Soil Mineral Nitrogen Content Research Articles

Green manure and long-term fertilization effects on soil zinc and cadmium availability and uptake by wheat (Triticum aestivum L.) at different growth stages

Zinc (Zn) deficiency in human populations depending on cereals as a main source of Zn is a global malnutrition problem. In this field study, we investigated the potential of green manure application to increase soil Zn availability and wheat grain Zn concentrations (biofortification) on a Luvisol with different long-term fertilizer management. We also studied cadmium (Cd), as wheat is a major contributor of this undesired non-essential element to human diets. Clover (Trifolium alexandrinum L.), mustard (Sinapis alba L.) or no green manure was grown on field plots which had been managed with farmyard manure or mineral fertilizers for 65years in Switzerland. After green manure incorporation into the soil, spring wheat (Triticum aestivum L.) was grown on all plots. The “diffusive gradients in thin films” (DGT) method and DTPA extraction were used to compare soil Zn and Cd availability among the treatments. In contrast to mustard, clover increased soil mineral nitrogen concentrations and wheat biomass; however, neither increased grain Zn concentrations. DGT-available Zn and Cd increased temporarily after both farmyard manure and mineral nitrogen fertilizer application. Higher DTPA-extractable soil Zn and Cd, lower wheat grain yields, but higher grain Zn concentrations were obtained with farmyard manure compared to mineral fertilizers, independent of the green manure treatment. Farmyard manure added Zn, Cd and organic matter that increased the soil binding capacity for Zn and Cd. The decomposition of clover residues caused higher wheat grain yields, but only marginally lower grain Zn concentrations. The absence of a stronger dilution of grain Zn was probably due to organic acid and nitrogen release from decomposing clover, which facilitated Zn uptake by wheat. The study revealed that both long- and short-term field management with organic matter alters soil Zn and Cd concentrations but that the long-term effects dominate their uptake by wheat, in Zn sufficient soil.

Toxicity of iron oxide nanoparticles to grass litter decomposition in a sandy soil

We examined time-dependent effect of iron oxide nanoparticles (IONPs) at a rate of 2000 mg kg−1 soil on Cynodon dactylon litter (3 g kg−1) decomposition in an arid sandy soil. Overall, heterotrophic cultivable bacterial and fungal colonies, and microbial biomass carbon were significantly decreased in litter-amended soil by the application of nanoparticles after 90 and 180 days of incubation. Time dependent effect of nanoparticles was significant for microbial biomass in litter-amended soil where nanoparticles decreased this variable from 27% after 90 days to 49% after 180 days. IONPs decreased CO2 emission by 28 and 30% from litter-amended soil after 90 and 180 days, respectively. These observations indicated that time-dependent effect was not significant on grass-litter carbon mineralization efficiency. Alternatively, nanoparticles application significantly reduced mineral nitrogen content in litter-amended soil in both time intervals. Therefore, nitrogen mineralization efficiency was decreased to 60% after 180 days compared to that after 90 days in nanoparticles grass-litter amended soil. These effects can be explained by the presence of labile Fe in microbial biomass after 180 days in nanoparticles amendment. Hence, our results suggest that toxicity of IONPs to soil functioning should consider before recommending their use in agro-ecosystems.

Nitrous Oxide Emissions From Household Vegetable Fields in The Rural Residential Areas of Hilly Subtropical Central China

Nitrous oxide (N2O) emissions from a household vegetable field in a rural residential area of hilly subtropical central China were observed using a static chamber-gas chromatographic method from January 2010 to December 2011. The N2O fluxes exhibited seasonal dynamics and the accumulated N2O emissions during the wet seasons accounted for 83.5% of the total N2O emissions. Soil mineral nitrogen (N) contents were found not limiting factors because of the application of large amounts of human excreta. The daily N2O fluxes showed a significant, positive correlation with soil temperature, soil moisture and soil NO3 --N content, and soil denitrification may be the major pathway responsible for N2O emissions. High-frequency, intensive application of liquid excreta stimulated the N2O emission process. The average annual N2O emission rate was 12.1 ± 0.9 kg N ha-1 year-1 in the examined household vegetable field, and the total N2O emissions from household vegetable fields originating from the N source of human excreta in the studied Jinjing catchment (135 km2) were estimated as 1.58 ± 0.16 ton N year-1. Such emissions can be considered as N2O re-emissions of the N input into the ecosystem, and the emission factor of N2O re-emissions was estimated to be 0.57%. The findings indicated that under the present management practices, household vegetable fields in the subtropics of China provide a relevant contribution to greenhouse gas emissions and a responsive mitigation scheme at a household scale is needed to reduce N2O emissions.

