Phosphorus transformations as affected by sampling date, fertilizer rate and phosphorus uptake in a soil under pasture

A phosphorus (P) fertilization study was conducted in the southeast of the Buenos Aires province in Argentina, to determine the effect of P fertilizer rate and sampling date on microbial biomass P, and of organic and inorganic P extractable with 0.5M NaHCO₃, in a soil under pasture. In addition, Bray-P, dry-matter production and P uptake were measured. Soil was sampled at different times over one year, and two to three years after application of 0, 50, 100 and 200 kg P ha ^–1. The addition of P fertilizer significantly increased total soil P and the labile fraction of P extractable with NaHCO₃, with the greatest change in the labile inorganic P form, but had no effect on microbial biomass P. Fractions of P showed different patterns of seasonal variation. Microbial biomass P had a peak in winter and a lowest value in summer, the opposite occurring with NaHCO₃-extractable organic P, while NaHCO₃-extractable inorganic P remained relatively constant throughout the year. The cumulative dry-matter yield after three years was 31% higher in the fertilized than in the unfertilized treatments; the highest being 27660 kg ha^–1 for 200 kg P ha^–1. Concentration of Bray-P increased by 0.18 mg P kg ^–1 for each additional kg P ha^–1 added, but remained relatively constant over the year. A significant correlation was found between available Bray-P and microbial biomass P (r = 0.53), and NaHCO₃-extractable organic P (r = 0.47), suggesting that these organic fractions may contribute to plant nutrition.     

不同土壤有效磷水平条件下施磷对设施辣椒产量和磷肥利用率的影响

适宜的根层磷养分供应是菜田磷肥推荐用量的基础。通过在开展多点磷肥施用试验,分析不同施肥措施对辣椒产量和磷肥农学利用率的影响。结果表明,除试验点2、试验点4和试验点8外处理间辣椒产量存在显著差异外,其他各试验点处理间辣椒产量差异不显著。与T1辣椒产量相比,T2、T3和T4辣椒产量都有所提高,但各处理间辣椒产量差异都不显著。各试验点各处理磷肥利用率由大到小依次为:处理2处理3处理4。因此,在土壤有效磷中等偏高磷水平条件下,设施辣椒菜田在施用有机肥的基础上不需要追施磷肥。     

Crop yield, nitrogen uptake and nitrate-nitrogen accumulation in soil as affected by 23 annual applications of fertilizer and manure in the rainfed region of Northwestern China

Application of chemical fertilizers and farmyard manure affects crop productivity and improves nutrient cycling within soil–plant systems, but the magnitude varies with soil-climatic conditions. A long-term (1982–2004) field experiment was conducted to investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers and farmyard swine manure (M) on seed and straw yield, protein concentration, and N uptake in the seed and straw of 19-year winter wheat (Triticum aestivum L.) and four-year oilseed (three-year canola, Brassica napus L. in 1987, 2000 and 2003; one-year flax, Linum usitatisimum L. in 1991), accumulation of nitrate-N (NO₃-N) in the soil profile (0–210 cm), and N balance sheet on a Huangmian soil (calcaric cambisols, FAO) near Tianshui, Gansu, China. The two main plot treatments were without and with farmyard swine manure (M); sub-plot treatments were control (Ck), N, NP, and NPK.␣The average seed yield decreased in the order MNPK ≥ MNP > MN ≥ NPK ≥ NP > M > N > Ck. The average effect of manure and fertilizers on seed yield was in the order M > N > P > K. The seed yield increase was 20.5% for M, 17.8% for N, 14.2% for P, and 2.9 % for K treatment. Seed yield response to fertilizers was much greater for N and P than for K, and it was much greater for no manure than for manure treatment. The response of straw yield to fertilization treatments was usually similar to that of seed yield. The N fertilizer and manure significantly increased protein concentration and N uptake plant. From the standpoint of increasing crop yield and seed quality, MNPK was the best fertilization strategy. Annual applications of N fertilizer and manure for 23 successive years had a marked effect on NO₃-N accumulation in the 0–210 cm soil profile. Accumulation of NO₃-N in the deeper soil layers with application of N fertilizer and manure is regarded as a potential danger, because of pollution of the soil environment and of groundwater. Application of N fertilizer in combination with P and/or K fertilizers reduced residual soil NO₃-N significantly compared with N fertilizer alone in both no manure and manure plots. The findings suggest that integrated and balanced application of N, P, and K fertilizers and␣manure at proper rates is important for protecting soil and groundwater from potential NO₃-N pollution and for maintaining high crop productivity in the rainfed region of Northwestern China.     

