Production of basil (Ocimum basilicum L.) under different soilless cultures

The experiment was conducted at Agricultural and Bio-Systems Engineering Department, Faculty of Agriculture Moshtohor, Benha University, Egypt (latitude 30° 21′ N and 31° 13′ E), during the period of May to July, 2019 season under the university guidelines and legislation. Basil seedlings were sown in the plastic cups (7 cm diameter and 7 cm height) filled with peat moss. The cups were irrigated daily using water with nutrient solution (Ca(NO₃)₂, 236 g L⁻¹, KNO₃, 101 g L⁻¹, K₂SO₄, 115 g L⁻¹, KH₂PO₄, 136 g L⁻¹, MgSO₄ 246 g L⁻¹ and chelates for trace elements into preacidified groundwater (from the following ppm concentration are achieved in this formulation: N = 210, P = 31, K = 234, Ca = 200, Mg = 48, S = 64, Fe = 14, Mn = 0.5, Zn = 0.05, Cu = 0.02, B = 0.5, Mo = 0.01)). Two weeks old basil seedlings were planted at 9.0 plant m⁻² in the experimental tanks. These seedlings were planted according to the permission of Benha university rules and legislation.

Culture systems description

Figure 1a,b show the experimental setup. It shows the system which consists of hydroponic system, aeroponic system, soilless substrate, solution system and pumps.

The hydroponic system (Deep Water Culture (DWC)) consists of three rectangular polyethylene tanks that used for basil plants culture. Dimensions of each tank are 80 cm long, 40 cm wide and 30 cm high. The slope of hydroponic tanks was 2% and stand 1 m high above the ground. The hydroponic tanks were covered with foam boards to support the plants. Each hydroponic tank provided with an air blower (Model NS 780—Flow Rate 850 L h⁻¹—Head 1.5 m—Power 15 W, China) to increase dissolved oxygen concentrations. The solution was circulated by a pump (Model First QB60—Flow Rate 30 L min⁻¹—Head 25 m—Power 0.5 hp, China) from the solution tank to the upper ends of the hydroponic tanks. Small tubes (16 mm) were used to provide tanks with solution in a closed system.

Aeroponic system consists of three rectangular polyethylene tanks that used for basil plants culture. Dimensions of each tank are 80 cm long, 40 cm wide and 50 cm high. The aeroponic tanks were established 1 m above the ground. Each aeroponic tank was divided into two parts, the lower part was made from polyethylene and the upper part was made from wood. The aeroponic tanks were covered with foam boards to support the plants. Each aeroponic tank was provided with two fog nozzles (Model M3MNWT5M – Orifice 2 mm – Discharge 8 L h⁻¹, India) located at the bottom of the tank sprayed nutrient solution into the tank in order to keep the roots wet. Small tubes (16 mm) were used to provide aeroponic tank with solution in a closed system.

Soilless substrates consist are placed in three rows are 2 m long. Each row consists standard peat moss slabs (1.00 m × 0.20 m × 0.075 m). Basil plants were placed on row peat moss slabs with a drip irrigation system. There were three plants per slab giving a mean density of 9.0 plant m⁻². Each plant was fed by a single drip.

The circular polyethylene tank of the nutrient solution system 500 L capacity was used for collecting the drained solution by gravity from the ends of the three systems. The nutrient solutions were prepared manually once per ten days^17,18 by dissolving appropriate amounts of Ca(NO₃)₂, 236 g L⁻¹, KNO₃, 101 g L⁻¹, K₂SO₄, 115 g L⁻¹, KH₂PO₄, 136 g L⁻¹, MgSO₄ 246 g L⁻¹ and chelates for trace elements into preacidified groundwater (from the following ppm concentration are achieved in this formulation: N = 210, P = 31, K = 234, Ca = 200, Mg = 48, S = 64, Fe = 14, Mn = 0.5, Zn = 0.05, Cu = 0.02, B = 0.5, Mo = 0.01). pH and Electrical Conductivity (EC) were further adjusted to 6.5–7.0 and 1.4–1.8 dS m⁻¹, respectively, after salt addition. The average air ambient temperature was 25.97 ± 4.37 °C and the average water temperature was 24.03 ± 3.92 °C. The average relative humidity was 65.4% and the light intensity was 338.55 ± 40.06 W m⁻².

Measurements

Three plants sample were taken during the vegetative and flowering stages (four and seven weeks after transplanting, respectively) for growth measurement and chemical analysis. Plant height, root length and the fresh and dry weight of leaves, stems and roots were determined. After measuring fresh mass, the plants were oven dried at 65 °C until constant weight was reached¹⁹. Total content of macro elements was evaluated after being digested²⁰. Nitrogen was determined by Kjeldahl digestion methods²¹. Potassium, Calcium and magnesium were determined by Photofatometer (Model Jenway PFP7—Range 0—160 mmol L⁻¹, USA) and phosphorus (P) was determined colorimetrically method²². The content of oil was determined in different organs: leaves, stems and inflorescences according to²³.

