Fertilizer Application Regimes Research Articles

Increasing phosphorus rate alters microbial dynamics and soil available P in a Lixisol of Zimbabwe.

Soil phosphorus (P) deficiency is a major challenge to food security in most parts of sub-Saharan Africa, including Zimbabwe, where farmers largely depend on local organic nutrient resources as fertilizer in the production of crops. Soil microorganisms can contribute to synchronous availability of soil P to plants through regulating immobilization and mineralization cycles of soil P pools but their activity may be influenced by antecedent soil P, P fertilizer application regimes and P uptake by plants. Using soils collected from plots where Crotalaria juncea (high quality), Calliandra calothyrsus (medium quality), cattle manure (variable quality), maize stover and Pinus patula sawdust (both low quality) were applied at the rate of 4 t C ha-1 with 16 kg P ha-1 at the start of every season over 16 seasons. A pot study was conducted to evaluate the influence of increasing inorganic P fertilizer rates (26 and 36 kg P ha-1) on soil microbial dynamics, soil P pools, and maize P uptake. Results indicated that nineteen (19) fungal and forty-two (42) bacterial colonies were identified over the study period. Fungi dominated bacteria on day one, with Aspergillus niger showing a 30-98% abundance that depends on organic resource quality. Overall, microbial diversity peaked activity characterized succession on day 29, which coincided with a significant (P<0.05) increase in P availability. Increasing P rate to 26 kg P ha-1 amplified the microbial diverse peak activity under medium-high quality resources while under the control the peak emerged earlier on day 15. Mucor and Bacillus had peak abundances on day 43 and 57, respectively, across treatments regardless of P rates. Treatment and P rate had a significant (P<0.01) effect on microbial P. Bacteria were more responsive to added P than fungi. Increasing P to 36 kg P ha-1 also stimulated an earlier microbial diverse peak activity under maize stover on day 15. Addition of P alone, without supplying complementary nutrients such as N, did not have a positive effect on maize P uptake. Farmers need to co-apply medium-high quality organic resources with high fertilizer P rates to increase microbial diversity, plant available P and maize growth on sandy soils (Lixisols). Our results suggest that there is a need to reconsider existing P fertilizer recommendations, currently pegged at between 26 and 30 kg P ha-1, for maize production on sandy soils as well as develop new fertilizer formulations to intensify crop production in Zimbabwe.

The current fertilizer regimes cause phosphorus deficit in paddy soils and decreased rice phosphorus uptake: a study in Shanghai, China

AbstractExcessive phosphorus (P) fertilization in intensive rice‐cultivation areas in China has caused serious environmental problems. However, relatively little research has been done on investigating the soil P balance in rice production systems based on different fertilizer regimes. Our study investigated the dynamic variation of soil P balance and rice P use efficiency and productivity from 2014 to 2018 in the paddy fields under synthetic fertilizer (CF) and manure application (OF) regimes based on the practices of local farmers. Flooding water on the paddy fields tends to cause P loss via runoff and leaching. A lysimeter system was used to monitor P loss from paddy fields, which overcame the limitations of real‐time monitoring discharge volume and sample‐collection. The results with relatively higher rainfall intensity in 2014 and 2015, in total, 4.69 kg P ha−1 under CF and 8.39 kg P ha−1 under OF were lost via runoff in 2014, with 13.6 kg P ha−1 under CF and 17.8 kg P ha−1 under OF in 2015, whereas from 2015 to 2018, no more than 5 kg P ha−1 was lost in CF or OF via runoff. Leaching showed a similar, varying trend for both CF and OF. Furthermore, during the 5 years, a continuous soil P deficit was observed, except in 2017 and 2018 for CF and 2018 for OF. The net P retention ranged from −15.31 to 6.2 kg ha−1 for CF and from −23.65 to 2.64 kg ha−1 for OF. The continuous P deficit in paddy soils might have reduced soil P storage. These huge P losses undermined rice yield production. In parallel, after 2014, the grain yield decreased from 10,885.7 in 2014 to 6266.7 kg ha−1 in 2017 under CF and from 10,607.6 to 6649.6 kg ha−1 under OF. Overall, these results reveal a risk of declining P storage in paddy soils and a potential menace on food safety under the current fertilizer management, suggesting that novel fertilizer strategies need to be developed for reserving P storage in paddy fields.

