WATER USE ON NON-IRRIGATED PASTURE-BASED DAIRY FARMS

Discipline: pasture/grazing; Key words: water use, water efficiency, leakage, milking parlour, pasture systems

Agriculture is the most significant water user in the world, accounting for an estimated 70% of global water withdrawals; most of this water is used for irrigation. South Africa is not much different in this context. Agricultural demand for water is expected to grow. As a consequence, where freshwater is scarce such as in large parts of the country, there should be an increased focus on improving the efficiency of water use and greater regulation of water use on environmental flows and water quality should be enforced. Water use in intensively managed, confinement dairy systems has been widely studied, but few reports exist regarding water use on pasture-based dairy farms. The objective of the study of Dr C.D. Higham and co-workers referenced below was therefore to quantify the seasonal pattern of water use to develop a prediction model of water use for pasture-based dairy farms. The study was published in the Journal of Dairy Science, Volume 100 of 2017, page 828 to 840, the title being: Water use on non-irrigated pasture-based dairy farms: Combining detailed monitoring and modelling to set benchmarks.

The authors measured stock drinking, milking parlour and total water use on 35 pasture-based, seasonal calving dairy farms in New Zealand over 2 years. The average stock drinking water was 60 litres per cow per day, with peak use in summer. On average, 26% of stock drinking water assumed to be consumed was actually lost through leakage from the water-distribution systems. Thus, the average corrected stock drinking water (equivalent to voluntary water intake [VWI]) was 36 litres per cow per day, and the peak water consumption was 72 litres per cow per day in summer. Milking parlour water use increased sharply at the start of lactation in July and plateaued in August until summer (February), after which it decreased with decreasing milk production. The average milking parlour water use between September and February was 58 litres per cow per day. The water requirements were affected by parlour type, with the rotary milking parlour water use greater than herringbone parlour water use. Regression models were developed to predict stock drinking and milking parlour water use. The models included a range of climate, farm, and milk production variables. The main drivers of stock drinking water use were maximum daily temperature, potential evapotranspiration, radiation and yield of milk and milk components. The main drivers for milking parlour water use were average per cow milk production and milking frequency. These models of water use are similar to those used in confinement (TMR) dairy systems, where milk yield is commonly used as a variable. The models presented fit the measured data more accurately than other published models and are easier to use on pasture-based dairy farms, as they do not include feed and variables that are difficult to measure on pasture-based farms.