Search

Recommendations for nitrogen (N) fertilization are based on the analysis of the soil mineral N (SMN) content of one composite sample that is assumed to represent the average concentration, but that almost by definition fails to properly represent the inherent spatial variability of the field. Improvement in N management can thus be achieved by high-resolution measurements of the soil N status. However, soil sampling, transportation, sample preparation and laboratory analysis are laborious, costly and time-consuming. Additionally, errors associated with all these steps (particularly sampling and sample preparation) are notorious sources of inaccuracy. In situand on-line measurement modes could overcome these drawbacks. This paper presents a state-of-the-art review of proximal soil sensing technologies for in situand on-line measurements of total nitrogen (TN) and mineral N in soils. Visible and near-infrared spectroscopy (vis-NIRS) and mid-infrared spectroscopy (MIRS) have been successfully used in in situand on-line measurement platforms for determining TN. The review also focuses on data fusion (DF) approaches not only to improve the prediction performance of TN by vis-NIRS and MIRS but also to delineate management zones for site-specific N management. Electrochemical sensors such as ion-selective electrodes (ISE) or ion-selective field-effect transistors (ISFET) were found to be the most suitable to measure SMN. However, it was found that both sensor technologies are difficult to use for on-line measurements because they require the preparation of a soil solution and sufficient time delay is needed to reach a stable plateau. These limitations restrict the implementation of electrochemical sensing tools for site-specific N management, although they are the best methods to measure SMN, a needed parameter as a direct measure to determine N recommendations. Research on proximal soil sensing (PSS) for N measurement in soils should focus on the development of robust and accurate in situand on-line sensors for SMN, whereas improvement in the performance of vis-NIRS and MIRS for TN prediction by using advanced modelling and DF techniques is recommended. This development is essential to promote the implementation of variable rate N fertilization (VRNF). The review suggested the fusion of on-line collected soil data with crop data, present and historical yield, topography and weather conditions as the optimal solution for map-based and sensor-based VRNF scenarios. Furthermore, a new approach for VRNF, designated as the map-sensor-based approach, is proposed. In this approach, management zones (MZ) maps for the soil is developed in advance at the beginning of the cropping season, and this information is combined with current crop growth status [e.g., normalized differential vegetation index (NDVI)], measured with a proximal crop sensor to calculate the recommendation and implement VRNF in real-time.

Soil pore network effects on organic matter turnover have, until now, been studied indirectly because of lack of data on the 3D structure of the pore network. Application of X-ray computed tomography (X-ray CT) to quantify the distribution of pore neck size and related pore sizes from undisturbed soil cores, with simultaneous assessment of carbon (C) mineralisation, could establish a relationship between soil organic matter (SOM) decomposition and soil pore volumes. Eighteen miniature soil cores (diameter 1.2cm, height 1.2cm) covering a range of bulk densities were incubated at 20°C for 35 days. Respiration was modelled with a parallel first- and zero-order kinetic model. The cores were scanned at 9.44µm resolution using an X-ray CT scanner developed in-house. Correlation analysis between the slow pool C mineralisation rate, ks, and pore volume per pore neck class yielded significant (P<0.05) positive correlations: r=0.572, 0.598, and 0.516 for the 150–250, 250–350, and >350µm pore neck classes, respectively. Because larger pores are most probably mainly air-filled, a positive relation with ks was ascribed to enhanced aeration of smaller pores surrounding large pores. The weak and insignificant relationship between the smallest pore neck class (<9.44µm) and ks could be explained by obstructed microbial activity and mobility or diffusion of exo-enzymes and hydrolysis products as a result of limited oxygen availability. This study supports the hypothesis that the impact of soil structure on microbial processes occurs primarily via its determination of soil water distribution, which is possibly the main driver for the location of C mineralisation in the soil matrix.

