Crop production,soil carbon and nutrient balances as affected by fertilisation in a Mollisol agroecosystem

A 19-year field experiment on a Mollisol agroecosystem was carried out to study the productivity of a wheat-maize-soybean rotation and the changes in soil carbon and nutrient status in response to different fertiliser applications in Northeast China. The experiment consisted of seven fertiliser treatments: (1) unfertilised control, (2) annual application of P and K fertilisers, (3) N and K fertilisers, (4) N and P fertilisers, (5) N, P and K fertilisers, (6) N, K and second level P fertilisers, and (7) N, P and second level K fertilisers. Without fertiliser, the Mollisols could support an average yield of 1.88 t ha⁻¹ for wheat, 3.89 t ha⁻¹ for maize and 2.12 t ha⁻¹ for soybean, compared to yields of 3.20, 9.30 and 2.45 t ha⁻¹ respectively for wheat, maize and soybean if the crop nutrient demands were met. At the potential yield level, the N, P and K removal by wheat are 79 kg N ha⁻¹, 15 kg P ha⁻¹, and 53 kg K ha⁻¹, by maize are 207 kg N ha⁻¹, 47 kg P ha⁻¹, and 180 kg K ha⁻¹, by soybean are 174 kg N ha⁻¹, 18 kg P ha⁻¹, and 55 kg K ha⁻¹. Crop yield, change in soil organic carbon (SOC), and the total and available nutrient status were used to evaluate the fertility of this soil over different time periods. This study showed that a fertiliser strategy that was able to maintain yields in the short term (19 years) would not maintain the long term fertility of these soils. Although organic carbon levels did not rise to the level of virgin soil in any treatment, a combination of N, P and K fertiliser that approximated crop export was required to stabilise SOC and prevent a decline in the total store of soil nutrients.     

Reducing nitrous oxide emissions and optimizing nitrogen-use efficiency in dryland crop rotations with different nitrogen rates

Recent interests in improving agricultural production while minimizing environmental footprints emphasized the need for research on management strategies that reduce nitrous oxide (N₂O) emissions and increase nitrogen-use efficiency (NUE) of cropping systems. This study aimed to evaluate N₂O emissions, annualized crop grain yield, emission factor, and yield-scaled- and NUE-scaled N₂O emissions under continuous spring wheat (Triticum aestivum L.) (CW) and spring wheat–pea (Pisum sativum L.) (WP) rotations with four N fertilization rates (0, 50, 100, and 150 kg N ha^?1). The N₂O fluxes peaked immediately after N fertilization, intense precipitation, and snowmelt, which accounted for 75–85% of the total annual flux. Cumulative N₂O flux usually increased with increased N fertilization rate in all crop rotations and years. Annualized crop yield and NUE were greater in WP than CW for 0 kg N ha^?1 in all years, but the trend reversed with 100 kg N ha^?1 in 2013 and 2015. Crop yield maximized at 100 kg N ha^?1, but NUE declined linearly with increased N fertilization rate in all crop rotations and years. As N fertilization rate increased, N fertilizer-scaled N₂O flux decreased, but NUE-scaled N₂O flux increased non-linearly in all years, regardless of crop rotations. The yield-scaled N₂O flux decreased from 0 to 50 kg N ha^?1 and then increased with increased N fertilization rate. Because of non-significant difference of N₂O fluxes between 50 and 100 kg N ha^?1, but increased crop yield, N₂O emissions can be minimized while dryland crop yields and NUE can be optimized with 100 kg N ha^?1, regardless of crop rotations.

     

Agro-ecological nitrogen management in soils vulnerable to nitrate leaching: a case study in the Lower Suwannee Watershed

