Long-term tillage,straw management and N fertilization effects on quantity and quality of organic C and N in a Black Chernozem soil

Soil, crop and fertilizer management practices may affect the amount and quality of organic C and N in soil. A long-term field experiment (growing barley, wheat, or canola) was conducted on a Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, to determine the influence of 19 (1980 to 1998) or 27 years (1980 to 2006) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [S_Rem]and straw retained [S_Ret]) and N fertilizer rate (0, 50 and 100 kg N ha⁻¹ in S_Ret and 0 kg N ha⁻¹ in S_Rem plots) on total organic C (TOC) and N (TON), and light fraction organic C (LFOC) and N (LFON) in the 0–7.5 and 7.5–15 cm or 0–5, 5–10 and 10–15 cm soil layers. The mass of TOC and TON in soil was usually higher in S_Ret than in S_Rem treatment (by 3.44 Mg C ha⁻¹ for TOC and 0.248 Mg N ha⁻¹ for TON after 27 years), but there was little effect of tillage and N fertilization on these parameters. The mass of LFOC and LFON in soil tended to increase with S_Ret (by 285 kg C ha⁻¹ for LFOC and 12.6 kg N ha⁻¹ for LFON with annual rate of 100 kg N ha⁻¹ for 27 years)_, increased with N fertilizer application (by 517 kg C ha⁻¹ for LFOC and 36.0 kg N ha⁻¹ for LFON after 27 years), but was usually higher under CT than ZT (by 451 kg C ha⁻¹ for LFOC and 25.3 kg N ha⁻¹ for LFON after 27 years). Correlations between soil organic C or N fractions were highly significant in most cases. Linear regressions between crop residue C input and soil organic C or N were significant in most cases. The effects of tillage, straw management and N fertilizer on soil were more pronounced for LFOC and LFON than TOC and TON, and also in the surface layers than in the deeper layers. Tillage and straw management had little or no effect on C:N ratios, but the C:N ratios in light organic fractions significantly decreased with increasing N rate (from 20.06 at zero-N to 18.91 at 100 kg N ha⁻¹). Compared to the 1979 results, in treatments that did not receive N fertilizer (CTS_Rem0, CTS_Ret0, ZTS_Rem0 and ZTS_Ret0), CTS_Rem0 resulted in a net decrease in TOC concentration (by 1.9 g C kg⁻¹) in the 0–15 cm soil layer in 2007 (after 27 years), with little or no change in the CTS_Ret0 and ZTS_Rem0 treatments, while there was a net increase in TOC concentration (by 1.2 g C kg⁻¹) in the ZTS_Ret0 treatment. Straw retention and N fertilizer application at 50 and 100 kg N ha⁻¹ rates showed a net positive effect on TOC concentration under both ZT (ZTS_Ret50 by 2.3 g C kg⁻¹ and ZTS_Ret100 by 3.1 g C kg⁻¹) and CT (CTS_Ret50 by 3.5 g C kg⁻¹ and CTS_Ret100 by 1.6 g C kg⁻¹) treatments in 2007 compared to 1979 data. In conclusion, the findings suggest that retention of straw, application of N fertilizer and elimination of tillage would improve soil quality, and this might increase the potential for N supplying power of the soil and sustainability of crop productivity.     

Long-term tillage,straw and N rate effects on some chemical properties in two contrasting soil types in Western Canada

Long-term use of soil, crop residue and fertilizer management practices may affect some soil properties, but the magnitude of change depends on soil type and climatic conditions. Two field experiments with barley, wheat, or canola in a rotation on Gray Luvisol (Typic Cryoboralf) loam at Breton and Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, were conducted to determine the effects of 19 or 27 years (from 1980 to 1998 or 2006 growing seasons) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [S_Rem] and straw retained [S_Ret]) and N fertilizer rate (0, 50 and 100 kg N ha^?1 in S_Ret, and 0 kg N ha^?1 in S_Rem plots) on pH, extractable P, ammonium-N and nitrate–N in the 0–7.5, 7.5–15, 15–30 and 30–40 cm or 0–15, 15–30, 30–60, 60–90 and 90–120 cm soil layers. The effects of tillage, crop residue management and N fertilization on these chemical properties were usually similar for both contrasting soil types. There was no effect of tillage and residue management on soil pH, but application of N fertilizer reduced pH significantly (by up to 0.5 units) in the top 15 cm soil layers. Extractable P in the 0–15 cm soil layer was higher or tended to be higher under ZT than CT, or with S_Ret than S_Rem in many cases, but it decreased significantly with N application (by 18.5 kg P ha^?1 in Gray Luvisol soil and 20.5 kg P ha^?1 in Black Chernozem soil in 2007). Residual nitrate–N (though quite low in the Gray Luvisol soil in 1998) increased with application of N (by 17.8 kg N ha^?1 in the 0–120 cm layer in Gray Luvisol soil and 23.8 kg N ha^?1 in 0–90 cm layer in Black Chernozem soil in 2007) and also indicated some downward movement in the soil profile up to 90 cm depth. There was generally no effect of any treatment on ammonium-N in soil. In conclusion, elimination of tillage and retention of straw increased but N fertilization decreased extractable P in the surface soil. Application of N fertilizer reduced pH in the surface soil, and showed accumulation and downward leaching of nitrate–N in the soil profile.     

