Phosphorus leaching through intact soil cores as influenced by type and duration of manure application

Leaching of phosphorus (P) in manure-amended soils has received increased attention as a significant source of non-point source P pollution. Intact soil cores were collected from fields on a farm in Southern New York to test the effects of long-term dairy or poultry manure application on P leaching. Nine fields were selected (four poultry, four dairy, and one unamended) to represent a broad range of P saturation levels (5.3 to 62.4%) in the topsoil (0–7.5 cm). Water was applied weekly at a rate matching a 1-year return period storm for the study area (230 mm h⁻¹). Dissolved reactive P (DRP) losses in leachate from all soil cores ranged from 0.007 to 0.055 kg P ha⁻¹, except in two fields with long-term histories of dairy and poultry manure application, where losses averaged 0.21 and 0.45 kg P ha⁻¹, respectively. Hydrographs of the field with the dairy manure history suggested preferential flow as an explanation of leachate P enrichment. In the poultry manure amended field, high levels of soil P saturation throughout the profile suggested subsoil P desorption as a factor controlling leachate P. Surface application of dairy manure to the soil cores (167 kg total P ha⁻¹) increased the mean leachate DRP concentration from 1.5 to 10.5 fold. After five leaching events spanning 22 days, DRP concentrations remained 2.0 to 13.4 fold above pre-manure application levels. This study points to saturation of P in subsoils by long-term manure application as a key concern to P loss in leachate and highlights the role of annual manure additions on subsurface P loss potential.     

Application of manure to no-till soils: phosphorus losses by sub-surface and surface pathways

The acceleration of surface water eutrophication attributed to agricultural runoff has focused attention on manure management in no-till. We evaluated losses of phosphorus (P) in sub-surface and surface flow as a function of dairy manure application to no-till soils in north-central Pennsylvania. Monitoring of a perennial spring over 36 months revealed that dissolved reactive P (DRP) concentrations increased 3- to 28-fold above background levels whenever manure was broadcast to nearby field soils. A study conducted with 30-cm deep intact soil cores indicated that incorporation of manure by tillage lowered P loss in leachate relative to broadcast application, presumably due to the destruction of preferential flow pathways. More P was leached from a sandy loam than a clay loam soil, although differences between soils were not as great as differences between application methods. In contrast, rainfall simulations on 2-m² field runoff plots showed that total P (TP) losses in surface runoff differed significantly by soil but not by application method. Forms of P in surface runoff did change with application method, with DRP accounting for 87 and 24% of TP from broadcast and tilled treatments, respectively. Losses of TP in leachate from manured columns over 7 weeks (0.22–0.38 kg P ha⁻¹) were considerably lower than losses in surface runoff from manured plots subjected to a single simulated rainfall event (0.31–2.07 kg TP ha⁻¹). Results confirm the near-term benefits of incorporating manure by tillage to protect groundwater quality, but suggest that for surface water quality, avoiding soils prone to runoff is more important.

Predicting nitrogen leaching with the modified LEACHM model: validation in soils receiving long-term application of animal manure composts

A variety of process-based models have been developed for predicting nitrogen (N) dynamics in agro-ecosystem; however, no reliable models have been validated for N leaching from soils receiving a long-term application of different types of animal manure composts. The Leaching Estimation and Chemistry Model (LEACHM) was recently modified by incorporating the basic structure of Rothamsted Carbon Model for extending its ability to describe soil organic matter decomposition and subsequent N leaching in soils rich in organic matter. We evaluate the applicability of the modified LEACHM in cropped Yellow soils receiving 10-year application of cattle or swine manure compost in addition to chemical fertilizers, where high-frequency field monitoring data of soil water contents, soil N contents and leachate N concentrations were available for the last 3 years. Particular attention was paid to determine all input parameters from independent measurements, parameterization from known soil properties or databases without optimisation to fit the measured field data. The model reasonably predicted temporal changes in the soil NH₄-N and NO₃-N contents, and inorganic N concentrations in the leachate as well as their differences due to different manure compost/chemical fertilizer applications. The simulations of leached N concentration yielded a Willmott index of agreement (IA) of 0.62–0.68, with those for soil moisture, soil nitrate content and crop N uptake all within an acceptable IA range. In view of the good performance without site-specific calibrations, the modified LEACHM appears to be a valuable tool for predicting N leaching from cropped soils receiving long-term manure compost applications.     