Nitrogen availability to maize as affected by fertilizer application and soil type in the Tanzanian highlands

Enhancing crop production by maintaining a proper synchrony between soil nitrogen (N) and crop N demand remains a challenge, especially in under-studied tropical soils of Sub-Saharan Africa (SSA). For two consecutive cropping seasons (2013–2015), we monitored the fluctuation of soil inorganic N and its availability to maize in the Tanzanian highlands. Different urea-N rates (0–150 kg N ha^?1; split into two dressings) were applied to two soil types (TZi, sandy Alfisols; and TZm, clayey Andisols). In the early growing season, soil mineralized N was exposed to the leaching risk due to small crop N demand. In the second N application (major N supply accounting for two-thirds of the total N), applied urea was more efficient in increasing soil inorganic N availability at TZm than at TZi. Such effect of soil type could be the main contributor to the higher yield at TZm (up to 4.4 Mg ha^?1) than that at TZi (up to 2.6 Mg ha^?1) under the same N rate. The best-fitted linear-plateau model indicated that the soil inorganic N availability (0–0.3 m) at the tasseling stage largely accounted for the final yield. Further, yields at TZi were still limited by N availability at the tasseling stage due to fast depletion of applied-N, whereas yields plateaued at TZm once N availability was above 67 kg N ha^?1. Our results provided a valuable reference for designing the N management to increase yield, while minimizing the potentially adverse losses of N to the environment, in different agro-ecological zones in SSA.     

Total and light fraction organic C in a thin Black Chernozemic grassland soil as affected by 27 annual applications of six rates of fertilizer N

Maintenance and sequestration of C is important to sustain and improve the quality and productivity of soils. The objective of this study was to determine the effects of 27 annual applications of six N rates (0, 56, 112, 168, 224 and 336 kg N ha^–1 yr^–1) on total organic C (TOC) and light fraction organic C (LFOC) in a thin Black Chernozemic loam soil. Nitrogen (ammonium nitrate) was surface-applied to bromegrass (Bromus inermis Leyss) managed as hay near Crossfield, Alberta, Canada. The concentration and mass of TOC and LFOC in the 0–5, 5–10, 10–15 and 15–30 cm soil layers increased with N rate and showed a quadratic response to N rate with significant R² values, with their maximum values at 336 kg N ha^–1 in the 0–5 cm layer and at 224 kg N ha^–1 in other layers. But the increase in TOC and LFOC per kg of N addition was maximized at 56 kg N ha^–1 and declined with further increase in N rate. These trends indicated that higher N rates would cause a faster build up of soil C, whereas lower N rates would achieve a greater increase in soil C per unit of N addition. Response of C mass to N application was much greater for LFOC (range of 697 to 156% increase) than for TOC (range of 67 to 17% increase). Percentage of LFOC in TOC mass increased with N rate. At the 168 to 336 kg N ha^–1 rates, almost all of the increase in TOC in the surface 10 cm soil occurred as LFOC. Thus, LFOC was more responsive to N application and was a good indicator of N effect on soil C. The trend of change in soil TOC and LFOC was similar to hay yield and C removal in hay, which suggests that increasing hay yield with N application concurrently also increases soil organic C. In conclusion, long-term annual applications of N fertilizer to bromegrass resulted in a substantial increase in TOC and LFOC in the soil, thereby indicating that N fertilization can be used to sequester more atmospheric C in prairie grassland soils.     

