Nitrogen Cycling with Respect to Environmental Load in Farm Systems in Southwest China

In Qibainong, a steep-mountainous karst region in southwestern China, self-sustaining societies have long existed, but increasing socioeconomic liberation has fuelled the recent rapid structural change of its economy. Consequently, environmental deterioration and exhaustion of resources have become problematic issues. We carried out a field survey in Qibainong in southwestern China and used both estimated and measured N flows and N balances from obtained results. Our results are summarized as follows (1) farmers used large amounts of chemical N fertilizers at intensities of 113–1124 kg N ha⁻¹; (2) substantial application of chemical fertilizer in Qibainong has contributed to an increase in potential NO₃-N leaching of 6–511 kg N ha⁻¹, followed by NH₃ volatilization; (3) crop products are largely distributed to feed livestock, the products of which are a major income source; (4) this area has a great requirement for imported food; (5) in addition, unused manure N (up to 191 kg N ha⁻¹) is generated by the increase in manure N production. Chemical fertilizer application, in addition to unused manure can be regarded as a major source of environmental damage. Based on the relationship between the N application rate and the NO₃-N leaching potential, we estimated the critical limit of the N application rate of chemical fertilizer + manure to be 297 kg N ha⁻¹. In Qibainong, unused manure, which is an important nutrient resource, was applicable within the critical limit. We recommend that all manure N produced within the village be used effectively on arable land, and that any shortages be supplemented by chemical N fertilizer up to 297 kg N ha⁻¹ to maintain water resource quality. Further improvement might be achieved through incorporating chemical fertilizers, P and K supplemented manure, and so on.     

Effects of nutrient cycling on grain yields and potassium balance

Soybean-maize rotation is a profitable cropping system and is used under rain fed conditions in north China. Since crop yields have been reported to decrease when K fertilizers are not used, we analyzed the productivity trends, soil-exchangeable and non-exchangeable K contents, and K balance in a continuous cropping experiment conducted in an area with an alfisol soil in the Liaohe River plain, China. The trial, established in early 1990 and continued till 2007, included 8 combinations of recycled manure and N, P, and K fertilizers. In the unfertilized plot, the yields of soybean and maize were 1,486 and 4,124 kg ha⁻¹ respectively (mean yield over 18 years). The yields of both soybean and maize increased to 2,195 and 7,476 kg ha⁻¹, respectively, in response to the application of inorganic N, P, and K fertilizers. The maximum yields of soybean (2,424 kg ha⁻¹) and maize (7,790 kg ha⁻¹) were obtained in the plots under treatment with N, P, and K fertilizers and recycled manure. K was one of the yield-limiting macronutrients: regular K application was required to make investments in the application of other mineral nutrients profitable. The decrease in the yields of soybean and maize owing to the absence of K application averaged 400 and 780 kg ha⁻¹, respectively. Soybean seed and maize grain yields significantly increased with the application of recycled manure. For both these crops, the variation coefficients of grain were lower with treatments that included recycled manure than without treatment. After 18 years, the soil-exchangeable and non-exchangeable K concentrations decreased; the concentrations in the case of treatments that did not include K fertilizers were not significantly different. Treatment with N, P, and K fertilizers appreciably improved the fertility level of the soil, increased the concentration of soil-exchangeable K, and decreased the non-exchangeable K concentration. In soils under treatment with N, P, and K fertilizers and recycled manure, the soil-exchangeable and non-exchangeable K levels in the 0–20 cm-deep soil layer increased by 34% and 2%, respectively, over the initial levels. Both soil-exchangeable and non-exchangeable K concentrations were the highest with on treatment with N, P, and K fertilizers and recycled manure, followed by treatment with N, P, and K fertilizers. These concentrations were lowest in unfertilized soils; the other treatments yielded intermediate results. The results showed a total removal of K by the crops, and the amount removed exceeded the amount of K added to the soil; in treatments that did not include K fertilizers, a net negative K balance was observed, from 184 to 575 kg ha⁻². The combined use of N, P, and K fertilizers and recycled manure increased the K content of the 0–20 cm-deep soil layer by 125% compared to the increase obtained with the application of N, P, and K fertilizers alone. The results clearly reveal that current mineral fertilizer applications are inadequate; instead, the annual application of recycled manure along with N, P, and K fertilizers could sustain future yields and soil productivity.     