Intensive vegetable production systems throughout South East Asia are characterised by large nutrient inputs and low nitrogen (N) use efficiencies. In Indonesia, intensive vegetable production is concentrated on volcanic highland soils starting from an altitude of around 700m above sea level. We measured potential N mineralisation from soil organic matter and from several representative organic materials in Andisols and Inceptisols with andic properties from Central Java, Indonesia. Unamended soils and soils amended with crop residues, animal manures, and compost were incubated during 3–4 months at 25°C in the laboratory, then we monitored N mineralisation. Relative N mineralisation was significantly smaller in the Andisols (average 3.6±1.0%) than the Inceptisols (7.4±2.9%), and was negatively related to oxalate-extractable aluminium (Alox) (r=–0.749) and soil organic carbon (r=–0.705). This is probably due to the strong protection of organic matter (and organic N) by binding to active Al compounds. Net N mineralisation from the added organic materials was highly variable (ranging from 68.1% for the broccoli residues to 2.6% for tithonia compost), and was best related to the organic N content (r=0.476). There were no significant correlations between net N mineralisation and biochemical fractions, which we attribute to the large variety of materials used in this study compared with previous studies. The data generated here on N mineralisation potential from soil organic matter, and from a variety of plant materials and animal manures that are commonly used in these intensive vegetable rotations, will allow for the rapid and efficient introduction of N fertiliser advice systems based on balance sheets.

Sandy cropland soils in NW Europe were found to contain unusually high organiccarbon OC levels, and a link with their landuse history has been suggested. This studys aim was to assess the discriminating power of physical and chemical fractionation procedures to yield information on soilorganicmatter OM stability for these soils. In relict and cultivatedheathland soils, much higher proportions of 6 NaOCl treatment–resistant but 10 HF–soluble OC MOC and N 32.2 and 29.9 were measured compared to a set of “permanent"cropland soils without a history of heathland land use 11.9 and 8.5. Also, the proportions of 6 NaOCl– and 10 HF treatment–resistant OC and N in the relict and cultivated heathlands 19.2 and 12.0 were higher than in the permanentcropland soils 17.7 and 5.7. Stepwise multiple linearregression yielded a significant relationship between the annual mineralization g C 100 g OC–1, soil OC g C kg–1 content, and MOC: Annual mineralization = 4.347 – 0.087 soil OC – 0.032 MOC R2= 0.65. Combinations of incubation experiments for quantification of the labile soil OM pool with chemical fractionation may thus yield meaningful data for development of soilorganicmatter models with measurable pools, but their applicability will be limited to specific combinations of former land use with soil, climate, and current management.

Reduced tillage (RT) management may increase surface soil organic carbon (SOC) and nitrogen (N), particularly due to accumulation of labile organic matter (OM). We investigated the effect of RT compared with conventional tillage (CT) on the distribution of SOC and N over different soil fractions from 7 pairs of fields with cereal–root crop rotations, in the Belgian loess belt. Surface soil samples (0–100mm) were physically fractionated according to a sequential sieving and density separation method into stable microaggregates, silt and clay, and free and occluded particulate OM fractions. RT management was previously found effective in increasing the organic C and organic N content of the surface soil (0–100mm) at these 7 sites. Here, physical fractionation showed that the difference in amount of organic C and N in free particulate OM (fPOM), intra-microaggregate particulate OM (iPOM), and silt and clay associated OM between the RT and CT soils contributed 34, 29, and 37% of the increase in SOC and 35, 32, and 33% of the increase in N. The contribution of OC and N in iPOM and fPOM increased significantly on a relative basis under RT management. Only a modest increase in iPOM and slight enhancement of microaggregation was observed in RT compared with CT soils. We suggest that the repeated disturbance of soil by harvest of root crops and repeated use of cultivators and harrows may limit the accumulation of physically protected POM under RT management of these Western European cereal–root crop rotations. Instead, most of the accumulated OC and N in the surface horizons under RT management is present as free unprotected POM, which could be prone to rapid loss after (temporary) abandonment of RT management.