Effect of mulching on soil environment, microbial floraand growth of potato under field conditions

Mulches modify hydrothermal regime, recycles plant nutrients, promote crop development and increase yields. The impact of straw mulch and different doses of recommended nitrogen was studied on soil microbial flora, soil physico-chemical properties and plant growth parameters of potato at different time intervals under field conditions. Maximum bacterial population (75× 107 cfu g-1 soil), plant growth promoting rhizobacteria count (63× 105 cfu g-1 soil) and fungal population (69× 103 cfu g-1 soil) were observed with the treatment having rice straw mulch @ 6 tonnes/ha and 100% N-level while diazotrophic count (42× 105 cfu g-1 soil) was found with treatment having mulch (6t) but no nitrogen fertilizer at 30 DAS. Mulched soil samples gave statistically higher microbial population. The soil pH and the electrical conductivity of soil were not significantly affected by the different applications. A slight improvement in soil organic content was observed in mulched (0.32%) over unmulched (0.24%) soil samples at 90 DAS. The mineral nitrogen content of soil i.e. ammonical (235.2 kg/ha) and nitrate (156.8 k/ha) nitrogen were greatly affected at 90 DAS by mulching and higher doses of nitrogen fertilization. The altered microbial population helps in improving the various growth parameters of potato plants. Maximum chlorophyll content (1.84 mg/g), maximum dry root-shoot biomass (0.7 g/pl and 5.8 g/pl) and maximum yield (366.8 q/ha) were observed with the treatment having mulch and 100% N-level. It is also concluded that mulch increased the minimum soil temperature by 2-30C and lower down the maximum by 2 to 80C.

Growth and yield formation of sugar beet ( Beta vulgaris L.) under strip tillage compared to full width tillage on silt loam soil in Central Europe

On silt loam sites in Central Europe, autumn strip tillage (ST) might offer an option to produce high sugar beet yields at lower costs and improved erosion control compared to full width tillage practices. Three field trials were conducted in 2013/14 and 2014/15 at Göttingen, Lower Saxony, Germany, to investigate the effect of three tillage systems (intensive tillage (IT), reduced tillage (RT), ST) and two fertilizer nitrogen levels (no fertilizer nitrogen (N0), fertilizer nitrogen required for optimum yield (Nopt)) on sugar beet growth. Compared to IT and RT, field emergence period under ST was prolonged by 5-7 days, which was presumably caused by a coarse and uneven seedbed. In the early growth stage, chlorophyll present in the leaves (SPAD value) was higher for IT and RT compared to ST, indicating a lower nitrogen supply for ST, especially under N0. This was supported by a slightly higher nitrogen concentration in the plant dry matter and a higher soil mineral nitrogen content in spring under IT and RT compared to ST. Leaf area index of sugar beet was almost equal between IT and RT, while values for ST tended to be lower. As a result, plant dry matter yield and white sugar yield were approximately 7 % higher for IT and RT compared to ST. Plant nitrogen uptake revealed a similar pattern, thus, nitrogen use efficiency was not affected by tillage systems. Penetration resistance and root length density in the top soil revealed no relation to the difference in yield. It was concluded that both, the prolonged field emergence period and the lower nitrogen supply under ST possibly impaired a rapid development of an adequate leaf canopy that facilitates efficient light interception and a high yield.

