Comparison of grassland management systems for beef cattle using self-contained farmlets: effects of contrasting nitrogen inputs and management strategies on nitrogen budgets, and herbage and animal production

Past research on nitrogen (N) inputs, losses and surpluses focused on separate components of grassland management, i.e., grazed or cut swards and the impact of fertiliser or slurry applications. In practice, however, grassland is both grazed and cut for conservation, and N fertiliser is supplied from both organic and inorganic sources. A whole systems approach was used to evaluate the effects of combinations of management strategies designed to reduce N losses on N budgets, and herbage and animal production in South West England. Three systems with contrasting N inputs were compared: CN, conventional mineral N application and broadcast slurry; TN, tactical mineral N application with slurry injection and the early housing of cattle; GC, a mixed grass/white clover sward with no mineral N addition and slurry injection. Comparisons were made on two contrasting soil types: a freely-draining sandy loam (Gleysol, Site 1), and a poorly drained clay (Luvisol, Site 2). 1 ha farmlets were grazed to a target sward height by beef cattle for a 5-year (Site 1) or a 4-year (Site 2) period. Herbage surplus to grazing requirements was cut for silage. On average, 185 kg N ha⁻¹ was applied annually to treatment TN compared with 280 kg N ha⁻¹ for CN. An additional 76, 102 and 67 kg N ha⁻¹ was applied in slurry to treatments CN, TN and GC, respectively. Substantial reductions in N surpluses were achieved for both treatments TN and GC compared with treatment CN (N surpluses ha⁻¹: 254, 168 and 119 kg at Site 1, and 247 kg, 190 and 73 kg at Site 2, for CN, TN and GC, respectively). The highest N input for treatment CN was associated with the greatest animal and herbage production. More land was required for grazing on treatment GC and less herbage was cut for silage so that self-sufficiency was not attained for winter fodder on this treatment. The early removal of cattle on treatment TN did not result in a significant increase in the amount of herbage cut for silage. It was concluded that the combinations of mitigation options used were successful in reducing N surpluses compared with the conventional N management system, but animal and herbage production was reduced.     

Manuring and fertilization effects on phosphorus accumulation in soils and potential environmental implications

Phosphorus application as manure to agricultural soils in intensive livestock farming and arable cropping systems often exceeds P offtake by crops. This surplus could lead to P accumulation in soils, making them long-term diffuse sources of P loss to water. We investigated the impact of a range of manuring and fertilization practices in intensive farming systems on the accumulation of P in soils, soil test phosphorus (STP), distribution of organic and inorganic P, P-sorption capacity and degree of soil saturation with P (DSSP). The results from the 10 long-term sites investigated showed increases in both total soil P content and STP values (Olsen-P and Mehlich-3 P), as a result of P surpluses. The net total P accumulation in the soils across the sites ranged from 16 to 232 kg P ha⁻¹ year⁻¹. The effects of long-term P surpluses were a significant reduction in P-retention capacity and increase in DSSP. The sites investigated would attain 25% DSSP in 10–150 years, depending upon the size of P surplus and sorption capacity. A combination of large P surplus and low P-sorption capacity could saturate soils to 25% DSSP within 10–30 years. The values of Olsen (85 mg P kg⁻¹) and Mehlich-3 (305 mg P kg⁻¹) extractable-P predicted for the 25% DSSP are likely to result in environmentally significant P losses.     

Nutrient flows in small-scale peri-urban vegetable farming systems in Southeast Asia—A case study in Hanoi

