Nitrogen And Phosphorus Research Articles

Bridging the attainable yield gaps of watermelon through nitrogen and phosphorus nutrients management in North-West Ethiopia

Optimum fertilizer is essential for obtaining high yields of watermelon. This three location study was conducted to investigate the effect of nitrogen and phosphorus (NP) fertilizer on the growth and fruit yield of watermelon. The experiment consisted of five levels of nitrogen (0,46,92,138 and 184 kg N ha−1) and four levels of phosphorus (0, 23, 46, and 69 kg P2O5 ha−1) combined full factorial. A randomized complete block design (RCBD) with three replications was used. NP interaction and location interactions had effects on the growth and yield. Earliness of maturity was observed with 92/46 kg N/P2O5 ha−1 at all locations. A biological maximum yield of 78.8, 58.4 and 64.5 t ha−1 was obtained with 92/69, 138/46, and 184/46 kg N/P2O5 ha−1 at Ribb, Woramit and Koga, respectively. Based on the regression analysis, an optimum yield of 69.0 t ha−1 was obtained with 117/98 kg N/P2O5ha−1 at Ribb while 111/70 kg N/P2O5 ha−1 gave 50.2 t ha−1 at Woramit. High N (221 kg ha−1) interacted with 71 kg P2O5ha−1 gave an optimum yield of 59.0 t ha−1 at Koga. Moreover, 115.4/97.8 kg N/P2O5 ha−1 gave a maximum net return of 684,431.10 Birr (US $18178.78) at Ribb while 110.2/69.6 kg N/P2O5 ha−1 gave a maximum net return of 496942.61Birr (US $13199.00) at Woramit. At Koga, a maximum net return of 581,229.72 (US $15437.71) was obtained with 218.9/70.2 kg N/P2O5 ha−1 application. Fruit weight ranged from 3.2 kg with 0/0 kg N/P2O5 ha−1 to 5.03 kg with 92/69 kg N/P2O5 ha−1at Ribb while from 3.08 kg with 0/0 kg N/P2O5 ha−1 to 5.36 kg with 184/46 kg N/P2O5 ha−1 at Woramit. At Koga, it ranged from 1.67 kg with 0/0 N/P2O5 ha−1 to 4.04 kg with 184/0 kg N/P2O5 ha−1. The highest N rate gave less TSS value at Ribb while the opposite was true at Woramit and Koga. It was concluded that 115/98, 110/70, and 219/70 kg N/P2O5 ha−1at Ribb, Woramit and Koga, respectively are economical optimum NP rates for the production of watermelon in northwest Ethiopia.

Effect of Long-Term Fertilization on Ammonia-Oxidizing Microorganisms and Nitrification in Brown Soil of Northeast China.

The objective of this study was to find out changes in ammonia oxidation microorganisms with respect to fertilizer as investigated by real-time polymerase chain reaction and high-throughput sequencing. The treatments included control (CK); chemical fertilizer nitrogen low (N) and high (N2); nitrogen and phosphorus (NP); nitrogen phosphorus and potassium (NPK) and organic manure fertilizer (M); MN; MN2; MNPK. The results showed that long-term fertilization influenced soil fertility and affected the abundance and community of ammonia-oxidizing microorganisms by changing the physical and chemical properties of the soil. The abundance and community structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) was influenced by soil organic carbon, total nitrogen, total soil phosphorus, available phosphorus, available potassium, and soil nitrate. Soil environmental factors affected the nitrification potential by affecting the structure of ammonia-oxidizing microorganisms; specific and rare AOA and AOB rather than the whole AOA or AOB community played dominant role in nitrification.

Nitrogen-Phosphorus Codoped Carbon Nanospheres as Lubricant Additives for Antiwear and Friction Reduction

