**3. Materials and methods**

#### **3.1 Experimental site and environmental conditions**

Series of experiments were conducted to address the themes of the Book Chapter.

An experiment was conducted to examine the effects of shading, watering regimes and mycorrhizal inoculation on the growth and development of oil palm seedlings in the nursery in the dry season. A series of experiments were conducted at the Nursery and Field (Plantations) of the Nigerian Institute for Oil Palm Research (NIFOR), Benin City, Edo State, Nigeria between 2013 and 2018. The Nigerian Institute for Oil palm Research (NIFOR) is located in the rainforest ecological zone of Nigeria between latitude 06<sup>o</sup> 33<sup>1</sup> N and longitude 05<sup>o</sup> 37<sup>1</sup> E. Annual rainfall ranges between is 1500 to 2000 mm, average temperature ranges between 28° to 34° centigrade and relative humidity between 54 to 80%.

Age of oil palm and intercrops of Cassava, Maize and Pepper affected mixture productivity and competitive functions in alleys of 2 to 6 years old oil palm fields. Fertilizers (inorganic/organic) promoted agronomic and physiological efficiencies of N use by alley species. The trials were conducted in NIFOR Nursery and Field (Plantations) between 2013 and 2018.

*Oil Palm-Based Cropping Systems of the Humid Tropics: Addressing Production… DOI: http://dx.doi.org/10.5772/intechopen.98257*

Section A: Studies were conducted to examine the responses of oil palm seedlings to shading, irrigation and AMF inoculation with respect to growth vigor and mortality events in the nursery during dry season. Soil samples were collected from top soil under five-year fallow vegetation and were sieved to remove stones and pebbles. Black polythene bags (1400 cm<sup>2</sup> ) were filled with 6 kg of the soil media and arranged in rows 90 cm both in the open sun and in the shade. The drip lines were placed along the rows after ten days. Two months old oil palm seedlets/ plantlets (*Tenera*) were obtained from NIFOR Pre-nursery and transplanted into the 6 kg pots (black polythene bags:1400 cm2 ) were filled with top soil obtained from fallow vegetation (secondary forest soil) and arranged in filed plots. Shades measuring 6 x 6 m was constructed using bamboo sticks and palm fronds were used to cover the top and sides. Gravity drip irrigation system was adopted using 200 liter capacity bucket placed on a 1.5 m wooden stand; drippers were installed to apply water (2 liters per palm application). Thermometers each were installed in the shade and in the open sun for the measurement of air temperature weekly and fortnightly intervals.

### **4. Soil and plant measurements**

Data were obtained on growth parameters, pattern of leaf production and senescence, weekly measurement of soil moisture content using a soil moisture sensor while thermometers were installed under shade and in no shade condition to measure soil and air temperatures. At the end of the experiment, 10 plants were gently uprooted and the root washed and shade dried for root measurements. Mycorrhizal Colonization of Roots and Mycorrhizal Spore Count were determined using standard methods [25].

#### **4.1 Irrigation strategy**

Oil palm seedlings were drip-irrigated weekly and fortnightly using gravity-drip irrigation system to apply 2 liters of water per plant at each irrigation via point source emitters (2 l/h discharge rate) which were installed on laterals per row of seedlings. Irrigation buckets were suspended on 1.5 m high stakes to provide the required hydraulic heads [26, 27]. There was a two-day pre-irrigation treatment (1.5litres/day) following oil palm seedling transplanting, and thereafter, the weekly and fortnight irrigation treatments were imposed.

Water requirement (WR) was determined using the relation:

$$\text{WR} = \text{A x B x C x D x E} \tag{1}$$

where: WR = Water requirement (l per day/plant) A = Open Pan evaporation (mm/day) B = Pan factor (1.0, 0.7 and 0.5), C = Spacing of plant (m<sup>2</sup> ), D = Crop factor (Crop coefficient (Kc) for oil palm seedling: initial (0.43) were obtained from Allen et al. [28].

The total water requirement (TWR) was obtained using the relation:

$$\text{TWR} = \text{WR} \ge \text{No.of} \text{ Plants} \tag{2}$$

Maximum allowable deficit (MAD) for oil palm was assumed as 50% of available water storage capacity of the soil (AWC).

Irrigation water requirement is determined using average season wise pan evaporation data for the area. Pan Evaporation (EPan) data used for the experiment

were obtained from measurement using a Class-A Pan (121 cm in diameter and 25.5 cm in depth) from the Meteorological Station, Department of Meteorology & Climate Science, Federal University of Technology, Akure, Nigeria located near the plots.