Biomass and nutrient uptake ofAilanthus excelsa as affected by N and P fertilization on an aridisol

A field experiment was conducted on a coarse sand soil having pH 8.8 and organic matter 0.06% in Indian arid region, to study the influence of N and P fertilizers on growth, biomass and nutrient content ofAilanthus excelsa, which is an important fodder species of arid and semi arid regions. Three levels of nitrogen (0, 9 and 18 g N tree^–1 as Urea) and of phosphorus (0, 3 and 6 g P₂O₅ tree^–1 as Single Superphosphate) in factorial combinations were taken in triplicate and the experiment was laid in Randomised Block Design. Application of 9 g N plant^–1 improved tree height by 15 to 25%, collar circumference by 30 to 37% and crown diameter by 18 to 26% in the initial 3 years. Total biomass increase due to 9 g N plant^–1 was 76% and 59%, respectively, after 1 and 2 years of planting. Application of 3 g P₂O₅ tree^–1 increased tree height by 8 to 18% and collar circumference by 17 to 24% during initial three years, and total biomass by 70% at 1 year and 30% at 2 years of age. Combined application of 18 g N and 3 g P₂O₅ tree^–1 (N₁₈P₃) was the best treatment which increased tree height by 49%, 85% and 35% and collar circumference by 56%, 10% and 11% at 1, 2, and 3 years of age, respectively. N₁₈P₃ treatment increased the total biomass by 181% at 1 year and 185% at 2 years of age. N and P applications improved considerably the branching of roots and root length and enhanced root biomass by 2 to 3 folds. N₁₈P₃ treatment increased the nitrogen uptake by 304% (4.02 g tree^–1) at 1 year and 211% (42.56 g tree^–1) at 2 years of age. The P uptake was maximum (290.4 mg tree^–1) due to N₁₈P₃ treatment in 1 year old and 11.37 g tree^–1 due to N₉P₆ treatment in 2 year old plantation.     

Nitrogen dynamics of grass as affected by N input regimes, soil texture and climate: lysimeter measurements and simulations

Nitrate leaching is often low from grasslands, primarily due to their long period of N uptake compared to arable crops. In the present paper we explore the combined effects of N input regime, soil type and climatic conditions through a combination of field lysimeter studies and simulation modeling of temporary grassland. A lysimeter consisting of eight 10 × 4 × 1 m individually drained cells was constructed in SW Norway, a region with a cool and wet marine climate. Six cells were filled with silty sand and two cells with coarse sand. The lysimeters were cropped first with barley for two years, followed by five years of grassland. Treatments included various combinations of N input (fertilizer, manure or both), and the results were analyzed by means of two coupled dynamic simulation models (CoupModel: a heat- and water transport model, and SOILN_–NO: a soil nitrogen model). The parameterized models were further used to assess a scenario with a more continental climate (somewhat cooler and drier). All treatments resulted in a net export of N, with N amounts removed at harvest ranging between 121 and 139% of that applied. Measured N yield from the treatment receiving manure only was almost as high as that from the treatment receiving fertilizer only, even though it received on average about 80 kg ha^–1 less inorganic N. Nitrogen losses through leaching were in the range of 5–23% of the N input, and soil type had a greater effect than source of N input. The inorganic N fraction of the leachate was 71–82% of the total N, and 98% of this was nitrate. The models gave reasonable simulation of N yields as well as of the timing and magnitude of nitrate leaching from the different treatments. They also clearly illustrated that the low nitrate leaching from the system is primarily attributable to a high plant N uptake. The scenario using weather data from a cooler and drier region showed a large decline in plant uptake of N outside the main cropping season, but simulated nitrate leaching was nevertheless significantly lower. With this scenario, precipitation was only 50% of that at the actual experimental site, and the lower temperatures during autumn and winter reduced net mineralization of soil organic N significantly. Thus, the reduction in precipitation and net mineralization of soil organic N apparently more than outweighed the effects of shorter growing season in the continental climate scenario.     