In many peri-urban areas of Southeast Asia, land use has been transformed from rice-based to more profitable vegetable-based systems in order to meet the increasing market demand. The major management related flows of nitrogen (N), phosphorus (P), potassium (K), copper (Cu) and zinc (Zn) were quantified over a 1-year period for intensive small-scale aquatic and terrestrial vegetable systems situated in two peri-urban areas of Hanoi City, Vietnam. The two areas have different sources of irrigation water; wastewater from Hanoi City and water from the Red River upstream of Hanoi. The first nutrient balances for this region and farming systems are presented. The main sources of individual elements were quantified and the nutrient use efficiency estimated. The environmental risks for losses and/or soil accumulation were also assessed and discussed in relation to long-term sustainability and health aspects.The primary source of nutrient input involved a combination of chemical fertilisers, manure (chicken) and irrigation water. A variable composition and availability of the latter two sources greatly influenced the relative magnitude of the final total loads for individual elements. Despite relatively good nutrient use efficiencies being demonstrated for N (46–86%) and K (66–94%), and to some extent also for P (19–46%), high inputs still resulted in substantial annual surpluses causing risks for losses to surface and ground waters. The surplus for N ranged from 85 to 882 kg ha⁻¹ year⁻¹, compared to P and K which were 109–196 and 20–306 kg ha⁻¹ year⁻¹, respectively. Those for Cu and Zn varied from 0.2 to 2.7 and from 0.6 to 7.7 kg ha⁻¹ year⁻¹, respectively, indicating high risk for soil accumulation and associated transfers through the food chain.Wastewater irrigation contributed to high inputs, and excess use of organic and chemical fertilisers represent a major threat to the soil and water environment. Management options that improve nutrient use efficiency represent an important objective that will help reduce annual surpluses. A sustainable reuse of wastewater for irrigation in peri-urban farming systems can contribute significantly to the nutrient supply (assuming low concentrations of potential toxic or hazardous substances in the water). Nutrient inputs need to be better related to the crop need, e.g. through better knowledge about the nutrient concentrations in the wastewater and improved management of the amount of irrigation water being applied.     

Nitrate leaching under vegetable field above a shallow aquifer in Slovenia

In the search for new technologies that would ensure optimum yield and environmental sustainability, various irrigation, nitrogen and cropping system management strategies for the production of vegetables with a shorter growing period were assessed at a benchmark site in Slovenia for the years 2006 and 2007. In the studied years four irrigation and fertilization treatments were applied: (1) 50% drip irrigation of plants water requirements ET_crop and the farmer's practice of fertilisation (broadcasting), (2) fertilisation and 100% drip irrigation (fertigation), (3) the farmer's practice of irrigation (sprinkler irrigation using water stored in plastic tanks) and fertilisation, and (4) control (the farmer's practice of irrigation but no fertilisation). An equivalent of 80, 80 and 200 kg ha⁻¹ of nitrogen (N), 50, 50 and 80 kg ha⁻¹ of phosphorous (P) and 120, 120 and 300 kg ha⁻¹ of potassium (K) was added for iceberg lettuce, endive and cabbage, respectively. Nitrogen (N) labelled fertilizer (¹⁵N) was applied to trace the movement of the applied N fertiliser. The tested irrigation and fertilisation techniques for the production of vegetables with a shorter growing period in the Slovenian climate showed that environmentally sustainable practices (split application of nutrients compared to broadcast incorporating fertilisation) should be a practice of choice in water protection zones. The results confirm that fertigation and improved irrigation scheduling can be an effective way of minimizing nitrate leaching, and should be considered for vegetable production in or close to groundwater protection zones.     

Assessing the potential for greenhouse gas mitigation in intensively managed annual cropping systems at the regional scale

We predicted changes in yields and direct net soil greenhouse gas (GHG) fluxes from converting conventional to alternative management practices across one of the world's most productive agricultural regions, the Central Valley of California, using the DAYCENT model. Alternative practices included conservation tillage, winter cover cropping, manure application, a 25% reduction in N fertilizer input and combinations of these. Alternative practices were evaluated for all unique combinations of crop rotation, climate, and soil types for the period 1997-2006. The crops included were alfalfa, corn, cotton, melon, safflower, sunflower, tomato, and wheat. Our predictions indicate that, adopting alternative management practices would decrease yields up to 5%. Changes in modeled SOC and net soil GHG fluxes corresponded to values reported in the literature. Average potential reductions of net soil GHG fluxes with alternative practices ranged from −0.7 to −3.3 Mg CO₂-eq ha⁻¹ yr⁻¹ in the Sacramento Valley and −0.5 to −2.5 Mg CO₂-eq ha⁻¹ yr⁻¹ for the San Joaquin Valley. While adopting a single alternative practice led to modest net soil GHG flux reductions (on average −1 Mg CO₂-eq ha⁻¹ yr⁻¹), combining two or more of these practices led to greater decreases in net soil GHG fluxes of up to −3 Mg CO₂-eq ha⁻¹ yr⁻¹. At the regional scale, the combination of winter cover cropping with manure application was particularly efficient in reducing GHG emissions. However, GHG mitigation potentials were mostly non-permanent because 60-80% of the decreases in net soil GHG fluxes were attributed to increases in SOC, except for the reduced fertilizer input practice, where reductions were mainly attributed to decreased N₂O emissions. In conclusion, there are long-term GHG mitigation potentials within agriculture, but spatial and temporal aggregation will be necessary to reduce uncertainties around GHG emission reductions and the delivery risk of the associated C credits.     