Nitrogen and phosphorus doping have been proven to be effective strategies for improving the tribological properties of carbon-based materials when used as lubricating oil additives. Herein, an efficient strategy is demonstrated for the preparation of nitrogen and phosphorus codoped organic carbon nanospheres (denote as N, P@CN) via a template-free interfacial copolymerization combined with ammonium hypophosphite-assisted carbonization. The N and P are found to be homogeneously distributed through the entire carbon shell. The tribological properties of as-prepared materials as base oil additives under different test conditions were evaluated. The as-prepared N, P@CNs exhibit good dispersibility and stability in base oil due to the presence of many organic functional groups. Moreover, they are considered to be thermal stable at elevated temperatures, and the existing robust structure makes them favorable as lubricant additives. The experiment results show that the friction reduction and wear resistance abilities of N, P@CNs were superior to that of pure base oil, because N, P@CNs can induce tribo-chemical reactions to form a protective film on the interfaces due to the combined effect of nitrogen and phosphorus. The obtained N, P@CNs could increase the load carrying capacity of base oil from 250 N to 1050 N. The coefficient of friction can be reduced to 0.08, and the corresponding wear volume loss can be decreased by 90%. These findings open up a possibility to prepare environmentally friendly lubricant additives, such as carbon nanospheres doped with other elements, to achieve excellent antiwear and friction-reducing characteristics.

Effects of inoculation of root-associative Azospirillum and Agrobacterium strains on growth, yield and quality of pea (Pisum sativum L.) grown under different nitrogen and phosphorus regimes

Nitrogen and phosphorus are essential for growth and development of crop plants and are required in large quantities for crops. However, nitrogen is less available to plants due to leaching, volatilization and denitrification and phosphorus due to insolubility that result in even higher fertilizer input. Plant growth promoting rhizobacteria (PGPR) have the potential to improve nutrient availability, reduce input cost and mitigate environmental issues incurred otherwise by substantial use of fertilizers in production of economically important horticultural crops such as pea. Therefore, this study was conducted with the objectives i) to determine whether the inoculation of pea plants with PGPR combined with the reduced mineral rates of nitrogen and phosphorus (NP) fertilizers will give similar growth, yield and quality as with full rates of NP fertilizer without inoculation and ii) what is the minimum percentage of NP that can be used for commercial pea cultivation. For this purpose, pea seeds were co-inoculated with a mixture of Azospirillum Er-20, a nitrogen fixing strain; and Agrobacterium tumefaciens Ca-18, a phosphorus solubilizing strain of rhizobacteria in combination with 60, 65, 70, 75, 80 and 100% (recommended) dose of NP fertilizer. The finding suggested that PGPR combined with NP fertilizer at a rate of 75% of the recommended dose led to increased plant height, fresh and dry weights of shoot and roots, number of leaves and branches, number and length of pods, number and seed weights and yield that were statistically equivalent to the full fertilizer rate (100% NP) without PGPR. Similar trend was observed for photosynthetic pigments (chlorophyll a and b, total chlorophyll concentration and total carotenoids), total phenolics and DPPH radical scavenging activity and antioxidant capacity. However, when PGPR were combined with NP doses less than 75% of the recommended amount, the results were not positively consistent. Without PGPR, NP rates lower than the recommended dose resulted in inconsistent effects and significantly reduced plant growth traits, pod characteristics and yield, photosynthetic pigments and antioxidant activity and capacity. Thus, we suggest that, under field conditions, synergistic inoculation of a nitrogen fixing strain and a phosphorus solubilizing strain can be used to reduce the input of NP fertilizers thus saving cost and preserving environment.

Effect of potassium levels on teff (Eragrostis tef (Zucc.) Trotter) growth and yield in Central Highland Vertisols of Ethiopia

Nutrient depletion and imbalance are among the major attributes that contribute to declining soil productivity in the highlands of Ethiopia. The blanket fertilizer recommendation, which considered only urea and Di-ammonium phosphate (DAP), was used over the past four decades to improve soil fertility for enhancing crop production. Nevertheless, the average national yields of small cereal including teff were low, despite application of nitrogen and phosphorus (NP) fertilizers. On-farm trials were conducted in the 2015/16 and 2016/17 cropping seasons at 18 locations on Ethiopian highland Vertisols to determine the response of teff to potassium (K) fertilization along with other limiting nutrients. Five K levels (0, 30, 60, 90 and 120 kg ha-1) in the form of murate of potash (KCl) were used in randomized complete block design with three replications. Separate analysis of variance was conducted for each sites and year. Least Significant Difference (LSD) test at P ≤ 0.05 was used to separate means whenever there were significant differences. Analysis of variance revealed a highly significant difference (P 50:1 and Mg: K >15:1 are likely to respond to potassium fertilization. The yield advantage accrued due to K application ranged from 30 to 77% in 2015/16 and 8 to 51% in 2016/17 seasons. The economic optimum K fertilizer application rates varied between 60 kg K ha-1 in 44% of the sites to 90 kg K ha-1 in 23% of the sites. The findings highlighted the need for revisiting fertilizer program to enhance the yield and nutrient uptake of teff in K responsive soils and developing critical levels for K in the study sites.