Spatial variability of Soil Nutrients and Influencing Factors in a Vegetable Production Area of Hebei Province in China

This study was conducted to determine soil nutrient spatial variability and the factors influencing it in a vegetable production area using traditional statistics and geo-statistics. The study area encompassed 55 ha and consisted of 182 farmer's plots belonging to six production groups in the Yutian county of China. Two hundred and seventeen soil samples were collected on a 50×50-m grid at depths of 0–20 cm prior to the plots being sown for cabbage. Vegetable production history, including varieties, rotation systems and fertilizer use, at the sampling sites was also examined. Soil pH, organic manure (OM), NO₃⁻–N, available P, K, Zn, and other nutrients and particle size were measured. The results showed that N, P, K and Zn were the main limiting nutrient factors in the soil. Distinct semi-variance structures of spatial variability were observed for soil NO₃⁻–N, available P, K and Zn, with the range of spatial correlation being 204–348 m. Significant spatial distribution similarity was found for soil NO₃⁻–N, P, K and Zn, with relatively high contents of all these nutrients in some areas of the study area and relatively low contents in other areas. The correlation of soil NO₃⁻–N, P and K content with vegetable production history and fertilizer application rates (N, P₂O₅ and K₂O) suggested that vegetable variety and history of fertilizer use are important factors to be considered in the development of a soil nutrient management program in the study area.     

Effect of organic manure and chemical fertilizer on nitrogen uptake and nitrate leaching in a Eum-orthic anthrosols profile

Distribution and accumulation of NO₃-N down to 4 m depth in the soil profile of a long term fertilization experiment with organic manure and N and P chemical fertilizer were studied after 12 years, wheat and corn were planted in each year. The apparent N recovery decreased with increased N and P fertilizer. NO₃-N was mainly accumulated in 0-1.2 m depth of the soil profile with a maximum of 34 mg N kg-¹ for the treatment with 120 kg N and 26 kg P per hectare, a secondary maximum of 7.2 mg N kg-¹ was found at 3.2 m depth in the same treatment. NO₃-N accumulation in the soil profile was minimized in the trials with highest manure application. Nitrogen that was not recovered was leached as NO₃-N deeper than 4 m depth, was immobilized in the profile or was lost by denitrification. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Effect of poultry litter and composts on soil nitrogen and phosphorus availability and corn production

Environmental problems associated with raw manure application might bemitigated by chemically or biologically immobilizing and stabilizing solublephosphorus (P) forms. Composting poultry litter has been suggested as a means tostabilize soluble P biologically. The objectives of this study were to assessthe nutrient (N, P) value of different-age poultry litter (PL) compostsrelativeto raw poultry litter and commercial fertilizer and determine effects ofpoultrylitter and composts on corn (Zea mays) grain yield andnutrient uptake. The research was conducted for two years on Maryland'sEastern Shore. Six soil fertility treatments were applied annually to aMatapeake silt loam soil (Typic Hapludult): (1) a check without fertilizer, (2)NH₄NO₃ fertilizer control (168 kg Nha^–1), (3) raw poultry litter (8.9 Mgha^–1), (4) 15-month old poultry litter compost (68.7Mg ha^–1), (5) 4-month old poultry litter compost(59 Mg ha^–1) and (6) 1-month old poultry littercompost (64 Mg ha^–1). We monitored changes inavailable soil NO₃-N and P over the growing season and post harvest.We measured total aboveground biomass at tasseling and harvest and corn yield.We determined corn N and P uptake at tasseling.Patterns of available soil NO₃-N were similar between raw PL-and NH₄NO₃ fertilizer-amended soils. LittleNO₃-N was released from any of the PL composts in the first year ofstudy. The mature 15-month old compost mineralized significant NO₃-Nonly after the second year of application. In contrast, available soil P washighest in plots amended with 15-month old compost, followed by raw PL-amendedplots. Immature composts immobilized soil P in the first year of study. Cornbiomass and yields were 30% higher in fertilizer and raw PL amendedplotscompared to yields in compost-amended treatments. Yields in compost-amendedplots were greater than those in the no-amendment control plots. Corn N and Puptake mirrored patterns of available soil NO₃-N and P. Corn Puptakewas highest in plots amended with 15-month old compost and raw PL, even thoughother composts contained 1.5–2 times more total P than raw PL. There wasalinear relationship between amount of P added and available soil P, regardlessof source. The similar P availabilities from either raw or composted PL,coupledwith limited crop P uptake at high soil P concentrations, suggest that raw andcomposted PL should be applied to soils based on crop P requirements to avoidbuild-up of available soil P.     