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 are reported for a 2480 ha catchment used for dairy farming, sheep–beef farming and forestry in Southland, New Zealand. Our approach was to reconcile measured loads of nutrients exported from the catchment with those estimated based on characterisation of farming practices within the catchment. The latter was based upon detailed surveys of farm practices and soil quality. Monthly stream monitoring showed that median nutrient (N and P), sediment and faecal bacteria concentrations exceeded guidelines recommended for surface waters. Measured specific yields for suspended sediment (SS), total N (TN) and phosphorus (P) discharged from the catchment were 58, 8.2 and 0.43 kg ha⁻¹ year⁻¹, respectively, for the 2001–2005 monitoring period. In comparison, model estimates of N and P losses in drainage and overland flow from farms in the catchment were 10.1 and 0.59 kg ha⁻¹ year⁻¹, respectively. Field measurements, farm management surveys and farm systems modeling have identified some land management practices that appear to be key sources of many of these pollutants. These sources include subsurface drainage systems (including the preferential flow of irrigated effluent through these soils), overland flow from the heavy soils used for dairy farming in the catchment and the practice of intensively wintering cows on forage crops. Modeling suggests that a significant improvement in catchment water quality could be achieved through the implementation of targeted best management practices (BMPs) on dairy farms in the catchment. These include (i) covered feedpad wintering systems for controlling N losses, (ii) nitrification inhibitor use on milking platforms, (iii) deferred irrigation and low rate application of farm dairy effluent and (iv) limiting soil Olsen P to economically optimum levels. The adoption of these BMPs will, in part, depend on their economic viability. This paper therefore presents a double-bottom-line analysis (i.e. environmental and economic) of some of these BMPs and discusses their potential to cost-effectively deliver improved water quality in the Bog Burn catchment.     

Alternative cropping systems for sustainable water and nitrogen use in the North China Plain

Serious water deficits and excessive nitrogen (N) applications are threatening the sustainability of intensive agriculture in the North China Plain (NCP). This study examined the possibility of replacing the conventional system (Con.W/M) of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.), with an optimized double cropping system (Opt.W/M), a 2-year system (winter wheat/summer maize-spring maize, W/M-M), and a monoculture system (spring maize, M) based on optimal water and N management strategies. From 2004 to 2010, a long-term field experiment conducted in the NCP showed that although >70 mm of irrigation water can be saved with Opt.W/M compared with Con.W/M, annual net groundwater use under Opt.W/M was still 250 mm, 65-90% of which was consumed during the winter wheat season. When wheat production was decreased, 35% and 61% of irrigation water could be reduced in W/M-M and M compared to Con.W/M, respectively. As a result, annual groundwater use was decreased to 190 mm in W/M-M and 94 mm in M. Meanwhile, the N fertilizer rate was reduced 59% and 72% in W/M-M and M compared to Con.W/M, respectively. There were no significant differences in net economic returns between Con.W/M and W/M-M across the 6-year period. In the 6 years, no significant economic loss was observed between Con.W/M and M except in the 2008-2010 rotation. The W/M-M and M systems showed great potential to reduce water and N application and achieve groundwater use balance, and thus should be considered for economic and sustainable agricultural development in the NCP.     

Competition between maize and pigeonpea in semi-arid Tanzania: Effect on yields and nutrition of crops

Productivity of maize–pigeonpea cropping systems is dependent on facilitative and competitive interactive effects on resource availability. Controlling these interactions may benefit farmers through increased productivity associated with optimized crop yields. Previous research on maize–pigeonpea culture in Sub-Saharan Africa has focused on yield and soil fertility, but provided inadequate information on the mechanisms of possible interspecific competition. We employed a factorial field experiment to examine yield and nutritional responses of maize and pigeonpea to cropping systems (sole maize, intercropping, and improved fallow), N and P fertilizer additions, and cattle manure additions in Dodoma, Tanzania. The study objectives were to assess competition between crops and to determine how manure or fertilizer inputs may mitigate such interactions to improve yields. Intercropping enhanced maize yield over sole maize only when fertilized, reflecting probable nutrient competition. Improved fallows alone or with fertilizers (1.2–1.6 Mg ha⁻¹) increased maize yields over sole maize (0.6 Mg ha⁻¹). These increases were attributed to pigeonpea facilitation through soil nutrient replenishment, reduced competition associated with sequential cropping arrangements, and added nutrients from fertilization. Combined fertilizer and manure applications also improved maize and pigeonpea yields. Plant nutrient diagnosis indicated primary and secondary P and Ca deficiencies, respectively associated with P-fixation and leaching of cations due to high soil acidity and exchangeable Al. Maize competed strongly in mixture suppressing biomass and grain yields of the unfertilized pigeonpea by 60% and 33%, respectively due to limited soil nutrients and/or moisture. These yield reductions suggest that the intercropped pigeonpea did not recover from competition after maize harvesting that reduced competition. Optimizing yields of both maize and pigeonpea would require the addition of prescribed fertilizer when intercropped, but applications can be reduced by half under the improved fallow system due to alleviating interspecific competition.     