Environmental benefits associated with reduced rates of nitrogen (N) application, while maintaining economically optimum yields have economic and social benefits. Although N is an indispensable plant nutrient, residual soil N could leach out to contaminate groundwater and surface water resources, particularly in sandy soils. A 2-year field study was conducted in an established bermudagrass (Cynodon dactylon) pasture in the Lower Suwannee Watershed, Florida, to evaluate N application rates on forage yield, forage quality, and nitrate (NO₃-N) leaching in rapidly permeable upland sandy soils. Four N application rates (30, 50, 70, and 90 kg N ha⁻¹ harvest⁻¹) corresponding to 0.33, 0.55, 0.77 and IX, respectively, of recommended N rate (90 kg N ha⁻¹ harvest⁻¹) for bermudagrass hay production in Florida were evaluated vis-à-vis an unfertilized (0 N) control. Suction cups were installed near the center of each plot at two depths (30 and 100 cm) to monitor NO₃-N leaching. The grass was harvested at 28 days intervals to determine dry matter yield, N uptake, and herbage nutritive value. Nitrogen application at the recommended rate produced the greatest total dry matter yield (~18.4 Mg ha⁻¹ year⁻¹), but a modeled economically optimum N rate of ~57 kg N ha⁻¹ harvest⁻¹ (~60% of the recommended N rate) projected an average dry matter yield of ~17.3 Mg ha⁻¹ year⁻¹, which represents >90% of the observed maximum yield. Nitrogen application increased nutritive quality of the grass, but increases in N application rate above 30 kg N ha⁻¹ did not result in significant increases in in vitro digestible organic matter concentration, and tissue crude protein was not significant above 50 kg N ha⁻¹. Across the sampling period, treatments with N rates ≤50 kg N ha⁻¹ harvest⁻¹ had leachate NO₃-N concentration below the maximum contaminant limit of <10 mg l⁻¹. Conversely, applying N at rates ≥70 kg N ha⁻¹ harvest⁻¹ resulted in leachate N concentration that exceeded the maximum contaminant limit, and suggest high risk of impacting groundwater quality, if such rates are applied to soils with coarse (sand) textures. The study demonstrates that recommendation of a single N application rate may not be appropriate under all agro-climatic conditions and, thus, a site-specific evaluation of best N management strategy is critical.     

Nitrogen leaching in an upland cropping system on an acid soil in subtropical China: lysimeter measurements and simulation

The effect of rainfall and nitrogen (N) input on nitrate leaching in a rain-fed peanut–oilseed rape system on an acidic soil in subtropical China was investigated in a field lysimeter experiment from 1997 to 2000. Drainage and nitrate leaching were simulated using the Water and Nitrogen Management Model (WNMM). Nitrate concentrations in the drainage water and nitrate leaching increased with increasing N application rate. Annual leaching losses ranged from 21.1 to 46.3 kg N ha⁻¹ (9.5–16.8%) for inputs between 0 and 150 kg N ha⁻¹. Growth of oilseed rape decreased the nitrate concentration in the drainage water, but growing N fixing peanuts did not. Rainfall had a greater impact on nitrate leaching than crop uptake. Nitrate concentrations in the drainage water were relatively low (1.95–4.33 mg N l⁻¹); this was caused by the high precipitation, the low nitrification rate, and the low residual nitrate in the soil. The loss of nitrate was low during the dry season (October–February) and in the dry year (rainfall 17% below average) mainly as a result of reduced drainage. WNMM satisfactorily simulated the inter-monthly variation in drainage and total nitrate leached, with respective relative root mean square errors of 42.7% and 70.2%, mean modelling efficiencies of 0.88 and 0.67, and mean relative errors of −3.82% and 21.8%. The modelled annual N losses were only 1–7% less than the observed values.     

Interactive effects of selected nutrient resources and tied-ridging on plant growth performance in a semi-arid smallholder farming environment in central Zimbabwe