Nitrogen dynamics following slurry injection in maize: soil mineral nitrogen

In northwestern Germany slurry injection below maize (Zea mays L.) seeds is gaining increasing interest of farmers, because of the expected enhanced nitrogen (N) and phosphorus (P) use efficiencies compared to the usual fertilizing practice. The present study aims to compare the spatial and temporal soil mineral nitrogen (SMN) dynamics for these fertilizing strategies. Field trials with four treatments (unfertilized control, broadcast application + N P mineral starter fertilizer (+MSF), injection and injection + nitrification inhibitor (NI)) were conducted using pig slurry on sandy soil in 2014 and 2015. Soil samples were taken from three soil layers at 30 cm intervals down to 90 cm, and at three positions (below the maize row, 15 and 30 cm distance to the row) at several dates over the growing season. Soil monoliths (15 × 15 × 10 cm) were sampled around the injection zone, and for all other soil zones an auger was used. In 2014 due to heavy rainfall all fertilized N was displaced from the top soil layer of the broadcast treatment until 6-leaf stage, while N displacement was significantly smaller after slurry injection (about 20 kg SMN ha−1 more in top layer). The lateral movement of injected slurry N was negligible. In 2015 almost no displacement of fertilized N out of the top soil layer occurred independently of treatments, because of lower rainfall. The release of slurry N was delayed following broadcast application and large SMN concentrations were detected in the injection zones until 10-leaf stage. The addition of a NI resulted in significantly increased ammonium N concentrations in the injection zone throughout the early growth stages [+46 % (2014) and +12 % (2015) at 6-leaf stage]. Thus, N displacement was delayed in 2014 and in 2015 at 6-leaf stage increased SMN concentrations (+1/3 with NI) were found around the slurry band. Due to slurry injection, especially when combined with a nitrification inhibitor, the applied nitrogen is located in a soil zone with better spatial availability for plant roots compared to broadcast application and the risk of nitrate leaching is significantly reduced.

The Interaction of Bacterial-Feeding Nematodes and IAA-Producing Bacteria in Gnotobiotic Microcosm System

The effect of the bacterial-feeding nematodes (Cephalobus sp.) grazing on IAA-producing bacteria (Pseudomonas sp. and Burkholderia sp.) stimulated both the microbial growth and activity and increased soil mineral nitrogen and IAA contents were investigated in pots with soil under controlled conditions. The soil, nematodes and the property of IAA were analyzed at regular basis. In gnotobiotic microcosm conditions, the bacterial-feeding nematodes grazing on bacteria stimulated both the microbial growth and activity and increased the mineral nitrogen and IAA content. The analysis of the IAA-producing bacteria (number, activity and IAA content) revealed a statistically significant in the presence of the bacterial-feeding nematodes. Our conclusion may be valid not only for experiments, but also for future application in agriculture.

Greenhouse gas fluxes from a grazed grassland soil after slurry injections and mineral fertilizer applications under the Atlantic climatic conditions of NW Spain

The number of studies that investigate how agricultural practices on dairy farms in the North West (NW) of Spain affect greenhouse gas (GHG) fluxes from soils is limited. Thus, the objective of this study was to quantify the effects of the application of mineral fertilizers and cattle slurry injections on GHG fluxes from a grassland soil with grazing dairy cattle, in Galicia (NW Spain). We also aimed to identify the type of fertilizer associated with high grass production and low GHG fluxes. To achieve this, fluxes of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2), grass yields and soil mineral nitrogen (N) contents were monitored after three applications (in spring, summer and autumn) of surface broadcasted mineral fertilizer (MN) and injected cattle slurry (CS) and compared with no fertilization (zero N). Dry soil conditions (<60% water-filled pore space (WFPS)) were observed during the spring and summer, contrasting with the higher soil WFPS (>60%) in autumn due to the more frequent rainfall. Overall, total cumulative N2O fluxes from CS were similar than from MN (P>0.05), indicating that denitrification in this C-rich soil was not stimulated by slurry-carbon applications. Large losses of CH4 and CO2 were related to CS, but overall only total cumulative CH4 fluxes were larger with respect to MN (P<0.05). Dry weather conditions would have stimulated organic matter mineralization in this soil, which resulted in the low efficiency of both fertilizers to increase yields. As we obtained similar total CO2 equivalents to produce same yields with both types of fertilization (P>0.05), this study did not show a clear type of fertilization related to low GHG fluxes and high yields. We believe that longer-term studies are required to provide more robust estimations and conclusions about the effect of fertilizer applications on GHG fluxes from grassland soils in NW Spain.

