Farm-scale nitrogen, phosphorus, potassium and sulfur balances and use efficiencies on Australian dairy farms

Abstract

Abstract. Efficient and effective nutrient management decisions are critical to profitable and sustainable milk production on modern Australian dairy farms. Whole-farm nutrient balances are commonly used as nutrient management tools and also for regulatory assessment on dairy farms internationally, but are rarely used in Australia. In this study, nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) imports and exports were measured during a standardised production year on 41 contrasting Australian dairy farms, representing a broad range of geographic locations, milk production, herd and farm size, reliance on irrigation, and soil types. The quantity of nutrients imported varied markedly -with feed and fertiliser generally the most substantial imports -and were principally determined by stocking rate and type of imported feed. Milk exports were the largest source of nutrient exports. Nitrogen balance ranged from 47 to 601 kg N/ha.year. Nitrogen-use efficiency ranged from 14 to 50%, with a median value of 26%. Phosphorus balance ranged from -7 to 133 kg P/ha.year, with a median value of 28 kg P/ha. Phosphorus-use efficiencies ranged from 6 to 158%, with a median value of 35%. Potassium balances ranged from 13 to 452 kg K/ha, with a median value of 74 kg K/ha; K-use efficiency ranged from 9 to 48%, with a median value of 20%. Sulfur balances ranged from -1 to 184 kg S/ha, with a median value of 27 kg S/ha; S-use efficiency ranged from 6 to 110%, with a median value of 21%. Nitrogen, P, K and S balances were all positively correlated (P < 0.001) with stocking rate and milk production per ha. Poor relationship between P, K and S fertiliser inputs and milk production from home-grown pasture reflected the already high soil fertility levels measured on many of these farms. The results from this study demonstrate that increasing milk production per ha will be associated with greater nutrient surpluses at the farm scale, with the potential for greater environmental impacts. We suggest that simplified and standardised nutrient balance methodologies should be used on dairy farms in Australia to help identify opportunities for improvements in nutrient management decisions and to develop appropriate industry benchmarks and targets.

Developing the EU Farm Accountancy Data Network to derive indicators around the sustainable use of nitrogen and phosphorus at farm level

“…Due to the lack of published results at a nationally representative level direct international comparisons are difficult. Comparison with smaller scale international studies suggest N and P balances in this study are relatively low, NUEs are quite typical and PUE are relatively high for the dairying systems in this study 3 (Aarts 2003;Groot et al 2006;Nevens et al 2006;Raison et al 2006;Bassanino et al 2007;Cherry et al 2012;Gourley et al 2012).…”

“…Phosphorus use efficiency can be considerably higher than that of N (e.g. Gourley et al 2012), in part, at least, due to the greater potential for loss of N to air and water at all stages of the production system. Specialist sheep had the highest mean PUE at 97.7%, however the median value for specialist sheep was the second lowest at 57.9%.…”

“…The farm gate P balance across all farm systems averaged 4.7 kg P ha -1 (Table 3). This is relatively low by international standards (Haygarth et al 1998;Raison et al 2006;Gourley et al 2012). In contrast to N, P management accounts for soil pools of plant-available P and these soil pools can be used to supply the P required for crop growth.…”

“…This doesn't take account of symbiotic N fixation, atmospheric N deposition or changes in soil organic matter stocks and hence does not consider all inputs and outputs (Godinot et al 2014). Gourley et al (2012) argue that while farm-level N balance and NUE can greatly assist management decision, P balance and use efficiency is less useful unless combined with soil fertility levels to account for accumulation or depletion trends. Hence, the approach could be developed further if soil test results for sample farms could be incorporated into the analysis.…”

“…Despite the additional N export in milk from milk-producing systems, the greater import of fertiliser and feed N to support the higher stocking rates associated with these systems leads to greater N surpluses. This highlights the close link between stocking rate and nutrient source pressure on environmental quality in livestock-based production systems (Gourley et al 2012). However, it should be noted that nutrient source pressure does not necessarily equate directly to nutrient losses to water or air, however, as this will be dependent on a range of management and biophysical factors Table 2).…”