Crop production in sub-Saharan Africa is constrained by numerous factors including frequent droughts and periods of moisture stress, low soil fertility, and restricted access to mineral fertilisers. A 2 year (2005/6 and 2006/7) field study was conducted in Shurugwi district, central Zimbabwe, to determine the effects of different nutrient resources and two tillage practices on the grain yield of maize (Zea mays L.) and soybean (Glycine max (L.) Merr). Six nutrient resource treatments (control, pit-stored manure, leaf litter, anthill soil, mineral fertiliser, mineral fertiliser plus pit-stored manure) were combined with two tillage practices (conventional tillage and post-emergence tied ridging). Basal fertilisation was done with 0 kg ha⁻¹ as control, 240 kg ha⁻¹ PKS fertiliser, 18 t ha⁻¹ manure, 10 t ha⁻¹ manure plus 240 kg ha⁻¹ PKS fertiliser, 35 t ha⁻¹ leaf litter, 52 t ha⁻¹ anthill soil. About 60 kg N/ha was applied to fertiliser only and fertiliser plus manure treatments as top dressing in the form of ammonium nitrate (34.5%N). A split-plot design was used with nutrient resource as the main plot and tillage practice as the subplot, and five farmers’ fields were used as replicates. Grain yield was determined at physiological maturity (140 and 126 days after planting for maize and soybean, respectively) and adjusted to 12.5% moisture content for maize and 11% for soybean. In the first season (2005/06), addition of different nutrient resources under conventional tillage increased (P < 0.05) maize grain yield by 102–450%, with leaf litter and manure plus fertiliser treatments, giving the lowest (551 kg ha⁻¹⁾ and highest (3,032 kg ha⁻¹) increments, respectively, compared to the control. For each treatment, tied-ridging further increased maize grain yield. For example, for leaf litter, tied-ridging further increased grain yield by 96% indicating the importance of integrating nutrient and water management practices in semi-arid areas where moisture stress is frequent. Despite the low rainfall and extended dry spells in the second season, addition of the different nutrient resources still increased yield which was further increased by tied-ridging in most treatments. Besides providing grain, soybean had higher residual effects on the following maize crop compared to Crotalaria gramiana, a green manure. It was concluded that the highest benefits of tied-ridging, in terms of grain yield, were realised when cattle manure was combined with mineral fertiliser, both of which are available to resource-endowed households. Besides marginally increasing yield, leaf litter and anthill which represent resources that can be accessed by very poor households, have a positive effect of the soil chemical environment.     

Effects of mulch,N fertilizer,and plant density on wheat yield,wheat nitrogen uptake,and residual soil nitrate in a dryland area of China

Understanding mulching influences on nitrogen (N) activities in soil is important for developing N management strategies in dryland. A 3 year field experiment was conducted in the Loess Plateau of China to investigate the effects of mulching, N fertilizer application rate and plant density on winter wheat yield, N uptake by wheat and residual soil nitrate in a winter wheat-fallow system. The split plot design included four mulching methods (CK, no mulch; SM, straw mulch; FM, plastic film mulch; CM, combined mulch with plastic film and straw) as main plot treatments. Three N fertilizer rates (N0, 0 kg N ha⁻¹; N120, 120 kg N ha⁻¹; N240, 240 kg N ha⁻¹) were sub-plot treatments and two wheat sowing densities (LD, low density, seeding rate = 180 kg ha⁻¹; HD, high density, seeding rate = 225 kg ha⁻¹) were sub-subplot treatments. The results showed that wheat yield, N uptake, and N use efficiency (NUE) were higher for FM and CM compared to CK. However, soil nitrate-N contents in the 0–200 cm soil profile were also higher for FM and CM compared to CK after the 3 year experiment. Wheat grain yields were higher for SM compared to CK only when high levels of nitrogen or high planting density were applied. Mulching did not have a significant effect on wheat yield, nitrogen uptake and NUE when soil water content at planting was much high. Wheat yield, N uptake, and residual nitrate in 0–200 cm were significantly higher for N240 compared to N120 and N0. Wheat yield and N uptake were also significantly higher for HD compared to LD. When 0 or 120 kg N ha⁻¹ was applied, HD had more residual nitrate than LD while the reverse was true when 240 kg N ha⁻¹ was applied. After 3 years, residual nitrate-N in 0–200 cm soil averaged 170 kg ha⁻¹, which was equivalent to ~40% of the total N uptake by wheat in the three growing seasons.     

Soil nitrate-N levels required for high yield maize production in the North China Plain

High profile nitrate-nitrogen (N) accumulation has caused a series of problems, including low N use efficiency and environmental contamination in intensive agricultural systems. The key objective of this study was to evaluate summer maize (Zea mays L.) yield and N uptake response to soil nitrate-N accumulation, and determine soil nitrate-N levels to meet N demand of high yield maize production in the North China Plain (NCP). A total of 1,883 farmers’ fields were investigated and data from 458 no-N plots were analyzed in eight key maize production regions of the NCP from 2000 to 2005. High nitrate-N accumulation (≥172 kg N ha⁻¹) was observed in the top (0–90 cm) and deep (90–180 cm) soil layer with farmers’ N practice during maize growing season. Across all 458 no-N plots, maize grain yield and N uptake response to initial soil nitrate-N content could be simulated by a linear plus plateau model, and calculated minimal pre-planting soil nitrate-N content for maximum grain yield and N uptake was 180 and 186 kg N ha⁻¹, respectively, under no-N application conditions. Economically optimum N rate (EONR) decreased linearly with increasing pre-planting soil nitrate-N content (r ² = 0.894), and 1 kg soil nitrate-N ha⁻¹ was equivalent to 1.23 kg fertilizer-N ha⁻¹ for maize production. Residual soil nitrate-N content after maize harvest increased exponentially with increasing N fertilizer rate (P < 0.001), and average residual soil nitrate-N content at the EONR was 87 kg N ha⁻¹ with a range from 66 to 118 kg N ha⁻¹. We conclude that soil nitrate-N content in the top 90 cm of the soil profile should be maintained within the range of 87–180 kg N ha⁻¹ for high yield maize production. The upper limit of these levels would be reduce if N fertilizer was applied during maize growing season.     