Modelling nitrous oxide emissions from mown-grass and grain-cropping systems: Testing and sensitivity analysis of DailyDayCent using high frequency measurements

The DailyDayCent biogeochemical model was used to simulate nitrous oxide (N2O) emissions from two contrasting agro-ecosystems viz. a mown-grassland and a grain-cropping system in France. Model performance was tested using high frequency measurements over three years; additionally a local sensitivity analysis was performed. Annual N2O emissions of 1.97 and 1.24kgNha−1year−1 were simulated from mown-grassland and grain-cropland, respectively. Measured and simulated water filled pore space (r=0.86, ME=−2.5%) and soil temperature (r=0.96, ME=−0.63°C) at 10cm soil depth matched well in mown-grassland. The model predicted cumulative hay and crop production effectively. The model simulated soil mineral nitrogen (N) concentrations, particularly ammonium (NH4+), reasonably, but the model significantly underestimated soil nitrate (NO3−) concentration under both systems. In general, the model effectively simulated the dynamics and the magnitude of daily N2O flux over the whole experimental period in grain-cropland (r=0.16, ME=−0.81gNha−1day−1), with reasonable agreement between measured and modelled N2O fluxes for the mown-grassland (r=0.63, ME=−0.65gNha−1day−1). Our results indicate that DailyDayCent has potential for use as a tool for predicting overall N2O emissions in the study region. However, in-depth analysis shows some systematic discrepancies between measured and simulated N2O fluxes on a daily basis. The current exercise suggests that the DailyDayCent may need improvement, particularly the sub-module responsible for N transformations, for better simulating soil mineral N, especially soil NO3− concentration, and N2O flux on a daily basis. The sensitivity analysis shows that many factors such as climate change, N-fertilizer use, input uncertainty and parameter value could influence the simulation of N2O emissions. Sensitivity estimation also helped to identify critical parameters, which need careful estimation or site-specific calibration for successful modelling of N2O emissions in the study region.

Switchgrass growth and pine–switchgrass interactions in established intercropping systems

AbstractIntercropping switchgrass (Panicum virgatum L.) with loblolly pine (Pinus taeda L.) has been proposed for producing bioenergy feedstock in the southeastern United States. This study investigated switchgrass growth and pine–switchgrass interactions at two established experimental fields (7‐year‐old Lenoir site and 5‐year‐old Carteret site) located on the coastal plain of eastern United States. Position effects (edge and center of switchgrass alley in intercropping plots) and treatment effects (intercropping vs. grass‐only) on aboveground switchgrass growth were evaluated. Interspecific interactions with respect to capturing resources (light, soil water, and nitrogen) were investigated by measuring photosynthetically active radiation (PAR) above grass canopy, soil moisture, and soil mineral nitrogen contents. Switchgrass growth was significantly (P = 0.001) affected by treatments in Lenoir and by position (P &lt; 0.0001) in both study sites. Relative to the center, PAR above grass canopy at edge in both sites was about 48% less during the growing season. Soil water content during the growing season at the edge of grass alley was significantly (P = 0.0001) lower by 23% than at the center in Lenoir, while no significant (P = 0.42) difference was observed in Carteret, in spite of more grass growth at center at both sites. Soil mineral nitrogen content at the center of intercropping plots in Lenoir (no fertilization during 2015) was significantly (P &lt; 0.07) lower than at the edge during the peak of growing season (June, July, and August), but not during early and late parts of growing season (May, September, and November). Position effects on soil water and mineral nitrogen were less evident under conditions with higher external inputs (rainfall and fertilization) and lower plant uptake during nongrowing seasons. Results from this study contributed to a better understanding of above‐ and belowground pine–switchgrass interactions which is necessary to properly manage this new cultivation system for bioenergy production in the southeastern United States.

