Chapter 3: The responses of selected crop species to brewery effluent irrigation
3.2 Methods and materials
3.2.1 Experimental species
Three plants species were grown for three months to determine which plant reduced the build-up of salt in the soil when irrigated with BE. Thirty saltbush (Atriplex nummularia) seedlings were purchased from a commercial nursery (Mountain herb estate, Pty Ltd,
Pretoria). Japanese millet (Echinochloa esculenta) and lucerne (Medicago sativa) seeds were obtained from a commercial seed supplier (Agricol Pty Ltd, Port Elizabeth) and were planted in polystyrene planter trays, filled with a mixture of 40% soil and 60% compost. These seeds
85 were germinated and allowed to grow for three weeks. Similar sized plants for each plant species were used in the experiment.
3.2.2 Treatments
The four crop treatments used in this experiment were as follows: lucerne, millet, saltbush and No Crop. The No Crop treatment served as the control. Each crop treatment was
irrigated with post-PFP effluent, where the pH was adjusted with 98% sulphuric acid (Protea Chemicals Pty Ltd, South Africa) to 6.5 or left unadjusted (Table 3.1). This resulted in eight experimental treatments being tested (Table 3.1).
Table 3.1 The eight treatments (T1-T8) used in this experiment.
Crop pH not adjusted pH adjusted to 6.5
Saltbush T1 T2
Millet T3 T4
Lucerne T5 T6
No Crop T7 T8
3.2.3 Experimental system
Plants were grown out doors in 23 l pots (Figure 3.1). These pots were filled with the same top soil (oxidic sandy loam, 5 - 10% silt, 20 - 25% clay and 65 - 70% sand) used in the experiment in Chapter 2. One saltbush plant was planted in each pot and 10 millet or lucerne plants were planted in each pot (Figure 3.1). Experimental treatments and their replicates were applied to pot using a complete randomisation design.
86
Figure 3.1 Saltbush, lucerne and millet plants eight weeks after planting (left) and the 40 pot experimental system 12 weeks after planting (right).
3.2.4 Irrigation regime
Plants were irrigated with one litre of post-PFP BE two to three times a week, depending on the moisture content of the soil, according to the method described in Chapter 2 (Section 2.2.4). The maximum amount of water irrigated at one time was one litre. This was done to ensure that leaching did not occur; water was not observed draining out the bottom of the pots after irrigation. However, after heavy rainfall events water was noticed leaching out of the bottom of the pots. In total each pot received 212 mm of irrigation water and 78 mm of rain during the twelve week growth trial.
3.2.5 Data collection
Irrigation water parameters
The water quality parameters measured during the experiment included ammonia, nitrite, nitrate, phosphate, chloride, chemical oxygen demand (COD), pH and electrical conductivity
87 (EC). These parameters were measured before each irrigation using the same equipment and techniques described in Chapter 2 (Section 2.2.5).
Plant productivity
At the beginning of the trial the mass of each plant planted in the pots was recorded (0.1 g).
At the end trial the mass of the each plant was also recorded (0.1 g). The height and width of plants was recorded (1 mm accuracy) at the start of the trial and every four weeks until the end of the trial. Chlorophyll concentration index (CCI) readings were recorded at the start of the trial and every four weeks until the end of the experiment, on the uppermost fully expanded leaf of each plant (CCM-200 Plus Chlorophyll Content Meter, Opti-Sciences Inc., USA). At the end of the trial three pots from each treatment were randomly selected and leaves from the plants in the pots were sent to a commercial analytical laboratory (BemLab Pty Ltd, Strand, South Africa). Therefore three leaf samples per treatment were analysed. These samples were tested for N, P, Na, Cl, K, Al, Ca, Cu, Fe, Mn, Mg and Zn content.
Photographs of the plants and stress symptoms of the plants were described and recorded to determine if the plants were experiencing any nutrient deficiencies or diseases. Daily temperature and rainfall data were recorded using a rainfall gauge situated next to the experiment and a thermometer (Hanna, HI 991300, United Kingdom).
Soil monitoring
The physical soil properties recorded included bulk density, moisture content, air filled porosity, infiltration rate and mean weight diameter (MWD). Each property was measured
88 at the start and end of the trial in every pot. The same methods and equations used to calculate the above properties in Chapter 2 (Section 2.2.5) were used in this experiment.
The chemical soil properties recorded included pH, EC, cation exchange capacity (CEC), C, NH4, P, Na, Cl, K, Ca, Cu, Mn, Mg and SAR. The pH and EC of the soil was recorded in each pot at the start and end of the trial according to the methods described in Chapter 2 (Section 2.2.5). At the beginning of the trial 10 samples were randomly taken from the soil before it was placed into the pots. At the end of the trial three samples were analysed per treatment, where a sample was soil from one pot. These samples were analysed for CEC, C, NH4, P, Na, Cl, K, Ca, Cu, Mn and Mg (BemLab Pty Ltd, Strand, South Africa). Sodium
adsorption ration was calculated using the same formula described in Chapter 2 (Section 2.2.5).
3.2.6 Statistical analysis
The same statistical analysis used in Chapter 2 (Section 2.2.6) was used to analyse the data in this experiment.