Identification of new microbial functional standards for soil quality assessment

Abstract. The activity of microorganisms in soil is important for a robust functioning of soil and related ecosystem services. Hence, there is a necessity to identify the composition, diversity, and function of the soil microbiome in order to determine its natural properties, functioning, and operating range as well as to assess ecotoxicological effects due to anthropogenic activities. Numerous microbiological methods currently exist in the literature and new, more advanced methods continue to be developed; however, only a limited number of these methods are standardised. Consequently, there is a need to identify the most promising non-standardised methods for assessing soil quality and to transform them into standards. In agreement with the “Ecosystem Service Approach”, new methods should focus more on soil microbial functions, including nutrient cycling and greenhouse gas emission, pest control and plant growth promotion, carbon cycling and sequestration, as well as soil structure development and filter function. The few existing standardised methods available that focus on the function of the soil microbiome mostly include measurements, like basal respiration, enzyme activities, and biodegradation of organic matter, under well-defined conditions in the lab. This paper sets out to summarise and expand on recent discussions within the International Organization for Standardization (ISO), Soil Quality – Biological Characterization sub-committee (ISO TC 190/SC 4), where a need was identified to develop scientifically sound methods which would best fulfil the practical needs of future users for assessing soil quality, going beyond the existing test systems. Of particular note is the current evolution of molecular methods in microbial ecology that use quantitative real-time PCR (qPCR) to produce a large number of new functional endpoints which are more sensitive as compared to “classical” methods. Quantitative PCR assesses the abundance of microbes that catalyse major transformation steps in nitrogen and phosphorus cycling, greenhouse gas emissions, chemical transformations including pesticide degradation, and plant growth promotion pathways based on the assessment of marker gene sequences that drive the related processes. In the assessment of soil quality methods, it was found that most methods focus on bacteria and related endpoints. Techniques to describe fungal communities as well as their functional traits are far less represented. As such, techniques to analyse fungal enzyme activities are proposed. Additionally, methods for the determination of microbial growth rates and efficiencies, including the use of glomalin as a biochemical marker for soil aggregation, are discussed. Furthermore, field methods indicative of carbon turnover, including the litter bag test and a modification to the tea bag test, are presented. However, it is obvious that with increasing developments in high throughput sequencing technologies and big data analyses, including metagenomics analysis, it will be possible to implement these technologies into the standardisation process for assessing the functions of the soil microbiome. Overall, it is suggested that endpoints should represent a potential function of soil microorganisms rather than actual activity levels, as the latter can largely be dependent on short-term variable soil properties such as pedoclimatic conditions, nutrient availability, and anthropogenic soil cultivation activities.

Effects of different mulching and fertilization on phosphorus transformation in upland farmland

In the present study, the impact of different soil surface mulching, fertilization on phosphorus mineralization and bio-availability of spring maize at various growth stages and soil layers (0–20 and 20–40 cm soil layer) were evaluated. The results indicated that the contents of total P and Olsen-Phosphorus (Olsen-P) in the soils of 0–20 cm soil layer were significantly higher than those in the 20–40 cm soil layer at different stages. The addition of organic fertilizer significantly increased the soil total P and Olsen-P content in the 0–20 cm soil layer. The different surface mulching, no mulching (NM), gravel mulching (GM) and film mulching (FM) were significantly affected by the content of Olsen-P in both soil layers during the critical growth period of spring maize. The Ca10–P contents in both soil layers were the maximum in terms of the inorganic phosphorus content in soils with different surface mulching and different fertilization. Surface mulching significantly affected the transformation of inorganic phosphorus in different soil layers of dry-land farmland, and accelerated the increase of Ca2–P content (first phosphorus source) in 0–20 cm soil layer by GM and FM. In addition, phosphorus combined with inorganic nitrogen fertilizer increased Ca8–P (second Olsen-P source) to a certain extent, and reduced the relative content of Ca2–P (first phosphorus source). Compared with phosphate (P), nitrogen and phosphorus (NP) treatments, manure and nitrogen and phosphorus (MNP) treatments increased the contents of Ca2–P (first phosphorus source) and Ca8–P (second effective phosphorus source), while it reduced the insoluble phosphorus source (O–P) content.