Leaching losses of nitrate nitrogen and dissolved organic nitrogen from a yearly two crops system,wheat-maize,under monsoon situations

A large amount of nitrogen (N) fertilizers applied to the winter wheat–summer maize double cropping systems in the North China Plain (NCP) contributes largely to N leaching to the groundwater. A series of field experiments were carried out during October 2004 and September 2007 in a lysimeter field to reveal the temporal changes of N leaching losses below 2-m depth from this land system as well as the effects of N fertilizer application rates on N leaching. Four N rates (0, 180, 260, and 360 kg N ha⁻¹ as urea) were applied in the study area. Seasonal leachate volumes were 87 and 72 mm in the first and second maize season, respectively, and 13 and 4 mm during the winter wheat and maize season in the third rotational year, respectively. The average seasonal flow-weighted NO₃-N concentrations in leachate for the four N fertilizer application rates ranged from 8.1 to 103.7 mg N l⁻¹, and seasonal flow-weighted dissolved organic nitrogen (DON) concentrations in leachate varied from 0.8 to 6.0 mg N l⁻¹. Total amounts of NO₃-N leaching lost throughout the 3 years were in the range of 14.6 to 177.8 kg ha⁻¹ for the four N application rates, corresponding to N leaching losses in the range of 4.0–7.6% of the fertilizers applied. DON losses throughout the 3 years were 1.4, 2.1, 3.6, and 6.3 kg N ha⁻¹ for the four corresponding fertilization rates. The application rate of 180 kg N ha⁻¹ was recommended based on the balance between reducing N leaching and maintaining crop yields. The results indicated that there is a potential risk of N leaching during the winter wheat season, and over-fertilization of chemical N can result in substantial N leaching losses by high-intensity rainfalls in summer.     

Nitrate loss from a tile-drained reclaimed marsh soil from SW Spain amended with different products

Tile drainage and soil amendments have been found to affect losses of nitrate N from agricultural soils. This work was aimed at measuring nitrate N losses in a tile-drained marsh soil from SW Spain under traditional fertilization and irrigation practices, and how these losses were influenced by the application of soil amendments. To this end, a randomised block experiment with three replications was performed during two consecutive growing seasons—2003 to 2004 with cotton and sugar beet, respectively—involving four different amendment treatments: (1) control without amendment, (2) phosphogypsum (PG), (3) manure, and (4) sugar factory refuse lime (SFRL). Flow-weighted (FW) nitrate–N concentrations in drainage water, estimated as the slope of the regression of the instantaneous nitrate–N flow as a function of drain flow rate, was decreased by PG in some drainage events in the 2003 season and in the four last events of the 2004 season when compared with control without amendment. The increased FW nitrate–N concentrations in drainage from SFRL in comparison to control in a drainage event of 2003 season, and in the four last events of 2004, can be explained by the contribution of N present in the amendment. These effects did not account for significant differences in nitrate–N loss among treatments over the whole season in 2003, when they ranged from 19.3 to 24.9 kg N ha⁻¹, accounting for 6–8% of applied N, nor in 2004, when they ranged from 4 to 6 kg N ha⁻¹, accounting for 3–4% of applied N. The decrease in mean FW nitrate–N concentration after the third drainage event in 2003 was not the consequence of the depletion of total soil nitrate–N because soil mineral N was increased on average by 205 kg N ha⁻¹ during the season. The high N extractions by sugar beet and the subsequent decrease in total soil nitrate–N can contribute to explain the decrease of mean FW nitrate–N concentrations along the 2004 season. Greater absolute nitrate–N loss in 2003 than in 2004 was explained by the lower efficiency of the furrow irrigation when compared with sprinkler irrigation. Results also revealed that traditional management of N fertilizer was inadequate: rates applied to cotton were excessive, increasing the risk of N losses not only during the cotton season, but also at the beginning of the following season.     

