.89 a	640.07 a	659.28 a