Responses of soil microbial biomass C and P to different long-term fertilization treatments in the yellow paddy soil

To explore the rational fertilization mode to improve the availability of soil phosphorus (P), we analyzed the changes and coupling characteristics of soil carbon (C) and P, microbial biomass C (MBC) and P (MBP) under different fertilization modes with a successive 22-year field experiment in yellow paddy soil. The experiment had 10 treatments, including no fertilization (CK), single application of nitrogen (N), combination of phosphorus and potassium (PK), combination of nitrogen and potassium (NK), combination of nitrogen and phosphorus (NP), combination of nitrogen, phosphorus and potassium (NPK), single application of organic fertilizer (M), and three organic-inorganic fertilizer combinations (1/4M+3/4NP, 0.5MNP, MNPK). The results showed that, compared with CK, the contents of total organic C (TOC), total P (TP), MBC and MBP in N and NK treatments decreased to some extent, while those in PK, NP and NPK treatments increased. Compared with the treatments of no fertilizer and inorganic fertilizer, the contents of TOC, MBC, MBP and MBP/TP ratio in treatments with manure significantly increased, among which M and MPNK treatments showed the strongest enhancement. The treatments with manure had the lowest MBC/MBP ratio, TOC/MBP ratio and MBC/TP ratio, while N treatment had the highest value. MBC, MBP, MBP/TP ratio, MBC/MBP ratio, TOC/MBP ratio and MBC/TP ratio were significantly correlated with TOC and available P, TOC was the direct factor affecting MBC, MBP, and MBP/TP ratio, while available P was the direct factor affecting MBC/MBP ratio, TOC/MBP ratio, MBC/TP ratio. In summary, soil MBP content and the coupling relationship between C and P could effectively distinguish the modes of production with single chemical fertilizer application and manure application, and could be used as biological indices in the evaluation of soil P fertility. Combined application of manure is an effective way to enhance P availability and increase its potential capacity and maintain soil biological health in yellow paddy soil.

Greenhouse Gas Emissions from the Tibetan Alpine Grassland: Effects of Nitrogen and Phosphorus Addition

The cycle of key nutrient elements nitrogen (N) and phosphorus (P) has been massively altered by anthropogenic activities. Little is known about the impacts on greenhouse gas (GHG) emission of the large nutrient additions occurring in the alpine grasslands of the Tibetan Plateau. We investigated soil surface emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) under control, N, P and combined nitrogen and phosphorus (NP) additions from July 2011 to September 2012. Compared to the control, CO2 flux significantly increased by 14.6% and 27.4% following P and NP addition, respectively. The interaction of NP addition had a significant influence on CO2 flux during the non-growing season and the spring thaw period. Compared to the control, CH4 flux decreased by 9.9%, 23.2% and 26.7% following N, P and NP additions, respectively, and no interactive effect of NP addition was found in any period. Soil N2O flux was significantly increased 2.6 fold and 3.3 fold, following N and NP addition treatments, respectively, and there was no interaction effect of NP addition together. The contribution of cumulative CO2 emission during the non-growing season was less than 20% of the annual budget, but cumulative CH4 and N2O emissions during the same period can account for 37.3–48.9% and 44.7–59.5% of the annual budget, respectively. Methane and N2O emissions did not increase greatly during the spring thawing period, with contributions of only 0.4–3.6% and 10.3–12.3% of the annual budget, respectively. Our results suggest that N and P addition could increase CO2 and N2O emissions and reduce CH4 emission. Furthermore, although the non-growing season is very cold and long, cumulative CH4 and N2O emissions are considerable during this period and cannot be neglected by future studies evaluating the greenhouse gas emission budget in the Tibetan plateau.

Soil organic carbon sequestration and fertility response to newly-built terraces with organic manure and mineral fertilizer in a semi-arid environment