Total soil organiccarbon SOC stocks for grassland soils in Flanders N Belgium were determined for the Kyoto Protocol reference year 1990 and 2000 in order to investigate whether these soils have been CO2sinks or sources during that period. The stocks were calculated by means of detailed SOC datasets, which were available at the community scale for the whole of Flanders. The total SOC stocks for Flemish grassland soils 1 m depth were estimated at 38 Mt SOC in 1990 and 34 Mt SOC in 2000. The loss of SOC resulted from a decrease in the SOC content of grassland soils 71 and could also partly 29 be explained by a decline in grassland area. Significant decreases in SOC for the 0–6 cm depth layer were found for the 1990s for the coarsertextured soils with SOC losses ranging between –0.3 and –0.5 over the 10 y period. Specific management practices that disturb the SOC balance such as conversion to temporary grassland and a reduction of animalmanure application are hypothesized to have contributed to the observed loss of SOC stocks. We furthermore conducted an analysis of uncertainty of the 1990 and 2000 grassland SOC–stocks calculation using Monte Carlo analysis. Probabilitydistribution functions were determined for each of the inputs of the SOCstock calculation, enabling us to assess the uncertainty on the 1990 and 2000 SOC stocks. The frequency distributions of these simulated stocks both closely approached lognormal distributions, and their 95confidence intervals ranged between 150 and 50 of the calculated mean SOC stock. The standard error on the measured decrease in SOC stocks in Flemish grassland soils during the 1990s was calculated to be 7–8 Tg SOC, which is equivalent to twice this decrease. This clearly shows that largescale changes in SOC stocks are uncertaintyridden, even when they are based on detailed datasets.

One of the most important problems in the Loess Plateau of China affecting sustainable agriculture is inefficient nutrient use. Field experiments were conducted to study the effects of different soil management practices on the nitrogen (N) dynamics and winter wheat yield on a loess soil in Luoyang, Henan province, China. The results showed that subsoiling with mulch (SS) consistently increased the yield of winter wheat primarily by better water harvest compared with conventional tillage (CT). The influence on yield of no till with mulch (NT) depended on the amount of precipitation. TC (2 crops per year) lowered the winter wheat yield mainly due to the unfavourable soil moisture conditions after growing peanut in summer; however, the harvested peanut gained an extra profit for the local farmer. N uptake by grain and straw and N export was highest for SS. Changes in frequency and intensity of tillage practice altered soil total N content and its distribution along the slope. SS and NT increased the N content of the surface layer (0–0.20 m) compared with CT, but there was no significant effect in deeper soil layers. Considerable amounts of nitrate-N were left in the profile 0–1.60 cm just after harvest under all treatments. The cumulative nitrate-N content to a depth of 1.60 m on average was 282 kg/ha, of which 56 kg/ha was in the layer 1.20–1.60 m, which is an indication of considerable nitrate leaching. From data of 7 consecutive years between 1999 and 2006, it could be concluded that SS resulted in the highest yield and total N content in the surface layer, and is the most sustainable tillage option for the circumstances of the study area.

Compost and other organic amendments have been proven to improve the soil physical quality. In Flanders, vegetable, fruit and garden (VFG) wastes are collected selectively and composted. We studied the effects of the combined application of three different doses of VFG compost and cattle slurry and one treatment with only mineral N applied, during 9 years on a range of soil physical properties: aggregate stability, saturated hydraulic conductivity, bulk density, total pore volume and soil moisture retention. The organic amendments had a significantly beneficial impact (p<0.05) on all soil physical properties, except for the soil moisture retention which was hardly influenced by any of the treatments. The combined application of VFG compost and cattle slurry resulted in the best soil physical conditions. No significant differences were found in soil physical parameters between the unfertilized plots and plots that were fertilized with mineral N.

We examined the effects of 10 yr of reduced tillage (RT) management, compared with conventional tillage (CT), on the chemical composition of soil organic matter (SOM) using a combination of physical fractionation and pyrolysis–field ionization mass spectroscopy (Py–FIMS). Surface soil samples (0–10 cm), which were collected from two adjacent CT and RT managed fields, were separated into particulate organic matter (POM) fractions and sand, silt, and clay size separates. Higher amounts of C (77%) and N (64%) were observed in all size separates of the RT soil and, in particular, the proportion of intramicroaggregate POM was two times as large as in the CT soil. The Py–FIMS spectra showed that larger proportions of free fatty acids, sterols, and N‐containing compounds were present in the RT soil's sand fraction than in the CT soil. Similar observations were also made for both free and intramicroaggregate POM fractions. In the silt and clay size fractions, no substantial differences in SOM composition were measured between tillage treatments, except that the RT soil's clay fraction had a higher proportion of N‐containing compounds and a lower proportion of alkylaromatics. Ratios of carbohydrate hexose to pentose subunits and of lignin monomers + phenols to lignin dimers confirmed a less decomposed character of the SOM in the silt and clay size fractions of the RT soil. These observations can be logically linked to the reduced mixing of crop residues and manure in the soil profile and higher surface soil microbial biomass under RT.