Nutrient loss pathways from grazed grasslands and the effects of decreasing inputs: experimental results for three soil types

Agriculture is a main contributor of diffuse emissions of N and P to the environment. For N the main loss pathways are NH₃-volatilization, leaching to ground and surface water and N₂(O) emissions. Currently, imposing restraints on farm inputs are used as policy tool to decrease N and P leaching to ground water and to surface water, and the same measure is suggested to combat emissions of N₂O. The response, however, to these measures largely depends on the soil type. In this study nutrient flows of three dairy farms in The Netherlands with comparable intensity on sand, peat and clay soils were monitored for at least 2 years. The first aim was to provide quantitative data on current nutrient loss pathways. The second aim was to explore the responses in partitioning of the nutrient loss pathways when farm inputs were altered. Mean denitrification rates ranged from 103 kg N ha⁻¹ year⁻¹ for the sandy soil to 170 kg N ha⁻¹ year⁻¹ for the peat soil and leaching to surface water was about 73 kg N ha⁻¹ year⁻¹ for the sandy soil, 15 kg N ha⁻¹ year⁻¹ for the clay soil and 38 kg N ha⁻¹ year⁻¹ for the peat soil. For P, leaching to surface water ranged from 2 kg P ha⁻¹ year⁻¹ for the sandy site to 5 kg P ha⁻¹ year⁻¹ for the peat site. The sandy soil was most responsive to changes in N surpluses on leaching to surface water, followed by the peat soil and least responsive was the clay soil. For P, a similar sequence was found. This article demonstrates that similar reductions of N and P inputs result in different responses in N and P loss pathways for different soil types. These differences should be taken into account when evaluating measures to improve environmental performance of (dairy) farms.     

Looking beyond fertilizer: assessing the contribution of nitrogen from hydrologic inputs and organic matter to plant growth in the cranberry agroecosystem

Even though nitrogen (N) is a key nutrient for successful cranberry production, N cycling in cranberry agroecosystems is not completely understood. Prior research has focused mainly on timing and uptake of ammonium fertilizer, but the objective of our study was to evaluate the potential for additional N contributions from hydrologic inputs (flooding, irrigation, groundwater, and precipitation) and organic matter (OM). Plant biomass, soil, surface and groundwater samples were collected from five cranberry beds (cranberry production fields) on four different farms, representing both upland and lowland systems. Estimated average annual plant uptake (63.3 ± 22.5 kg N ha⁻¹ year⁻¹) exceeded total average annual fertilizer inputs (39.5 ± 11.6 kg N ha⁻¹ year⁻¹). Irrigation, precipitation, and floodwater N summed to an average 23 ± 0.7 kg N ha⁻¹ year⁻¹, which was about 60% of fertilizer N. Leaf and stem litterfall added 5.2 ± 1.2 and 24.1 ± 3.0 kg N ha⁻¹ year⁻¹ respectively. The estimated net N mineralization rate from the buried bag technique was 5 ± 0.2 kg N ha⁻¹ year⁻¹, which was nearly 15% of fertilizer N. Dissolved organic nitrogen represented a significant portion of the total N pool in both surface water and soil samples. Mixed-ion exchange resin core incubations indicated that 80% of total inorganic N from fertilizer, irrigation, precipitation, and mineralization was nitrate, and approximately 70% of recovered inorganic N from groundwater was nitrate. There was a weak but significant negative relationship between extractable soil ammonium concentrations and ericoid mycorrhizal colonization (ERM) rates (r = −0.22, P < 0.045). Growers may benefit from balancing the N inputs from hydrologic sources and OM relative to fertilizer N in order to maximize the benefits of ERM fungi in actively mediating N cycling in cranberry agroecosystems.     