Research on soil net nitrogen mineralization in Stipa grandis grassland with different stages of degradation

Net nitrogen mineralization is one of the nitrogen cycling process, and it is very important to understand nitrogen mineralization characteristics in degradation grassland. In the upper 0–10 cm soil layer of Stipa grandis P. A. Smirn. grassland in the Xilin river basin, Inner Mongolia, we studied the soil net nitrogen mineralization and nitrification among three varying stages of degradation grassland and analyzed the relationship between the mineralization rate of the soil net nitrogen and environmental factors, using the resin-core incubation method. Our results demonstrated that, from May to October 2012, the accumulated net nitrogen mineralization was 21.620 mg kg–1, 12.486 mg kg–1, and 48.053 mg kg–1 in the slightly, medium, and heavily degraded grasslands, respectively and varied greatly among the three stages of degradation shown by the S. grandis grassland plots. During the cultivation period, the variation of net nitrogen mineralization and nitrification was similar to the variation of soil mineral nitrogen. The higher soil mineral nitrogen content indicated higher mineralization of net nitrogen. In July and August, soil moisture was positively correlated with the net nitrogen mineralization rate, and the correlation coefficients between these two factors of 0.73, 0.58, and 0.79 for the slightly, medium, and heavily degraded plots, respectively. The rates of net nitrogen mineralization and nitrification were negatively correlated with soil total nitrogen, but positively correlated with C/N ratio, and weakly correlated with other physicochemical properties.

Effect of tillage and crop (cereal versus legume) on greenhouse gas emissions and Global Warming Potential in a non-irrigated Mediterranean field

Crop rotation with legumes and conservation tillage systems are advisable practices in rainfed Mediterranean agro-ecosystems, since, in these areas, soils are broadly characterized by low organic matter contents and low fertility. These management practices can substantially modify the dynamics of soil greenhouse gas (GHG) emissions, carbon sequestration and carbon dioxide (CO2) emissions derived from system inputs and farm operations. In this context, a field experiment was conducted under Mediterranean conditions to evaluate the effect of three long-term tillage systems (no tillage (NT), minimum tillage (MT) and conventional tillage (CT)) and two crops (vetch (V, Vicia sativa L.) versus barley (B, Hordeum vulgare L.)) on nitrous oxide (N2O), methane (CH4) and CO2 emissions during one year. Crop yields, soil mineral nitrogen concentrations, dissolved organic carbon and GHG fluxes were measured during the growing season. Soil organic carbon was measured in spring 2012 (18 years after the beginning of a long-term tillage experiment) and together with input and fuel consumption by farm machinery was used to compare the Global Warming Potential (GWP) of the different crop and tillage treatments. Cumulative fluxes of N2O ranged between 0.16 (B-MT) and 0.29 (V-MT) kgN2O-Nha−1yr−1, resulting in a lower impact on Net GWP than in previous studies. A significant ‘tillage×crop’ interaction was observed in cumulative N2O emissions (V resulted in higher N2O losses than barley in CT and MT, whereas similar fluxes were observed under NT), which was influenced by soil water-filled pore space, dissolved organic carbon content and denitrification losses, in spite of the presumable predominance of nitrification. Neither tillage nor crop influenced CH4 or CO2 emissions. Yield-scaled N2O emissions (YSNE) were low (<4gN2O-NkgabovegroundNuptake−1) and significantly higher in B than in V. The most sustainable crop and tillage treatments in terms of GWP were non-fertilized-V and NT, due to higher carbon sequestration and lower fuel consumption under NT and the absence of mineral N fertilizers in V. These crop and tillage treatments could be considered good management strategies in rainfed Mediterranean agro-ecosystems since they provide the best balance between soil emissions, YSNE and Net GWP.

The Influence of Physical Properties of Sod-Podzol Soil on its Ammonifying and Nitrifying Capacity

The research was conducted by the Chair of Agricultural Chemistry and Crop Farming of the Mari State University. The model experiment helped to study the influence of temperature, moisture, and density on nitrifying and ammonifying capacity of sod-podzol midclay low-humic soil. It was found out that change of physical properties factors of sod-podzol soil influenced nitrifying and ammonifying capacity and mineral nitrogen content. Maximum content of nitrate and mineral nitrogen and the biggest nitrifying capacity were at a soil temperature of +15°C and had the following corresponding values: 74.4, 81.3, and 31.9 mg/kg. Moistening conditions optimal for developing nitrifying and ammonifying bacteria were formed at a soil moisture of 20-25% (60-75% WFC). At this moisture there were the biggest figures of nitrifying capacity (31.5-35.0 mg/kg) and maximum values of content of nitrate nitrogen (74.0-77.5 mg/kg) and mineral nitrogen (78.7-82.3 mg/kg). Soil firming had a negative effect on the microflora of soil. With soil density increase from 1.1 to 2.0 g/cm3 nitrifying capacity decreased from 21.0 mg/kg down to 10.4 mg/kg, while nitrate nitrogen content in soil decreased from 63.5 to 32.1 mg/kg. The best conditions for nitrification and ammonification in sod-podzol soil were as follows: soil temperature of +15°C, soil moisture of 20-25%, and soil density of 1.1 g/cm3. Dependence of mineral nitrogen content in soil on its temperature and moisture was curvilinear and was described by a second-order regression equation, while dependence on its density was linear and was described by a first-order regression equation.