Nutrient recovery from yellow water to soil-crop systems.

The potentials of the nutrient recovered (NRM), via a facile green and sustainable approach from human urine, as a fertilizer in soil-crop system was studied. Nutrient was recovered using a highly decentralized modular reactor, with packed bed of granular gastropod shell. The cultivations of Zea mays (maize) and Solanum lycopersicum (tomato) were the cases studied. The total nutrient composition, the P-speciation, and the safety-risk assessment of the NRM were determined. Using NPK as the standard fertilizer, and a non-fertilized soil as the control, the fertilizing potential of the NRM was evaluated. The influence of the different fertilizer application regimes on the wet and dry biomass nutrient composition, after-harvest soil nutrient composition, and pH values was studied. The NRM contained 106mg/g of TN and 374.6mg/g of TP, and the P species identified were Ca2-P (31.66%), Ca8-P (14.99%), and Ca10-P (53.32%). The growth rate of the NRM crops were lower than that of the NPK crops until the 17th day, when the NRM crops grew faster than that of the NPK and control (p < 0.05). The NRM is beneficial to acidic soils and also acts as a slow nutrient releasing fertilizer.

Fertilizer responsiveness of high-yielding drought-tolerant rice in rainfed lowlands

ABSTRACT Recent advances in rice breeding in tropical Asia led to the release of high-yielding drought-tolerant cultivars. Together with the use of these cultivars, improved nutrient management under drought should further increase rice productivity in rainfed lowland ecosystems. The objectives of this study were to evaluate cultivar differences in the responses of plant growth and grain yield to fertilizer application regimes. We compared 13 drought-tolerant rice cultivars with two irrigated rice cultivars under three nutrient management conditions in irrigated and rainfed lowlands in the Philippines during the wet seasons of 2014 and 2015. Drought stress was mild in both years, with a yield reduction of 11 to 12%, and there was no significant cultivar × nutrient management interaction in yield. The drought-tolerant cultivar NSIC Rc282 proved fertilizer-responsive, and had similar yield to those of the popular high-yielding cultivar NSIC Rc222 under all conditions. An ancillary experiment in 2016 confirmed that NSIC Rc282 was more drought-adapted than NSIC Rc222, with 11% to 37% higher yield under stress. In order to maximize the yield, NSIC Rc282 required N application only when the drought ended, whereas NSIC Rc222 required additional N during the drought. This shows that the details of drought-adaptive nutrient management differ between irrigated and drought-tolerant rice cultivars. We suggest that the introduction of high-yielding drought-tolerant rice cultivars will both improve productivity and increase the nutrient-use efficiency in rainfed environments.

Differential accumulation of microbial necromass and plant lignin in synthetic versus organic fertilizer-amended soil

While it is recognized that the accumulation and turnover of soil organic carbon (SOC) is driven by plant inputs and their subsequent microbial-mediated transformations, the roles of plant residue chemistry and microbial processes in controlling SOC dynamics under different fertilizer application regimes have not been well explored. In the present study, amino sugars and lignin phenols were used as biomarkers to investigate the changes in microbial necromass and plant-derived components in a 30-year cultivated Mollisol (0–20 cm) in response to different fertilizer application treatments, including synthetic fertilizers (NPK, 165 kg N ha−1, 82.5 kg P2O5 ha−1, and 82.5 kg K2O ha−1 per year), pig manure at two application rates of 30 and 60 t ha−1 per year, and combinations of manure and synthetic fertilizers (30 or 60 t ha−1 manure per year plus 165 kg N ha−1, 82.5 kg P2O5 ha−1, and 82.5 kg K2O ha−1 per year). Compared with the unfertilized plot (Control), 30-year application of synthetic fertilizers increased microbial biomass (161%) and amino sugar production (19.7%), but did not alter lignin phenol and SOC concentrations despite the increased plant input. Comparatively, long term manure applications increased the concentration of SOC (30.8–70.9%), as well as that of amino sugars (82.9–107%) and lignin (96.8–212%) in soil. Nevertheless, despite the enhanced microbial biomass from low to high manure application rate, the proportion of amino sugars in the SOC decreased, reflecting a diluted contribution of microbial necromass in SOC pool buildup at high-rate manure application. On the contrary, the proportions of lignin phenols in the SOC in the manure treatments, as well as the ratios of lignin phenols and amino sugars (0.26–0.42), were larger than that in the NPK treatment (0.22) and increased with increasing manure application rate. Therefore, the manipulation of synthetic or organic fertilizer on SOC dynamics is associated with differential accumulation of microbial necromass and plant lignin in agro-ecosystems. The manure amendment enhanced the contribution of plant-derived components more than microbial necromass to long term SOC accumulation.