Fertiliser strategies for improved nutrient use efficiency on sandy soils in high rainfall regimes

Fertiliser application strategies for maize (Zea mays L.) production on sandy soils under high rainfall regimes need to be carefully designed to minimise nutrient losses through leaching and maximise crop yield. Experiments were conducted to determine N, P, and K leaching in sandy soils with 3–6% clay in surface layers under maize production, and the effectiveness of different N, P, and K fertiliser timing and splitting strategies on leaching of N, P, and K and on maize yield. In a column experiment on an Oxic Paleustult (Korat series) with 3% clay, leaching of N, P, and K from fertiliser (114N-17P-22K in kg ha⁻¹) was significant under simulated rainfall, but decreased to negligible levels with 3–5 split applications of fertiliser. Maize N and K uptake increased with 3–5 split applications, but not P uptake. Despite continued intense rainfall and further fertilizer additions, leaching was not recorded after day 30, and this was attributed to the effect of plant water uptake on reducing deep drainage. Split applications of fertilizer maintained NP and K in the 0–30 cm layer during 30–60 days when maize nutrient demand was likely to be at its highest, while in the recommended fertilizer regime NPK in the surface layers declined after 30 days. In a field experiment on an Oxic Paleustult (Korat series) with 6% clay, 3–4 splits of fertiliser increased N and K uptake and increased maize yields from 3.3 to 4.5 Mg ha⁻¹. Postponing basal fertiliser application from pre-planting to 7–15 days after emergence increased uptake of N, P, and K and grain yield emphasising the greater risk of nutrient losses from fertiliser applied at planting than later. Strategies designed to reduce the amount of nutrients applied as fertiliser at planting, such as split application and postponing basal application can decrease the risk of leaching of N, P, and K from fertiliser and improve nutrient use efficiency, and grain yield of maize on sandy soils under high growing season rainfall regimes.     

Soil nitrogen response to coupling cover crops with manure injection

Coupling winter small grain cover crops (CC) with manure (M) application may increase retention of manure nitrogen (N) in corn (Zea mays L.), -soybean [Glycine max (L.) Merr], cropping systems. The objective of this research was to quantify soil N changes after application of liquid swine M (Sus scrofa L.) at target N rates of 112, 224, and 336 kg N ha⁻¹ with and without a CC. A winter rye (Secale cereale L.)-oat (Avena sativa L.) CC was established prior to fall M injection. Surface soil (0–20 cm) inorganic N concentrations were quantified every week for up to 6 weeks after M application in 2005 and 2006. Soil profile (0–120 cm in 5, 20-cm depth increments) inorganic N, total N, total organic carbon and bulk density were quantified for each depth increment in the fall before M application and before the CC was killed the following spring. Surface soil inorganic N on the day of application averaged 318 \textmg  \textN  \textkg ^{- 1}_\textsoil 318\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}}} in 2005 and 186 \textmg  \textN  \textkg ^{- 1}_\textsoil 186\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}} } in 2006 and stabilized at 150 \textmg  \textN  \textkg ^{- 1}_\textsoil 150\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}}} in both years by mid-November. Surface soil NO₃-N concentrations in the M band were more than 30 times higher in the fall of 2005 than in 2006. The CC reduced surface soil NO₃-N concentrations after manure application by 32% and 67% in mid- November 2005 and 2006, respectively. Manure applied at 224 kg N ha⁻¹ without a CC had significantly more soil profile inorganic-N (480 kg N ha⁻¹) in the spring after M application than manured soils with a CC for the 112 (298 kg N ha⁻¹) and 224 (281 kg N ha⁻¹) N rates, and equivalent inorganic N to the 336 (433 kg N ha⁻¹) N rate. These results quantify the potential for cover crops to enhance manure N retention and reduce N leaching potential in farming systems utilizing manure.     

Quantification of seasonal soil nitrogen mineralization for corn production in eastern Canada

Precise estimation of soil nitrogen (N) supply to corn (Zea mays L.) through N mineralization plays a key role in implementing N best management practices for economic consideration and environmental sustainability. To quantify soil N availability to corn during growing seasons, a series of in situ incubation experiments using the method of polyvinyl chloride tube attached with resin bag at the bottom were conducted on two typical agricultural soils in a cool and humid region of eastern Canada. Soil filled tubes were retrieved at 10-d intervals within 2 months after planting, and at 3- to 4-week intervals thereafter until corn harvest. Ammonium and nitrate in the soil and resin part of the incubation tubes were analyzed. In general, there was minimal NH₄⁺-N with ranges from 1.5 to 7.3 kg N ha⁻¹, which was declined in the first 30 d and fluctuated thereafter. Nitrate, the main form of mineral N, ranged from 20 to 157 kg N ha⁻¹. In the first 20–50 d, main portion of the NO₃⁻-N was in the soil and thereafter in the resin, reflecting the movement of NO₃⁻ in the soil, which was affected by rainfall events and amount. Total mineralized N was affected by soil total N and weather conditions: There was more total mineralized N in the soil with higher total N, and rainy weather stimulated N mineralization. The relationship between the accumulated mineral N and accumulated growing degree-days (GDD) fitted well into first order kinetic models. The accumulated mineralized soil N during corn growing season ranged from 96 to 120 kg N ha⁻¹, which accounted for 2–3% of soil total N. Corn plants took up 110–137 kg N ha⁻¹. While the mineralized N and crop uptake were in the same magnitude, a quantitative relationship between them could not be established in this study.     