State and potential management to improve water quality in an agricultural catchment relative to a natural baseline

Land use change and the expansion of dairying are perceived as the cause of poor water quality in the 1881 km² Pomahaka catchment in Otago, New Zealand. A study was conducted to determine the long-term trend at four sites, and current state in 13 sub-catchments, of water quality. Drains in 2 dairy-farmed sub-catchments were also sampled to determine their potential as a point source of stream contamination. Data highlighted an overall increase in the concentration of phosphorus (P) fractions at long-term sites. Loads of contaminants (nitrogen (N) and P fractions, sediment and Escherichia coli) were greatest in those sub-catchments with the most dairying. Baseline (without human influence) contaminant concentrations suggested that there was considerable scope for decreasing losses. At most sites, baseline concentrations were <20% of current median concentrations. Contaminant losses via drainage were recorded despite there being no rainfall that day and attributed to applying too much effluent onto wet soil. Modelling of P concentrations in one dairy-farmed sub-catchment suggested that up to 58% of P losses came from point sources, like bad effluent practice and stock access to streams. A statistical test to detect “contaminated” drainage was developed from historical data. If this test had been applied to remove contaminated drainage from samples of the two dairy-farmed sub-catchments, median contaminant concentrations and loads would have decreased by up to 58% (greater decreases were found for E. coli, ammoniacal-N and total P than other contaminants). This suggests that better uptake of strategies to mitigate contamination, such as deferred effluent irrigation (and low rate application), could decrease drainage losses from dairy-farmed land and thereby improve water quality in the Pomahaka catchment.     

Managing crop residues, fertilizers and leaf litters to improve soil C, nutrient balances, and the grain yield of rice and wheat cropping systems in Thailand and Australia

This paper reports on the influence that residue and fertilizer management have on nutrient balances, soil organic matter (SOM) dynamics, and crop yields of a flooded rice system in northeast Thailand (1992–1997) and a wheat–forage legume rotation in eastern Australia (1992–1998). Both soils had been subject to at least 18 years of cultivation and had lost up to 90% of the original labile (C_L) and 85% of the total carbon (C_T).For the rainfed rice cropping systems of northeast Thailand, a system is described in which small applications of leaf litter from locally grown trees are applied annually to rice paddy soils prior to transplanting. Annual applications of 1500 kg ha⁻¹ of leaf litter from different locally grown shrubs for five seasons resulted in increases in rice grain yield in 1997 of between 20 and 26% above the no-leaf litter control. Nutrient balances, determined by the difference between the inputs (fertilizer and added leaf litters) and outputs (grain and straw), indicated net positive balances of up to 457 kg N ha⁻¹, and 60 kg P ha⁻¹, after five seasons of leaf litter applications. Sulfur and potassium balances resulted in net deficits of up to −13 kg S ha⁻¹ and −52 kg P ha⁻¹, where no leaf litter was applied and rice straw was removed following harvest. Soil carbon (C) concentrations increased significantly only where higher fertilizer rate and rice stubble retention were combined.The poor management of fertilizers and crop residues, and excessive cultivation has also resulted in large soil fertility losses in the grain growing areas of Eastern Australia. After five wheat and two legume/fallow crops, negative N balances of up to −303 kg ha⁻¹ were calculated for the treatments where wheat stubble was not retained and bare fallow leys were used. The balance of nutrients such as K, which are contained in larger proportions in stubble, were found to be up to −362 kg ha⁻¹ on the straw-removed treatments and up to +29 kg ha⁻¹ on the straw-retained treatments. Forage legume leys resulted in short term increases in C_L and the carbon management index (CMI).Sustainable farming systems require that crop yields are stable through the maintenance of soil fertility and the balance of nutrients in the system. Increases in soil C levels require sustained periods of balanced fertilization and residue retention.     