Herbage biomass and uptake under low-input grazing as affected by cattle and sheep excrement patches

Urea deep placement (UDP) has demonstrated its benefits of saving N fertilizer and increasing nitrogen use efficiency (NUE) and grain yields. However, studies on its environmental impacts, particularly on nitrous oxide (N₂O) and nitric oxide (NO), are limited. We conducted multi-location field experiments in Bangladesh to determine the effects of UDP versus broadcast prilled urea (PU) on N₂O and NO emissions, NUE, and rice yields. N₂O and NO emissions were measured from three N fertilizer treatments—no N, UDP, and PU—using automated gas sampling and analysis systems continuously for two rice-growing seasons—Aus (May–August) and Aman (August–December). Fertilizer-induced peaks in N₂O emissions were observed after broadcast application of PU but were rarely observed after UDP. Total seasonal N₂O and NO emissions, yield-scaled emissions, and fertilizer-induced emissions were affected by fertilizer treatments and sites. Though nitrogen fertilizer increased emissions significantly over the control, emissions resulting from UDP and PU were similar. Effects of N placement on grain yields and NUE were site- and season-specific. Of the N placement methods, UDP increased grain yields by 13% (p < 0.05) during the Aman season and gave similar yields in spite of lower N application during the Aus season. UDP increased N recovery from 25 and 16% of broadcast PU to 61 and 73% during the Aus and the Aman seasons, respectively in one site, but was similar in another site. On the other hand, alternate wetting and drying irrigation reduced grain yield and N recovery at the BRRI site during the Aman season.     

Nitrate in upper groundwater on farms under tillage as affected by fertilizer use,soil type and groundwater table

Indicators are needed to check whether policies on protection of groundwater are effective and if regulations are complied with. We evaluated various indicators at different scales, both in space and in time, and at different degrees of complexity. Groundwater was sampled on 34 arable farms for 3 years. Nitrate concentration in upper groundwater was low on clay soil. On sandy soil, peat layers reduced the nitrate concentration with about 80 mg/l on average. Sandy soils with high groundwater tables had nitrate concentrations that were less than half of those at sandy soils with low groundwater tables. The relationship between different fertilization variables and nitrate in groundwater was investigated for sandy soils without peat layers. N surplus poorly correlated with nitrate concentrations in groundwater when individual sampling points were studied, but clearly increased when data were averaged at the farm level. Soil mineral nitrogen correlated best with nitrate concentrations in groundwater. The relationships show that especially on well drained soil drastic measures will be inevitable to reach good water quality.     

Yield variation of rainfed rice as affected by field water availability and N fertilizer use in central Benin

Rice is mainly grown under rainfed conditions in West Africa. Unpredictable and variable rainfall, poor soil quality, and suboptimal crop management practices are the main determinants of low productivity. We assessed the effects of soil water availability and fertilizer application, and their interaction on the yield of rainfed rice in Glazoué, Department of Zou-Collines, central Benin between 2010 and 2013. On-farm fertilizer management trials and field surveys were conducted in 13–39 farmers’ fields per year. Field water conditions were visually assessed three times per week during the rice-growing season and flood and drought indices were calculated on the basis of number of days with ponded water and dry surface soil relative to the total number of days for the vegetative, the reproductive and whole rice-growing period. Variations in flood and drought indices were related to the sand content of the soil. While nitrogen was the most limiting nutrient, average response to N fertilizer application was low with an agronomic N use efficiency of only 7–9 kg grain per kg of N applied. Year-to-year variation in rainfall and spatial variation in field water status affected both rice yield and response to N fertilizer. Some 47% of the observed yield variation was explained by field water status and the amounts of N fertilizer applied, with rice response to N fertilizer being less when water was limited. We conclude that the prevailing blanket fertilizer recommendations are unlikely to contribute to yield increases in rainfed systems of West Africa. There is a need for field-specific recommendations that consider soil texture and the spatial–temporal dynamics of water availability.     

Growth response,yield and yield components of upland cotton (Gossypium hirsutum L) as affected by rates and time of nitrogen application in the Nigerian savannah

Effects of rate and time of nitrogen fertilization on growth, yield and yield components of upland cotton (Gossypium hirsutum L) were studied in two years (1975–76). Four rates of nitrogen application (0, 26, 52 and 78 kg ha^–1) timed at 3 or 8 weeks after sowing were compared. Seed cotton yield components increased significantly with increased N application at least up to 52 kg N ha^–1, with yield increases between 49% and 73%. Seed cotton yield was influenced by treatments mainly through boll number. Both crop growth rate and fruiting were enhanced by nitrogen fertilization. Applying N at 8 weeks (flowering) favoured yield only slightly over that at 3 weeks (thinning), but improved crop growth and fruiting by about 64% and 24%, respectively. There were significant N rate × time interactions in favour of fertilization at flowering. Applying 52 kg N ha^–1 at 8 weeks seems best for cotton in the Nigerian savannah.     

