Sustainable utilisation of phosphorus within the dairy farm

Abstract

According to the Dairy Australia Limited 2018, dairy is Australia's 3rd largest rural industry. Also, fresh milk was sold for $2,242 million over 12 months (between February 2017 and January 2018) in Australian supermarkets. Thus, it is important to supply appropriate fodder for the milking cows through grazing pastures in dairy industries. Applying pond by-products produced by two-pond effluent treatment system, such as pond sludge, crust and effluent to the land (grazing paddock), has become a common method to enhance the recycling of nutrients within the dairy farm. This in turn yields several environmental benefits. Pond by-products provide nutrients for the plant growth and enhance the recycling of nutrients within the dairy farms. The recycling and reuse of pond by-products in dairy farms plays an essential role in the sustainable management of nutrients, particularly phosphorus (P). The purpose of this study was to investigate the variation in the P fractions contained in the pond by-products and soil treated with pond by-products within the dairy farms located in the Southern Highland dairy region, NSW, Australia. The study included three aspects: (i) identifying P fractions in various pond by-products; (ii) analysing P fractions in paddock soil treated with pond by-products; and (iii) conducting pot studies for assessing phosphorus use efficiency. This study indicated that the dairy pond sludge produced by the two-pond effluent treatment system contains significant amounts of plant available P, such as labile P and stable P. P fractionation analysis of the pond sludge showed that labile P and stable P in pond sludge was abundant with both being distributed evenly (50:50) compared to raw manure (stockpile, 80:20). The ratio of labile P and stable P is related to environmental effects on the soil and to plant growth upon land application. P fractionation of soil treated with pond sludge showed that land application of pond sludge increased all P fractions and improved soil fertility. Labile P and stable P increased by 30% and 45%, respectively, after pond sludge application. Additionally, paddocks treated with pond sludge had similar P distribution to the other paddock soil treated with other fertilisers simultaneously. The results of the pot experiment identified that ryegrass dry matter (DM) yield increased in soil treated with pond sludge. DM yield increased by 22% and 29%, respectively, in secondary pond sludge and primary pond sludge application pots compared to the control pots. Additionally, the soil applied with pond sludges was able to retain more water owing to the increased organic content. It was also found that all P fractions in soil treated with pond sludge increased at the end of the pot experiments. Potassium contained in the pond by-products in this study was relatively higher than in other studies. However, higher potassium in pond by-products did not increase grass tetany ratio in ryegrass. The distribution of the P fractions in pond sludge is affected by raw manure and pond treatment conditions. Additionally, environmental condition and P contents in pond by-products affect the distribution of P fractions in soil treated with pond sludge and effluent. Thus, the pre-analysis of the pond by-products and paddock soil is necessary to get an efficient pond sludge application rate before land application of pond sludge on the grazing paddock. Based on the findings, optimum pond sludge application rate can be determined using sequential fractionation. This in turn will help (i) to increase the dry matter yield of the grass; (ii) to reduce the potential loss of nutrient through runoff and leachate; and (iii) potentially replace the use of chemical fertiliser on dairy paddocks.

Date of Award	2019
Original language	English