**Abstract**

Although the adaptation of forage palm to the Brazilian semi-arid, it may be influenced by soil and climatic conditions of this region, irregular rainy periods, high annual evapotranspiration and soils with a low water retention capacity. These factors may reduce crop production during dry seasons, including forage. The present research aimed at analyzing the effect of irrigation with different water depths and levels of salinity on Orelha de Elefante Mexicana cultivar. The study was carried out in pots in the Federal University of Campina Grande, from September 2017 to December 2018. Experimental design was randomized blocks in a factorial scheme 4 x 4, with 4 replications. Four irrigation water depths were applied (25, 50, 75, and 100%), as a function of water retention capacity of soil and four levels of electrical conductivity: 0.60; 3.00; 5.40 and 7.80 dS m<sup>1</sup> . Morphometric and production variables were evaluated. Plant growth was not affected by irrigation water depth and levels of salinity, except the thickness of secondary cladode. Primary cladodes showed the greatest average values (4.03 cladodes) for 376.00 mm depth. The other variables evaluated did not present significant effects under treatments. Saline water did not affect the total production of the cultivar.

**Keywords:** *Opuntia stricta* (Haworth) Haworth, water availability, water salinity

#### **1. Introduction**

Brazilian semi-arid is characterized by irregular rainy periods, high annual evapotranspiration and soils with a low water retention capacity, limiting livestock activities in this region [1]. These conditions affect the production during dry seasons, including the reduction of forage for animal feed. In this context, Orelha de Elefante

Mexicana (Haworth) Haworth) is an important forage palm that can mitigate the effects of low performance of the livestock. Thus, the efficiency of soil water use by *Opuntia* species is around 100 and 150 liters of water for each kilogram of dry matter produced, while grasses need 250 and 350 liters to produce the same quantity of dry matter [2].

Forage palm species are cactus with a great exploitation potential in the Brazilian northeast, constituting an important resource during periods of drought, due to its high potential of phytomass production in semi-arid region [3]. Despite forage palm adaptation to the region, local meteorological conditions influence plant development, since hydric deficit may cause a reduction of water content and hydric potential, resulting in loss of turgescence, closure of stomata and reduction of growth, which, consequently, promote a decrease in the final production. Thus, irrigation practice is very important to the production system [4].

The usage of poor water quality has been an alternative for producers in the northeast region to minimalize water scarcity in plants. However, it is important to highlight that the available water in several Brazilian semi-arid regions has high soluble salt contents. In this context, palm water needs may modify, changing water absorption process and evapotranspiration due to salt accumulations in soil, contributing to its degradation [5]. According to Ribeiro, Moreira, Seabra Filho and Menezes [6], salinity is one of the abiotic stresses limiting agricultural production the most, since it presents negative effects on vegetal development.

Crops that are sensible to saline water show the need of studies that aim at analyzing viable technologies to producers, in order to minimize salt effects on plants.

Thus, the present research aimed to evaluate the effect of water depths and levels of saline water on the growth and production of forage palm Orelha de Elefante Mexicana (*O. stricta* (Haworth) Haworth).

#### **2. Material and methods**

#### **2.1 Localization and characterization of the experimental area**

The study was conducted open to sky at the experimental area of the Federal University of Campina Grande (UFCG), in the municipality of Campina Grande (7° 12<sup>0</sup> 52,56"S; 35°54<sup>0</sup> 22,26"O and 532 m of altitude), state of Paraíba, from September 26, 2017 to December 11, 2018, totalizing 442 days. According to Köppen climate classification, the region has a mesometric, sub-humid, Csa climate, dry season (4 to 5 months) and rainy season (autumn to winter).

During the experiment, climate conditions were monitored by the automatic weather station at Brazilian National Institute of Meteorology (INMET), (7.22°S; 35.90°O and 546 m of altitude), located approximately 1200 m of distance (horizontal line) from the experimental area (**Figure 1**).