The actual evapotranspiration (ETc) of oil palm seedlings the irrigation regimes was calculated with the water balance equation (Eq. (1)) [26].

$$\text{ET} + \text{I} + \text{P} + \Delta \text{S-Dp} - \text{Rf} \tag{3}$$

where, ET, is actual crop evapotranspiration (mm); I, the amount of irrigation water applied (mm); P the precipitation (mm); ΔSW, changes in the soil water content (mm); Dp, the deep percolation (mm); Rf, amount of runoff (mm). Since the amount of irrigation water was controlled, deep percolation and run off were assumed to be negligible.

Soil water measurements were taken throughout the growing season using the gravimetric method.

The volume of water required per plant (irrigation requirement, IR) was estimated as:

$$\mathbf{I}\_{\rm R} = \mathbf{E} \mathbf{T}\_{\rm peak} \* \mathbf{area} / \mathbf{crop} / \mathbf{E}\_{\rm n} \tag{4}$$

where En is emitter uniformity for drip irrigation system (0.94) and area per crop.

Peak evapotranspiration (ETpeak) rate for the crop under drip irrigation treatment was estimated as:

$$\text{ET}\_{\text{peak}} = \text{ETo} \ast \text{P} / 85\tag{5}$$

where ETpeak is peak evapotranspiration rate for the month or period, ETo is the reference evapotranspiration, for the month/period (e.g. 5.1 mm/day), P is the proportion of total land area covered by the crop leaf area (cm) which is assumed 80% (after [26]).

Crop evapotranspiration (ETa) was also calculated using data obtained from FUTA in the formula of Doorenbos and Pruitt [29] and [28] in the form:

$$\text{ETa} = \text{KcETo} \tag{6}$$

where ETo is potential evapotranspiration and Kc is the crop coefficient.

Weather variables at site of experiment during crop growth cycle (soil and air temperatures, vapor pressure deficit (vpd), solar radiation, wind speed will be monitored from Meteorological Observatory, 500 m from site of experiment). Data collected were subjected to analysis of variance (ANOVA) while significant treatment means were separated using the Duncan Multiple Range Test (DMRT).

Section B: Experiments were conducted between 2016 and 2017 cropping seasons to examine the effects of age of oil palm in plantation on the growth, competitive interactions and mixture productivity of cassava, maize and pepper in oil palm-based strip intercropping system in the rainforest of Nigeria. The studies were conducted on 2, 3, 4 and 5 years old oil palm fields for oil palm field which were established in the fields during 2014, 2015, 2016 and 2017 using *Tenera (hybrid)*.

The experiment was 3 x 3 factorial combination of ages (2, 3, 4 and 5 years) of oil palm plantations and 3 species of arable crops arranged in a split-plot design interrow spaces (alley) between oil palm plans constitute the main plot and arable crops species as sub-plot treatment. Treatments were replicated 3 times. The

*Oil Palm-Based Cropping Systems of the Humid Tropics: Addressing Production… DOI: http://dx.doi.org/10.5772/intechopen.98257*

planting space for oil palms was 9 x 9 m triangular with eight (8) stands per field plot. The plots were spaced by 1 m between plots and replicates (inter row) and 1 m at the borders. Strip intercropping system was adopted in the experiments. Spacing cassava, maize and pepper was 1 x1m given a plant population of 141 plants per plot.

### **4.2 Data collection**

Oil palm data collections include number of leaves, canopy extent and number of fresh fruit bunch (FFB). These data were collected quarterly. The canopy extent was recorded in meters and canopy spread calculated using the multiplication values of the palm measured in two dimensions of 'North–South spread' and 'East– West spread' and canopy volume of oil palm trees. Oil palm canopy volume and ground coverage by Tripathy et al. [30] and canopy spread (Cs) was estimates as:

$$\mathbf{Cs} = \mathbf{Ns} \ge \mathbf{EW} \tag{7}$$

where: Cs = canopy spread, NS = North–South, EW = East–West.

Oil palm yield traits were sampled which include the number of fresh fruit bunches (FF) and weight of fresh fruit bunch (FBB) and total bunch yield per treatment plots. The growth and yield data were collected from ten tagged plants randomly selected from the experimental plots. Data collected include number of leaves, canopy extent and number of fresh fruit bunch (FFB). Palm yield traits: yield per palm, number of fresh fruit bunches (FF) and weight of fresh fruit bunch/ palm and total palm yield/experimental plot. At harvesting, cassava tuber weight, maize seed weight and pepper fruit weight for each individual plant was according to estimate – the intra- land variability. Biomass yield, dry above ground biomass at harvest and final yield were determined from the sampled plants.