Influence of time and method of alfalfa stand termination on yield,seed quality,N uptake,soil properties and greenhouse gas emissions under different N fertility regimes

A field experiment was conducted in a 7-year old alfalfa stand to compare the influence of time and method of terminating alfalfa stands on crop yield, seed quality, N uptake and recovery of applied N for wheat (Triticum aestivum L.) and canola (Brassica napus L.), soil properties (ammonium-N, nitrate-N, bulk density, total and light fraction organic C and N), and N₂O emissions on a Gray Luvisol (Typic Cryoboralf) loam near Star City, Saskatchewan, Canada. The treatments were a 3 × 3 × 4 factorial combination of three termination methods [herbicide (H), tillage (T), and herbicide + tillage (HT)], three termination times (after cut 1 and cut 2 in 2003, and in spring 2004) and four rates of N (0, 40, 80 and 120 kg N ha⁻¹) applied at seeding to wheat-canola rotation from 2004 to 2007. In the termination year, soil nitrate-N was considerably higher in T or HT treatments than in the H treatment and decreased with delay in termination. In the first crop year, seed and straw yields of wheat grown on T and HT treatments were significantly greater than H alone (by 1,055–1,071 kg seed ha⁻¹ and by 869–929 kg straw ha⁻¹), due to greater content of soil available N in T treatments. Yields decreased with delay in termination time. In general, yield and N uptake in seed and straw, and protein concentration tended to increase with increasing N rate. A greater yield increase occurred on the H compared to T and HT treatments from the first increments of N applied. Nitrous oxide emissions were generally low and there were no treatment differences evident when cumulative 4-year N₂O-N losses were compared. Appropriate N fertilization was able to compensate for yield reductions due to delayed termination timing, but could not do so entirely for yield reductions on the H compared to T or HT termination method. The amounts of TOC, TON, LFOC and LFON after four growing seasons were usually higher or tended to be higher under H treatment than under T treatment in the 0–5 cm soil layer, but the opposite was true in the 5–10 cm or 10–15 cm soil layers.     

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.     

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.     

Recovery of mineral fertiliser N and slurry N in continuous silage maize using the <Superscript>15</Superscript>N and difference methods

The stable isotope technique and the difference method are common approaches for estimating fertiliser N uptake efficiency. Both methods, however, have limitations and their suitability may depend on N management and environmental conditions. A field experiment was conducted on a humus sandy soil in northern Germany to estimate fertiliser N uptake efficiency of silage maize in the year of application (Zea mays L.) by the stable isotope and the difference method as influenced by the type of N fertiliser (mineral vs. cattle slurry), the application mode (separate or combined application), and N rate. Seven N treatments were included (0, 50, 100 and 150 kg mineral N ha⁻¹; 20, 40 m3 cattle slurry ha⁻¹; 50 kg mineral N ha⁻¹ plus 40 m3 slurry ha⁻¹), where either mineral N or slurry N was labelled, and mineral N was split into two dressings. In addition, 4.1 kg ha⁻¹ labelled mineral N was incorporated into otherwise unlabelled treatments (0, 20, 40 m3 ha⁻¹, and 50 kg mineral N ha⁻¹ plus 40 m3 ha⁻¹) to estimate N uptake from the upper soil layer. Uptake of ¹⁵N was followed in leaves, stalk, ear, and the whole crop. Fertiliser N uptake efficiency (FNUE_15N) of mineral fertiliser N obtained by the isotope technique ranged between 51 and 61%. Recovered fertiliser N was mainly found in the ear, while less labelled N remained in leaves and the stalk. The nitrogen rate tended to increase the amount of recovered N, but the effect was not consistent among plant parts and the whole crop. Plant N uptake from non-fertiliser N was found to increase N input up to 100 kg N ha⁻¹. Nitrogen recoveries of the two mineral N dressings were similar for the different plant parts as well as for the whole crop. Fertiliser N uptake efficiency (FNUE_diff) of mineral N estimated by the difference method resulted in substantially higher values compared to FNUE_15N, varying between 56 and 98%. More N was taken up from the upper soil layer with increasing N supply, which is regarded as a major error source of the difference method. Slurry N was taken up less efficient in the year of application than mineral fertiliser N as indicated by recovery rates of 21–22% (FNUE_15N) and 39–62% (FNUE_diff), respectively. When mineral N and slurry were applied together, the difference method estimated significantly lower N uptake efficiencies for both mineral and slurry N compared to a single application, while values obtained by the isotope method were not affected.     

