Nutrient imbalances of smallholder dairy farming systems in Indonesia: The relevance of manure management

Nitrogen (N) and phosphorus (P) imbalances from dairy farming systems (DFSs) lead to environmental problems, such as eutrophication. This study aimed to quantify nutrient deficits and losses from DFSs with different manure management systems (MMSs) at the farm level and at the levels of its sub-systems. We compared NP balances of 30 farms with four different MMSs: applying manure directly on forage land, without treatment (ADL), selling or exporting manure (SEL), using manure for anaerobic digestion (ADI), and discharging manure (DIS). NP balances were calculated based on differences between in- and outflows. Results showed that N balances at DFS averaged 222 kg N farm−1 yr−1 and did not differ between MMSs. Average P balances at DFS differed between MMSs; balances were highest for DIS (83 kg P farm−1 yr−1), and lowest for SEL (−25 kg P farm−1 yr−1). Soil P balances did not differ between MMSs and were mostly negative, except for four ADL farms. Annually, all dairy farms in Lembang region are estimated to cause a nutrient loss of ∼1061 tons of N and ∼ 290 tons of P, and extract 8 tons of P from soils. Overall, high NP imbalances are caused by discharging manure into the environment. To reduce imbalances, collection and on-farm use of manure must be improved, and excess manure needs to be sold to crop farms. The carrying capacity for high-input high-output dairy farming is determined by the capacity of arable farms to apply the manure surpluses.