Terraces are a popular and widely-distributed engineered agricultural landscape in mountainous regions. In this study, the effects of adding manure on soil organic C (SOC) sequestration, soil aggregate distribution, C/N ratio and activities of enzyme were evaluated in newly-built terraces over 7 growing seasons from 2004 to 2010 on the semi-arid Loess Plateau of China.Experimental treatments including CK (control treatment with no fertilizer), NP (nitrogen and phosphorus), M (manure) and MNP (manure, nitrogen and phosphorus) were employed with a field pea–spring wheat–potato cropping system. SOC built up quickly in M and MNP treatments, while applying fertilizer alone (NP) was not effective in increasing soil C. The C sequestration rates are high in the early stages in manure treatments, and then decrease with consequent increases of soil C pool and finally became zero as soil C reaches an equilibrium level. The simulation results showed that the maximum increase of SOC in newly-built terraces was 3.4gkg−1. Organic amendment significantly increased soil water stable macro-aggregates (>0.25mm). The largest aggregates (>2mm) in manure treatments have important implications for C sequestration, with 29.4% and 30.6% of total SOC in M and MNP, respectively. Application of fertilizer alone could not form the largest aggregates (>2mm) in the 7 years. SOC content was significantly higher in M and MNP than in CK and NP in all soil aggregate size classes. Manure treatments improved soil C/N ratio, while fertilizer treatment (NP) decreased soil C/N ratio. A significant sigmoid relationship was found between C/N ratio and cumulative inputs of SOC and TN in manure treatments, and a significant logistic relationship was found C/N ratio and cumulative TN inputs in NP treatment. After 7 years, fertilizer alone was as important as manure for improving activity of urease. Manure treatments improved activities of alkaline phosphatase and β-glucosidase compared with no manure treatments. The overall results show that applying fertilizer alone (NP) was not effective in accelerating the build-up of fertility and adding manure is essential in improving soil fertility and accelerating the build-up of fertility in newly-built terraces in a semi-arid environment.

Application of Response Surface Methodology for Determining Optimal Factors in Maximization of Maize Grain Yield and Total Microbial Count in Long Term Agricultural Experiment, Kenya

The Agriculture sector is the main stay of the Kenyan economic development contributing over 70% of the Gross Domestic Product (GDP). The sector is faced with numerous challenges leading to frequent and recurrent food shortages. Declining maize grain yield is one among the major challenges that call for urgent interventions to address the looming food crisis in the country. Maize play a big role in the Kenyan food security and in most case lack of the same is taken to mean food insecurity. It is due the importance attached to the crop that a Long Term Agricultural Experiments (LTAE) was set up specifically to research on the Maize grain yield. Many paper published on the LTAE in the country are only single factors analysis and lack the application of Response Surface Methodology (RSM) approaches in solving challenges facing the low and declining maize grain yield (y1), total microbe population (y2) a crucial component of Soil Organic Matter (SOM) and their optimization. The focus of this paper therefore is the application of RSM in maize grain yield and total microbial population optimization. Specifically, the paper determined the most significant factors for maize grain yield and total microbial population (bacteria, fungi, actinomycetes, rhizobia), (screening phase of the paper), constructed of an efficient and appropriate experimental design for evaluating the optimal settings of maize yield and total microbial population count and determined univariate optimal settings for maize grain yield and total microbial population. The primary data was summarized from LTAE in National Agricultural Research Laboratories (NARL) in Kabete under the Kenya Agriculture and Livestock Research Organization (KALRO) and secondary data imputed for experimental points falling outside the set field experimental design points. Two treatment factors were identified as the most significant treatment factors (Farm Yard Manure (FYM) and Nitrogen and Phosphorus (NP)) at their low levels and Circumscribed Central Composite Design (CCCD) with two star points as the most efficient design. CCCD passed most optimal criteria of DAET. Univariately, optimal setting for maize grain yield was realized at 3.8x103 kg/ha and that of the total microbial population at 3.6x106 count. The study confirmed that it was possible to optimize the input treatment factor that lead to the optimization of both maize grain yield and maintaining maximal total microbial population count at its optimal levels.

Evaluation of the Most Significant Treatment Factors for Maize Grain Yields and Total Microbial Count in Long Term Agricultural Experiment (LTAE), Kenya