Long-Term Effect of Tillage, Water and Nutrient Management Practices on Mineral Nitrogen, Available Phosphorus and Sulphur Content under Rice-Wheat Cropping System

The Indo-Gangetic plains of South Asia depends on rice-wheat based cropping system for their food security. Sustainable management of this system is difficult because of differential requirements in respect of soil and environmental conditions. A judicious and scientific management of this system in relation to tillage, water and nutrient is crucial for sustaining productivity. The present paper aims to study the interactive effects of tillage, water and nutrient management practices on mineral nitrogen (N), available phosphorus (P) and sulphur (S) content in soil under rice-wheat cropping system after completion of 7th cropping cycle. Soil samples were collected from a long-term field experiment which was initiated in 2001 at Indian Agricultural Research Institute (IARI) farm. The experiments consisted of two tillage, three water and seven nutrient management practices, which were allocated to main, sub and sub-sub plots (split-split plot design), respectively. Results indicated that, mineral N and available P content in soil was higher in puddled soil as compared to non-puddled condition. The P content in soil decreased with moisture content whereas, available S increased. Organic source of nutrients could not maintain the level of mineral N in soil even as that recorded in control whereas, plots that received FYM and crop residue along with mineral fertilizers showed significantly higher mineral N content than the plot where nutrients were supplied through chemical fertilizers. Integration of crop residues along with mineral fertilizers had a beneficial effect on the availability of P in soil.

Bacterial Modes of Action for Enhancing of Plant Growth

The greatest issue affecting the sustainability of broad acre cropping both environmentally and economically is the requirement of fertilizers. These are based on mined phosphorous or other mineral ores, ammonia produced through the Harbour-Bosch process and industrially manufactured potash. As global demand for fertilizers increases, the costs associated with the production for each of these major nutrients increases. Biofertilizers such as plant growth promoting bacteria (PGPB) are a possible biotechnology that could alleviate the need for addition of increasing amounts of fertilizers. These bacteria naturally occur in soils and aggressively colonize around plant roots and have been shown to have plant growth promoting effects. PGPB are known to influence plant growth by various direct and indirect mechanisms; while some can affect plant physiology directly by mimicking synthesis of plant hormones, others increase mineral availability and nitrogen content in soil. Here we review the previously characterized modes of action for enhancement of plant growth by PGPB such as nitrogen fixation, nutrient solubilization and production of auxins and enzymes, as well as discussing more recent proposed modes of action such as secondary metabolites.

Soil nitrogen dynamics after slurry injection in field trials: Evaluation of a soil sampling strategy