#### **4.3 Indicators of crop mixture productivity and competitive interaction**

Different measures or indices of productivity have been developed to determine the productivity of crops in crop mixtures. These indices include relative yield, relative yield total and land equivalent ratio, aggressivity. Relative yield is the biomass or yield of a species in mixture or intercropping expressed as a ratio of its yield in monoculture [31]. Relative yield total (RYT) is the sum of the relative yields of the species in mixture expressed as a ratio of its yield in monoculture [31]. Land equivalent ration (LER) is an indication of biological efficiency of intercropping in use of environmental resources compared to the sole crop [32]. The percentage land saved from intercropping was estimated using the formular described by Willey [14]. Aggressivity is a measure of competitive relationships between two crops in mixed cropping [21] and an important competition function to determine the competitive ability of a crop when grown in association with another crop [33]. This index compares the yields between intercropping and monoculture, as well as their respective land occupancy [34, 35].

Section C: Studies were conducted to examine the effects of fertilizer (NPK compound fertilizer, poultry manure and pelletized organic fertilizer) and age (3, 4 and 6 years) of oil palm on nutrient uptake and use efficiencies of strip intercropped cassava, maize and pepper in an oil palm-based intercropping system. Cassava, maize and pepper were strip-intercropped in the alleys of 3, 4 and 6 years oil palm fields. The fertilizers (NPK, Ferti plus and poultry manure) were respectively applied at the rate of 67.5, 168.75 and 337.5 g/plant) as determined by the soil test.

The indices of N uptake and agronomic and physiological efficiencies of N use were calculated using the procedures described in the literature [36–38]. Nutrient uptake refers to the ability of crop to extract or absorb nutrients from the soil. The uptake of nitrogen was calculated as the product of the measured N concentrations in shoot biomass and reproductive structures (fruit/seed/tuber) the weight of the biomass (shoot and reproductive structures) [37, 38]. The proportion of total plant N partitioned to the shoot is called the N harvest index (NHI). It is also defined as the percentage of grain N uptake to total plant N uptake [37]. Nutrient Use Efficiency (NUE): This is a term used to indicate the ratio between the amount of fertilizer N removed from the field by the crop and the amount of fertilizer applied. NUE is expressed in several ways as the efficiency of conversion of nutrient taken up by the plant into crop biomass. This ratio describes the efficiency of N fertilizer utilization in crop production.

Agronomic Efficiency (AE) is calculated as the unit of yield increase per unit nutrient applied. It reflects the direction of production impact of applied fertilizer and also relates to economic return. The calculation of AE requires knowledge of yield without nutrient input, so is only known when research plots with zero nutrient is been implemented on the farm [11]. AE is expressed as the efficiency of conversion of nutrient taken up by the plant into crop biomass.

Physiological Efficiency of N use (PE), is defined as the yield increase in relation to the increase in crop uptake of the nutrient in above ground parts of the plant (Dobermann [36]. Similar to AE, it needs a plot without application of the nutrient of interest to be implemented, and requires measurement of nutrient concentrations in crop biomass (shoot and reproductive structures).

The Apparent Recovery Efficiency (ARE) is the ratio of nutrient uptake to nutrient applied, it is also defined as the difference in nutrient uptake in above ground parts of the plant between the fertilizer treated and untreated crop relative to quantity of nutrient applied. Nutrient utilization efficiency (NUE) is calculated as the product of physiological and recovery efficiency. It is calculated based on the method described by Dobermann [36]. Internal Utilization Efficiency (IE) is defined as the yield in relation to total nutrient uptake. It varies with genotype, environment and management. It is an indication of the efficiency of internal nutrient conversion, which may be affected by other stresses (deficiencies of other nutrients, drought stress, heat stress, mineral toxicities, pest etc.) [36]. The total factor productivity (TFP) relates an index of output to a composite index of all inputs while Partial Factor Productivity measure relates output to a single input. Partial Factor Productivity (PFP) is a simple production efficiency expression, calculated in units of crop yield per unit of nutrient applied [36].

Data analysis: Data collected were subjected to analysis of variance (ANOVA) and significant treatment means were separated for 5% (P < 0.05) probability level.

## **5. Results and discussion**