Freezing–thawing effects on phosphorus leaching from catch crops

It is suggested that catch crops be grown to reduce phosphorus (P) losses. However, after exposure to freezing–thawing cycles (FTCs), catch crop material can become a source of P losses to waters in moderately cold climates. This study screened potential P leaching from intact plant material of eight catch crop species: chicory (Cichorium intybus L.), cocksfoot (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), red clover (Trifolium pratense L.), phacelia (Phacelia tanacetifolia L.), white mustard (Sinapis alba L.), oilseed radish (Raphanus sativus L. oleiformis) and white radish (R. longipinnatus). The catch crops were grown in six field experiments on clay soils, where soil lysimeters (0.25 m deep) with intact crops were extracted in autumn and used for leaching experiments before and after seven FTCs in the laboratory. The eight catch crops did not reduce P leaching before FTCs. After FTCs, leachate total-P concentrations from ryegrass, oilseed radish and red clover lysimeters were significantly (p = 0.0022) higher than those from the other species and the control without a catch crop. FTCs significantly (p = 0.0064) altered total-P concentration and the proportions of different forms of P. There was a significant increase in total-P concentration in leachate from ryegrass (p = 0.0008) and oilseed radish (p = 0.02). Thus the potential risk of P leaching from ryegrass and oilseed radish material after FTCs must be considered, since they are commonly grown as nitrogen catch crops in the Nordic countries. Moreover, the roots of the tested catch crops contained 7–86 % total-P, which is important when evaluating P leaching risks.     

Nitrogen- or phosphorus-based pig manure application rates affect soil test phosphorus and phosphorus loss risk

Pig manure is an effective source of plant nutrients that must be properly managed to prevent these nutrients from reaching surface and ground water. We conducted a 3-year study in southern Manitoba to investigate how the choice of cropping system and manure management practices affect soil test phosphorus (STP) concentration and loss of phosphorus (P) to groundwater. The experiment had a split-plot design with two cropping systems (annual and perennial) as main plots, and five nutrient management treatments as subplots: N-based liquid pig manure, P-based liquid pig manure, N-based solid pig manure, P-based solid pig manure and an unfertilized control. We did not measure an appreciable increase in STP concentration below the 0.15 m depth. However, manure application at an N-based rate resulted in increased STP concentration in the 0–0.15 m depth interval. After 3-year, STP concentration in the N-based treatments (48 and 43 mg Olsen P kg^?1 for solid and liquid respectively) were significantly greater than for the P-based treatments (26 and 17 mg Olsen P kg^?1 for solid and liquid respectively). The mass of P in the leachate was small, ranging from a low of 1 g P ha^?1 in 2009 to a high of 100 g P ha^?1 in 2011. Both P- and N-based manure application rates produced no apparent risk of P leaching at our site, but the N-based manure application rate increased STP concentration in the surface soil, which could lead to the loss of P in surface runoff.     