Nutrient evolution in soil and cereal yield under different fertilization type in dryland

Under semiarid conditions the response of crops to synthetic fertilizers is often reduced. Organic fertilizers can be used to provide a continuous source of nutrients for the crops. The soil nitrogen and crop yield in a rotation of durum wheat (Triticum durum)–fallow-barley (Hordeum vulgare)–vetch (Vicia sativa) were studied during 4 years when synthetic fertilizer (chemical), compost (organic) or no fertilizer (control) were applied in a field with high initial contents of soil NO₃–N (> 400 kg N ha⁻¹), phosphorus (22 mg kg⁻¹) and potassium (> 300 mg kg⁻¹). Changes in soil organic matter, phosphorus and potassium were also measured. During the crop period, chemical fertilization significantly increased the content of soil NO₃–N in the first 0.30 m of soil with respect to organic fertilization and the control. The yield of wheat and barley was not increased after applying chemical or organic fertilizer with respect to the unfertilized plots. The estimated losses of nitrogen were similar for the three types of fertilization, as well as the uptake of nitrogen for the total biomass produced. The initial levels of organic matter and phosphorus were maintained, even in the plots that were not fertilized, while the potassium decreased slightly. Thus, the rotation and burying of crop residues were enough to maintain the crop yield and the initial content of nutrients.     

Response of dryland wheat to fertilizer nitrogen in relation to stored water,rainfall and residual farm yard manure

Yield response of dryland wheat to fertilizer N application in relation to components of seasonal water (available soil moisture and rainfall) and residual farm yard manure (FYM) was studied for five years (1983–84 to 1987–88) on a maize-wheat sequence on sandy loam soils in Hoshiarpur district of Punjab, India. Four rates of N viz. 0, 40, 60 and 80 kg ha^–1 in wheat were superimposed on two residual FYM treatments viz. no FYM (F₀) and 15 t ha^–1 (F₁₅) to preceding maize. FYM application to maize increased the residual NO₃-N content by 19–30 kg ha^–1 in the 180 cm soil profile. For a given moisture distribution, F₁₅ increased attainable yields. Over the years, F₁₅ increased wheat yield by 230 to 520 kg ha^–1. Response to fertilizer N was lower in FYM amended plots than in unamended plots. Available soil moisture at wheat seeding and amount and distribution of rainfall during the vegetative and the reproductive phases of crop development affected N use efficiency by wheat. Available soil moisture at seeding alone accounted for 50% variation in yield. The residual effect of FYM on wheat yield could be accounted for by considering NO₃-N in 180 cm soil profile at seeding. The NO₃-N and available soil moisture at wheat seeding along with split rainfall for two main phases of crop development and fertilizer N accounted for 96% variation in wheat yield across years and FYM treatments.     