Agriculture and its related economic activities form the main livelihood for Kenya population. The sector faces numerous challenges that have led to food insecurity in the country. Maize production plays a significant role in the country’ economic development contributing significantly to the national overall Gross Domestic Product (GDP). Declining maize grain yield is one of the major challenges that require interventions to avert the looming food crisis. To address the challenge various Long Term Agricultural Experiments (LTAE) and studies on soil fertility maintainance options have been developed. However, such studies have explored only single factors at a time with limited application of robust statistical application. Statistical procedures could offer best set of few treatment factors that explain the maize grain yields in LTAEs in Kenya and beyond. The focus of this paper was the application of robust statistical methods in obtaining set of minimum treatment factors that could be used in the determination maize grain yield in LTAE. Specifically, the paper sought to describe the trend in maize grain yield over the experimental period, characterize the input factors for maize grain yield and to determine the most significant treatment factors for maize grain yield and total microbial population count (bacteria, fungi, actinomycetes, rhizobia). The primary data was summarized from LTAE in National Agricultural Research Laboratories (NARL), Kabete under the Kenya Agriculture and Livestock Research Organization (KALRO) and secondary data imputed for experimental points falling outside the set field experimental design points. Two treatment factors were isolated (Farm Yard Manure (FYM) and Nitrogen and Phosphorus (NP)) at their low factor levels as the most significant treatment factor in maximizing the maize grain yield and total microbial population count. It was possible to select a minimum set of treatment factors in LTAE that are critical in predicting the maize grain yield.

Impacts of fertilization practices on pH and the pH buffering capacity of calcareous soil

ABSTRACTModern intensive agricultural practices, particularly the use of nitrogen fertilizers, have accelerated soil acidification on a global scale. The soil pH buffering capacity (pHBC) is often used to quantify the soil acidification rate. Calcareous soils have relatively higher pH and pHBC, reflecting the presence of carbonate minerals; however, the impact of long-term fertilization treatment on pH and pHBC is poorly understood for calcareous soils. Here, calcareous soil samples (0–20 cm) were collected from fields receiving six different fertilization treatments for 22 years: control (CK, unfertilized but planted); nitrogen (N); nitrogen and phosphorus (NP); nitrogen, phosphorus and potassium (NPK); combined manure and NPK (NPKM); and combined corn-stover and NPK (NPKS). Both pH and pHBC significantly decreased for all treatments relative to CK. NPKS treatment had the lowest soil pH. Compared with CK, the soil pHBC decreased 5.7 to 17.3% under different treatments. The calcium carbonate (CaCO3) content was significantly reduced by fertilization treatments, with a maximum decrease under the NPKS treatment. Structural equation model (SEM) analysis revealed that calcium carbonate and soil organic matter (SOM) made important contributions to effective cation exchangeable capacity (ECEC). Soil pHBC was directly controlled by ECEC, while CaCO3 and SOM indirectly contributed to the pHBC through ECEC. These results indicated that NPKS treatment induces more severe soil acidification, reflecting the higher H+ input and lower pHBC under this treatment.

Response of organic nitrogen in Black Soil to long-term different fertilization and tillage practices in Northeast China

Yan L., Li H., Zhang J., Zhang Z., Zhu P., Gao Q., Lu W. (2016): Response of organic nitrogen in Black Soil to longterm different fertilization and tillage practices in Northeast China. Soil & Water Res., 11: 124–130. A long-term (18 years) effect of different fertilization and tillage management practices– fallowing treatment (no fertilizer, no cultivation); CK (no fertilizer, cultivation); N (nitrogen fertilizer); NP (nitrogen and phosphorus fertilizer); NK (nitrogen and potassium fertilizer); PK (phosphorus and potassium fertilizer); NPK (nitrogen, phosphorus, and potassium fertilizer); M1NPK (chemical fertilizer plus manure); 1.5M1NPK (1.5 times M1NPK); NPKS (mineral fertilizer plus straw); Rot (3-year crop rotation of maize-maize-soybean with M1NPK), and M2NPK (2 times manure plus mineral fertilizer) – on the content of total nitrogen and organic forms of nitrogen and the nitrogen content in different particle-size fractions were studied in topsoil (0–20 cm) in Black Soil of NE China by using the methods of Bremner. The results showed that the combined application of organic and mineral fertilizers could significantly increase the contents and proportions of total nitrogen and organic nitrogen forms in soil. Comparing to CK treatment, the content of total nitrogen and hydrolyzable nitrogen increased in the fallow and organic materials treatments. Compared with M1NPK treatment, rotation was more beneficial to increasing organic nitrogen content, especially remarkably increasing amino acid nitrogen. The nitrogen response of sand, silt, and clay was most sensitive on manure; the effects of fallow and manure treatments on sand were notable, the nitrogen content in sand with NPKS increased by 40.86% compared with CK treatment. Our results imply that fallow/rotation managements, and manure/straw application can improve soil fertility.