Modelling heavy metal and phosphorus balances for farming systems

Accounting for agricultural activities such as P fertilization in regional models of heavy metal accumulation provides suitable sustainable management strategies to reduce nutrient surpluses and metal inputs in agricultural soils. Using the balance model PROTERRA-S, we assessed the phosphorus (P), cadmium (Cd) and zinc (Zn) flux balances in agricultural soils of a rural region in Switzerland for different farm types and crop types. The P requirements of crops on arable farms were mainly supplied by commercial fertilizers and sewage sludge, while on animal husbandry farms P fertilizer demands were met by animal manure alone. Metal accumulation in soil was very different between the balance units. Estimated net Cd fluxes ranged between 1.0 and 2.3 g ha^–1 yr^–1 for arable farm types, 0.6 and 2.0 g ha^–1 yr^–1 for dairy and mixed farm types, and 9.1 and 17.8 g ha^–1 yr^–1 for animal husbandry farm types. Largest net Zn fluxes of 17.9–39.8 kg ha^–1 yr^–1 were estimated for animal husbandry farms, whereas for arable farm types net Zn fluxes of 101–260 g ha^–1 yr^–1 and for dairy and mixed farm types of 349–3360 g ha^–1 yr^–1 were found. The results indicate that P management is a primary factor determining the variation of these net Cd and net Zn fluxes. The latter were highly sensitive to the Zn/P concentration ratio in animal manure, atmospheric deposition and crop concentrations. Variation of net Cd fluxes resulted mainly from uncertainty in crop concentrations, atmospheric deposition, leaching parameters and uncertainty in Cd/P concentration ratio of commercial fertilizers. In addition, element balances were sensitive to empirical assumptions on fertilization strategy of farmers, such as the partitioning of manure between balance units.     

Fertigation combined with catch crop maximize vegetable yield and minimize N and P surplus

Excessive fertilization is a common agricultural practice that often results in high risk of nitrogen (N) and phosphorus (P) losses in vegetable production in China. To reduce these losses, it is crucial to control residual nutrient levels in the rootzone and maintain crop growth. A 3-year field experiment was therefore conducted to investigate the effects of optimal fertigation (OF), OF combined with summer catch crop (OF-SCC; sweet corn with residue incorporation after harvest) or wheat straw application (OF-WSA; soil amended with wheat straw before cucumber seedling transplanting) on soil nutrients, soil residual N and P levels in the rootzone. The conventional management (flood irrigation with excessive fertilization and bare fallow during the summer period) served as control. The results showed that, although OF reduced irrigation amount, N input and P input by 49, 50 and 53%, respectively, it did not affect N and P uptake and fruit yields, and significantly reduced N and P surplus in the rootzone by 60 and 59%, respectively, when compared to the control. The SCC extracted 72–74 kg N ha^?1 year^?1 and 10–13 kg P ha^?1 year^?1 from soils. In addition, SCC and WSA increased soil soluble organic N in the rootzone but had little influence on N and P surplus. Generally, OF was efficient in reducing soil residual N and P, while SCC could temporarily retarded N leaching and improved nutrient recycling in the rootzone. Our results infer that OF combined with SCC is an efficient method for reducing soil N and P losses.     

Stratification of soil phosphorus,pH, and macro-cations under intensively cropped grass ley

The large amounts of nutrients applied to and removed from soil by intensive grass production may cause quick changes in the nutrient pools available to plants and exposed to leaching and runoff losses. Stratification of applied nutrients is especially important for phosphorus (P), which moves slowly in soil. To study the vertical distribution of extractable nutrients and soil pH in different types of ley soil, P fertilisers were incorporated or placed prior to sowing or broadcast annually at ten sites for 3 years. Then the soils were sampled in several layers 2.5 or 5 cm deep and analysed for pH and the concentrations of phosphorus, potassium (K), calcium (Ca), and magnesium (Mg) extractable with acid ammonium acetate. In mineral soils, broadcast P mainly remained within the uppermost 2.5 cm of soil, in which the concentrations of extractable P more than doubled during the study period. When commonly used NK and NPK fertilisers were applied, the uppermost 5 cm of soil was acidified by about 0.5 pH units and its Ca value decreased by about 25%. Broadcast K enriched a thin surface layer even if the K balance was negative. Estimation of the concentration of dissolved phosphate in runoff suggested that the high P losses that are possible at excessive levels of soil test P can be diminished by perennial grasses supplied with abundant water and other nutrients. Surface-applied P appeared to increase the losses, but even a shallow placement seemed to prevent them efficiently if all fertiliser granules become covered with soil.     