AbstractSlurry injection below maize seeds is a rather new application technique developed to improve the nitrogen use efficiency of liquid organic manure. To enable the characterization of the spatial and temporal soil mineral nitrogen (SMN) dynamics after slurry injection, the present study aims to develop an appropriate soil sampling strategy. Three consecutive experiments were conducted. The first testing of the soil sampling approach was conducted in an existing field trial where the slurry was injected down to a depth of 12 cm (upper rim) below the soil surface. The soil profile (75 cm wide) centered below the maize row was sampled grid‐like to a depth of 90 cm. Around the injection zone, soil monoliths (SM) were sampled using a purpose‐built soil shovel. Below the SMs and in the interrow space (15 and 30 cm distance to the row) a standardized auger procedure was performed. The second experiment aimed at improving the sampling strategy with a focus on sample homogenization quality and necessary sample sizes per pooled sample. Furthermore, the risk of a carryover of slurry components along the soil core due to drilling an auger through a slurry band was analyzed. In the third experiment this improved sampling strategy was validated. Results from the first testing of the sampling procedure showed that the strategy is suitable, although some problems occurred (especially the high spread in values among the replications causing high coefficients of variation (CV) of mostly 40–60%). The improvement trial revealed that due to the high gradient of SMN concentration in the direct range of the injection zone an intensive homogenization of these samples is required. Suitable sample sizes (twelve auger samples and six soil monolith samples per pooled sample) have to be collected to obtain reliable SMN values. Drilling an auger through a slurry band to sample subjacent soil layers has to be avoided. Following this enhanced sampling strategy, in the final validation trial the spread in values were considerably reduced and resulted in CV values of mostly &lt; 20%. The developed sampling strategy enables the characterization of the spatial and temporal SMN dynamics when slurry has been band‐injected below a maize row. The method can be transferred to other row crops and different slurry injection spacing.

Soil water and mineral nitrogen content as influenced by crop rotation and tillage practice in the Swartland subregion of the Western Cape

Adoption of conservation agricultural practices, reduced tillage and crop rotation in the grain-producing areas of the Western Cape, South Africa, resulted in a gradual build-up of organic matter on the soil surface. It was expected that the increase in organic matter cover would influence soil water content and nitrogen mineralisation potential of the topsoil. The effect of crop rotation and tillage practice on soil water (g g−1) and mineral-N content (mg kg−1) in the 0–200 mm soil layer during 2010 and 2011 was assessed. Crop rotation, wheat monoculture (WWWW), lupin–wheat– canola–wheat (LWCW) and wheat–medic rotation (McWMcW) and tillage, conventional-till (CT), minimum-till (MT), no-till (NT) and zero-till (ZT) were studied. Crop rotation did not influence soil moisture content. Soil water content in CT tended to be lower compared with the other tillage treatments tested. A tendency of higher mineral-N in CT was observed, although not for all sampling dates. Mineral-N content did not differ between ZT, NT and MT. It is concluded that tillage influenced soil water and mineral-N content, whereas crop rotation only influenced mineral-N if the system included a legume crop (medic). Results obtained could be valuable in developing management strategies for wheat grown under different production systems.

Effects of legume species introduction on vegetation and soil nutrient development on abandoned croplands in a semi-arid environment on the Loess Plateau, China

Revegetation facilitated by legume species introduction has been used for soil erosion control on the Loess Plateau, China. However, it is still unclear how vegetation and soil resources develop during this restoration process, especially over the longer term. In this study, we investigated the changes of plant aboveground biomass, vegetation cover, species richness and density of all individuals, and soil total nitrogen, mineral nitrogen, total phosphorus and available phosphorus over 11years from 2003 to 2013 in three treatments (natural revegetation, Medicago sativa L. introduction and Melilotus suaveolens L. introduction) on the semi-arid Loess Plateau. Medicago significantly increased aboveground biomass and vegetation cover, and soil total nitrogen and mineral nitrogen contents. The Medicago treatment had lower species richness and density of all individuals, lower soil moisture in the deep soil (i.e., 1.4–5m), and lower soil available phosphorus. Melilotus introduction significantly increased aboveground biomass in only the first two years, and it was not an effective approach to improve vegetation biomass and cover, and soil nutrients, especially in later stages of revegetation. Overall, our study suggests that M. sativa can be the preferred plant species for revegetation of degraded ecosystems on the Loess Plateau, although phosphorus fertilizer should be applied for the sustainability of the revegetation.

