Model based scenario studies to optimize the regional nitrogen balance and reduce leaching of nitrate and sulfate of an agriculturally used water catchment

Oxidation of pyrite by nitrate (autotrophic denitrification) was identified as the main cause for sulfate increase in drinking water wells in an agriculturally used watershed, located in the north of Lower Saxony (Germany). Nitrate, which inducts this microbial catalyzed process, is drained into ground water predominantly from agricultural fertilization. The increase of sulfate in the ground water can only be stopped by reducing nitrate leaching into the ground water. To analyze the negative influence of agricultural fertilization on the quality of ground water different fertilization strategies were deducted for an investigated area of 890 ha. Calculated on the basis of nutrient balance of soil surface, the current average nitrogen balance in the investigated area amounts to 91 kg N ha^-1 a⁻¹. Farm-gate balance of nutrients is a strong indicator for assessing potential nutrient losses caused by leaching. This indicator shows comparable accuracy to the calculated nutrient balance of soil surface which demands, however, much more data input for calculations. Nitrate concentrations in seepage water in 2 m depth layer of the soil from agricultural fields were simulated with the model HERMES for the whole investigated area (agricultural land + forest). The nitrate concentration in seepage water was calculated for the whole area on the basis of farm-gate nutrient balance as an annual average, which amounts to 14.0 mg NO₃–N l⁻¹ (62 mg NO₃ l⁻¹). In order to keep the nitrate concentration of the ground water below the threshold value for drinking water (EU-water directive: 11.3 mg NO₃–N l⁻¹ (50 mg NO₃ l⁻¹) and to limit pyrite oxidation, different scenarios with simulation studies to optimize fertilization measures were developed. Only those scenarios which assured reduction of an average nitrate concentration in the drainage water below 11.3 mg NO₃–N l⁻¹ (50 mg NO₃ l⁻¹) without profit cuts for the farms were analyzed.

Effect of crop residue management on nitrogen dynamics and balance in a lowland rice cropping system

Two field experiments were conducted in a rice–fallow–rice cropping sequence during consecutive dry and wet seasons of 1997 on a Fluvic Tropaquept to determine the fate and efficiency of broadcast urea in combination with three residue management practices (no residue, burned residue and untreated rice crop residue). Ammonia volatilization losses from urea (70 kg N ha^–1) broadcast into floodwater shortly after transplanting for 11 d were 7, 12 and 8% of the applied N from no residue, burned residue and residue treated plots, respectively. During that time, the cumulative percent of N₂ + N₂O emission due to urea addition corresponded to 10, 4.3 and nil, respectively. The ¹⁵N balance study showed that at maturity of the dry season crop, fertilizer N recovery by the grain was low, only 9 to 11% of the N applied. Fifty to 53% of the applied ¹⁵N remained in the soil after rice harvest, mainly in the upper 0–5 cm layer. The unaccounted for ¹⁵N ranged from 27 to 33% of the applied N and was unaffected by residue treatments. Only 4 to 5% of the initial ¹⁵N-labeled urea applied to the dry season rice crop was taken up by the succeeding rice crop, to which no additional N fertilizer was applied. Grain yield and N uptake were significantly increased (P=0.05) by N application in the dry season, but not significantly affected by residue treatments in either season.     

Nutrition response of Norway spruce and willow to varying levels of calcium and aluminium