Effect of cation exchange on the distribution and movement of cations in soils with variable charge. II. Effect of lime or phosphate on potassium and magnesium leaching

The effect of Ca(OH)₂ or Ca(H₂PO₄)₂ 2H₂O (MCP) on potassium (K) or magnesium (Mg) leaching through and out of columns of soil with predominantly variable charge was studied. Calcium hydroxide was mixed with soil from the A and B horizon to raise the pH to about 6 or 7, and MCP, equivalent to 952 mg P, was mixed with the A horizon of each soil. Various concentrations of KCl or MgCl₂ were applied as a pulse to the soil surface and leached with five pore volumes of deionised water.Calcium hydroxide or MCP addition increased leaching losses of K and Mg initially present in the soil.Liming to about pH 6 reduced leaching of applied K and Mg in all soils. This was attributed to the increase in the cation exchange capacity (CEC). Applied K leached to a greater extent at pH 7 than at pH 6 in the A horizon of each soil despite a two-fold increase in CEC. However, when Mg was applied to all soils and K applied to soil from B horizons, leaching decreased as the pH increased from 6 to about 7.The addition of MCP increased the CEC of all soils, but this had little effect on the leaching of applied K compared with the untreated soils.A proportion of applied K or Mg was displaced from the soil column for all Ca(OH)₂ or MCP treatments. In many columns, no increase in exchangeable K or Mg in the lower segments of the soil column was found. Where this occurred the activity ratio in the leachate was the same as the equilibrium activity ratio.     

Greenhouse tomato–cucumber yield and soil N leaching as affected by reducing N rate and adding manure: a case study in the Yellow River Irrigation Region China

The effect of reducing N rate fertilization and manure addition on greenhouse vegetable yields and soil N leaching was studied in a greenhouse tomato?Ccucumber rotation system in the Yellow River Irrigation Region of Ningxia Plain, North China. The treatments were: 1-no fertilizers, 2-conventional fertilization, 3-reduced fertilizer application, and 4-reduced fertilizer application + regulation of soil C/N ratio applied by the high C/N ratio of dairy manure. The results indicated that reduced fertilizer application in tomato and cucumber season had no significant influence on vegetable yield comparing with control. The amounts of leachate had no significant differences under all fertilizer treatments at the same investigated period. In comparison with conventional fertilization, both total N and NO₃?CN leaching decreased in the low fertilizer treatments. The cumulative total N and NO₃?CN leached from fertilizers N were less than 9?% during the tomato?Ccucumber rotation system. NO₃?CN was the predominant form of leaching N, represented about 70?% of total N in the leachate. Soluble organic N represented 14.7?C33.3?% of total N leached. Vegetable yields did not increase significantly as applied N rates increased. However, soil N leaching increased largely with N rates. Reducing fertilizer N rate while adding dairy manure regulated soil C/N ratio could be appropriate fertilization practices for reducing soil N leaching and achieving high vegetable yields in the greenhouse systems.     

Transformations of soil and manure phosphorus after surface application of manure to field plots

Transfer of phosphorus (P) from surface-applied manures to runoff is an important source of pollution, but few studies have closely monitored P dynamics in manure, soil, and runoff through time. We monitored manure and soil P over 14 to 17 months in field experiments in Texas and Pennsylvania, USA following dairy and poultry manure surface application. Manure was applied to porous fabric that enabled discrete sampling of both manure and underlying soil. Manure mass consistently decreased while manure total P was essentially constant through time. Manure water extractable P decreased rapidly for the first two months, likely due to rainfall leaching, but then maintained stable concentrations thereafter, with other forms of manure P gradually transformed to water extractable forms. Soil P from the upper 2 cm rapidly increased after manure application in association with manure leaching by rain. After 2 to 3 months, soil P peaked and either remained constant or gradually declined. Similar trends occurred at 2–5 and 5–10 cm, but with lesser magnitudes. At 10–15 cm, soil P changed little over time. In Pennsylvania, naturally occurring runoff from 0.7-m × 1.3-m plots without and without manure was also monitored. Runoff dissolved P concentrations were greatest for the first event after manure application and decreased steadily through time, but remained greater than P concentrations from control plots, and were always well related to manure water extractable P. This study reveals that management practices for water quality protection must consider the potential for manure P transformations to contribute dissolved P to runoff long after manure is applied.     