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.     

资源型功能磷肥对早稻产量、养分吸收及利用的影响

通过田间试验研究资源型功能磷肥对水稻产量、养分吸收及利用的影响。结果表明,与高浓度磷肥(HP)处理相比,两试验点3个资源型功能磷肥处理(LP1、LP2和LP3)平均增产8.3%和7.6%,磷肥吸收利用率平均提高29.4%和20.7%。资源型功能磷肥不仅能显著增产,还能显著促进磷的吸收及利用,应该大力推广施用。     

Yield and nitrogen uptake by rice as affected by variety,method of planting and new nitrogen fertilizers

A field experiment conducted for two years (1977 and 1978) at the Indian Agricultural Research Institute, New Delhi showed that yield and nitrogen uptake by rice was more in the case of medium duration (135 days) variety Improved Sabarmati than in the case of the short duration (105 days) variety Pusa-33. Highest yield and nitrogen uptake by rice was recorded when it was transplanted and lowest when rice was direct-seeded (drilled in moist soil). Broadcasting sprouted seeds on puddled seed bed gave yield and nitrogen uptake in between transplanting and direct-seeding and provides a reasonably acceptable method of planting. Rice responded well to nitrogen and the economic optimum dose was found to be 160–170 kg N ha^–1. Urea briquettes gave the highest yield and nitrogen uptake by rice and was superior to sulphur-coated urea or neem-cake-coated urea with respect to N-uptake. All these new nitrogen fertilizers were superior to urea and therefore hold considerable promise in rice culture.     

The carbon footprint of maize production as affected by nitrogen fertilizer and maize-legume rotations

Studies on the sustainability of crop production systems should consider both the carbon (C) footprint and the crop yield. Knowledge is urgently needed to estimate the C cost of maize (Zea mays L.) production in a continuous monoculture or in rotation with a leguminous crop, the popular rotation system in North America. In this study, we used a 19-year field experiment with maize under different levels of synthetic N treatments in a continuous culture or rotation with forage legume (Alfalfa or red clover; Medicago sativa L./Trifolium pratense L.) or soybean (Glycine max L. Merr) to assess the sustainability of maize production systems by estimating total greenhouse gas (GHG) emissions (kg?CO₂ eq?ha^?1) and the equivalent C cost of yield or C footprint (kg?CO₂ ?eq?kg^?1?grain). High N application increased both total GHG emissions and the C footprint across all the rotation systems. Compared to continuous maize monoculture (MM), maize following forage (alfalfa or red clover; FM) or grain (soybean; SM) legumes was estimated to generate greater total GHG emissions, however both FM and SM had a lower C footprint across all N levels due to increased productivity. When compared to MM treated with 100?kg?N?ha^?1, maize treated with 100?kg?N?ha^?1, following a forage legume resulted in a 5?% increase in total GHG emissions while reducing the C footprint by 17?%. Similarly, in 18 out of the 19-year period, maize treated with 100?kg?N?ha^?1, following soybean (SM) had a minimal effect on total GHG emissions (1?%), but reduced the C footprint by 8?%. Compared to the conventional MM with the 200?kg?N?ha^?1 treatment, FM with the 100?kg?N?ha^?1 treatment had 40?% lower total GHG emissions and 46?% lower C footprint. Maize with 100?kg?N?ha^?1 following soybean had a 42?% lower total GHG emissions and 41?% lower C footprint than MM treated with 200?kg?N?ha^?1. Clearly, there was a trade-off among total GHG emissions, C footprint and yield, and yield and GHG emissions or C footprint not linearly related. Our data indicate that maize production with 100?kg?N?ha^?1 in rotation with forage or grain legumes can maintain high productivity while reducing GHG emissions and the C footprint when compared to a continuous maize cropping system with 200?kg?N?ha^?1.     