Decreased forest tree growth has often been attributed to increasing soil acidification, especially from high concentrations of soluble Al³⁺ and low base saturation. The growth of willow cuttings (Salix viminalis L. 78183) and Norway spruce seedlings (Picea abies L. Karst) were measured in a greenhouse in the presence of variable Ca²⁺ at uniform NH ₄ ⁺ concentrations. Sets of willows were grown in sand culture, one watered with Ingestad's nutrient solution (INS, pH 5.4) and the other watered with acidified Ingestad's nutrient solution (NSA, pH 3.8). Three levels of Ca²⁺ and Al³⁺ concentrations (in NSA only) were established for all nutrient solutions. Sets of Norway spruce seedlings were grown in calcareous sand and watered with INS, one of pH 5.4 and the other of pH 2.1 (resulting in two Ca²⁺ concentrations after acid neutralization by CaCO₃). In the field, observations were made on the correlation of naturally occurring soil solution Al³⁺ and Ca²⁺ to spruce needle Al, Ca²⁺ and N concentrations. In the willow studies, both the above- and below-ground biomass were negatively influenced by the presence of Al³⁺. Aluminium decreased the growth of rooted cuttings (more in roots than shoots), reduced the uptake of N, Ca²⁺, Mg²⁺ and P, significantly lowered the weight of fine roots, and caused overall reductions of tissue nutrient concentrations. As Al³⁺ concentrations increased, increased concentrations of Ca²⁺ were needed by the willow to help ameliorate the effects of Al³⁺. In field samples of spruce needles and soil, CAB (CAB = Log₁₀ Ca²⁺ /Al³⁺) was positively correlated with N concentration. From a combination of greenhouse and field studies the mechanisms for Ca²⁺ amelioration of Al³⁺ toxicity in trees appear to be i) the effect of Ca²⁺ on reduced absorption of Mn²⁺ and Al³⁺, ii) the effects of Ca²⁺ on NH ₄ ⁺ and P absorption, iii) and the stimulation of tree growth.     

Nutrient cycling in organic farms: stall balance of a suckler cow herd and beef bulls

In organic agriculture, the internal farm nutrient cycle must bequantified to ensure high system productivity accompanied by environmentallysound production processes. In contrast to common farm-gate and field balances,budgeting at the stall level is seldom undertaken. When budgeting mixed farmingsystems, a substantial lack of nutrients can be detected in the forageand straw input – stall – manure output nutrient flow chain.Therefore, stall balances focus on a central component of whole-farm nutrientbudgets for developing efficient nutrient management strategies. At theexperimental farm for organic agriculture at Wiesengut in Hennef, Germany, allsolid mass flows for a suckler herd and a herd of beef bulls were measured.Relative balance values obtained for dry matter and C (45 to 56%), N (16to 36%), P (–7 to 22.5%), K (0 to 13%) and ash(–4 to 7%) varied over a wide range. Balances are very sensitive tovariations in mass flow and nutrient content for components with high nutrientcontents and/or a large contribution to total mass flow (e.g. manure, silage).In developing strategies to minimise N losses, by reducing N surplus in theration, one must consider, that, in contrast to dairy farms, a suckler herd forbeef production integrated in an organic farm has to adapt to crop productiondemands.     

Photocatalytic oxidation of nitrogen oxide over titania–zeolite composite catalyst to remove nitrogen oxides in the atmosphere

The photooxidation of NO with oxygen over Hycom TiO₂ and zeolite (A and Y form zeolite: TiO₂-AZ and TiO₂-YZ) composite catalysts was studied to remove NO_x in the atmosphere. The photocatalytic oxidation activity of the titania in the composite catalyst in a proportion of AZ:TiO₂=3:7 is about three times larger than that in the bare titania. The adsorption behaviors of NO and NO₂ for the bare titania sample obey Langmuir adsorption equations of NO and NO₂, respectively. In the titania–zeolite composite catalysts, the adsorption data indicate the increase in the amount of NO adsorption on the TiO₂ phase and the decrease in the amount of NO₂ adsorption, compared with the bare titania. The acceleration of NO photooxidation rate, resulting from the increase in the amount of NO adsorbed and the decrease in the amount of NO₂ adsorbed, thus occurs on the TiO₂ phase. IR spectra, when irradiating the catalysts with UV, showed the immediate formation of nitrate and NO₂ species on the catalyst. The results lead to the conclusion that the zeolites promote the photocatalytic oxidation of NO over the titania.     