Phosphorus Loss in Tile Drains from a Reclaimed Marsh Soil Amended with Manure and Phosphogypsum

Reclamation of Guadalquivir river marshes (SW Spain) constitutes a representative example of wetland reclamation in Southern Europe. Nowadays, this is an important area of tile-drained soils (40,000 ha) with an intensive irrigated agricultural production where high fertilizer rates are usually applied. In tile-drained soils, flow through macropores or cracks, which connect the nutrient rich topsoil with drain lines, can be an important pathway for nutrient transfer from soil. In order to study P loss in these soils and how it is affected by soil amendment usually applied in the zone (phosphogypsum and manure) an experiment was performed during two consecutive growing seasons on a reclaimed marsh soil from the Guadalquivir Valley. In the first season (1998–1999), sugar beet (Beta vulgaris L.) was grown under sprinkler irrigation at a rate of 2.5 mm h⁻¹; in the second (2000), cotton (Gossypium hirsutum L.) was grown under furrow irrigation at 8–10 mm h⁻¹. The amendments applied included manure (30 Mg ha⁻¹), and phosphogypsum (13 and 26 Mg ha⁻¹). Drainage events were recorded, and water samples collected and analyzed for total P (TP), dissolved total P (DTP), and dissolved reactive P (DRP). Total P in drainflow ranged from 0 to 0.818 mg l⁻¹ in the 1998–1999 season and from 0 to 0.565 mg l⁻¹ in the 2000 season. The major P form in drainflow was DRP, which accounted for about 50% of TP in the two growing seasons (the mean DRP concentration was 0.068 mg l⁻¹ in 1998–1999 and 0.043 mg l⁻¹ in 2000). Dissolved organic P accounted for a higher portion of DTP in the first season (37%) than in the second (13%). A larger load of phosphorus was observed on plots receiving manure. This treatment significantly increased (P<0.05) the cumulative drainflow during the 1998–1999 growing season (sprinkler irrigation, low drainflow rates). This is consistent with the increased losses of TP, DTP, DAHP, and DRP resulting from this treatment in this growing season. In the following season, DTP loading were significantly increased by manure (P<0.05). This seems to be related mainly to significantly increased DOP losses (P<0.01), particularly during the first drainage event. The higher fraction of applied water was lost by drainage under furrow irrigation (high drainflow rates) is consistent with the high TP load during the 2000 growing season (199–285 g ha⁻¹) relative to the 1998–1999 season (20–59 g ha⁻¹). This difference in P losses was much greater than those resulting from amendment of the soil.     

Concentration and vertical distribution of total soil phosphorus in relation to time of abandonment of arable fields

Abandonment of agricultural soils is a common practice in Western Europe to increase the area of nature and to counteract agricultural overproduction. However, it has been suggested that abrupt changes in management of land, such as abandonment of heavily fertilized agricultural fields, could trigger leaching of phosphorus into deeper soil layers and groundwater. In a previous study we observed that total phosphorus (P) in the upper 10 cm of ex-arable soils in the Netherlands was negatively related to the time of abandonment. In a subsequent study in the region reported here, we measured total P concentrations at different soil depths in four ex-agricultural fields that differed in time since abandonment to examine if the decrease in total P with increasing time of abandonment could be due to leaching of P into deeper soil layers. At each site total P concentration decreased with increasing depth, and for each soil profile depth, total P also decreased with increasing years since abandonment. We calculated, based on estimated P fertilizer gifts over the last decades and the regression coefficient of the relation between total P in a core of 95 cm and time of abandonment, the amount of net total P that should have accumulated in the oldest ex-arable field to reach the P level of the most recently abandoned field. The continuation of accumulation of P for a longer period of time in recently abandoned fields appeared to be the most reasonable explanation for the decrease of P with years of abandonment. Therefore, abandonment of agricultural land does not seem to trigger a ‘chemical time bomb’ to explode as no large amounts of P seem to leach into deeper soil layers.     