Nitrate distribution and accumulation in an Ustochrept soil profile in a long term fertilizer experiment

Distribution and accumulation of NO₃—N, down to 210 cm depth, in the soil profile of a long term fertilizer experiment were studied after 16 cycles of cropping (maize-wheat-fodder cowpea). The application of fertilizer N without P and K or in combination with only P resulted in higher NO₃—N concentration in the soil profile than the application of N with P and K. With an annual application of 320 kg N ha^–1 alone, a peak in NO₃—N accumulation occurred at 135 cm soil depth. However, with the application of NPK, no peak in NO₃—N distribution was discernible and its content at most of the sampling depths was either less than or equal to N and NP treatments. The annual application of 10 tons farm yard manure (FYM) per ha along with NPK resulted in a relatively lower NO₃—N content in the sub soil. The amount of NO₃—N accumulation in the soil profile decreased as the cumulative N uptake by the crops increased. Application of fertilizer amounts greater than that of the recommended (100% NPK) resulted in low percent N recoveries in crops and greater NO₃—N accumulation in the soil profile.     

Nitrate and phosphorus loss from agricultural land: implications for nonpoint pollution

The impact of agriculture on flood plains and surface water quality has received much attention in temperate countries in recent years. Little attention has been given to loss of nutrients and its impact on the quality of buffer zones and adjacent streams in many tropical environments due to the believe that fertilizer use is still very low compared to temperate countries. This may not be totally true especially in agricultural research stations and University experimental fields where a large amount fertilizers are used continuously for many years. This study was conducted in 2 years (Four seasons) to evaluate the accumulated effect of a long term fertilizer application of an agricultural land on an adjacent stream. Results showed that applied fertilizer significantly contributed to the high levels of nitrate and phosphorus in the stream water. Highest concentration of soil NO₃-N and P were found in 0–15, 15–30 and 30–45 cm soil depths with about 75% reduction in these amounts in the 60–75 cm depth for NO₃-N and 77% reduction at the same depth for soil available phosphorus, the topsoil constituting about 45% of the concentration of the two plant nutrients assessed. There were evident of leaching of basic cations below 15 cm soil depth as indicated in the increased soil pH. There were significantly (P < 0.05) higher soil NO₃-N and P in the dry season relative to the wet season. The long term application of fertilizers to the sandy loam soil significantly contributed to nitrate and phosphate pollution of the stream in excess of the maximum level accepted for potable water. The stream’s pH, temperature, nitrate and phosphate were significantly higher in the dry season. Correlation analyses indicated that agricultural runoffs from the topsoil contributed significantly to the pollution of the stream. There was also positive and significant correlation between the soil nitrate and soil phosphorus at different soil depths, thus indicating that the N and P might have been applied jointly as compound fertilizer and move down the slope through runoff.     

Nitrogen balance and accumulation pattern in three contrasting prairie soils receiving repeated applications of liquid swine and solid cattle manure