English

In Northern Ghana, harvesting of the bulk of paddy, which is cultivated under rain-fed conditions, coincides with the harmattan season. This season is characterized by low relative humidity and dry weather conditions which hasten drying and increase the tendency of the paddy to crack during milling. The farmers also store paddy for longer periods in anticipation of higher price in the open market, thus the paddy may deteriorate as a result of fluctuations in seasonal temperature and relative humidity. This study assessed the effects of fertilizer application regimes and storage duration on cracking and breaking during milling in 4 aromatic rice varieties. Across the varieties, grains that showed signs of cracks will eventually break during milling, and grain susceptibility to cracking significantly (P&lt;0.05) increased when stored beyond 30 days. Gbewaa rice recorded significantly (P&lt;0.05) higher cracking (49.2%) followed by Amankwatia (43.9%), CSIR-AGRA (40.4%) and Exbaika (40.3%). Fertilization regime of 2 basal applications and 2 topdressings at panicle initiation and booting-heading stages resulted in grains that were well-filled and thick to resist drying and cracking. Key words: Aromatic varieties, nitrogen fertilizer, straight-milling, paddy cracking, consumer taste. &nbsp

Response of soil compaction to the seasonal freezing-thawing process and the key controlling factors

The seasonal freezing-thawing process can alleviate saline farmland soil compaction, and improve soil aeration and soil water retention. However, the response of soil compaction to the seasonal freezing-thawing process and the key factors affecting soil compaction are still unclear. Therefore, in this study, we conducted a regional monitoring of soil compaction and other soil physical and chemical properties before and after the 2016–2017 seasonal freezing-thawing period in Yongji Irrigation Area, Hetao Irrigation District, North China. We used a combination of genetic algorithm-projection pursuit evaluation, grey relational analysis and stepwise regression to analyze the measured soil physical and chemical properties and their variations during the freezing-thawing period. Using this method combination, we obtained one projection value to represent the whole-profile soil compaction, and found the most important influencing soil physical and chemical properties—soil water content, groundwater level and total inorganic nitrogen. Ultimately, we developed a regression model to predict soil compaction given the values of the predictive variables (soil water content, groundwater level and total inorganic nitrogen) at the same depth and time. The importance of autumn irrigation and planting structure, as well as the spatial heterogeneity of field management regime on the relationship between freezing-thawing processes and soil compaction were highlighted. Our findings provide solid foundations for regional field management policies, especially irrigation and drainage policies. Future studies are recommended to focus on the effect of different irrigation regimes, different drainage regimes and different nitrogen fertilizer application regimes on the relationship between the seasonal freezing-thawing processes and saline farmland soil compaction.

Planting Dates and Nutrition Management Regimes Impact Positively on Bulb Size, Quality and Yield of Rain-fed Onion