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.     

Effect of seasonal rainfall,N fertilizer and tillage on N utilization by dryland wheat in a semi-arid environment

Crop yield and N uptake in semi-arid environments are typically limited by available water and/or N. Since remobilization of shoot N is a major source of grain N, an understanding of how it is influenced by soil N and water supply, and tillage, is required. In 2003, 2005 and 2006, we determined the influence of N supply (0 or 60 kg fertilizer N ha⁻¹) and tillage [no tillage (NT) or conventional tillage (CT)] on N translocation and N use efficiency of wheat (Triticum aestivum L.) at Scott, Saskatchewan, Canada. Wheat production and N use, and their response to N fertilizer or tillage, were largely influenced by water availability. Wheat N uptake and remobilization were strongly correlated with normalized rainfall in May and June (r = 0.985 and 0.935, respectively, both significant at the P = 0.01 level). In a moisture-stressed year (2003), grain yield was higher under NT than CT, and fertilizer N was ineffective due to low N demand. Nitrogen application increased shoot dry matter (DM), and N uptake and remobilization only in 2006, a year with near-average precipitation. In a wet and cool year (2005), wheat showed no response to tillage or fertilizer N as available soil N was high. Root DM and N content varied slightly only with year or treatment. When N uptake at heading was substantially greater than 100 kg ha⁻¹, N loss occurred during plant senescence, and it was higher with N fertilization: in 2005 and 2006, N-fertilized wheat lost 33–35 kg N ha⁻¹. Nitrogen use efficiency was: (1) higher under NT than CT, due to higher N utilization efficiency, (2) higher with no added N due to higher uptake and utilization efficiencies, and (3) low when water availability was low or excessive. Tillage system had little effect on the uptake, remobilization or loss of N. Fertilizer N application in a year with average rainfall increased wheat production, N accumulation and remobilization, and N loss during senescence.     

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.     

Conservation tillage,local organic resources and nitrogen fertilizer combinations affect maize productivity,soil structure and nutrient balances in semi-arid Kenya

Smallholder land productivity in drylands can be increased by optimizing locally available resources, through nutrient enhancement and water conservation. In this study, we investigated the effect of tillage system, organic resource and chemical nitrogen fertilizer application on maize productivity in a sandy soil in eastern Kenya over four seasons. The objectives were to (1) determine effects of different tillage-organic resource combinations on soil structure and crop yield, (2) determine optimum organic–inorganic nutrient combinations for arid and semi-arid environments in Kenya and, (3) assess partial nutrient budgets of different soil, water and nutrient management practices using nutrient inflows and outflows. This experiment, initiated in the short rainy season of 2005, was a split plot design with 7 treatments involving combinations of tillage (tied-ridges, conventional tillage and no-till) and organic resource (1 t ha⁻¹ manure + 1 t ha⁻¹ crop residue and; 2 t ha⁻¹ of manure (no crop residue) in the main plots. Chemical nitrogen fertilizer at 0 and 60 kg N ha⁻¹ was used in sub-plots. Although average yield in no-till was by 30–65% lower than in conventional and tied-ridges during the initial two seasons, it achieved 7–40% higher yields than these tillage systems by season four. Combined application of 1 t ha⁻¹ of crop residue and 1 t ha⁻¹ of manure increased maize yield over sole application of manure at 2 t ha⁻¹ by between 17 and 51% depending on the tillage system, for treatments without inorganic N fertilizer. Cumulative nutrients in harvested maize in the four seasons ranged from 77 to 196 kg N ha⁻¹, 12 to 27 kg P ha⁻¹ and 102 to 191 kg K ha⁻¹, representing 23 and 62% of applied N in treatments with and without mineral fertilizer N respectively, 10% of applied P and 35% of applied K. Chemical nitrogen fertilizer application increased maize yields by 17–94%; the increases were significant in the first 3 seasons (P < 0.05). Tillage had significant effect on soil macro- (>2 mm) and micro-aggregates fractions (<250 μm >53 μm: P < 0.05), with aggregation indices following the order no-till > tied-ridges > conventional tillage. Also, combining crop residue and manure increased large macro-aggregates by 1.4–4.0 g 100 g⁻¹ soil above manure only treatments. We conclude that even with modest organic resource application, and depending on the number of seasons of use, conservation tillage systems such as tied-ridges and no-till can be effective in improving crop yield, nutrient uptake and soil structure and that farmers are better off applying 1 t ha⁻¹ each of crop residue and manure rather than sole manure.     