The expansion of intensive livestock operations in western Canada has increased concerns about overloading of nutrients in manured lands. The magnitude of nutrient accumulation and its distribution in the soil profile varies with soil-climatic conditions. The objective of this study was to determine loading and distribution of manure-derived nitrogen (N) in the soil profile as influenced by repeated manure applications. Four field experiments were conducted at three sites (Dixon, Melfort and Plenty) in Saskatchewan under longer-term manure management. The four field experiments provide contrasts in soil type, climatic conditions, manure type, application and cropping history to enable the effect of these factors to be evaluated. Liquid hog manure (LHM—Experiment 1) and solid cattle manure (SCM—Experiment 2) treatments were applied annually over 8 years at Dixon (Black Chernozemic loam soil—Udic Boroll in sub-humid climate), while only LHM was applied at Plenty (Dark Brown Chernozemic heavy clay soil—Typic Boroll in semi-arid climate) over 6 years (Experiment 3), and at Melfort (Dark Gray Luvisol silty clay loam soil—Mollic Cryoboralf in humid climate) over 5 years (Experiment 4). Soil samples were collected in the spring and autumn of 2003 and 2004, and were analyzed for organic N, ammonium-N (NH₄⁺-N) and nitrate-N (NO₃⁻-N) concentrations. Plant samples were collected to determine the impact of manure application rate on plant N uptake and crop N removal. The annual application of LHM (37,000 L ha⁻¹ yr⁻¹) and SCM (7.6 Mg ha⁻¹ yr⁻¹) at agronomic rates at Dixon (added N balances crop demand for that year), or larger rates of LHM (111,000 L ha⁻¹) applied once every 3 years (Melfort) did not significantly elevate NO₃⁻-N in soil compared to the unfertilized control. Lower crop removal and reduced leaching of NO₃⁻-N due to drier conditions as occurred at the Plenty site contributed to greater accumulation of nitrate in the top 60 cm at equivalent rates compared to the other two sites. At large manure rates, excess N from the balance estimates could not be accounted for in soil organic N and was assumed to be lost from the soil-plant system. At the Dixon LHM site, deep leaching of NO₃⁻-N was observed at the excessive rate (148,000 L ha⁻¹ yr⁻¹) up to the 150 cm depth, compared to the control. At Dixon, the large annual application rate of SCM (30.4 Mg ha⁻¹ yr⁻¹) did not significantly increase NO₃⁻-N in the 0–60 cm soil compared to the control, which was attributed to lower mineralization of organic N from the SCM. Over the short and medium term, LHM application at large rates every year poses a greater risk for loading and deep migration of NO₃⁻-N in soil than large rates of SCM. Larger single applications made once every 3 years were not associated with accumulation or deep leaching. To prevent loading, rates of applied manure nitrogen should be reduced when crop N removal potential is diminished by high frequency of drought.     

Greenhouse tomato–cucumber yield and soil N leaching as affected by reducing N rate and adding manure: a case study in the Yellow River Irrigation Region China

The effect of reducing N rate fertilization and manure addition on greenhouse vegetable yields and soil N leaching was studied in a greenhouse tomato?Ccucumber rotation system in the Yellow River Irrigation Region of Ningxia Plain, North China. The treatments were: 1-no fertilizers, 2-conventional fertilization, 3-reduced fertilizer application, and 4-reduced fertilizer application + regulation of soil C/N ratio applied by the high C/N ratio of dairy manure. The results indicated that reduced fertilizer application in tomato and cucumber season had no significant influence on vegetable yield comparing with control. The amounts of leachate had no significant differences under all fertilizer treatments at the same investigated period. In comparison with conventional fertilization, both total N and NO₃?CN leaching decreased in the low fertilizer treatments. The cumulative total N and NO₃?CN leached from fertilizers N were less than 9?% during the tomato?Ccucumber rotation system. NO₃?CN was the predominant form of leaching N, represented about 70?% of total N in the leachate. Soluble organic N represented 14.7?C33.3?% of total N leached. Vegetable yields did not increase significantly as applied N rates increased. However, soil N leaching increased largely with N rates. Reducing fertilizer N rate while adding dairy manure regulated soil C/N ratio could be appropriate fertilization practices for reducing soil N leaching and achieving high vegetable yields in the greenhouse systems.     

Nitrogen fertigation of greenhouse-grown strawberries

Two greenhouse experiments were conducted with strawberries (Fragaria ananassa) grown in plastic pots filled with 12 kg of soil, and irrigated by drip to evaluate the effect of 3 N levels and 3 N sources. The N levels were 3.6, 7.2 or 10.8 mmol Nl^–1 and the N sources were urea, ammonium nitrate and potassium nitrate for supplying NH₄/NO₃ in mmol Nl^–1 ratios of 7/0, 3.5/3.5 or 0/7, respectively. Both experiments were uniformly supplied with micronutrients and 1.7 and 5.0 mmoll^–1 of P and K, respectively. The fertilizers were supplied through the irrigation stream with every irrigation. The highest yield was obtained with the 7.2 mmol Nl^–1 due to increase in both weight and number of fruits per plant. With this N concentration soil ECe and NO₃-N concentration were kept at low levels. Total N and NO₃-N in laminae and petioles increased with increasing N level. With the N sources the highest yield was obtained with urea due to better fruit setting. The N source had no effect on soil salinity and residual soil NO₃-N; residual NH₄-N in the soils receiving urea and ammonium nitrate were at low levels.     