Bulb size, appropriate time of planting and sufficient growth nutrients may determine the quality of seeds and productivity of onion. Studies were conducted during the cropping seasons of year 2015 and 2016 to assess the effects of planting date and nutrients management regimes on bulb size, quality and yield of rain-fed onion using seeds of variety Prema as planting material. Three levels of transplanting dates namely early transplanting (N1)), transplanting of seedlings two weeks after early transplanting (N2), and transplanting of seedlings four weeks after early transplanting (N3) were factorially combined with the following six fertilizer application regimes: F1 (no fertilizer application), F2 (application of 375 kg/ha of NPK 23:10:10), F3 (application of 10 t/ha fertisoil compost), F4 (application of 187.5 kg/ha of NPK 23:10:10 plus 5 t/ha of fertisoil compost), F5 (application of 125 kg/ha of NPK 23:10:10 plus 6.6 t/ha of fertisoil compost) and F6 (application of 250 kg/ha of NPK 23:10:10 plus 3.3 t/ha of fertisoil compost). Seedlings from the above treatment combinations were planted using RCBD in three onion growing communities in the Northern Region of Ghana. At harvest, bulbs were sorted into three groups (large, medium and small bulbs). Results from the studies indicated that in each group of bulb size, N1 x F4 plants produced the highest bulb fresh weight and bulb diameter. Plants from these regimes also produced the highest bulb quality and bulb yield. Farmers should nurse onion seeds early, latest by first week of June in the rainy season, so as to transplant seedlings by first week of July and apply 187.5 kg/ha of 23:10:10 NPK plus 5 t/ha fertisoil compost for improved bulb sizes in the study area.

Estimating nutrient uptake requirements for soybean using QUEFTS model in China.

Estimating balanced nutrient requirements for soybean (Glycine max [L.] Merr) in China is essential for identifying optimal fertilizer application regimes to increase soybean yield and nutrient use efficiency. We collected datasets from field experiments in major soybean planting regions of China between 2001 and 2015 to assess the relationship between soybean seed yield and nutrient uptake, and to estimate nitrogen (N), phosphorus (P), and potassium (K) requirements for a target yield of soybean using the quantitative evaluation of the fertility of tropical soils (QUEFTS) model. The QUEFTS model predicted a linear–parabolic–plateau curve for the balanced nutrient uptake with a target yield increased from 3.0 to 6.0 t ha−1 and the linear part was continuing until the yield reached about 60–70% of the potential yield. To produce 1000 kg seed of soybean in China, 55.4 kg N, 7.9 kg P, and 20.1 kg K (N:P:K = 7:1:2.5) were required in the above-ground parts, and the corresponding internal efficiencies (IE, kg seed yield per kg nutrient uptake) were 18.1, 126.6, and 49.8 kg seed per kg N, P, and K, respectively. The QUEFTS model also simulated that a balanced N, P, and K removal by seed which were 48.3, 5.9, and 12.2 kg per 1000 kg seed, respectively, accounting for 87.1%, 74.1%, and 60.8% of the total above-ground parts, respectively. These results were conducive to make fertilizer recommendations that improve the seed yield of soybean and avoid excessive or deficient nutrient supplies. Field validation indicated that the QUEFTS model could be used to estimate nutrient requirements which help develop fertilizer recommendations for soybean.

Effects of Different Irrigation and Fertilizer Application Regimes on Soil En-zyme Activities and Microbial Functional Diversity in Rhizosphere of Ratoon-ing Rice

Effects of Different Irrigation and Fertilizer Application Regimes on Soil En-zyme Activities and Microbial Functional Diversity in Rhizosphere of Ratoon-ing Rice

Increase in soil organic carbon in a Mollisol following simulated initial development from parent material

Better understanding of the effects of land use and agricultural management on organic carbon (C) sequestration is needed to optimize the restoration of fertility in degraded soil, maintain agricultural sustainability and mitigate emissions of greenhouse gases with C sequestration. Most current studies of C sequestration focus on mature soil, whereas there has been little research on soil development from C‐poor parent material. The aim of this study was to assess soil organic carbon (SOC) stocks and C sequestration rates during the early stages of development of a Mollisol from parent material under different types of vegetation, fertilizer application regimes and organic matter inputs, and to compare the results with C sequestration of a mature Mollisol under similar management. Carbon stocks were recorded from 2004 to 2012 in the parent material of a Mollisol under natural fallow (NatF), alfalfa (Medicago sativa L.) (Alfa) or soya beans (Glycine max (Merrill.) L.) and maize (Zea mays L.) (S–M) rotations with and without fertilizer application and crop residues returned or removed at harvest. There was a positive non‐linear relation between C inputs and SOC stocks; increases in SOC stocks decreased with larger additions of C. After 8 years of treatments, the SOC stocks at 0–20‐cm depth had increased in the order S–M + fertilizer + all residues returned (61%) &gt; Alfa (60%) &gt; S–M + fertilizer + part of residues returned (50%) &gt; NatF (30%) &gt; S–M + fertilizer without residue return (17%) &gt; S–M without fertilizer or residue return (7%). These increases in SOC stocks corresponded to annual C sequestration rates of 0.02–0.83 Mg C ha−1 year−1. In contrast, SOC stocks in the 0–20‐cm layer of the mature Mollisol changed little under similar treatments in a wheat (Triticum aestivum L.)–maize–soya bean rotation. Our results have practical implications for how vegetation and agricultural practices could be used to optimize soil restoration and C sequestration in a temperate continental monsoon climate.Highlights What management practices and vegetation lead to carbon sequestration during soil development? Use of a subsoil (parent material) to study soil development. Carbon stocks increased as much in alfalfa as in soya bean–maize rotations with residue return. Perennial legume systems sequester carbon comparable to annual systems with larger carbon inputs.