Assessment of phosphorus leaching losses from a free draining grassland soil

Intact soil monoliths (70 cm deep, 50 cm diameter), collected from a free draining Lismore silt loam soil (Udic Haplustept) under grassland, were used to evaluate phosphorus (P) leaching for two years. The objective of the study was to investigate the effect of the application of mineral P fertiliser (at 45 or 90 kg P ha^–1 y^–1) and/or farm dairy effluent (FDE) (30 to 60 kg P ha^–1 y^–1) on P losses by leaching. Annual mean total P (TP) concentrations and losses were higher from the treatments that received both FDE and P fertiliser (203–429 g L^–1; 1.4–2.5 kg ha^–1) compared with P fertiliser alone (77–151 g L^–1; 0.6–1.3 kg ha^–1). The form of applied P influenced the pattern of P forms leached. For example, significantly higher P losses in different P forms were observed for the combined mineral P fertiliser and FDE treatment (P45/FDE200) than fertiliser alone (P90/N200/U). This is due to the inclusion of liquid FDE in the former treatment although the total P inputs were similar for both treatments. This illustrates the potential of these soils to adsorb soluble inorganic P applied from mineral P fertiliser, while FDE contained unreactive P forms that were mobile in the soil profile. There was a distinct pattern of P forms leached in the following order: particulate unreactive P (PUP: 40–70%)>dissolved unreactive P (DUP: 14–53%)>particulate reactive P (PRP: 5–12%)>dissolved reactive P (DRP: 1–11%). Results also suggest that changing the irrigation method from flood to spray may be the most effective means to reduce P loss in these stony, free-draining soils.     

Effects of pig and dairy slurry application on N and P leaching from crop rotations with spring cereals and forage leys

Two crop rotations dominated by spring cereals and grass/clover leys on a clay soil were studied over 2 years with respect to nitrogen (N) and phosphorus (P) leaching associated with pig or dairy slurry application in April, June and October. Leaching losses of total N (TN), total P (TP), nitrate-N and dissolved reactive P (DRP) were determined in separately tile-drained field plots (four replicates). Mean annual DRP leaching after October application of dairy slurry (17 kg P ha^?1) to growing grass/clover was 0.37 kg ha^?1. It was significantly higher than after October application of pig slurry (13 kg ha^?1) following spring cereals (0.16 kg ha^?1) and than in the unfertilised control (0.07 kg P ha^?1). The proportion of DRP in TP in drainage water from the grass/clover crop rotation (35 %) was higher than from the spring cereal rotation (25 %) and the control (14 %). The grass/clover rotation proved to be very robust with respect to N leaching, with mean TN leaching of 10.5 kg ha^?1 year^?1 compared with 19.2 kg ha^?1 year^?1 from the cereal crop rotation. Pig slurry application after cereals in October resulted in TN leaching of 25.7 kg ha^?1 compared with 7.0 kg ha^?1 year^?1 after application to grass/clover in October and 19.1 kg ha^?1 year^?1 after application to spring cereals in April. In conclusion, these results show that crop rotations dominated by forage leys need special attention with respect to DRP leaching and that slurry application should be avoided during wet conditions or combined with methods to increase adsorption of P to soil particles.     

Phosphorus status of soil and leaching losses: results from operating and dismantled lysimeters after 15 experimental years