Land use impact on nitrogen discharge by stream: a case study in subtropical hilly region of China

As a crucial factor of water eutrophication, nitrogen (N) discharge by agricultural non-point sources (NPS) has become a worldwide concern, and so has its relationship to land use. This study was aimed at the quantitative relationships between N discharge by stream and land use. It was conducted in the Meicun watershed of Xuancheng County, Anhui Province, in the subtropical low hilly area of China. The study integrated dynamic monitoring of nutrient discharge by stream water and Geographic Information Systems (GIS) analysis of land use of the watershed. Results showed that NO₃⁻-N discharge ranged between 50 and 60% of the total nitrogen (T-N) and was 2.5–3.0 times as much as NH₄⁺-N. There was a significant difference between forested and mixed sub-watersheds for NH₄⁺-N, NO₃⁻-N and T-N concentrations. Significant correlations existed between NH₄⁺-N, NO₃⁻-N and T-N concentrations in stream water and the area percentages of forest and paddy fields. The study found that the discharges of NH₄⁺-N, NO₃⁻-N and T-N decreased exponentially with forest area increase, but a steep decline for NO₃⁻-N and T-N seemed to occur when the forest percentage surpassed 70% and then there was almost no change. Similarly, the discharges of NH₄⁺-N, NO₃⁻-N and T-N increased exponentially with the paddy fields increase, but a steep augmentation occurred for NO₃⁻-N and T-N when the paddy percentage surpassed 20% and then it remained at a plateau. The study showed that in the subtropical hilly region, paddy fields could increase N discharge due to farming management practices. Thus, primary measures to reduce N in the receiving water body would include a change in farming management and building an ecological interception system for paddy fields.     

The transformations and balance of nitrogen in Japanese paddy fields

Research on the transformations and balance of nitrogen in Japanese paddy field is reviewed. During the past decade substantial progress has been made in estimating more accurate nitrogen balance. However, available data do not provide reliable assessments of nitrogen losses or gains, especially of biological nitrogen fixation, denitrification and leaching. Accordingly, data obtainable now permit only a partial accounting of the nitrogen balance in flooded paddy soils. Accurate estimates on inputs and outputs of nitrogen are required. The problems in estimating these gains and losses are discussed, and the need for more nitrogen balance studies in the field is emphasized.     

The use of farmgate balances and soil surface balances as estimator for nitrogen leaching to surface water

Farmgate balances (FGBs), defined as the difference between nutrient input and nutrient output at farm level, are currently used as a tool to monitor changes in nitrogen (N) and phosphorus (P) leaching to groundwater and surface water. We postulate that the estimator value of FGBs for N and P leaching to groundwater and surface water depends on (1) the distribution of N and P surpluses over fields within farms, and (2) the partitioning of the surplus over the various nutrient loss pathways. In this study, we assessed intra-farm variability of N and P surpluses and its possible consequences on N leaching to surface waters. Furthermore, we investigated the effect of policies to decrease N and P surpluses at farm level on N and P surpluses at field level. FGBs were derived for six dairy farms in a hydrologically rather isolated polder with grassland on peat soil for three years (1999, 2000 and 2001). Soil surface balances (SSBs), defined as the differences between nutrient input and nutrient output at field level, were derived for the accompanying 65 fields for the same years. On average, FGB surpluses decreased from 271 kg N ha^–1 y^–1 and 22 kg P ha^–1 y^–1 in 1999 to 213 kg N ha^–1 y^–1 and 13 kg P ha^–1 y^–1 in 2001. Variances in N and P surpluses between fields per farm were compared with variances between farms. For N, variances between fields per farm exceeded variances between farms for all years. A non-linear model was fitted on the measured N loading of the surface water. This model showed that N leaching to surface water was underestimated by 5–46% if the variability in N surpluses between fields per farm was not taken into account. We concluded that estimation of N leaching to surface water, based on data at farm level, can lead to underestimation of the N leaching due to the large variability in N surpluses between fields per farm. The extent of this bias by a given distribution of N surpluses within farms was largely controlled by the partitioning of the N surplus over the various nutrient loss pathways, notably denitrification.     