Following mineralization of N‐rich crop residues, large amounts of mineral N can be released into the soil. Manipulating N mineralization of crop residues may be an option to reduce NO3−in soil. The potential to manipulate the N release from vegetable crop residues by using organic wastes was tested under field conditions. At the start of the experiment, cauliflower (Brassica oleracea L. var. botrytisL.) residues (∼73 Mg fresh matter ha−1) together with an immobilizer waste (∼5 Mg C ha−1of straw, green waste compost, sawdust, or paper sludge) were incorporated into a silt loam soil. After 154 d, a remineralizing waste (∼1 Mg C ha−1of vinasse or dairy sludge) was incorporated. During the field experiment, the mineral N content in the soil was measured at regular time intervals, and net N release, NO3−leaching, and denitrification were simulated using a N mineralization–immobilization model coupled to a NO3−leaching model. Straw, green waste compost, and sawdust were able to immobilize between 54 and 68% of the N released by the cauliflower residues and reduced NO3−leaching by 56 to 68%. Paper sludge released an extra amount of N due to its low C/N ratio. No consistent remineralization of N could be found in any of the treatments, probably due to an unsuitable composition of the remineralizer wastes. Manipulating N release of N‐rich crop residues by using organic wastes may be a suitable method to reduce NO3−leaching; however, stimulating remineralization of immobilized N by the start of the following spring may not be easy to achieve.

ABSTRACTOrganic farming is put forward as a sustainable alternative to the conventional way of farming. However, until now there has been practically no research on soil related aspects of organic farming in Flanders. Therefore, in this study, the carbon, nitrogen, sulphur and phosphorus status of the fields on organic farms was measured and was related to characteristics of the farms involved (land use, soil texture, management intensity and time since conversion to organic farming) and was, where possible, compared with the general soil fertility status of agricultural soils in Flanders. The SOC (soil organic carbon) contents tended to be larger in the fields of the organic farms studied than in conventional farming. This content was correlated positively with the management intensity of the fields. However, some of the organic fields still had rather low SOC contents. To increase this content organic farmers will need to apply more organic materials with large C:N and C:P ratios taking into account the strict current manure legislation. The mineral N contents on the organic farms measured in the period between 1 October 2003 and 15 November 2003, indicating the risk of nitrate leaching, were well below the average values of the different land use classes of conventional agricultural soils in East Flanders. The available P content of the organic fields was high to very high as is also the case for conventional agriculture in East Flanders and was strongly related to the management intensity.

Abstract Manipulating the N release from high-N crop residues by simultaneous mixing of these residues with organic biological waste (OBW) materials seems to be a possible method to reduce NO3− leaching. The aim of this study was to examine whether the incorporation of OBW materials together with a high-N crop residue (celery) had also an effect on N2O emission from horticultural soil under short-term and optimised laboratory conditions. A sandy loam soil and celery residues were mixed with different OBW materials and brought into PVC tubes at 80% water-filled pore space and 15°C. Every 2.5 h, a gas sample was taken and analysed by gas chromatography for its N2O concentration. The soil amended with only celery residues had a cumulative N2O emission of 9.6 mg N kg−1 soil in 50 h. When the celery residues were mixed with an OBW material, the N2O emission was each time lower than the emission from the celery-only treatment (between 3.8 and 5.9 mg N kg−1 soil during maximum 77 h), except with paper sludge (17.2 mg N kg−1 soil in 100 h). The higher N2O emission from the paper sludge treatment was probably due to its unusually low C:N ratio. Straw, green waste compost 1 (GWC1) and 2 (GWC2), saw dust, and tannic acid reduced the N2O emission of the celery treatment by 40 to 60%. Although the N2O reduction potential can be expected to be lower and with differing dynamics under field conditions, this study indicates that apart from reducing NO3− leaching, OBW application may at the same time reduce N2O emissions after incorporation of high-N crop residues.