Estimating nutrient uptake requirements for rice in China

Accurate knowledge of the nitrogen (N), phosphorus (P), and potassium (K) requirements for rice (Oryza sativa L.) in China is essential to quantitatively estimate optimal fertilizer application regimes to maximize crop yield and increase nutrient use efficiency. On-farm experiments were collected in China's major rice-producing regions from 2000 to 2013, to determine the relationship between grain yield and nutrient uptake in the above-ground plant dry matter using the quantitative evaluation of the fertility of tropical soils (QUEFTS) model. The large datasets obtained which covered broader rice growing areas and ecology types (both indica and japonica) in China. The dataset was divided into two groups: single-season rice and early/middle/late rice, according to QUEFTS analysis. The QUEFTS model predicted a linear increase in grain yield if nutrients were taken up in balanced amounts until yield reached about 60–70% of yield potential. To produce 1000kg of single-season rice grain, 14.8kgN, 3.8kg P, and 15.0kgK were required in the above-ground plant dry matter, and the corresponding internal efficiencies (IEs) were 67.6kg grain per kg N, 263.2kg grain per kg P, and 66.7kg grain per kg K. For early/middle/late rice, the amount of 17.1kgN, 3.4kgP, and 18.4kgK were required in the above-ground plant dry matter to produce 1000kg of grain, and corresponding IEs were 58.5kg grain per kgN, 294.1kg grain per kgP, and 54.3kg grain per kgK. The QUEFTS model provides a scientific foundation for filtering high-yielding and high-efficiency variety, optimizing fertilizer application rate and developing nutrient management strategies to increase yield and nutrient use efficiency. This is the first report on comparison of the nutrient uptake of different ecology types in rice production area of China using QUEFTS model and test their feasibility through field validation.

Assessment of maize and dry bean productivity under different intercrop systems and fertilization regimes.

The productivity of different maize-dry bean intercrop systems (single and double rows of dry bean planted between two maize rows at low and high bean population) was assessed in 2006/07-08 seasons at different fertilizer application regimes (unfertilized control, low, adjusted low and optimum). Sole maize and dry bean plots were included as checks and together with the intercrop systems, they constituted the main treatment while the fertilizer regimes constituted the sub treatment. Treatments were arranged as a split plot design with three replications. There was a significant season x fertilizer interaction effect on maize grain and total biomass yields, and a significant season x cropping system interaction on dry bean grain yield. Grain yield for both crops were significantly (P<0.001) higher in 2007/08 with the highest maize grain yield of 2644 kg ha-1 obtained at optimum fertilizer rate. Dry bean grain yield of 875 and 829 kg ha-1 obtained in 2007/08 at optimum and adjusted low fertilizer rates, respectively were comparable. The highest mean grain yield of 2101 kg ha-1 for maize and 728 kg ha-1 for dry bean across the two seasons were obtained in single-bean row intercrop planted at low and high population, respectively. The single dry bean row intercrop system gave the highest productivity based on the total LER values and thus appears the most appropriate for small-scale farmers. Key words: Fertilizer application, food security, intercrop, land equivalent ratio (LER), planting density and seed inoculation.