Urease inhibitor reduces N losses and improves plant-bioavailability of urea applied in fine particle and granular forms under field conditions

A field lysimeter/mini plot experiment was established in a silt loam soil near Lincoln, New Zealand, to investigate the effectiveness of urea fertilizer in fine particle application (FPA), with or without the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT - “Agrotain”), in decreasing nitrogen (N) losses and improving N uptake efficiency. The five treatments were: control (no N) and ¹⁵N-labelled urea, with or without NBPT, applied to lysimeters or mini plots (unlabelled urea), either in granular form to the soil surface or in FPA form (through a spray) at a rate equivalent to 100 kg N ha⁻¹. Gaseous emissions of ammonia (NH₃) and nitrous oxide (N₂O), nitrate (NO₃⁻) leaching, herbage dry-matter (DM) production, N-response efficiency, total N uptake and total recovery of applied ¹⁵N in the plant and soil varied with urea application method and with addition of NBPT. Urea with NBPT, applied in granular or FPA form, was more effective than in application without NBPT: N₂O emissions were reduced by 7-12%, NH₃ emissions by 65-69% and NO₃⁻ leaching losses by 36-55% compared with granular urea. Urea alone and with NBPT, applied in FPA form increased herbage DM production by 27% and 38%, respectively. The N response efficiency increased from 10 kg DM kg⁻¹ of applied N with granular urea to 19 kg DM kg⁻¹ with FPA urea and to 23 kg DM kg⁻¹ with FPA urea plus NBPT. Urea applied in FPA form resulted in significantly (P < 0.05) higher ¹⁵N recovery in the shoots compared with granular treatments and this was improved further when urea in FPA form was applied with NBPT. These results suggest that applying urea with NBPT in FPA form has potential as a management tool in mitigating N losses, improving N-response efficiency and increasing herbage DM production in intensive grassland systems.     

Impact of land clearing methods and cropping systems on labile soil C and N pools in the humid zone Forest of Nigeria

Labile soil C and N play vital roles in soil–plant nutrient dynamics, especially in the low input cropping system and are vulnerable to perturbation. Surface (0–0.15 m) soils from three land clearing methods (slash and burn, bulldozed non-windrowed and bulldozed windrowed) and each with two cropping systems (5-and 4-year cropping/2-year cassava fallow) were collected in the humid forest ecosystem of Nigeria.The soils were analysed for total C and N, microbial biomass C and N (SMB C and N), particulate organic matter C and N (POM C and N), water-soluble C, potentially mineralizable N (PMN) and mineral N. The size of the labile C and N and their relative contributions to the organic C and total N differed significantly among land clearing methods, irrespective of the cropping system. Soils under slash and burn had a significantly (p > 0.05) higher particulate organic matter C, N (10.80 and 0.16 g kg⁻¹, respectively) and microbial biomass C and N (1.07 and 0.12 g kg⁻¹) compared to the bulldozed windrow, regardless of the cropping system. Four years cropping/2-year cassava fallow resulted in a significant higher labile C and N, relative to 5-year cropped plots across the land clearing methods. Effect of the treatments on the concentration of PMN and mineral N mirrored the SMB N and POM N. However, the quantity of most of the labile C and N pool and crop yield obtained from the slash and burn and bulldozed non-windrowed treatment did not differ significantly. Hence, bulldozed non-windrowed clearing could be a viable alternative to slash and burn in the case of large-scale farming in ensuring reduced losses of soil organic matter and nutrient during land clearing in the humid tropics.     

生活污水灌溉对麦秸还田稻田氨挥发排放的影响

以养分回用为目的,在原状土柱模拟试验条件下,采用间歇密闭式抽气法研究了生活污水灌溉对麦秸还田稻田田面水铵态氮浓度、田面水pH以及稻田氨挥发损失的影响.结果表明:1麦秸还田显著增加了田面水NH_4~+-N浓度,生活污水灌溉则显著降低了田面水NH_4~+-N浓度.2正常灌溉施肥秸秆不还田稻田处理的总氨挥发量为58.29 kg·hm-2,占总施氮量的24.29%;麦秸还田显著增加了稻田的氨挥发损失,氨挥发损失量增加了近一倍,达总施氮量的45.66%;而生活污水灌溉显著降低了稻田氨挥发损失量,氨挥发损失量降至总施肥量的17.26%(秸秆不还田)和32.72%(秸秆还田).秸秆还田与生活污水处理具有显著的正交互作用.在3个肥期中,分蘖肥期氨挥发损失率最高,占总氮肥用量的7.38%~24.44%.3无论秸秆还田与否,氨挥发通量与田面水NH_4~+-N浓度之间均存在极显著的正相关关系,与田面水pH值则相关性不显著.麦秸还田增加了稻田氨挥发损失,而麦秸还田与生活污水灌溉耦合能降低稻田氨挥发损失,同时污水中的氮可替代44.41%的化肥氮,减少稻季化肥用量,具有显著的生态环境效益.     