Nitrogen and residue management effects on agronomic productivity and nitrogen use efficiency in rice–wheat system in Indian Punjab

Development of a sustainable and environment friendly crop production system depends on identifying effective strategies for the management of tillage and postharvest crop residues. Three-year (2004–2007) field study was initiated on two soil types to evaluate the effect of straw management (burning, incorporation and surface mulch) and tillage (conventional tillage and zero tillage) before sowing wheat and four nitrogen rates (0, 90, 120 and 150 kg N ha⁻¹) on crop yields, N use efficiency, and soil fertility in the northwestern India. Effect of tillage and straw management on nitrogen transformation in soils was investigated in a laboratory incubation study. In sandy loam, grain yield of wheat with straw mulch-zero-till (ZT) was 7% higher compared to when residues were burnt-ZT but it was similar to straw burnt-conventional till (CT), averaged across 3 years. In silt loam, grain yield of wheat with straw mulch-ZT was 4.4% higher compared to straw incorporated-CT, but it was similar to straw burnt-CT. Response to N application was generally observed up to 150 kg N ha⁻¹ except in 2004–2005 on sandy loam where N response was observed up to 120 kg N ha⁻¹, irrespective of straw and tillage treatments. In sandy loam, RE was lower (49%) for straw burnt-ZT than in other treatments (54–56%). In silt loam, RE was higher in straw mulch-ZT compared with straw incorporation-CT (65 vs. 58%). In sandy loam, AE was higher in straw burnt-CT and straw mulch-ZT compared with the other treatments (19.2 vs. 16.9 kg grain kg⁻¹ N applied). In silt loam, AE was lower in straw incorporation-CT than in other treatments (16.0 vs. 17.6 kg grain kg⁻¹ N applied). Rice yield and N uptake were not influenced by straw and tillage management treatments applied to the preceding wheat. Recycling of rice residue (incorporation and surface mulch) compared with straw burning increased soil organic carbon and the availability of soil P and K. There was more carbon sequestration in rice straw mulch with zero tillage (25%) than in straw incorporation with conventional tillage (17%). Soil N mineralization at 45 days after incubation was 15–25% higher in straw retention plots compared with on straw burnt plots.     

Effect of polymer-coated urea and tillage on the dynamics of available N and nitrous oxide emission from Gray Luvisols

Two field experiments were conducted to assess the effectiveness of polymer-coated urea (PCU) vs. conventional urea (urea) in minimizing nitrate accumulation in soil and nitrous oxide (N₂O) emission while optimizing available N supply. The trials were located on Dark Gray Luvisols (Typic Cryoboralf) near Beaverlodge, Alberta (2004–2007) and Star City, Saskatchewan (2004–2006), in the north western Canadian Prairies. The treatments comprised of combinations of two tillage systems (conventional and no tillage), the two forms of urea (applied at commercial rates, 50–60 kg N ha⁻¹), and time of application (side-banded in spring or fall). Tillage had little effect on the measured soil variables. Available N at the anthesis growth stage was higher with spring- than fall-banded N in three of four site-years, and with PCU than urea in two site-years. At seeding, nitrate in the soil layers to 60-cm depth, especially the top 15 cm, was mostly higher for fall- than spring-banded treatments but differed less between the forms of urea. Fall application, therefore, has greater potential for gaseous N and leaching losses early in the growing season when crops have low N requirements, and hence is not advisable. Nitrous oxide emission from spring to fall was higher with the fertilized treatments in three of five site-years and not different between fertilized and unfertilized treatments in the other site-years. At Beaverlodge, N₂O loss was low in 2 years and showed few significant treatment effects. At Star City, N₂O loss was 1.5- to 1.7-fold higher from urea than PCU treatments, and up to 1.5-fold lower from spring than fall application. It is concluded that although PCU can increase available N during the growth period and reduce N₂O loss in some years compared with urea, the time of N application had a consistently greater effect than the type of urea in enhancing crop N recovery and reducing N loss to the environment.     