Effects of Straw Mulching Plus Nitrogen Fertilizer on Nitrogen Efficiency and Grain Yield in Winter Wheat

Long-term application of nitrogen fertilizer is approved to cause low nitrogen use efficiency in crops and environ- mental pollution by NO3--N accumulation in soil. Straw returning to field takes the advantages of improving physical and chemi- cal characteristics and nutrition status of soil, resulting in yield promotion of crops. The nitrogen managements for straw mulching cultivation have been studied well in single cropping system. The wheat (Triticum aestivum L.)-maize (Zea mays L.) double crop- ping system is typical in North China Plain, however, nitrogen fertilizer application regimes in straw-mulching double-cropping system extended rapidly in the region are poorly studied. In the current fixed-plot field experiments, we aimed at the changes of nitrogen use efficiency and grain yield under straw mulching plus a series of amount of nitrogen fertilizer in winter wheat, and provided some advices on nitrogen application regime in mulch farming. A wheat cultivar, Zhoumai 14, was used in a two-factor randomized block design with 3 replicates. A total of 10 treatments were coded as N0, N90, N180, N270, and N360 for only ni- trogen fertilizer applied (0, 90, 180, 270, and 360 kg ha-1, respectively) and S+N0, S+N90, S+N180, S+N270, and S+N360 for straw mulching plus nitrogen applications (nitrogen rates as above), respectively. About 7 500 kg ha-1 straw residue from previous cropping season was ploughed into soil. Compared with no straw mulching treatments, S+N treatments increased dry matter ac- cumulation during wheat growth. The S+N treatments showed the amount and proportion of dry matter accumulation lower before heading than N treatments, but significantly higher at the period of heading to maturity. Under the same nitrogen fertilizer rates, grain yields of S+N90, S+N180, S+N270, and S+N360 were higher than those of corresponding N treatments by 7.1%, 8.4%, 11.1%, and 10.2%, respectively. The S+N270 treatment had the largest amount and increasing ratio of grain yield with significant differences from other S+N and those of N treatments, indicating that S+N270 might be the proper treatment in wheat production. Nitrogen fertilizer use efficiency, nitrogen use efficiency, and agronomic nitrogen use efficiency in S+N treatments were higher than those of N treatments by 3.3–9.2%, 0.7–4.0, and 2.7–7.3 kg kg-1, respectively. Our results indicate that returning straw to field has positive effects on winter wheat under the experimental conditions, and straw mulching plus nitrogen fertilizer has larger productivity than only applying nitrogen fertilizer.

Effects of nitrogen fertilizer rates and ratios of base and topdressing on wheat yield, soil nitrate content and nitrogen balance

Application of nitrogen (N) fertilizer is one of the most important measures that increases grain yield and improves grain quality in winter wheat (Triticum aestivum L.) production. Presently, there is a large number of investigations (experiments) in the field on different nitrogen fertilizer application regimes. However, there still exists a serious problem of low nitrogen use efficiency, especially in winter wheat high yield conditions: unsuitable nitrogen fertilizer, which often leads to lower yield and large accumulation of nitrate in the soil, bringing a potential risk to the environment. In order to explore the optimal regime of nitrogen fertilizer application suitable for environment and economy, a field experiment on the different rate and ratio of base and topdressing of nitrogen fertilizer at the different growth periods of winter wheat was conducted. The field experiment was undertaken from the fall of 2003 to the summer of 2004 in the village of Zhongcun in Longkou city, in the Shandong Province of China. The field experiment with three repeats for each treatment was designed in a split-plot. The major plot was applied with urea at a nitrogen fertilizer rate of three levels, namely, 0 kg·hm−2 (CK), 168 kg·hm−2 (A), and 240 kg·hm−2 (B). In the sub-plot, the ratios of base and topdressing nitrogen fertilizer at the different development periods of wheat were 1/2:1/2 (A1 and B1), 1/3:2/3 (A2 and B2) and 0:1 (A3 and B3). Treatment B1 was under a regime used now in the local region. It was found that the amount of N accumulation in plants had no significant difference between treatments applied with nitrogen fertilizer. The grain yield and grain protein content were all elevated remarkably by applying nitrogen fertilizer compared with those of treatment CK. There was no significant difference in the grain yield and grain protein content between A2 and B2 and B3. However, when compared with those of B2 and B3, in A2 there was an increase in nitrogen use efficiency and residual soil NO3−-N and N losses were reduced. Under the condition of the same rate of nitrogen fertilizer, increasing topdressing nitrogen rate clearly elevated the grain yield, grain protein content and nitrogen use efficiency. The results indicated that the residual soil NO3−-N in A1 and B1 accumulated higher than that of CK in 80–160 cm soil layers at the jointing stage, but that of A2 had no significant difference compared with that of CK in 0–200 cm soil layers. At the maturity stage, more residual soil NO3−-N was detected in B2, B3 and A3 than that in CK in 120–180 cm soil layers, which could not be absorbed by the roots of wheat, but led to be eluviated easily. The amount of soil NO3−-N accumulation in treatment A2 had no significant difference compared with that of treatment CK in the 100–200 cm soil layer. In conclusion, A2, whose nitrogen fertilizer rate was 168 kg·hm−2 and the ratio of base and topdressing was 1/3:2/3, had a higher grain yield and grain protein content, and heightened N use efficiency and minimized the risk of NO3−-N leaching. This should be one of the most appropriate nitrogen fertilizer application regimes in wheat production in local regions in China.