Rates of accumulation of cadmium and uranium in a New Zealand hill farm soil as a result of long-term use of phosphate fertilizer

In New Zealand, phosphate (P) fertilisers used in agriculture are the main sources of the potentially toxic elements cadmium (Cd) and uranium (U), which occur as unwanted contaminants. New Zealand is developing draft soil guideline values (SGV) for maximum concentrations of Cd. To assess when soils under pasture for sheep production might reach a particular SGV, we analysed archived soil samples from a 23 yr P fertiliser trial. The pasture sites were at Whatawhata, North Island, New Zealand, and had received P fertiliser at the rates of 0, 30, 50 and 100 kg P ha⁻¹ yr⁻¹. From 1983 to 1989, P was applied as single superphosphate, from 1989 to 2006, P was applied as triple superphosphate. Soils from replicate paddocks were sampled annually to a depth of 75 mm on easy (10-20°) and steep (30-40°) slope classes. Total P, Cd and U were analysed by ICP-MS after acid digestion. Data were analysed by fitting trend lines using linear mixed models for two slope classes and for two sampling periods 1983-1989 and 1989-2006 when the soil sampling method and fertiliser type had been changed.The changes in total P, Cd and U were directly related to the type and amount of P fertiliser applied, the control treatment showed no significant change in P, Cd or U. At 50 and 100 kg P ha⁻¹ yr⁻¹ there were generally linear increases in total P and total U, and the same trend line applied to both time periods, but the rate of increase in P was greater on the easy slope class. For Cd, a “broken stick” model was needed to explain the data. Pre-1989, Cd increased in the 50 and 100 kg P ha⁻¹ yr⁻¹ treatment (0.036-0.045 mg kg⁻¹ yr⁻¹, respectively): post 1988 the rate of increase declined markedly on those two treatments (0.005-0.015 mg kg⁻¹ yr⁻¹, respectively), and declined absolutely in the 30 kg P ha⁻¹ yr⁻¹ treatments. The maximum content of Cd was in the 100 kg P ha⁻¹ yr⁻¹ treatment which reached 0.931 mg Cd kg⁻¹ on the easy slope. For U there were steady linear increases for the 30, 50 and 100 kg P ha⁻¹ treatments, and no significant difference between the steep and easy slopes, nor the two sampling periods, the maximum concentration obtained was 2.80 mg U kg⁻¹ on the 100 kg P ha⁻¹ treatment. The results suggest that at rates of P fertiliser likely to be applied to hill farms (<50 kg P ha⁻¹ yr⁻¹), and using P fertiliser with low Cd content, then the Cd concentration in this soil will never reach a SGV of 1 mg kg⁻¹.     

Environmental cross-compliance mitigates nitrogen and phosphorus pollution from Swiss agriculture

In 1993 the Swiss agricultural policy was revised with – amongst other goals – the objective of improving the environmental performance of agriculture. A voluntary agri-environmental scheme to promote integrated production (IP) was introduced. In 1999 the IP standards were integrated in cross compliance requirements and termed Proof of Ecological Performance (PEP). We evaluated the effectiveness of this policy in terms of reducing diffuse nitrogen (N) and phosphorus (P) pollution of ground and surface water. We combined monitoring schemes covering the reference period from before the introduction of IP/PEP (1990–1992) with the evaluation of cause/effect relationships in selected case-study areas. The evaluation showed an overall reduction of diffuse N and P pollution from agriculture even though some goals were not reached. Nitrate leaching declined, but only a 3–4 mg L⁻¹ reduction was observed rather than the intended decrease of 5 mg L⁻¹. The P pollution of surface waters from agriculture decreased by only 10–30% instead of 50%. The intended reduction of the nitrogen surplus of Swiss agriculture by 33% was not attained, but the P surplus of Swiss agriculture was more than halved. IP/PEP practices that improved N and P management included reduced N and P fertiliser inputs and pig and poultry feedstuffs with reduced N and P contents, both of which are a consequence of the requirement of equilibrated farm nutrient balances, as well as increased use of cover cropping and of conservation tillage systems.     