Crop residue,manure and fertilizer in dryland maize under reduced tillage in northern China: I grain yields and nutrient use efficiencies

The rapidly increasing population and associated quest for food and feed in China has led to increased soil cultivation and nitrogen (N) fertilizer use, and as a consequence to increased wind erosion and unbalanced crop nutrition. In the study presented here, we explored the long-term effects of various combinations of maize stover, cattle manure and nitrogen (N) and phosphorus (P) fertilizer applications on maize (Zea mays L.) yield and nutrient and water use efficiencies under reduced tillage practices. In a companion paper, we present the effects on nutrient balances and soil fertility characteristics. The ongoing factorial field trial was conducted at Shouyang Dryland Farming Experimental Station in northern China from 1993 onwards. The incomplete, determinant-optimal design comprised 12 treatments, including a control treatment, in duplicate. Grain yields and N, P, and potassium (K) uptakes and N, P and K use efficiencies were greatly influenced by the amount of rain during the growing season (GSR), and by soil water at sowing (SWS). There were highly significant interactions between GSR and added stover and manure, expressed in complex annual variations in grain yield and N, P and K use efficiencies. Annual mean grain yields ranged from 3,000 kg ha⁻¹ to 10,000 kg ha⁻¹ and treatment mean yields from 4,500 kg ha⁻¹ to 7,000 kg ha⁻¹. Balanced combination of stover (3,000–6,000 kg), manure (1,500–6,000 kg) and N fertilizer (105 kg) gave the highest yield. Stover and manure were important for supplying K, but the effects differed greatly between years. Overall mean N recovery efficiency (NRE) ranged from 28% to 54%, depending on N source. NRE in wet years ranged from 50% to 90%. In conclusion, balanced combinations of stover, manure and NP fertilizer gave the highest yield and NRE. Reduced tillage with adding stover and manure in autumn prior to ploughing is effective in minimizing labor requirement and wind erosion. The potentials of split applications of N fertilizer, targeted to the need of the growing crop (response farming), should be explored to further increase the N use efficiency.     

Benefits of organic residues and chemical fertilizer to productivity of rain-fed lowland rice and to soil nutrient balances

Low yields and high risk characterize many rain-fed lowland rice environments, including those in Laos. Drought and fluctuating soil-water conditions (from aerobic to anaerobic states) can limit productivity and the efficient use of applied nutrients. Although addition of organic matter may improve the efficiency of fertilizer use, on-farm residues, for example farmyard manure (FYM), rice straw and rice hulls, are, currently, poorly utilized in these systems. Single and multi-year experiments were designed to evaluate the effect of these residues on rice productivity and efficiency of fertilizer use at four sites. Rice yield without fertilizer but with addition of residues ranged from 1.1 to 1.7 t ha⁻¹ across sites and years. In response to fertilizer, yields increased on average by 1.4 t ha⁻¹. For all sites and years there was a significant response of yield to organic residues applied without fertilizer, with responses ranging from 0.2 to 1.4 t ha⁻¹. In 58% of cases there was no residue×fertilizer interaction (benefits of residues when applied with fertilizer were additive). In 38 and 4% of cases the interaction was negative (no response to residues if fertilizer was already applied) or positive (synergistic), respectively. In the multi-year studies, the type of interaction varied between years, suggesting that seasonal events, rather than soil type, determine the type of interaction. The greatest benefits of applying organic and chemical fertilizers together were observed in years when soil-water conditions were unfavorable (fluctuating anaerobic–aerobic conditions). The long-term effects of these different management strategies on soil nutrient balances suggest that N, P, and K balances were maintained as a result of balanced commercial fertilizer management but that addition of residues further enhanced these balances. All residues, when applied alone, resulted in positive soil Si balances; only with FYM were long-term N, P, and K balances maintained or positive, however. For resource-poor farmers, applying on-farm residues can be a sustainable approach to increasing productivity.     