Undersowing winter oilseed rape with frost-sensitive legume living mulches to improve weed control

Living mulches are generally seen as a possible way to decrease the reliance on pesticides. We investigated the effect of a frost-sensitive legume living mulch on weed control during the autumn and cash crop performance, in winter oilseed rape crops. A field trial was carried out over two years, comparing seven legume species—fenugreek, spring faba bean, grass pea, lentil, field pea, berseem clover and spring common vetch—and three legume mixtures, as living mulches, in crops with two levels of soil mineral nitrogen content before sowing. The presence of the legume living mulch decreased weed abundance before winter. Field pea, berseem clover, common vetch and the common vetch/faba bean/berseem clover mixture were particularly effective, regardless of the growing conditions, decreasing weed abundance by 20–75% with respect to that in the crop grown alone, in the absence of herbicide application. Weed abundance before winter was negatively correlated with total intercrop biomass, and this relationship was dependent on the legume species considered and soil mineral nitrogen content. As with other legume intercrops, the level of soil mineral nitrogen had a strong influence on intercrop structure, modifying the proportion of legume biomass produced. The legume/oilseed rape biomass ratio was also found to be a useful indicator in all growing conditions: the higher the ratio, the more efficient the weed control. However, a high ratio was associated with a higher risk of competition with the cash crop. The choice of the most appropriate legume living mulch is therefore a compromise between the anticipated ecosystem services and the potential disservices provided by the legume mulch. The introduction of a legume living mulch did not entirely prevent weed growth, but was clearly a relevant agroecological solution for decreasing herbicide, while increasing the sustainability and diversity of weed-control strategies in cropping systems.

Simulating the impact of water saving irrigation and conservation agriculture practices for rice–wheat systems in the irrigated semi-arid drylands of Central Asia

Resource scarcity (labor, water, and energy) and high production costs are challenging the sustainability of conventional methods for rice and wheat establishment in Central Asia. Water saving irrigation and conservation agriculture (CA) practices (e.g., dry seeded rice, zero tillage wheat, residue retention) are potential alternative, resource-saving establishment methods. The Decision Support System for Agrotechnology Transfer (DSSAT) Cropping System Model (CSM) can both be a valuable ex-ante and ex-post tool to evaluate the effects of water saving irrigation and resource saving CA-practices. The CSM-CERES-Rice and CSM-CERES-Wheat models of DSSAT were evaluated using experimental data from the 2008 to 2010 rice and wheat seasons as monitored in Urgench, the Khorezm region of Uzbekistan for growth, development of these crops, as well as soil mineral nitrogen (N) and volumetric soil moisture content in these cropping systems. Thereafter, the models were used to explore the long-term impact of water saving irrigation and CA-practices on grain yield, soil organic carbon (SOC) dynamics, N dynamics, and water balance in a rice–wheat rotation for 39 years starting from 1971. The simulation results showed that the simulated yield of water-seeded rice without residue retention and flood irrigation (WSRF-R0-FI) is likely to remain the highest and constant over 39 years. The simulated yield of dry seeded rice (DSR) with alternate wet and dry (AWD) irrigation and varying levels of residue retention was penalized for the initial years. However, the simulated rice yield increased after 13 years of CA-practices and continued to increase for the remaining years. Wheat did not experience a yield penalty for any of the treatments and simulated yield increased over time across all CA-practices based treatments. In the long-term, the effect of tillage methods and different residue levels for both rice and wheat were apparent in terms of grain yield and SOC build up. The results of the sensitivity analysis showed that WSR using AWD irrigation with puddling (WSRF-R0-AWD-Puddled) could give equivalent yield with that of WSRF-R0-FI and that irrigation water for rice could be reduced from 5435mm to 2161mm (or by 60%). Deep placement of urea in DSR (CT-DSR-AWD-DPUS) has the potential to increase yields of DSR by about 0.5tha−1. Despite the huge water saving potential through the adoption of water saving AWD irrigation in DSR, a major challenge will be to prevent N losses. Substantial amounts of N losses through leaching, immobilization by residue mulch, combined with gaseous losses through volatilization and denitrification are the major causes for the lower simulated yield of rice for the AWD treatments. During the rice season, the implementation of water saving irrigation can improve water use efficiency by reducing percolation and seepage losses, which is an option in particular for WSRF-R0-FI. For both crops, the water use efficiency can be improved by lowering evaporation losses e.g. through residue retention on the soil surface. The creation of a sub-surface hard pan (puddling) and deep placement of urea super granules/pellet (DPUS) fertilizer could be the key for water saving and better yields of rice. Because CA-practices require almost three times less irrigation water than conventional method, and provide a long-term positive impact on grain yields of both crops, the CA-practices should be considered for double, no-till, rice–wheat cropping systems in the irrigated semi-arid drylands of Central Asia.