51    IRRIGATION OF PASTURE WITH MEAT-PROCESSING
PLANT EFFLUENT
J.M. Russell, Chemist
R.N. Cooper, Section Leader
Meat Industry Research Institute of New Zealand (Inc.)
Hamilton, New Zealand
INTRODUCTION
In New Zealand many meat-processing plants are located in rural areas. As a result these plants
often must construct and operate their own effluent treatment plants. Irrigation of wastewater is an
attractive treatment option in many of these rural localities because: 1) suitable land areas are
available; 2) there is no surface, point-source discharge of treated effluent; 3) construction and
operating costs are often similar to other treatment technologies such as lagooning or physico-
chemical treatment; 4) there is an economic return in the form of livestock or crops from the
treatment site; and 5) some or all of the nutrients in the effluent are recovered.
Meat-processing plant effluents contain moderate concentration of the plant nutrients N, P and K.
For example, the effluent produced by a large New Zealand plant killing 10,000 lambs and 800 cattle
per day and operating for 200 days a year could contain each year 2 x 10' kg N, 3 x 104 kg P and 1.6
x 105 kg K.
Two approaches to effluent irrigation can be envisaged. The first is to apply the effluent at such a
rate that all nutrients are utilized efficiently. In this case shortfalls in the application of some nutrients
would be made up by supplemental fertilizer application. Under a farming regime growing grass for
hay, the nutrient uptakes of N, P and K are about 350, 40 and 200 kg/ha/yr, respectively.1 Using the
annual nutrient production figures given in the previous paragraph, the calculated land areas required
to use the nutrients in the meat plant effluent would be 570 ha, 750 ha and 800 ha for N, P and K,
respectively. This suggests a design area of 800 ha with supplemental N and P additions. If the area
were grazed, an even larger area would be required. Reticulation and management of such a large
irrigation scheme may be difficult.
The second approach to effluent irrigation is to apply the effluent at a rate in excess of herbage
requirements. To ensure that no adverse effects occur with this approach, the effect of irrigation on
the crops, soil, groundwater and grazing animals must be monitored and compared with the effects of
alternative land uses in this area.
Our research has been directed at defining an upper limit for nutrient application by means of
laboratory and field trials. The results from the laboratory-scale trials have been described elsewhere. 2'3'4 This paper examines the effects of 4 years application of meat plant effluent at average
loading rates of 605 and 1215 kg N/ha/yr and 3 years' application at an average rate of 2600 kg
N/ha/yr on the pasture, groundwater and soil, under a non-grazed (harvested) management regime.
EXPERIMENTAL
Experimental Plots Sixteen 5-m2 experimental plots were established on a Horotiu sandy loam
(Entic Dystrandept, medial over sandy skeletal, thermic) in the Waikato basin approximately 15 km
north-west of Hamilton, New Zealand. A 1-m deep trench was dug around each plot, a PVC membrane was placed in the trench and the trench was then back-filled with soil. This membrane extended
approximately 15 cm above ground level preventing runoff and lateral movement of water. Primary-
treated meat-processing effluent was applied every other week at average nitrogen loadings of 0
(control), 605 (I,) and 1215 (I2) Kg/ha/yr for the period January 1982 to May 1986 and at 2600 (I3) kg
N/ha/yr between January 1982 and January 1985. There were 4 replicate plots at each loading.
Samples of effluent were collected and analyzed for chemical oxygen demand (COD), total Kjeldahl
nitrogen (TKN), ammonia-nitrogen (NH3-N), fat, total suspended solids (TSS) and total phosphorus
(TP) according to Standard Methods.^
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