The combined effect of fertiliser nitrogen and phosphorus on herbage yield and changes in soil nutrients of a grass/clover and grass-only sward

The combined effect of reduced nitrogen (N) and phosphorus (P) application on the production of grass-only and grass/clover swards was studied in a five-year cutting experiment on a marine clay soil, established on newly sown swards. Furthermore, changes in soil N, P and carbon (C) were measured. Treatments included four P (0, 35, 70 and 105 kg P ha^–1 year^–1) and three N levels (0, 190 and 380 N kg ha^–1 year^–1) and two sward types (grass-only and grass/clover). Nitrogen was the main factor determining the yield and quality of the harvested herbage. On the grass-only swards, N application increased the DM yield with 28 or 22 kg DM kg N^–1, at 190 or 380 kg N ha^–1 year^–1, respectively. The average apparent N recovery was 0.78 kg kg^–1. On the grass/clover swards, N application of 190 ha^–1 year^–1 increased grass production at the cost of white clover, which decreased from 41 to 16%. Phosphorus application increased grass yields, but did not increase clover yields. A positive interaction between N and P applications was observed. However, the consequences of this interaction for the optimal N application were only minor, and of little practical relevance. Both the P-AL-value and total soil P showed a positive response to P application and a negative response to N application. Furthermore, the positive effect of P application decreased with increasing N application. The annual changes in P-AL-value and total soil P were closely related to the soil surface surplus, which in turn was determined by the level of N and P application and their interaction. The accumulation of soil N was similar on both sward types, but within the grass-only swards soil N was positively affected by N application. The accumulation of organic C was unaffected by N or P application, but was lower under grass/clover than under grass-only.     

Effect of Continuous use of Sodic Irrigation Water with and without Gypsum, Farmyard manure, Pressmud and Fertilizer on Soil Properties and Yields of Rice and Wheat in a Long term Experiment

A long term field experiment was conducted for 8 years during 1994–2001 to evaluate the effect of N, P, K and Zn fertilizer use alone and in combination with gypsum, farmyard manure (FYM) and pressmud on changes in soil properties and yields of rice and wheat under continuous use of sodic irrigation water (residual sodium carbonate (RSC) 8.5 meq l⁻¹, and sodium adsorption ratio (SAR) 8.8 (m mol/l)^1/2 at Bhaini Majra experimental farm of Central Soil Salinity Research Institute, Karnal, India. Continuous use of fertilizer N alone (120 kg ha⁻¹) or in combination with P and K significantly improved rice and wheat yields over control (no fertilizer). Phosphorus applied at the rate of 26 kg P ha⁻¹ each to rice and wheat significantly improved the yields and led to a considerable build up in available soil P. When N alone was applied, available soil P and K declined from the initial level of 14.8 and 275 kg ha⁻¹ to 8.5 and 250 kg ha⁻¹ respectively. Potassium applied at a rate of 42 kg K ha⁻¹ to both crops had no effect on yields. Response of rice to Zinc application occurred since 1997 when DTPA extractable Zn declined to 1.48 kg ha⁻¹ from the initial level of 1.99 kg ha⁻¹. Farmyard manure 10 Mg ha⁻¹, gypsum 5 Mg ha⁻¹ and pressmud 10 Mg ha⁻¹ along with NPK fertilizer use significantly enhanced yields over NPK treatment alone. Continuous cropping with sodic water and inorganic fertilizer use for 8 years slightly decreased the soil pH_e and SAR from the initial value of 8.6 and 29.0 to 8.50 and 18.7 respectively. However, treatments involving the use of gypsum, FYM and pressmud significantly decreased the soil pH and SAR over inorganic fertilizer treatments and control. Nitrogen, phosphorus and zinc uptake were far less than additions made by fertilizer. The actual soil N balance was much lower than the expected balance thereby indicating large losses of N from the soil. There was a negative potassium balance due to greater removal by the crops when compared to K additions. The results suggest that either gypsum or FYM/pressmud along with recommended dose of fertilizers must be used to sustain the productivity of rice – wheat system in areas having sodic ground water for irrigation.     