Effects of Organic and Inorganic Fertilizers on Soil and Plant Nutrients and Yields of Pearl Millet and Wheat under Semi-arid Inceptisols in India

A study was conducted to assess fertilizer effect on pearl millet–wheat yield and plant-soil nutrients with the following treatments: T1, control; T2, 100% nitrogen (N); T3, 100% nitrogen and phosphorus (NP); T4, 100% nitrogen, phosphorus and potassium (NPK); T5, 100% NPK + zinc sulfate (ZnSO4) at 25 kg ha−1; T6, 100% NPK + farmyard manure (FYM) at 10 t ha−1; T7, 100% NPK+ verimcompost (VC) at 2.5 tha−1; T8, 100% NPK + sulfur (S) at 25 kg ha−1; T9, FYM at 10 t ha−1; T10, VC at 2.5 t ha−1; T11, 100% NPK + FYM at 10 t ha−1 + 25 kg S ha−1 + ZnSO4 at 25 kg ha−1; and T12, 150% NPK treatments. Treatments differed significantly in influencing soil-plant nutrients and grain and straw yields of both crops. Grain yield had significant correlation with soil-plant N, P, K, S, and zinc (Zn) nutrients. The study indicated superiority of T11 for attaining maximum pearl millet grain yield (2885 kg ha−1) and straw yield (7185 kg ha−1); amounts of N (48.9 kg ha−1), P (8.8 kg ha−1), K (26.3 kg ha−1), S (20.6 kg ha−1), and Zn (0.09 kg ha−1) taken up; and amounts of soil N (187.7 kg ha−1), P (13.7 kg ha−1), K (242.5 kg ha−1), S (10.1 kg ha−1), and Zn (0.70 kg ha−1). It was superior for wheat with grain yield (5215 kg ha−1) and straw yield (7220 kg ha−1); amounts of N (120.7 kg ha−1), P (13.8 kg ha−1), K (30 kg ha−1), S (14.6 kg ha−1), and Zn (0.18 kg ha−1) taken up; and maintaining soil N (185.7 kg ha−1), P (14.5 kg ha−1), K (250.5 kg ha−1), S (10.6 kg ha−1), and Zn (0.73 kg ha−1). Based on the study, 100% NPK + FYM at 10 tha−1 + Zn at 25 kg ha−1 + S at 25 kg ha−1 could be recommended for attaining maximum returns of pearl millet–wheat under semi-arid Inceptisols.

Changes in Olsen Phosphorus Concentration and Its Response to Phosphorus Balance in Black Soils under Different Long-Term Fertilization Patterns.

The Olsen phosphorus (P) concentration of a soil is a key index that can be used to evaluate the P supply capacity of the soil and to estimate the optimal P fertilization rate. A study of the relationship between the soil Olsen P concentration and the P balance (P input minus P output) and their variations among different fertilization patterns will help to provide useful information for proper management of P fertilization. In this paper, the two investigated long-term experiments were established on black soils in the northeast region of China. Six fertilization treatments were selected: (1) unfertilized (CK); (2) nitrogen only (N); (3) nitrogen and potassium (NK); (4) nitrogen and phosphorus (NP); (5) nitrogen, phosphorus, and potassium (NPK); and (6) nitrogen, phosphorus, potassium and manure (NPKM). The results showed that the average Olsen P concentrations in the black soils at Gongzhuling and Harbin (16- and 31-year study periods, respectively), decreased by 0.49 and 0.56 mg kg-1 a-1, respectively, without P addition and increased by 3.17 and 1.78 mg kg-1 a-1, respectively, with P fertilization. The changes in soil Olsen P concentrations were significantly (P<0.05) correlated with the P balances at both sites except for the NP and NPK treatments at Gongzhuling. Under an average deficit of 100 kg ha-1 P, the soil Olsen P concentration at both sites decreased by 1.36~3.35 mg kg-1 in the treatments without P addition and increased by 4.80~16.04 mg kg-1 in the treatments with 100 kg ha-1 of P accumulation. In addition, the changes in Olsen P concentrations in the soil with 100 kg ha-1of P balance were significantly correlated with the P activation coefficient (PAC, percentage of Olsen P to total P, r=0.99, P<0.01) and soil organic matter content (r=0.91, P<0.01). A low pH was related to large changes of Olsen P by 1 kg ha-1 of P balance. These results indicated that soil organic matter and pH have important effects on the change in soil Olsen P by 1 kg ha-1 of P balance.