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.     

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.     

Nitrogen in soils,plants, surface water and shallow groundwater in a bahiagrass pasture of Southern Florida,USA

Despite substantial measurements using both laboratory and field techniques, little is known about the spatial and temporal variability of nitrogen (N) dynamics across the landscapes, especially in agricultural landscapes with cow–calf operations. This study was conducted to assess the comparative levels of total inorganic nitrogen, TIN (NO₃–N + NH₄–N) among soils, forage, surface water and shallow groundwater (SGW) in bahiagrass (Paspalum notatum, Flueggé) pastures. Soil samples were collected at 0–20, 20–40, 40–60, and 60–100 cm across the pasture’s landscape (top slope, TS; middle slope, MS; and bottom slope, BS) in the spring and fall of 2004, 2005 and 2006, respectively. Bi-weekly (2004–2006) groundwater and surface water samples were taken from wells located at TS, MS, and BS and from the run-off/seepage area (SA). Concentrations of NH₄–N, NO₃–N, and TIN in SGW did not vary with landscape position (LP). However, concentrations of NH₄–N, NO₃–N, and TIN in water samples collected from the seep area were significantly (P ≤ 0.05) higher when compared to their average concentrations in water samples collected from the different LP. Average concentrations of NO₃–N (0.4–0.9 mg l⁻¹) among the different LP were well below the maximum, of 10 mg l⁻¹, set for drinking water. The maximum NO₃–N concentrations (averaged across LP) in SGW for 2004, 2005 and 2006 were also below the drinking water standards for NO₃–N. Concentration of TIN in soils varied significantly (P ≤ 0.05) with LP and soil depth. Top slope and surface soil (0–20 cm) had the greatest concentrations of TIN. The greatest forage availability of 2,963 ± 798 kg ha⁻¹ and the highest N uptake of 56 ± 12 kg N ha⁻¹ were observed from the TS in 2005. Both forage availability and N uptake of bahiagrass at the BS were consistently the lowest when averaged across LP and years. These results can be attributed to the grazing activities as animals tend to graze more at the BS. The average low soil test value of TN (across LP and soil depth) in our soils of 10.9 mg kg⁻¹ (5.5 kg N ha⁻¹) would indicate that current pasture management including cattle rotation in terms of grazing days and current fertilizer application (inorganic + feces + urine) for bahiagrass pastures may not have negative impact on the environment.     

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.     

Effects of conservation tillage,crop residue and cropping systems on changes in soil organic matter and maize–legume production: a case study in Teso District

The effects of conservation tillage, crop residue and cropping systems on the changes in soil organic matter (SOM) and overall maize–legume production were investigated in western Kenya. The experiment was a split-split plot design with three replicates with crop residue management as main plots, cropping systems as sub-plots and nutrient levels as sub-sub plots. Nitrogen was applied in each treatment at two rates (0 and 60 kg N ha⁻¹). Phosphorus was applied at 60 kg P/ha in all plots except two intercropped plots. Inorganic fertilizer (N and P) showed significant effects on yields with plots receiving 60 kg P ha⁻¹ + 60 kg N ha⁻¹ giving higher yields of 5.23 t ha⁻¹ compared to control plots whose yields were as low as 1.8 t ha⁻¹ during the third season. Crop residues had an additive effect on crop production, soil organic carbon and soil total nitrogen. Crop rotation gave higher yields hence an attractive option to farmers. Long-term studies are needed to show the effects of crop residue, cropping systems and nutrient input on sustainability of SOM and crop productivity.     

Effect of increased N use and dry periods on N<Subscript>2</Subscript>O emission from a fertilized grassland