Nitrous oxide emissions from a fertilized grazed grassland in Ireland

A field experiment was undertaken to compare nitrous oxide (N 2O) emissions from a grazed pasture receiving three different nitrogen (N) fertilizer application rates (0, 225 and 390 kg ha − 1 ) and to identify the effects of controlling variables over a 2-year period (2002 and 2003). The N 2O-N losses, expressed as a percent of the N applied, in the cooler and wetter 2002 were 0.2–2.0%. In contrast, the percentage loss in the warmer and drier 2003 (3.5–7.2%) were substantially higher. An empirical model was developed to enable simulations and scenario analysis to be undertaken, assuming various climatic scenarios and N fertilizer application regimes. Results suggest that inter-annual variability due to climatic factors increases with the amount of applied fertilizer N and decreases with frequency of application.

Assessing the Contribution of Genetic Enhancements and Fertilizer Application Regimes on Canola Yield and Production Risk in Manitoba

The number of canola varieties released, since the enactment of Plant Breeders' Rights (PBR) legislation in Canada in 1990, has increased substantively. The effect of genetic enhancements, including PBR, on canola yield and its variance is estimated for canola production regions of Manitoba using the Just‐Pope production function. Diagnostic tests reveal the presence of heteroscedasticity in the data. The percentage of varieties seeded with PBR has a negligible effect on canola yield. Hybrid and herbicide tolerant varieties (HY/HT) seeded on over 90% of canola production area increases average yield by about 6.8%. Increased spatial diversity (more varieties planted on fewer acres) has reduced canola yield by up to 1.7%. Temporal diversity (turnover of varieties) has no significant impact on yield. Nitrogen and sulphur fertilizers are yield increasing. The variance of yield is not impacted by PBR, HY/HT, other technology measures, or by fertilizer other than potassium. Canola breeding programs have not compromised canola yield stability. Depuis l'adoption de la Loi sur la protection des obtentions végétales (LPOV) au Canada en 1990, le nombre de variétés de canola mises au point a augmenté considérablement. L'effet des améliorations génétiques, y compris l'effet de la LPOV, sur le rendement du canola et sa variance a été estimé dans les régions du Manitoba productrices de canola à l'aide de la fonction de production Just‐Pope. Des tests de diagnostic ont révélé la présence d'hétéroscédasticité dans les données. Le pourcentage de variétés ensemencées depuis la LPOV a un effet négligeable sur le rendement de canola. Les variétés hybrides et les variétés tolérantes aux herbicides (HY‐HT) ensemencées sur plus de 90% des superficies cultivées en canola ont augmenté le rendement moyen d'environ 6.8%. L'accroissement de la diversité spatiale (plus de variétés sur moins de superficies) a diminué le rendement du canola jusqu'à 1.7%. La diversité temporelle (rotation des variétés) n'a aucun impact significatif sur le rendement. Les engrais azotés et soufrés augmentent les rendements. La variance du rendement n'est pas influencée par la LPOV, ni les HY‐HT, ni les autres mesures technologiques ni les engrais autres que le potassium. Les programmes de sélection du canola n'ont pas compromis la stabilité du rendement du canola.