The objectives of the present study were: (1) to evaluate the predicting value of the most important European soil P tests for P leaching losses; and (2) to investigate how these soil P tests reflect the development of P depth profiles in original homogeneous soils of lysimeters. The study included more than 100 lysimeters, located at the Lysimeter Station Falkenberg/Saxony-Anhalt, UFZ-Centre for Environmental Research Leipzig-Halle GmbH, Germany. Soil textures were sand, sandy loam, loam and silt. The management forms were arable land, grassland and fallow with various variation in fertilisation, crop rotation and irrigation. Samples were collected from the A-horizons and from the whole profiles of eight set-aside and dismantled lysimeters at 10-cm sections. The concentrations of total P were determined monthly in the leachates and evaluated for a three-year period. The concentrations of P extracted by ammonium acetate lactate (AL-P), double lactate (DL-P), sodium bicarbonate (Olsen-P) and ammonium oxalate (OX-P) as well as P_t were significantly correlated with each other (P<0.05–P<0.001) for arable soils. The relevant regression coefficients were strongly influenced by soil texture, soil use and management. The mean annual P concentrations of the leachates were in the range 0.4–1.2 mg l^–1 for sands and <0.001–0.1 mg l^–1 for the textures sandy loam, loam and silt. These corresponded to P leaching losses of 0.001–2846 g ha^–1 yr^–1. Mean annual and maximum P concentrations and leaching losses were significantly (r>0.954, P<0.001) predicted by the OX-P concentrations of arable topsoils in lysimeters filled with sand. For sandy loam under grass the agronomic soil P tests (AL-P, DL-P and Olsen-P) enabled reasonable predictions of P in leachate. Under arable use, factors such as fertilisation, management intensity, depth of tillage and irrigation resulted in weak correlations between soil P concentrations and P in leachate. It was shown for the first time that all P extractants reflected P enrichments in topsoils and subsoils and the development of distinct depth profiles. Influence of soil use on the depth distribution of P was more pronounced in the 0–20 cm layer than in the subsoils. Here, the original homogeneous substrate had oscillating P concentrations at 10-cm increments under all soil uses. These could not be explained by Al_ox and Fe_ox but were significantly correlated with the C_t contents and bulk density. This indicates that vertical movement of P containing organic matter along with differences in porosity contributed to the heterogeneous P distribution in the lysimeter subsoils. This new evidence must be considered if data sets from long-term lysimeter experiments are used to calibrate and validate P leaching models.     

Nitrogen leaching and crop availability in manured catch crop systems in Sweden

Results are presented from five years (1990–1995) of a field leaching experiment on a sandy soil in south-west Sweden. The aim was to study N leaching, change in soil organic N and N mineralization in cropping systems with continuous use of liquid manure (two application rates) and catch crops. N leaching from drains, N uptake in crops and mineral N in the soil were measured. Simulation models were used to calculate the N budget and N mineralization in the soil and to make predictions of improved fertilization strategies in relation to manure applications and changing the time for incorporation of catch crops. In treatments without catch crops, a normal and a double application of manure increased average N leaching by 15 and 34%, respectively, compared to treatment with commercial fertilizer. Catch crops reduced N leaching by, on average, 60% in treatments with a normal application of manure and commercial fertilizer, but only by 35% in the treatment with double the normal application rate of manure. Incorporation of catch crops in spring increased simulated net N mineralization during the crop vegetation period, and also during early autumn. In conclusion, manured systems resulted in larger N leaching than those receiving commercial fertilizer, mainly due to larger applications of mineral N in spring. More careful adaptation of commercial N fertilization with respect to the amounts of NH₄-N applied with manure could, according to the simulations, reduce N leaching. Under-sown ryegrass catch crops effectively reduced N leaching in manured systems. Incorporating catch crop residues in late autumn instead of spring might be preferable with respect to N availability in the soil for the next crop, and would not increase N leaching.     

Are Partial Nutrient Balances Suitable to Evaluate Nutrient Sustainability of Land use Systems? Results from a Case Study in Central Sulawesi,Indonesia