The impact of crop growth sub-model choice on simulated water and nitrogen balances

It is the aim of this study to analyse how different crop growth model routines affect the simulation of water flow and nitrogen transport of a crop rotation in agricultural fields. The model system Expert-N is briefly described and used to test the crop growth sub-models against data of a six-year field experiment on sandy soils. Expert-N is a modular soil–plant–atmosphere model system, which comprises different sub-models to simulate one-dimensional vertical transport of water, solute and heat in the unsaturated zone. It includes several sub-models to describe organic matter turnover and has three generic crop growth sub-models. The latter are derived from the crop models CERES, SPASS and SUCROS. Simulations were performed using the different sub-models for each of the cereal crops in the sugar beet, winter wheat, winter barley, winter rye crop rotation. Results show the impact of crop model choice on simulated water balances and turnover of C and N. It is concluded that the simulation of root growth and plant residue mineralisation needs some improvement.     

Influence of nitrogen dopants on N-doped TiO2 electrodes and their applications in dye-sensitized solar cells

Three different types of nanocrystalline, N-doped TiO₂ electrodes were synthesized using several nitrogen dopants through wet methods. The obtained nanocrystalline, N-doped TiO₂ electrodes possessed different crystallite sizes, surface areas, and N-doping amounts. Characterizations were performed to reveal the nitrogen-doping processes for the wet methods using ammonia, urea, and triethylamine as the nitrogen dopants. Additionally, a high conversion efficiency of 8.32% was achieved by the dye-sensitized solar cells, based on the N-doped TiO₂ electrodes. For instance, in comparison with the commercial P25 (5.76%) and pure anatase TiO₂ electrodes (7.14%), significant improvements (44% and 17%, respectively) in the efficiencies were obtained. The findings also indicated that the ammonia nitrogen dopant was more efficient than other two nitrogen dopants. The electron transports, electron lifetimes, and charge recombination in the dye-sensitized N-doped TiO₂ solar cells also differed from those in the pure TiO₂-based dye-sensitized solar cells (DSCs). Specifically, an enhanced photocurrent of ca. 36% in N-doped DSCs resulted from the synergistic effects of the high dye uptake and the efficient electron transport. Moreover, the relationship between charge and voltage revealed that less charge was needed to get a high open-circuit voltage in the N-doping films.     

Application of liquid cattle manure and inorganic fertilizers affect dry matter,nitrogen accumulation,and partitioning in maize

Efficient use of N applied in the form of organic and inorganic fertilizers is important in maize (Zea mays L.) production to maximize producer’s economic returns and maintain soil and water quality. A field study was conducted for three consecutive years (2003–2005) in Thessaloniki, Greece to investigate whether liquid cattle manure can be used to replace inorganic fertilizers and also whether inorganic fertilizer can be applied preplant or as a combination of preplant and sidedress and can affect maize growth, development and N use efficiency. The treatments were control (unfertilized), liquid dairy cattle manure (Manure), application of 260 kg N ha⁻¹ year⁻¹ as basal dressing (N-single), application of 130 kg ha⁻¹ year⁻¹ N as basal dressing before sowing and 130 kg N ha⁻¹ when plants were at the eight-leaf stage (V8) (N-split). In 2 out of the 3 years of the study there was a significant positive effect of fertilizer application on maize growth, development, N uptake, and partitioning compared with the control. Dry matter production was increased by an average of 39% during the 2 years in plots fertilized either with manure or inorganic fertilizers than the control plots. Also from the yield components kernel weight per ear and number of kernels per ear were increased by an average of 35% and 32%, respectively in the fertilized plots compared with the control plots. Chlorophyll level was affected as it was increased by an average of 18%, 14%, and 18% at the ten-leaf stage (V10), silking and milk stage, respectively in the fertilization treatments compared with the control. Similar trend was observed in the other parameters that were studied. No differences were found between the manure and the different times of N application which indicates that manure can be used to replace inorganic fertilizer. Applying N either preplant in a single application or in split application (half of N preplant and half as sidedress) did not have any effect on any characteristics that were studied indicating that preplant application can be used as it is more cost effective. The present study indicates that liquid cattle manure can be used to replace inorganic fertilizers and also that there was no difference between preplant and sidedress application of N.     