Comparison of soil N availability and leaching potential,crop yields and weeds in organic,low-input and conventional farming systems in northern California

Increasing dependence on off-farm inputs including, fertilizers, pesticides and energy for food and fiber production in the United States and elsewhere is of questionable sustainability resulting in environmental degradation and human health risks. The organic (no synthetic fertilizer or pesticide use), and low-input (reduced amount of synthetic fertilizer and pesticide use), farming systems are considered to be an alternative to conventional farming systems, to enhance agricultural sustainability and environmental quality. Soil N availability and leaching potential, crop yields and weeds are important factors related to agricultural sustainability and environmental quality, yet information on long-term farming system effects on these factors, especially in the organic and low-input farming systems is limited. Four farming systems: organic, low-input, conventional (synthetic fertilizer and pesticides applied at recommended rates) 4-year rotation (conv-4) and a conventional 2-year rotation (conv-2) were evaluated for soil mineral N, potentially mineralizable N (PMN), crop yields and weed biomass in irrigated processing tomatoes (Lycopersicon esculentum L.) and corn (Zea mays L.) from 1994 to 1998 in California’s Sacramento Valley. Soil mineral N levels during the cropping season varied by crop, farming system, and the amount and source of N fertilization. The organic and low-input systems showed 112 and 36% greater PMN pools than the conventional systems, respectively. However, N mineralization rates of the conventional systems were 100% greater than in the organic and 28% greater than in the low-input system. Average tomato fruit yield for the 5-year period (1994–1998) was 71.0 Mg ha⁻¹ and average corn grain yield was 11.6 Mg ha⁻¹ and both were not significantly different among farming systems. The organic system had a greater aboveground weed biomass at harvest compared to other systems. The lower potential risk of N leaching from lower N mineralization rates in the organic and low-input farming systems appear to improve agricultural sustainability and environmental quality while maintaining similar crop yields.     

Denitrification on Andosols in an intensive dairy farming region of central Japan

Evaluation of denitrification capacities is necessary to develop a sustainable manure management system in order to reduce NO₃⁻ leaching and N₂O emissions from agricultural soils. Denitrification rates were measured using the acetylene inhibition technique on intact soil cores from eight Andosols under three different cropping systems in an intensive livestock catchment of central Japan. The N application rates ranged from 200 to 800 kg N ha⁻¹ yr⁻¹. The denitrification rates were highly variable across fields, and were influenced significantly by land uses and manure forms. Compared with upland fields, paddy rice fields had a greater denitrification rate up to 1380 and 85 mg N m⁻² day⁻¹ in the top 30-cm soil layer during flooding and non-flooding periods, respectively. In upland fields, the maximum value for the top 30-cm soils was 44 mg N m⁻² day⁻¹ and most of the rates were less than 10 mg N m⁻² day⁻¹. The greater denitrification rates were often associated with slurry application rather than composted dry manure. Overall, denitrification from Andosols in this study displayed a lower capacity than that of non-Andosols.     

Nitrogen fertilizer reduction in rice production for two consecutive years in the Taihu Lake area

Agricultural activities are the main source of non-point pollution in the Taihu Lake region, and therefore reduction of nitrogen (N) fertilizer is imperative in this area. A two-year experiment was carried out in a paddy field of summer rice-winter wheat rotation in the Taihu Lake area, and the rice growing seasons were mainly concerned in this research. Grain yield, N accumulation at rice crucial stages, N use efficiency, as well as N losses via run off during rice growing season were determined under different N application rates. No significant differences were observed in grain yield under N fertilizer application rates of 135-270 kg N ha⁻¹ (50-100% of the conventional N application rate). Nitrogen accumulation before the heading stage (Pre-NA) accounted for 61-95% of total nitrogen absorption in mature rice, and was positively correlated with straw dry matter at harvest. Positive correlations were found between Pre-NA and straw (0.53, p < 0.05), and between grain yield and N accumulation after the heading stage (Post-NA) (0.58, p < 0.05), suggesting that increasing nitrogen accumulation after the heading stage is crucial for grain yield improvement. Poor agronomic efficiency of applied N (AE_N), partial factor productivity of applied N (PFP_N) and internal utilization efficiency of applied N (IE_N) were observed for the higher soil fertility and a higher N fertilizer input; a simple N fertilizer reduction could significantly increase the nitrogen use efficiency in this region. Nitrogen loss via runoff was positively linearly related to N application rates and severely affected by rainfall events. The highest-yielding N rates were around 232-257 kg N ha⁻¹, accounting for 86-95% of the conventional N application rates for the rice season. To reduce N losses and enhance N use efficiency, the recommendable N fertilization rate should be lower than that of the highest yield rate for rice season. Our findings indicated that nitrogen fertilizer reduction in the Taihu Lake area is feasible and necessary for maintaining grain yield, enhancing nitrogen use efficiency, and reducing environmental impact. However, the longer-term yield sustainability for the proper N application rate needs to be further investigated.     