Effect of rate and source of N fertilizer on yield,quality and N recovery of bromegrass grown for hay

Isotopic exchange of phosphate was investigated in soils which had received 0–176 kg P ha^–1 as triple superphosphate in the field. The soils were kaolinitic oxisols from near Manaus, Brazil, and Pescador, Colombia, and an allophanic andept with much organic matter from Popayán, Colombia. When fresh phosphate was added to these soils in the laboratory the residues of triple superphosphate decreased the intensity of phosphate in the liquid phase that was associated with a specific quantity of exchangeable phosphate. However, residues of triple superphosphate increased phosphate taken up by maize at Manaus. Residues did not cause this effect in soils from Colombia in which the major minerals were halloysite and imogolite.The cause of the anomalous results in kaolinitic soils may be that in the field, during long contact between soil and phosphate, the latter penetrated into the mineral crystal so that, although it maintained adequate concentration for crops, exchange of the residues was slower in the laboratory than exchange of the fresh phosphate that was added for the measurements. In the andept the effect may have been caused by strong sorption of fertilizer phosphate onto hydrous oxides of aluminium released from organic matter by lime.The results indicated that although short term exchange data may be useful to differentiate phosphate sorption characteristics in untreated soils they may not, at least in some soils, represent long term behaviour of phosphate residues in relation to phosphate taken up by crops.     

Comparative response of bread and durum wheat cultivars to nitrogen fertilizer in a rainfed Mediterranean environment: soil nitrate and N uptake and efficiency

A 3-year multi-site study was carried out on rainfed Vertisols under Mediterranean conditions in southern Europe to determine the influence of the N fertilizer rate on soil nitrates, N uptake and N use efficiency in bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. Durum Desf.) in rotation with sunflower (Heliathus annuus L.). Nitrogen fertilizer rates were 0, 100, 150 and 200 kg N ha⁻¹ applied in equal proportions at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with a split plot arrangement and four replications. Nitrogen harvest index (NHI), N uptake/grain yield (NUp/GY), N use efficiency (NUE), N utilization efficiency (NUtE), N uptake efficiency (NUpE) and N apparent recovery fraction (NRF) were calculated. Differences were observed in N use efficiency between the two modern bread wheat and durum wheat cultivars studied. In comparison to durum, bread wheat displayed greater N accumulation capacity and a more efficient use of N for grain production. While under N-limiting conditions, the behavior was similar for both wheat types. No difference was noted between wheat types with regard to changes in soil residual levels over the study period at the various sites. The 100-kg ha⁻¹ N fertilizer rate kept soil nitrates stable at a moderate level in plots where both wheat types were sown.     

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.     

Movement and distribution of fertilizer nitrogen as affected by depth of placement in wetland rice

Experiments were conducted to monitor the movement and distribution of ammonium-N after placement of urea and ammonium sulfate supergranules at 5, 7.5, 10, and 15 cm. By varying depths of fertilizer placement, it is possible to determine the appropriate depth for placement machines. There were no significant differences in grain yields with nitrogen placed 5 and 15 cm deep. However, grain yields were significantly higher with deep placement of nitrogen than with split application of the fertilizer. The lower yields with split-applied nitrogen were due to higher nitrogen losses from the floodwater. The floodwater with split application had 78–98µg N ml^–1 and that with deep-placed nitrogen had a negligible nitrogen concentration.Movement of NH ₄ ⁺ -N in the soil was traced for various depths after fertilizer nitrogen application. The general movement after deep-placement of the ammonium sulfate supergranules was downward > lateral > upward from the placement site. Downward movement was prevalent in the dry season: fertilizer placed at 5–7.5 cm produced a peak of NH ₄ ⁺ -N concentration at 8–12 cm soil depth; with placement at 15 cm, the fertilizer moved to 12–20 cm soil depth. Fertilizer placed at 10 cm tended to be stable. In the wet season, deep-placed N fertilizer was fairly stable and downward movement was minimal.A substantially greater percentage of plant N was derived from¹⁵N-depleted fertilizer when deep-placed in the reduced soil layer than that applied in split doses. The percent N recovery with different placement depths, however, did not vary from each other. The results suggest that nitrogen placement at a 5-cm soil depth is adequate for high rice yields in a clayey soil with good water control. In farmers' fields where soil and water conditions are often less than ideal, however, it is desirable to place nitrogen fertilizer at greater depths and minimize NH ₄ ⁺ -N concentration in floodwater.