Effects of improved drainage and nitrogen source on yields, nutrient uptake and utilization efficiencies by maize (Zea mays L.) on Vertisols in sub-humid environments

Nitrogen is the most limiting plant nutrient in Vertisols in Kenya. Soil properties, climatic conditions and management factors as well as fertilizer characteristics can influence fertilizer nitrogen (N) use efficiency by crops. Vertisols, characterized by low-basic water infiltration rate, are prone to waterlogging under sub-humid and humid conditions. We determined effects of drainage, N source and time of application on yields, nutrient uptake and utilization efficiencies by maize grown on Vertisols in sub-humid environments. Treatments comprised two furrows (40 cm and 60 cm deep) and a check (i.e., no furrow), calcium nitrate to furnish NO₃-N, ammonium sulphate to supply NH₄-N at 100 kg N ha⁻¹, a control (i.e., no fertilizer N), and fertilizer N application at sowing, 40 days after sowing, and split (i.e., half the rate at sowing and half 40 days after sowing). A split-plot design was used in which drainage formed the main plots and N source × time of N application formed the sub-plots. Higher grain and total dry matter yields, harvest index, leaf N content, uptake of N, P and K, as well as N agronomic (NAE) and recovery (NRE) efficiencies were obtained from drained compared to undrained plots. The increase ingrain yields as a result of drainage varied from 31 to 45% for control, 35 to 43% for NO₃-N, and 16 to 21% for NH₄-N treatments. Drainage resulted in total N uptake increases from 50 to 80 kg N ha⁻¹ in control plots, 80 to 130 kg N ha⁻¹ in NO₃-N treated plots, and 90 to 130kg N ha⁻¹ in NH₄-N treated plots. Ammonium-N source was superior to NO₃-N source in terms of higher yields, NAE, and NRE in undrained plots, but the two N sources behaved similarly in drained plots. Delayed or split NO₃-N application gave higher yields, NAE and NRE than when all N was applied at sowing in undrained plots. There was no difference between 40 cm and 60 cm deep furrows in terms of crop yields and nutrient use efficiencies. Thus, draining excess water with furrows at least 40 cm deep is essential for successful crop production in these Vertisols under sub-humid conditions. This revised version was published online in November 2006 with corrections to the Cover Date.     

Liming,nitrogen and phosphorus fertilization and the annual volume increment of Norway spruce stands on long-term permanent plots in Southwestern Germany

The amount, fluctuation and duration of increment response to fertilization (liming) in three regions of southwestern Germany is described. After liming, additional yield increases slowly while after N-fertilization, there is a rapid yield increase. A long-lasting high response was found to a combination of liming, P- and N-fertilization. This response was regionally different and was influenced by climatic conditions during the years after fertilization.     

Iron ion-exchanged zeolite: the most active catalyst at 473 K for selective reduction of nitrogen monoxide by ethene in oxidizing atmosphere

Among various metal ion-exchanged zeolites, metal loading alumina, and oxides, iron ion-exchanged mordenite was the most active for the selective reduction of nitrogen monoxide to nitrogen by ethene in the presence of oxygen at the temperature as low as 473 K. The catalytic activities of iron ion-exchanged zeolites depended on the zeolite structure and the iron ion exchange level. The effects of the zeolite structure are in the order of MOR > FER > MFI > Y > LTL at 473 K. The activity of iron ion-exchanged mordenite increased with the increment in the exchange level and levelled off above about 60%.     

Changes in nitrogen budgets and nitrogen use efficiency in the agroecosystems of the Changjiang River basin between 1980 and 2000