Temporal changes in N2O efflux from cropped and fallow agricultural fields

Nitrous oxide (N2O) is implicated in both global warming and catalytic destruction of stratospheric ozone layer. Although, its atmospheric abundance is increasing unabated due to intensification of agricultural activities in recent years, but the estimates of both source and sink strengths of N2O are still highly uncertain. This study was conducted to measure seasonal variation in N2O efflux from the cropped and fallow fields with different levels of fertilizer application and moisture regimes. There was a pulse in N2O emission after the application of N-fertilizer and also after irrigation. This indicated that N2O production was stimulated either by nitrifying bacteria with addition of NH4+ as the substrate in oxic condition or by denitrifying bacteria in partial anoxic condition created by irrigation. Besides, emission of more N2O from the cropped than fallow fields, with the same treatments of chemical fertilizers and irrigation, underlined the importance of plants in transportation of N2O from the rhizosphere to troposphere. This observation indicates that the plants have also a transport pathway of N2O as reported in the case of CH4 transport through aquatic plants.

Effects of exponential nutrient-loading on morphological and nitrogen characteristics and on after-planting performance of Eucalyptus globulus seedlings

Exponential nutrient-loading (50 mg N seedling −1) and conventional (25 mg nitrogen [N] seedling −1) fertilizer application regimes at Jayfields nursery (New South Wales, Australia) were investigated as potential ways of attaining a specified foliar nitrogen (N) concentration of 15–20 g kg −1 in Eucalyptus globulus seedlings at planting. Foliar N concentration, specific leaf area (SLA) and % dry matter (DM) were assessed during the nursery production phase. Foliar N, SLA and % DM were similar at 6, 8, 10 and 12 weeks after germination in the nursery. However, at age 16 weeks after germination (immediately prior to planting), foliar N and SLA were higher, and % DM lower, in exponential nutrient-loaded seedlings than conventionally fertilized seedlings. After-planting height and biomass accumulation of seedlings raised under exponential nutrient-loading and conventional fertilization regimes were investigated at three trials typical of the range of sites established with E. globulus plantations, in the ‘Green Triangle’ region (northwest Vic., Australia). Although seedling heights were not significantly different between nursery treatments at all sites, biomass was 1.5- to 2-fold greater in exponential nutrient-loaded seedlings than conventionally fertilized seedlings. Application of N greater than the conventional 25 mg seedling −1 is required to attain the specification of 15–20 g kg −1 foliar N concentration at Jayfields nursery, thereby maximising after-planting performance in the Green Triangle.

Evaluating effects of nursery and post-planting nutrient regimes on leaf chemistry and browsing of eucalypt seedlings in plantations

We examined the effects of nursery and field nutrient treatments on leaf chemistry and browsing during establishment of Eucalyptus globulus (two trials; Cressy and Dunalley) and Eucalyptus nitens (one trial; Tyenna) seedlings. Seedlings had high- or low-fertilizer application treatments in the nursery, were fertilized or not in the field and were individually fenced (used for leaf chemistry sampling) or not (used for browsing assessment). The high-fertilizer nursery treatment resulted in relatively high foliar nitrogen (N) and low tannin content (all seedling types), and high total essential oils (seedling batch planted at Cressy only), but nursery fertilizer level did not affect dry matter, neutral detergent (NDF) or acid detergent fibre (ADF) or lignin. After planting, levels of N, tannins and total essential oils changed over time, but the degree differed between sites. Field fertilizing generally had no effect on leaf chemistry during 10 weeks after planting. Across sites, the pattern of browsing was the same. Seedlings with the high-fertilizer nursery treatment were browsed more than the low-fertilizer nursery treatment, though the difference was only significant at two of the three sites. Thus trends in browsing damage were consistent with differences in foliar N and tannins as a result of nursery- and not field fertilizing treatment. Manipulation of seedling chemistry, using particular fertilizer application regimes in the nursery, may be one tool for managers wishing to decrease seedling damage by browsers, particularly when browsing severity is not extreme.