Effect of the integrated use of legume residue,poultry manure and inorganic fertilizers on maize yield,nutrient uptake and soil properties

Identification of a sustainable integrated soil fertility management option in the tropics will not only salvage the degraded soils but also enhances the attainment of the goal of food security. This study was conducted in 2004 and 2005 on a degraded tropical Alfisol in south western Nigeria to evaluate the effect of legume residue, poultry manure and inorganic fertilizers on maize yield, nutrient uptake and soil properties. The treatments consisted of two rates of poultry manure (0 and 5 t ha⁻¹), three rates of N fertilizer (0, 50 and 100 kg N ha⁻¹ applied as urea), three rates of P fertilizer (0, 30 and 60 kg P ha⁻¹ applied as single super phosphate) and two soybean treatments (with or without incorporation of legume residue) in various combinations as a factorial experiment in Randomized Complete Block design with three replicates. Results showed that poultry manure alone led to significant increase in maize yield (60%) and soil organic matter (45%). In contrast, legume residue incorporation gave significantly lower increase in yield (7%) and soil organic matter (11%). However, the combined application of poultry manure and legume incorporation led to 72% increase in maize yield as opposed to 63 and 10% increase recorded when manure alone or legume alone were incorporated, respectively. Optimal maize yield was achieved when manure application was integrated with P fertilizer application. The interaction of P fertilizer and legume incorporation indicated that soil phosphorus and maize P concentration were significantly increased with the application of the P fertilizer and legume incorporation. Hence, the application of P fertilizer alone is most likely to be economical compared with its integration with legume incorporation.     

Nitrogen fertilizer value of activated sewage derived protein: Effect of environment and nitrification inhibitor on NO 3 - release,soil microbial activity and yield of summer cabbage

Yield response of summer cabbage (Brassica oleracea varcapitata cv. Hispi F₁) to N applied as organic (activated sewage sludge derived protein [Protox] and dried blood) and inorganic (ammonium nitrate, ammonium sulphate, sodium nitrate and urea) fertilizers was compared in relation to the N availability characteristics of the materials. Effects of the nitrification inhibitor dicyandiamide (DCD) on N release, crop yield and N status were also assessed. In addition CO₂ efflux was measured from amended soil to determine effects of fertilizer application on soil microbial activity. The organic N sources were mineralized quickly on application to soil and exhibited similar patterns of NH₄-N depletion and NO₃-N accumulation as functions of thermal-time as with mineral fertilizers. However, the yield response to organic N was marginally smaller (though not significantly) compared with mineral forms; probably because less N was released to the crop. This was reflected in smaller total N concentrations and N recoveries in plants supplied with organic fertilizer. Applied DCD increased the thermal-time for complete nitrification of NH₄-N sources and raised the total N content of the crop, but had no overall effect on crop growth. In contrast to inorganic N sources which generally reduced CO₂ efflux from soil, application of protein-based fertilizers increased the rate of soil microbial activity directly by raising substrate availability. Sewage sludge derived protein provided an effective alternative to mineral fertilizers for the nutrition of summer cabbage whilst minimising stress of the soil environment which may occur following the application of conventional forms of inorganic N to the soil.     

Nitrous oxide emissions from a light-textured arable soil of North-Western Russia: effects of crops,fertilizers, manures and climate parameters

Direct nitrous oxide emissions from a light-textured arable soil typical of North-Western Russia and subject to different management systems were measured during three growing seasons (May–September) in 2003–2005. Cumulative fluxes varied between 0.26 ± 0.06 and 2.98 ± 1.56 kg N₂O–N ha⁻¹, with the lowest flux produced where no N was added as mineral fertilizers/manures or where green manure/low inputs of mineral fertilizer were used as a source of N. Highest cumulative fluxes were measured from the plots where high inputs of farmyard manure were used. Of the crops studied, potatoes produced the highest N₂O fluxes; this was attributed to the use of furrows, in which the soil tended to be more compact with higher water-filled pore space, making the soil more prone to denitrification than that in fields without furrows. The available N content of the soil at the start of each growing season was quite low and cumulative N₂O fluxes were significantly affected by N-fertilizer application within one growing season. However, for different growing seasons with highly changeable rainfall patterns and with different soil management for different crops, the quite high yearly correlation between N application and N₂O fluxes was much reduced.     