Grain legume rotation benefits to maize in the northern Guinea savanna of Nigeria: fixed-nitrogen versus other rotation effects

The yield increases often recorded in maize following grain legumes have been attributed to fixed-N and ‘other rotation’ effects, but these effects have rarely been separated. Field trials were conducted between 2003 and 2005 to measure these effects on maize following grain legumes in the northern Guinea savanna of Nigeria. Maize was grown on plots previously cultivated to two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), maize, and natural fallow. The plots were split into four N fertilizer rates (0, 30, 60 and 90 kg N ha⁻¹) in a split plot design. The total effect was calculated as the yield of maize following a legume minus the yield following maize, both without added N and the rotation effect was calculated as the difference between rotations at the highest N fertilizer rate. The legume genotypes fixed between 14 and 51 kg N ha⁻¹ of their total N and had an estimated net N balance ranging from −29.8 to 9.5 kg N ha⁻¹. Positive N balance was obtained only when the nitrogen harvest index was greater than the proportion of N derived from atmosphere. The results also indicated that the magnitude of the fixed-N and other rotation effects varied widely and were influenced by the contributions of the grain legumes to the soil N-balance. In general, fixed-N effects ranged from 124 to 279 kg ha⁻¹ while rotation effects ranged between 193 and 513 kg ha⁻¹. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize after maize, respectively.     

Nutrient Flows in Suckler Farm Systems Under Two Levels of Intensity

The potential release of nutrients from animal farms into soil, water and the atmosphere is a major concern in agronomy. Farm gate balances are widely utilised to validate the compatibility of a farming system to the surrounding environment, although they do not reveal the internal nutrient flow as influenced by production intensity and hence might mask local and spatial nutrient surpluses or deficiencies. In a three years experiment on Rengen Research Station (Eifel Mountains) of the University of Bonn (Germany) we examined the entire nutrient cycle of two suckler farm systems without (extensive, system “A”) and with (intensive, system “B”) nutrient input and with 20 suckler cows on 19 hectare each. Stall and grassland nutrient balance sheets give insight into sources of nutrient surpluses and losses in the farm compartments. The annual budgets of N in system “A” were nearly balanced (−18 to 15 kg N ha⁻¹ yr⁻¹) compared to system “B” which calculated 81–120 kg N ha⁻¹ yr⁻¹ surplus due to considerable N input with forage and higher dry matter contribution of white clover leading to higher annual N2 fixation. The maximum of total annual nutrient flow within the entire systems was 388, 42 and 317 kg ha⁻¹ yr⁻¹ with N, P, and K, respectively. Most of these nutrients circulated with forage and excreta on the pastures. This led to considerable losses mainly of nitrogen (44–50 kg N ha⁻¹ yr⁻¹) even in the extensive system. The intake, excretion and resulting losses of N were mainly determined by the allowance of N rich pasture forage and was mostly independent from nutrient input. Compared to the grazing season, stall balances were similar in both systems and all years and revealed very low surpluses with all nutrients. The authors deduce that internal nutrient flow analyses should be added to conventional balance sheets, including a ranking of nutrients related to chemical bond, solubility, volatility and predisposition to losses in the farm’s compartment and environment. An erratum to this article is available at .     