Nutrient input–output balances are often used as indicators for the sustainability of land use systems. In a case study on plot scale in Central Sulawesi, Indonesia, we measured nutrient input–output balances of natural rainforest and two unfertilized land use systems (maize, and coffee/cacao agroforestry). These are the two major land use systems on converted rainforest sites in this part of Sulawesi. We wanted to test if (a) plant nutrient balances are negative, (b) which pathway is most important for losses of plant nutrients, and (c) if partial plant nutrient balances are suitable to evaluate sustainability of the land use systems. We measured nutrient inputs by precipitation and nutrient outputs by harvest export and leaching. We selected two locations, the first was situated on a fertile Cambisol developed on alluvial sediment soil, and the second on a less fertile Cambisol developed on weathered phyllite substrate. Nutrient losses through leaching were higher on sites with higher soil fertility. Nutrient balances in natural forest on fertile soils were negative for N, Ca, K and Mg. Inputs of P by precipitation and outputs by leaching were below detection limit. On less fertile soils, leaching of N and K in natural forest was lower than inputs by precipitation. As net nutrient losses were highest in agroforestry, followed by maize and natural forest stands, forest conversion into agricultural land will result in increased nutrient losses. Main output pathway of N, P and K was harvest, whereas main output pathway for Ca and Mg was through leaching. The annual losses of nutrients we measured were higher than in comparable studies on nutrient poor soils; however losses were only small fractions of available nutrient stocks. Our results showed negative partial nutrient balances in both agricultural systems. Nutrient balances in this study were more influenced by native soil fertility than by land use. Because we found indirect evidence that some nutrient pathways, which were not measured, may have significantly changed the overall balance (biological N fixation, weathering), we conclude that partial nutrient balances are no good indicators for sustainability of land use systems.     

Organic and inorganic phosphorus forms in soil as affected by long-term application of organic amendments

Organic amendments contribute significantly to the phosphorus (P) supply in agroecosystems. However, their long-term effects on specific P forms in soils are not completely understood. The objective of this study was to investigate the concentration of organic P forms and inorganic P pools in soil and the activity of enzymes involved in the P turnover in a long-term field experiment running since 1998 in Northern Germany as affected by P amendments. The following treatments with different P supplies were sampled in 2012, 14 years after the establishment of the experiment: control (no P), cattle manure (manure), biowaste compost (compost), and biowaste compost in combination with triple-superphosphate (compost + TSP). The classification of organic P forms by using enzyme additions to NaOH–EDTA soil extracts showed non-hydrolyzable organic P as the dominant form in soil followed by inositol hexakisphosphate (Ins6P)-like P. Non-hydrolyzable and total organic P concentrations in soil were highest in the combined compost + TSP treatment, which received the highest amount of inorganic P. The values of the bioavailable P pools (water-extractable P and double lactate-extractable P) were in accordance with the P balance (P addition with the amendments minus P removal with harvested crops) independently of the type of amendment. The results of this research suggest that the distribution of soil P forms is more reliant on the turnover processes in the soil than on the forms of P added.     

Ways to reduce nitrogen pollution from Swedish pork production

The aim of this paper is to examine measures in Swedish pork production to improve N-use efficiency and to reduce N-pollution of water and air. The entire chain of feed production, animal feed conversion and the use of animal manure is included, as well as the spatial allocation of pork production. A calculation model is developed using experimental data. It is simple and possible to use in practical environmental control. Using catch crops and halving N-input in feed grain production reduces N-leaching up to 25% per hectare. These measures have considerably less effect on leaching per kilo of produced animal growth and NH₃-losses than on leaching per hectare. Reduced protein level in feed and Specific Pathogen Free pig production reduce both leaching and volatilisation, especially per kilo of animal growth. These animal-centred measures can also be profitable for many producers. Spreading all manure in spring and rapid incorporation is an effective way to reduce N-losses. However, as with catch crops and reduced fertilization, it is associated with considerable costs for the producers. A combination of best manure handling, catch crops and low protein feeding can reduce N-leaching and volatilisation up to 50%. Leaching from pig production on clay soil in Central Sweden is only one third of that on sandy soil in southwest Sweden. Spatial allocation of pork production also influences the environmental effects of N losses. These effects can be more negative in coastal zones with high N-deposition and low N-retention before the water reaches the sea, than in interior regions of Sweden with low original deposition. The results indicate that improved animal protein conversion, and especially suitable spatial allocation of pig production, are more cost-effective than additional measures in feed production and manure handling.