To investigate both the temporal and spatial changes in the nitrogen use efficiency (NUE) of agroecosystems in the different agricultural regions of the Changjiang (Yangtze) River basin, we constructed a nitrogen (N) budget by using a database of county-level agricultural statistics that was collected every 10 years from 1980 to 2000. Based on the mass balance model, we defined the NUE of agroecosystems as the proportion of all N inputs that are exported via the harvested crop biomass. According to our estimates, the mean total N inputs increased from 8.68 Tg N in 1980 to 13.4 Tg N in 1990 and to 19.8 Tg N in 2000 due to regional human activities. The proportion of anthropogenic new reactive N to the total inputs increased from 42% in 1980 to 68% in 2000 while the proportion of recycled N decreased. N from synthetic fertilizers was the largest contributor to the basin and dramatically increased to 12.23 Tg N in 2000, corresponding to a fivefold increase over that in 1980. While the amount of N from atmospheric deposition, biological N fixation, and recycled N varied slightly between 1980 and 2000, the proportion of N in harvested crops to the total N inputs decreased. Furthermore, the proportion of N lost by denitrification, volatilization, and riverine N transport, and that stored in soil increased between 1980 and 2000 as a result of intensified agricultural activities. It was found that the change pattern of the NUE differs both temporally and spatially. In the Sichuan basin and the plains in the middle and lower reaches that comprise the main agricultural regions of the Changjiang River basin, the NUE increased between 1980 and 1990; however, it dramatically decreased in almost the entire area between 1990 and 2000. On the other hand, in the mountainous and hilly regions of the lower Jinshajiang and Wujiang watersheds, the NUE decreased between 1980 and 1990 but increased between 1990 and 2000. As a result, the total amount of N transported to the surface waters from the agroecosystem reached 4.32 Tg N in 2000, showing a 2.4-fold increase over that in 1980. The export of riverine N increased, and the areas that exported large amounts of riverine N expanded widely from the Changjiang lower plain to the Changjiang middle plain and the surrounding areas between 1980 and 2000. It was apparent that the high rates of N fertilizer application were the most important factor that led to the dramatic decrease in NUE between 1990 and 2000.     

Yield and soil nutrient balance of a sugarcane plant–ratoon system with conventional and organic nutrient management in sub-tropical India

A 3-year field trial of sugarcane, comprising 11 treatment combinations of different organic manures with and without Gluconacetobacter diazotrophicus (Gd), NPK and an absolute control, on an inceptisol was conducted to assess the effect of these treatments on sugarcane total and economic yield, the benefit:cost ratio, nutrient balance and soil quality in a sugarcane plant–ratoon system. The highest cane yield (78.6 t ha⁻¹) was recorded in the plant crop given vermicompost + Gd, whereas ratoon yields (first and second) were highest (80.8 and 74.9 t/ha⁻¹, respectively) with sulphitation press mud cake (SPMC) + Gd. In both plant and ratoon crops, a number of different organic manures produced the highest cane yield that was also statistically similar to those obtained with using the recommended NPK levels (76.1, 78.2 and 71.7 t/ha for plant crop and subsequent two ratoons, respectively). The highest benefit:cost (B:C) ratio in the plant and two ratoon crops (1.28, 2.36, 2.03 respectively) were obtained with the addition of SPMC + Gd. The nutrient balance for NPK in the soil was highest in the SPMC + Gd treatment. The highest increase in organic C (94%) and total N (87%), in comparison to the initial level, and soil microbial biomass C (113%) and soil microbial biomass N (229%), in comparison to the control treatment, was recorded with the addition of SPMC + Gd. The maximum decrease in soil bulk density (BD) (12%) with an increase in soil aggregate (17%) and water infiltration rate (35%) was obtained with the addition of SPMC. Overall, the sugarcane crop responded well to different organic manures in a multiple ratooning system with a better economic output and improved soil quality. Strategic planning in terms of an integrated application of these manures with inorganic chemicals will not only sustain our soils but will also be beneficial for our farmers in terms of reducing their dependence and expenditure on chemical fertilizers.     

Determination of the mineralization of nitrogen from composted chicken manure as affected by temperature

Incubations at 5, 10 or 20°C of composted chicken manure in a sand, clay or loam soil consistently released nitrogen. A statistical model fitted to the data confirmed that the temperature dependence followed an Arrhenius pattern. The data were used to test the hypothesis that composted manure behaves more like native soil organic matter than fresh residues and this idea is illustrated with the use of a computer simulation model. Extrapolation of the model results in several climates suggests that about 40% of the organic N in composted chicken manure becomes available to crops during the first year and 6–12% during each subsequent year.