Emissions of N<Subscript>2</Subscript>O from fertilized and grazed grassland on organic soil in relation to groundwater level

Intensively managed grasslands on organic soils are a major source of nitrous oxide (N₂O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N₂O ha⁻¹ year⁻¹ for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses a relatively high calculated emission factor of 4.7 kg N–N₂O ha⁻¹ year⁻¹. In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N₂O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N₂O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might control N₂O emissions such as groundwater level. In this paper we report on the relations between N₂O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured N₂O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N₂O–N ha⁻¹ year⁻¹ and 11.6 kg N–N₂O ha⁻¹ year⁻¹ for the dry and wet conditions, respectively. Especially under dry conditions, measured N₂O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The N₂O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and wet field, respectively and were strongly related to average groundwater level (R ² = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data for fertilized and grazed grasslands on organic soils.     

Nitrogen loss: an emerging issue for the ongoing evolution of New Zealand dairy farming systems

Here we present a case study of two New Zealand dairy farms located in the southern North Island (latitude 40°S) in which we review the evolution of the system over the past 30 years with particular focus on the relation between intensification and N loss to the environment. Over the period evaluated the two case farms lifted per cow production by over 40% and approximately doubled per ha milk production, partly through identification of efficiencies in farm system design and partly through intensification by feed importation. Based on the production data, animal consumption (t DM ha⁻¹ year⁻¹) and N loss to the environment (kg N ha⁻¹ year⁻¹) were modelled for four scenarios representing the two case farms in the early 1980s and in the 2007/2008 production season. For one case farm, the system was modelled for two further scenarios before and after changes aimed at increasing feed conversion efficiency. Increase in N loss to the environment from dairy farm operations arising from intensification between the early 1980s and the 2007/2008 season were largely offset by a change in the system of farm dairy effluent disposal that reduced N loss. Comparing model output for system configurations with low (38%) and high (49%) feed conversion efficiency, production was 893 and 1,115 kg milk solids (MS) ha⁻¹, N loss to the environment was 19 and 20 kg N ha⁻¹ year⁻¹, and ‘environmental efficiency’ was 21 and 18 kg N leached tonne⁻¹ MS produced, respectively.     

Phosphorus and nitrogen cycles in the vegetation of differently managed buffer zones

Vegetated buffer zones (BZs) between a cultivated field and a watercourse reduce erosion and load of particle-bound phosphorus (P), but decay of abundant vegetation increases the potential of BZs to act as a source of readily algal-available P. To quantify temporal variations in P and nitrogen (N) contents of the grassy vegetation of BZs on a clay soil (Vertic Cambisol) in south-western Finland, plant samples were collected six times between May 2005 and April 2006 from natural BZs, BZs grazed by cattle and BZs harvested by cutting and removal of the yield. The total dry weight biomass peaked in early August at 2,130–2,360 and 5,500–6,270 kg ha⁻¹ for the grazed and the other BZs, respectively. In August, 3,840–4,830 kg ha⁻¹ were removed from the harvested BZs while the entire biomass of the non-harvested BZs remained in the field. In October, total P and N contents varied from 2.4–10.2 to 19–72 kg ha⁻¹, respectively, the lowest amounts being for the young harvested BZ and the highest for the non-harvested BZs. A considerable decrease of P and N contents occurred in the biomass up to 6.1 and almost 30 kg ha⁻¹, respectively, after the first frosts. Harvesting of BZs is recommended to decrease the amount of P and N in the BZs and reduce the risk of P and N leaching outside the growing season.     

Relative performance of neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) coated urea vis-à-vis ordinary urea applied to rice on the basis of soil test or following need based nitrogen management using leaf colour chart

Neem coated urea (NCU) applied to rice can result in high N use efficiency as it contains nitrification inhibition properties. Field experiments were conducted for three years (2005–2007) at Ludhiana (sandy loam soil) and Gurdaspur (clay loam soil) for evaluating the relative performance of NCU vis-à-vis ordinary urea as a source of N for transplanted wetland rice. Along with a no-N control, the two N sources were tried at three N levels––40, 80 and 100% of the recommended level of 120 kg N ha⁻¹. Different doses of N were applied in three equal split doses at transplanting, 21 and 42 days after transplanting (DAT). For need based site specific N management for improved N use efficiency, the two sources of N were applied using leaf colour chart (LCC). In this treatment a basal dose of N at the rate of 20 kg N ha⁻¹ was applied after 7 DAT and LCC readings were recorded at weekly intervals starting 14 DAT. Whenever the intensity of green colour of the first fully opened leaf from the top was less than shade 4 of the LCC, N was applied at the rate of 30 kg N ha⁻¹.