Evaluation of current fertilizer practice and soil fertility in vegetable production in the Beijing region

A survey on current fertilizer practices and their effects on soil fertility and soil salinity was conducted from 1996 to 2000 in Beijing Province, a major vegetable production area in the North China Plain. Inputs of the major nutrients (NPK) and fertilizer application methods and sources for different vegetable species and field conditions were evaluated. Excessive N and P fertilizer application, often up to about 5 times the crop requirement in the case of N, was very common, especially for high-value crops. Potassium supply may have been inadequate for some crops such as leafy vegetables. Urea, diammonium orthophosphate ((NH₄)₂HPO₄) and chicken manure were the major nutrient sources for vegetable production in the region. Over 50% of N, 60% of P and nearly 90% of K applied originated from organic manure. Total N application rate for open-field Chinese cabbage from organic manure and inorganic fertilizers ranged from 300 to 900 kg N ha^–1 on 78% of the farms surveyed. More than 35% of the surveyed greenhouse-grown tomato crops received > 1000 kg N ha^–1 from organic and inorganic sources. A negative K balance (applied K minus K removed by the crop) was found in two-thirds of the surveyed fields of open-field Chinese cabbage and half of the surveyed fields of greenhouse-grown tomato. Plant-available N, P and K increased with increasing length of the period the greenhouse soils had been used for vegetable production. Similarly, soil salinity increased more in greenhouse soils than in open-field soils. The results indicate that balanced NPK fertilizer use and maintenance of soil quality are important for the development of sustainable vegetable production systems in this region.     

Effects of fertilization on nutrient budget and nitrogen use efficiency of farmland soil under different precipitations in Northeastern China

Based on a consecutive 16-year field trial and meteorological data, the effects of fertilization on the nutrient budget and nitrogen use efficiency in farmland soil under different precipitation years were studied. With no fertilization treatment, the grain yield of maize was 3,520 kg ha⁻¹ (mean yield over 13 years). But the maximum yield increased to 7,470 kg ha⁻¹ when treated with mineral N, P and K fertilizers and recycled manure. The nutrient uptake also increased by twofold to threefold in NPKM treated field compared with that in the control treatment. The highest yields were obtained in years with normal precipitation, despite the different fertilization schemes. The lowest yields were obtained in drought or waterlogging years, which were 44.7–58.5% of the yields in years with normal precipitation. It also appeared that the deficits of N, P and K were greater in the years with proper precipitation than those in arid or flood years, because more production was removed from the field. Soil total N decreased significantly when treated with mineral fertilizer or recycled manure alone. The maximum deficit of soil total N was observed in control treatment (557 kg ha⁻¹) from 1990 to 2005. The N treatment resulted in a significant negative balance of P, due to the high yield of the crop in response to applied N. The application of NP or N to soils resulted in a greater negative K balance than that of the control. The greatest negative balance of total P and available P were obtained under the control and N treatment, and the highest deficit of soil total K and exchangeable K were obtained under NP treatment. We found that the rate of 150 kg N ha⁻¹ year⁻¹ was inadequate for maintaining soil N balance, and amendment of soil with organic source could not stop the loss of soil P and K. The applying rates of 150 kg N ha⁻¹ year⁻¹, 25 kg P ha⁻¹ year⁻¹, and 60 kg K ha⁻¹ year⁻¹ combined with 2–3 t ha⁻¹ organic manure were recommended to maintain soil fertility level. The nitrogen use efficiency (NUE) was greatly improved in the years with proper precipitation and balanced fertilization. Higher NUE and grain yields were achieved under NPK and NPKM treatments in years with normal precipitation. The results clearly demonstrated that both organic and mineral fertilizers were needed to increase crop production, improve NUE and maintain soil fertility level.