Evaluation of two soil carbon models using two Kenyan long term experimental datasets

RothC and Century are two of the most widely used soil organic matter (SOM) models. However there are few examples of specific parameterisation of these models for environmental conditions in East Africa. The aim of this study was therefore, to evaluate the ability of RothC and the Century to estimate changes in soil organic carbon (SOC) resulting from varying land use/management practices for the climate and soil conditions found in Kenya. The study used climate, soils and crop data from a long term experiment (1976–2001) carried out at The Kabete site at The Kenya National Agricultural Research Laboratories (NARL, located in a semi-humid region) and data from a 13 year experiment carried out in Machang’a (Embu District, located in a semi-arid region). The NARL experiment included various fertiliser (0, 60 and 120 kg of N and P₂O₅ ha⁻¹), farmyard manure (FYM—5 and 10 t ha⁻¹) and plant residue treatments, in a variety of combinations. The Machang’a experiment involved a fertiliser (51 kg N ha⁻¹) and a FYM (0, 5 and 10 t ha⁻¹) treatment with both monocropping and intercropping. At Kabete both models showed a fair to good fit to measured data, although Century simulations for treatments with high levels of FYM were better than those without. At the Machang’a site with monocrops, both models showed a fair to good fit to measured data for all treatments. However, the fit of both models (especially RothC) to measured data for intercropping treatments at Machang’a was much poorer. Further model development for intercrop systems is recommended. Both models can be useful tools in soil C predictions, provided time series of measured soil C and crop production data are available for validating model performance against local or regional agricultural crops.     

Does Tephrosia candida as fallow species, hedgerow or mulch improve nutrient cycling and prevent nutrient losses by erosion on slopes in northern Viet Nam?

Agroforestry is considered to be a promising alternative to short-fallow shifting cultivation or other monocropping systems. An on-farm experiment was established in 1996 in northern Viet Nam to examine the contribution of the leguminous bush Tephrosia candida (Roxb.) D.C. as a fallow or hedgerow species and as a mulch producer to improve nutrient cycling and prevent nutrient losses by erosion. The systems tested were upland rice monocropping (Mono), natural fallow (NaFa), fallow of Tephrosia (TepFa), hedgerow intercropping with upland rice (Oryza sativa L.) and internal mulching using pruned Tephrosia biomass (TepAl), and upland rice with external mulching using Tephrosia biomass (TepMu). Over two cropping seasons, from April 1996 to April 1998, nutrients recycled and inputs and exports were recorded, as well as changes in C-, N- and P-pools, and in pH in the 0–5 cm topsoil layer.The Tephrosia systems (TepFa, TepAl, TepMu) prevented nutrient losses by erosion effectively. Compared to the NaFa system, the TepFa system accumulated 34% more N in the above-ground plant parts and increased topsoil N by 20%, probably due to N-fixation. There was a trend that the less labile P-pools (NaOH-P) were reallocated into the more labile P-pools (Bicarb-P) in the soil of the TepFa system. Burning released significant amounts of the inorganic P-pools in both the NaFa and TepFa systems and this effect seemed to be more pronounced in the TepFa than in the NaFa. Organic input to crop export ratios for N and P were >1 in the TepAl and TepMu treatments. This was due to a sufficient quantity and quality of the Tephrosia mulching material. However, moderately labile NaOH-extractable organic P seemed to be depleted in the topsoil due to high P uptake in the TepMu treatment. Thus, nutrient cycling and nutrient balances were improved under the Tephrosia systems. But for long-term P sustainability, there is a belief that a combined use of mulching and mineral P fertiliser is needed.