The effect of soil fumigation on N mineralization and nitrification needs to be better quantified to optimize N fertilizer advice and predict NO−3concentrations in crops and NO−3leaching risks. Seven soils representing a range in soil texture and organic matter contents were fumigated with Cyanamid DD 95 (a mixture of 1,3‐dichloropropane and 1,3‐dichloropropene). After removal of the fumigant, the fumigated soils and unfumigated controls were incubated for 20 wk and N mineralization and nitrification were monitored by destructive sampling. The average short‐term N mineralization rates (ks) were significantly larger in the fumigated than in the unfumigated soils (P= 0.025), but the differences in ksbetween fumigated and unfumigated soils could not be related to soil properties. The average long‐term N mineralization rates (kl) were slightly larger in the fumigated soils but the difference with the unfumigated soils was not significant. Again, the differences in klvalues could not be related to soil properties. Nitrification was inhibited completely for at least 3 wk in all soils, and an effect on nitrification could be observed up to 17 wk in one soil. An S‐shaped function was fitted to the nitrification data corrected for N mineralization, and both the rate constant (γ) and the time at which maximum nitrification was reached (tmax) were strongly correlated to soil pH. However, since no correlations were found between the effect of fumigation on N mineralization and soil properties, taking into account the effects of fumigation in fertilizer advice and in the prediction of NO−3leaching risks will need further research.

In Western Europe, agriculture is one of the major contributors to the pollution of ground- and surface waters. Environmental concern has created the need for protection of these waters against eutrophication, caused by nutrient losses from e.g. agricultural sources. Leaching models may be used to predict nitrate-N losses to the environment and a plethora of such leaching models already exist. Four nitrate leaching models (Burns model, SLIM, SACFARM and ANIMO), with varying degree of complexity and parameter requirements, were used to simulate leaching in a bare fallow soil on a number of fields in the Wijlegem catchment in Flanders, Belgium. The models' performance was evaluated both statistically and graphically. Although all models predicted nitrate content in the soil profile within acceptable limits, the slightly adjusted Burns model appeared to simulate both the nitrate nitrogen and the water content best for the calibration field. Similar results were obtained for the evaluation field experiments: the Burns–α model simulated the moisture and nitrate content fairly well, while SLIM performed well in simulating the nitrate content. In conditions with limited data availability, simple (management) models, needing only a limited number of parameters to be measured or calibrated, may yield better simulation results than complex mechanistic models.

We have studied the short term C mineralization of six wastes from important food industries, one sludge from a biogas plant and three composts. All the wastes were characterized chemically and fractionated according to the Van Soest method. The fresh wastes were incubated under controlled environment conditions to determine the C mineralization rate. Based on first order mineralization kinetics, we calculated the hypothetical amount of stable C in the wastes as the amount of C that would not be mineralized within one year under field conditions. The percentage of stable organic C in the organic matter was in general much larger in the composts than in the other wastes, but when expressed on dry matter, the non-composted wastes had comparable or larger amounts of stable organic C than the composts and have a considerable potential for supplying organic matter to soils, and hence for C sequestration. The amount of stable organic C could best be predicted by the total N content of the wastes (Ra2= 0.855), whereas the results of the fractionation had very little predictive power, probably due to problems related to the high ash content of some of the wastes. An index that combined stable organic C and N and P content in the wastes was calculated to assess possible limitations for applying these wastes in agriculture. Under current nutrient legislation in Western Europe, a number of these wastes will only be usable in small amounts, but these and other food industry wastes could still prove to be valuable soil amendments in nutrient poor situations, for increasing soil organic C content and supplying nutrients.

The article discusses the highlights of the 1st International ISHS Symposium on Sustainable Vegetable Production in South East Asia held in Java, Indonesia from March 14-17, 2012. The event was attended by about 100 participants, representing 21 different nationalities from South East Asia and the Pacific. Topics discussed include nutrient supply, fertilization and organic matter management.