To better understand the effects of increased N input and dry periods on soil nitrous oxide (N₂O) emission, we examined a unique data-set of weather, soil microclimate, N input, and N₂O emissions (using the eddy covariance method), measured at a fertilized grassland over the period 2003–2008. We found that the N₂O emission (11.5 kg N ha⁻¹ year⁻¹), the ratio of N₂O emission to N input (3.4), and the duration of elevated N₂O flux (57 days) in 2003 were about two times greater than those of the following years. 2003 had the highest annual N input (343 kg N ha⁻¹ year⁻¹) which exceeded the agronomical requirements for Irish grasslands (up to 306 kg ha⁻¹ year⁻¹). In the summer of 2003, the site had a significantly higher soil temperature, lower WFPS and lowest rainfall of all years. Large N₂O emission events followed rainfall after a long dry period in the summer of 2003, attributed to dominant nitrification processes. Furthermore, in the non summer periods, when temperature was lower and WFPS was higher and when there were prior N applications, lower N₂O emissions occurred and were attributed to dominant denitrification processes. Throughout the study period, the N input and soil dryness related factors (duration of WFPS under 50%, summer average WFPS, and low rainfall) showed exponential relationships with N₂O emission and the ratio of N₂O emission to N input. Based on these findings, we infer that the observed anomalously high N₂O emission in 2003 may have been caused by the combined effects of excess N input above the plant uptake rate, elevated soil temperature, and N₂O flux bursts that followed the rewetting of dry soil after an unusually long dry summer period. These results suggest that high N input above plant uptake rate and extended dry periods may cause abnormal increases in N₂O emissions.     

Influence of organic amendments on growth, yield and quality of wheat and on soil properties during transition to organic production

A transition period of at least 2 years is required for annual crops before the produce may be certified as organically grown. The purpose of this study was to evaluate the effects of three organic amendments on the yield and quality of wheat (Triticum aestivum L.) and on soil properties during transition to organic production. The organic amendments were composted farmyard manure (FYMC), vermicompost and lantana (Lantana spp. L.) compost applied to soil at four application rates (60 kg N ha⁻¹, 90 kg N ha⁻¹, 120 kg N ha⁻¹ and 150 kg N ha⁻¹). The grain yield of wheat in all the treatments involving organic amendments was markedly lower (36–65% and 23–54% less in the first and second year of transition, respectively) than with the mineral fertilizer treatment. For the organic treatments applied at equivalent N rates, grain yield was higher for FYMC treatment, closely followed by vermicompost. In the first year of transition, protein content of wheat grain was higher (85.9 g kg⁻¹) for mineral fertilizer treatment, whereas, in the second year, there were no significant differences among the mineral fertilizer treatment and the highest application rate (150 kg N ha⁻¹) of three organic amendments. The grain P and K contents were, however, significantly higher for the treatments involving organic amendments than their mineral fertilizer counterpart in both years. Application of organic amendments, irrespective of source and rate, greatly lowered bulk density (1.14–1.25 Mg m⁻³) and enhanced pH (6.0–6.5) and oxidizable organic carbon (13–18.8 g kg⁻¹) of soil compared with mineral fertilizer treatment after a 2-year transition period. Mineral fertilized plots, however, had higher levels of available N and P than plots with organic amendments. All the treatments involving organic amendments, particularly at higher application rates, enhanced soil microbial activities of dehydrogenase, β-glucosidase, urease and phosphatase compared with the mineral fertilizer and unamended check treatments. We conclude that the application rate of 120 kg N ha⁻¹ and 150 kg N ha⁻¹ of all the three sources of organic amendments improved soil properties. There was, however, a 23–65% reduction in wheat yield during the 2 years of transition to organic production.     

Tied-ridging and fertilizer use for sorghum production in semi-arid Ethiopia

Grain sorghum [Sorghum bicolor (L.) Moench] yield is often constrained by low soil water and nutrient availability in Ethiopia. The integration of tied-ridging for water conservation with fertilizer application in semi-arid sorghum production areas of northern and central Ethiopia was evaluated in five trials in 2005–2007. Three tillage practices and four fertilizer application treatments were evaluated in a complete factorial. The tillage practices included tied-ridging before (TR_br) and after (TR_r) the on-set of rains, and shilshalo, a traditional ridging practice for preventing runoff and controlling weeds practiced with the traditional oxen-drawn plow. The fertilizer treatments (N–P) were 0-0, 10-10, 22-0, and 32-10 kg ha⁻¹. Grain yield was increased over shilshalo with tied-ridging by 6–45%. Grain yield was increased by 26% with pre-plant application of N plus P and by 16% with side-dress N application in central Ethiopia, but yield was not increased in the northern Ethiopia trials. Tied-ridging did not increase the yield response to nutrient application. Tied-ridging before or after on-set of rains was found to be equally effective in increasing yields and should be considered for sorghum production in semi-arid areas of northern and central Ethiopia. Response to applied N and P was probably constrained by soil water deficits, even with tied-ridging and especially in the drier environments of northern Ethiopia. Application of N and P should be considered if mean yield levels are above 2.5 Mg ha⁻¹.