#### **2.2 Experimental design and treatments**

Experimental design was randomized blocks in a factorial scheme 4x4, with 4 replications, totalizing 64 experimental parcels. Four irrigation water depths were applied (L1 = 25%, L2 = 50%, L3 = 75% and L4 = 100%) as a function of soil water depletion taking into consideration the value of soil water retention capacity and four levels of electrical conductivity: S1 = 0.60 dS m�<sup>1</sup> ; S2 = 3.00 dS m�<sup>1</sup> ; S3 = 5.40 dS m�<sup>1</sup> and S4 = 7.80 dS m�<sup>1</sup> ; applied on forage palm Orelha de Elefante (*O. stricta* (Haworth) Haworth).

*Effect of Irrigation Depths and Salinity Levels on the Growth and Production of Forage… DOI: http://dx.doi.org/10.5772/intechopen.104985*

#### **Figure 1.**

*Mean air temperature conditions (mean temperature), relative humidity of air (mean temperature), total precipitation (Ptotal) and reference evapotranspiration (ET0) of the region in analysis during the research.*


#### **Table 1.**

*Physical characterization of soil.*


#### **Table 2.**

*Chemical characterization of soil (fertility).*

The research was carried out in 120 L pots open to the sky, with a space of 1.30 m between rows and 1.00 m between plants and one plant per pot. The pots were used as drainage lysimeters.

A layer of crushed stone (2.40 kg) was put at the bottom of each pot, covered with a texture fabric, a layer of coarse sand (2.10 kg) and 170 kg of soil (0.268 m<sup>3</sup> ). Soil analysis was performed in the Irrigation and Salinity Laboratory (LIS) of The Federal University of Campina Grande. Physical characterization (**Table 1**), Fertility (**Table 2**) and Salinity (**Tables 3** and **4**) were evaluated.

#### **2.3 Plant material and fertilization**

The cladodes of forage palm (Orelha de Elefante Mexicana) evaluated in the experiment were obtained from the Experimental station Lagoa Bonita, National Institute of Semi-arid (INSA), located in the countryside of the municipality of


#### **Table 3.**

*Chemical characterization of soil (salinity).*


#### **Table 4.**

*Initial chemical characterization of soil (salinity).*

Campina Grande – PB. Secondary cladodes with a homogeneous height were used. After cutting cladodes, they remained during 15 days in shadow to shed moisture and heal injures. Cladodes were treated with bordeaux mixture 48 hours before sowing, in order to prevent fungi and bacteria [7, 8]. Planting was performed at a 45° angle to avoid the fall of the rackets, considering the wind factor in east-west.

Fertilizations followed the recommendations of Novais, Neves and Barros [9] for experiments using urea, potassium chloride (KCl) and monoammonium phosphate (MAP), keeping equal doses in every pot. Fertilization was divided in 30% as basal dressing and the difference was divided and applied every month during the experiment.

#### **2.4 Irrigation**

Treatments were carried out at 108 days after sowing and concluded at the end of the cycle (442 days after sowing), totalizing 334 days of application, period necessary for establish forage palm.

Water depths were determined based on water retention capacity of soil (D1 = 25%, D2 = 50%, D3 = 75% and D4 = 100% of WRC), with a variable irrigation frequency and determined by the depletion of soil water content that corresponded to the water depths to be replaced. Water retention capacity was determined by water availability in soil, according to Salassier, Soares & Mantovani [10]:

$$\text{AWC} = (\text{FC-WP}) \ge \rho \tag{1}$$

$$\text{WRC} = \text{AWC} \ge \text{Z} \tag{2}$$

Where, AWC: Available water capacity in soil (mm cm�<sup>1</sup> of soil); FC – field capacity (% of weight); WP: wilting point (% of weight); *ρ<sup>b</sup>* – bulk density (g cm�<sup>3</sup> ); WRC – water retention capacity (mm) and Z – effective root system depth (mm).

