The results from 14 field trials comparing the long-term (20 to 120 years) effects of fertilisers and manures (farmyard manure, slurry, and green manure) on crop production and soil properties are reviewed. In total there were 24 paired comparisons of the effects of manure and fertiliser. Some of the trials also contained a control (no nutrient inputs) treatment. The input of nutrients as either fertilisers or manures had very large effects (150–1000%) on soil productivity as measured by crop yields. Manured soils had higher contents of organic matter and numbers of microfauna than fertilised soils, and were more enriched in P, K, Ca and Mg in topsoils and nitrate N, Ca and Mg in subsoils. Manured soils also had lower bulk density and higher porosity, hydraulic conductivity and aggregate stability, relative to fertilised soils. However, there was no significant difference (P < 0.05) between fertilisers and manures in their long-term effects on crop production. In the context of this set of international trials, the recent evidence from the Rothamsted classical long-term trials appears to be exceptional, due to the larger inputs of manures and larger accumulation of soil OM in these trials. It is suggested therefore that manures may only have a benefit on soil productivity, over and above their nutrient content, when large inputs are applied over many years. The evidence from these trials also shows that, because the ratio of nutrients in manures is different from the ratio of nutrients removed by common crops, excessive accumulation of some nutrients, and particularly P and N, can arise from the long-term use of manures, relative to the use of fertilisers. Under these conditions greater runoff of P, and leaching of N may result, and for soils with low P retention and/or in situations where organic P is leached, greater P leaching losses may occur. The use of manures, relative to fertilisers, may also contribute to poor water quality by increasing its chemical oxygen demand. It is concluded therefore that it cannot generally be assumed that the long-term use of manures will enhance soil quality – defined in terms of productivity and potential to adversely affect water quality – in the long term, relative to applying the same amounts of nutrients as fertiliser.

The long-term effects of manures and fertilisers on soil productivity and quality: a review

Delivery and cycling of phosphorus in rivers: A review

Beneficial and detrimental effects of dietary condensed tannins for sustainable sheep and goat production—Progress and challenges

Summary


1. Many ecosystems are influenced simultaneously by multiple stressors, and the consequences of stressors are often unpredictable on the basis of knowledge of single effects. Agriculture affects streams world-wide via nutrient enrichment, elevated fine sediment and water abstraction for irrigation, but the combined impacts of these stressors are unknown.



2. We manipulated all three stressors simultaneously in an 18-day experiment and determined their individual and pair-wise combined effects on benthic invertebrates, algal biomass and leaf decay. We added nutrients (phosphorus plus nitrogen) and/or fine sediment (grain size 0·2 mm) to 18 experimental stream channels (dimensions 250 × 15 × 15 cm) supplied with water from a nearby stream. Three sediment and three nutrient treatments (high, intermediate, natural) were applied to each of six channels while flow was reduced by 80% in half the channels. Invertebrates (composition, abundance) and algae (chlorophyll a) were assayed using ceramic tile substrata and leaf decay was assayed using bundled leaves of a native shrub. Invertebrates colonizing leaf packs were also sampled.



3. Effects of sediment addition and flow reduction on biological response parameters were twice as common as nutrient enrichment effects. Nutrient enrichment increased total invertebrate abundance on tiles, algal biomass accrual and leaf decay rates, whereas both sediment addition (at the highest level) and flow reduction had mostly negative effects (e.g. reduced algal biomass, invertebrate abundance and/or taxonomic richness).



4. Stressors interacted often, and interactions between sediment and flow were particularly common. The negative impact of added sediment on aquatic biota was stronger at reduced flow, especially on tile substrata that were more exposed to the current than leaf-pack substrata.



5. Synthesis and applications. Our key findings imply that abstracting water from a stream already subjected to high fine sediment inputs may have far worse effects on the invertebrate fauna than abstraction from a similar stream with lower sediment levels. Aquatic resource managers should be aware of this important interaction between multiple stressors.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2664.2010.01809.x

Multiple stressors in agricultural streams: interactions among sediment addition, nutrient enrichment and water abstraction

This paper reviews animal treading and the associated effects on soil physical properties and pasture productivity from treading-induced soil compaction and pugging. Response curve relationships between soil physical properties (e.g. macroporosity, air-filled porosity, bulk density) and pasture and crop yield are reviewed. Optimum soil macroporosity for maximum pasture and crop yield ranges from 6 to 17% v/v, but there is a paucity of yield response curves for pastoral systems, particularly critical or optimum values of soil physical properties. There is little information available on the effects of cattle treading on soil physical properties and consequently pasture yield in seasons when soil pugging and poaching is minimised. Such information is needed to provide practical and rigorously tested decision support tools for land managers during grazing seasons. Knowledge of yield response curves, and critical or optimum values of soil physical properties for field pasture-based grazing systems, is required for improved farm-system production and economic decision support.

/pdf/pasture-yield-and-soil-physical-property-responses-to-soil-442opz3jps.pdf

Pasture yield and soil physical property responses to soil compaction from treading and grazing — a review

Linkages between land management activities and water quality in an intensively farmed catchment in southern New Zealand

Linkages between land management activities and stream water quality in a border dyke-irrigated pastoral catchment

Dairy farming, nitrogen losses and nitrate-sensitive areas

The environmental and economic performances of low, medium and high input dairy farming systems were evaluated for model farms within catchments in Waikato, Taranaki Canterbury and Southland. These four catchments, predominantly under dairy landuse, are part of a long term systems study of farm productivity and catchment-specific environmental issues. Within each catchment, environmental and economic performance indicators were derived for model farms by using the farm systems modelling tool UDDER and the OVERSEERâ„¢ nutrient budgeting programme. Our analyses indicated that high input systems, currently defined as farms within the top quartile of farm inputs, either as imported feed or fertiliser nitrogen (N), were often the least profitable, as defined by Earnings Before Interest and Tax (EBIT). These high-input systems consistently had the greatest environmental emissions of N and greenhouse gases, and the greatest energy consumption, on a per hectare and a per kg milksolids basis. The most profitable farm input system depended on payout and the catchment under study. Evaluation of the whole-farm system using these modelling tools demonstrated the relatively large contribution that stock wintering made to N emissions from farms within the two South Island catchments. Where reductions in N losses are sought, it would seem prudent to initially target mitigations at this part of the farm system. Keywords: dairy farming, environmental emissions, farm systems modelling, OVERSEERâ„¢ nutrient budgets, UDDER farm systems tool

https://www.nzgajournal.org.nz/index.php/ProNZGA/article/download/2558/2186

B.S. Thorrold

Papers

Linkages between land management activities and water quality in an intensively farmed catchment in southern New Zealand

Linkages between land management activities and stream water quality in a border dyke-irrigated pastoral catchment

Dairy farming, nitrogen losses and nitrate-sensitive areas

A desktop evaluation of the environmental and economic performance of model dairy farming systems within four New Zealand catchments

LIC Lecture - The development of environmental best practices for intensive dairying