Water samples were taken, at inlet and outlet of the culture units for measuring nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were measured every week at 10 am during the experimental period.

Total production cost

The cost calculation based on the following parameters was also performed:

Fixed costs (Fc)

Depreciation costs (D_c)

where D_c is the depreciation cost, EGP (Egyptian pound) year⁻¹. ($ = 15.63 EGP). P_d is the system price, EGP. S_r is the salvage rate (0.1Pd) EGP. L_d is the system life, year.

Interest costs (In):

where I_n is the interest, EGP year⁻¹. i_n is the interest as compounded annually, decimal (12%). Shelter, taxes and insurance costs (Si).

Shelter, taxes and insurance costs were assumed to be 3% of the purchase price of the automatic feeder (Pm).

Then:

Variable (operating) costs (Vc)

Repair and maintenance costs (R_m):

Energy costs (E):

where E is the energy costs, EGP h⁻¹. EC is the electrical energy consumption, kWh. EP is the energy price, 0.57 EGP kW⁻¹.

Labor costs (L_a):

where L_a is the Labor costs, EGP h⁻¹. Salary of one worker = 10 EGP h⁻¹. No. of workers = 1.

Then:

Total costs (T_c)

Table 1 shows the input parameters of calculate total production costs of basil plants grown in different soilless systems.

Nutrients consumption rate

The Nutrients consumption rate were calculated as the differences between the nutrients at inlet and outlet of culture units by the following formula²⁴:

where C_Nc is the nutrients consumption rate, mg day⁻¹ plant ⁻¹. Nc_in is the nutrients at inlet of the hydroponic unit, mg L⁻¹. Nc_out is the nutrients at outlet of the hydroponic unit, mg L⁻¹. Q is the discharge, L h⁻¹.

Model development of nutrient consumption

Model assumptions:

• N, P, K, Ca and Mg are the nutrients used in study.

• The plants are uniformity distributed in the solution, so they work as a uniform sink for water and minerals with space at any time.

• The root systems are uniformly dispersed in the solution with uniform root length density at any time.

• The whole root system uptake characteristics are uniform.

• Water losses by evaporation are negligible.

The simplest nutrient consumption models relate the nutrient consumption to the concentration gradient using some sort of proportionality factor such as root permeability or conductivity^25,26. The nutrient consumption was determined by using the following equation:

where NC is the nutrient consumption, mg plant⁻¹ day⁻¹. ∆C is the concentration gradient, mg plant⁻¹ day⁻¹. a_NC is the proportionality factor, dimensionless.

A similar model of nutrient consumption takes into consideration the differing effects caused by variations in root growth stage. Assuming that growth follows a first order differential equation and assuming that the root growth is exponential²⁷, then Eq. (11) can be derived. This equation is presented in similar form to Eq. (10) and use the following equation:

where C_planto is the concentration of the nutrients in the plant at time t₀, mg plant⁻¹. A_r is the root surface area at time t, cm² plant⁻¹. A_r0 is the root surface area at time t₀, cm² plant⁻¹.

Root surface area was calculated from root length and mean root radius using the following equation:

The root length increment using the following equation²⁸:

where ∆L_r is the root length increment, cm day⁻¹. ∆DW_root is the daily amount of root dry mass increment, g day⁻¹. v is the ratio of root length and mass of roots, cm g⁻¹.

The daily amount of dry weight of roots is calculated from the following equation²⁹:

where LAI is the leaf area index.

Leaf area index was changed in the same proportions as root length density to maintain a constant ratio between roots and shoots. The leaf area index is calculated from the following equation³⁰:

where LAI_max is the maximum leaf area index. K₂ and k₁ are the coefficients of the growth functions.

All computational procedures of the model were carried out using Excel spreadsheet. The computer program was devoted to mass balance for predicting the nutrients consumption. The differences between the predicted and measured values were evaluated using RMSE indicator (root means square error) which is calculated using the following equation:

The parameters used in the model that were obtained from the literature are listed in Table 2. Figure 2 shows flow chart of the model.

Statistical analysis

Three replicates of each treatment were allocated in a Randomize Complete Block Design (RCBD) in the system. Data were analyzed one-way ANOVA (analysis of variance) using statistical package for social sciences (spss v21). Means were separated using New Duncan Multiple Range Test (DMRT). Data presented are mean ± standard division (SD) of four replicates.

Source: Ecology - nature.com