Variation of water storage was determined based on Lopes et al. [11] at 0.15 m:

$$
\Delta \mathbf{TWS} = (\theta\_2 \mathbf{-} \theta\_1) \ge \mathbf{z} \tag{3}
$$

Where, ΔTWS – water storage variation (mm d�<sup>1</sup> ); θ<sup>2</sup> – average humidity at the end time (cm<sup>3</sup> cm�<sup>3</sup> ) corresponding to the day; θ<sup>1</sup> – average humidity at the initial

*Effect of Irrigation Depths and Salinity Levels on the Growth and Production of Forage… DOI: http://dx.doi.org/10.5772/intechopen.104985*

time (cm3 cm�<sup>3</sup> ) corresponding to humidity of the previous day; z – depth for balancing.

For the evaluation of the reduction in moisture as the function of water retention capacity perceptual, daily collections of soil samples were performed at 15 and 30 cm (corresponding to the radicular zone of great distribution of forage palm *O. stricta* (Haworth) Haworth), in order to determine moisture using electric oven [12].

Based on the physical analysis of soil, soil-water characteristic curve was determined and adjusted by van Genuchten model using the computer program *Soil Water Retention Curve fit* (SWRT fit), considering granulometry (%) and density particles values (g cm�<sup>3</sup> ) [13]. Thus, water content in soil (humidity in a given volume cm3 cm�<sup>3</sup> ) was determined as a function of humidity, obtained by gravimetry method, using an electric oven in the radicular system depth.

Water was prepared by adding commercial sodium chloride (without iodine), calcium chloride and magnesium chloride in the proportions 7:2:1, respectively, in order to increase electrical conductivity of water, according to the methodology proposed by Richards [14]. The dilutions were performed in four 500 L polyethylene pots, in which, every pot corresponded to a different saline level. The water used came from the Water and Sewerage Company of Paraíba (CAGEPA). Chemical water analyses were performed in the Irrigation and Salinity Laboratory (LIS/UFCG) (**Tables 5** and **6**).

#### **2.5 Growth variables**

Growth variables were analyzed at the end of the cycle, at 334 days after treatments application or 442 days after sowing, according to the methodology proposed by Borges et al. [15] and consisted of: length of primary cladode (PCL, cm) and secondary cladode (SCL, cm); width of primary cladode (PCW, cm) and secondary cladode (SCW, cm); perimeter of primary cladode (PCP, cm) and secondary cladode (SCP) and thickness of primary cladode (PCT, mm) and secondary cladode (SCT, mm). A measure type was used for height, width, length and perimeter; and a digital caliper for thickness, 0.05 mm precision.

Primary (PCA cm2 ) and secondary (ACS, cm<sup>2</sup> ) cladode areas were estimated considering cladode width and length, following the methodology proposed by Santos et al. [16] for forage palm (*Opuntia*):

$$\text{CA} = \text{CL} \ge \text{CW} \ge 0.693 \tag{4}$$

CA – cladode area (cm<sup>2</sup> ); CL – cladode length (cm); CW – cladode width (cm) and; 0.693 – correction factor as a function of cladode.


**Table 5.**

*Chemical parameters of rainy water used in the experiment.*


**Table 6.**

*Chemical parameters of tap water used in the experiment.*

#### **2.6 Production variables**

At 442 days after sowing, or 334 days after treatments application, production evaluations were performed. Number of primary cladodes (NPC), secondary cladodes (NSC) and total number of cladodes (TNC) per plant were obtained by direct counting, according to Borges et al. [15].

#### **2.7 Statistical analyses**

Growth and production data were submitted to the distribution normality test (Shapiro–Wilk test) at 5% probability. The variables that did not demonstrate distribution normality were altered using quadratic root. After normality test, variance analysis by F test at 1 and 5% probability was used for isolate irrigation depths factors and for the interaction depths versus salinity.

Data that presented significant effects were adjusted by polynomial, linear and quadratic regression. Statistical analyses (Shapiro–Wilk and F test) were performed using Sisvar software, 5.6 version [17].