Carbon and nitrogen allocations in corn grown in Central and Northeast China: different responses to fertilization treatments

In order to reveal the impact of various fertilization strategies on carbon (C) and nitrogen (N) accumulation and allocation in corn (Zea mays L.), corn was grown in the fields where continuous fertilization management had been lasted about 18 years at two sites located in Central and Northeast China (Zhengzhou and Gongzhuling), and biomass C and N contents in different organs of corn at harvest were analyzed. The fertilization treatments included non-fertilizer (control), chemical fertilizers of either nitrogen (N), or nitrogen and phosphorus (NP), or phosphorus and potassium (PK), or nitrogen, phosphorus and potassium (NPK), NPK plus manure (NPKM), 150% of the NPKM (1.5NPKM), and NPK plus straw (NPKS). The results showed that accumulated C in aboveground ranged from 2 550–5 630 kg ha−1 in the control treatment to 9 300–9 610 kg ha−1 in the NPKM treatment, of which 57–67% and 43–50% were allocated in the non-grain organs, respectively. Accumulated N in aboveground ranged from 44.8–55.2 kg ha–1 in the control treatment to 211–222 kg ha−1 in the NPKM treatment, of which 35–48% and 33–44% were allocated in the non-grain parts, respectively. C allocated to stem and leaf for the PK treatment was 65 and 49% higher than that for the NPKM treatment at the both sites, respectively, while N allocated to the organs for the PK treatment was 18 and 6% higher than that for the NPKM treatment, respectively. This study demonstrated that responses of C and N allocation in corn to fertilization strategies were different, and C allocation was more sensitive to fertilization treatments than N allocation in the area.

Leaf N:P stoichiometry across plant functional groups in the karst region of southwestern China

Soil nitrogen and phosphorus are the most important factors influenced the leaf N:P ratios across plant functional groups in the karst region of southwestern China, and plant diversity are also important to certain groups. Leaf nitrogen:phosphorus (N:P) stoichiometry, which affects plant growth, nutrient cycling, and primary production in terrestrial ecosystems, is influenced by soil N and P, among other factors. However, it remains unclear how biotic and abiotic factors influence leaf N and P stoichiometry of different plant functional groups in the karst ecosystem of southwest China. We measured the leaf N and P of different plant functional groups, as well as soil total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), and available phosphorus at 0–15 cm depth under each plant functional group. The linear mixed models (LMMs) results showed that the leaf N, P, and N:P ratios were characterized by functional groups. Higher leaf P, but lower leaf N and N:P ratios, were found in grasses than in shrubs and trees. The leaf N was higher in trees than that in shrubs. Additionally, the leaf N and N:P ratios were higher in legumes than that in nonlegumes. The LMMs results showed that the Shannon–Wiener diversity indexes (H′), soil TN, and TP significantly impacted the leaf N:P ratios (with grass–shrub–tree group as random factor), and Simpson diversity indexes (DS), soil TN, AN, and TP significantly impacted the leaf N:P ratios (with nonlegume-legume group as random factor). It suggested that soil TN and TP had major effects on the leaf N:P ratios of all the studied functional groups in the karst region, while DS and H′ diversity indexes, and soil AN significantly impacted the leaf N:P ratios in several specific groups.

Seasonal distribution of phytoplankton assemblages and nutrient-enriched bioassays as indicators of nutrient limitation of phytoplankton growth in Gwangyang Bay, Korea

To assess the effect of nutrient limitation on phytoplankton growth, and its influence on seasonal variation in phytoplankton community structure, we investigated abiotic and biotic factors in surface and bottom waters at 20 stations in inner and offshore areas of Gwangyang Bay, Korea. Algal bioassay experiments were also conducted using surface water, to assess the effects of nutrient addition on the phytoplankton assemblages. The fate of major nutrients in the bay was strongly dependent on the discharge of freshwater from the Seomjin River. River flow during the rainy season provides a high nitrogen (N) influx, pushing the system toward stoichiometric phosphorus (P) limitation. However, at some times during the rainy season there was insufficient N to maintain phytoplankton growth because it was rapidly consumed through nutrient uptake by phytoplankton under stratified environmental conditions. Diatoms made a relatively large contribution to total phytoplankton biomass. The dominant diatoms, particularly in winter and summer, were Skeletonema marinoi-dohrnii complex and Skeletonema tropicum, respectively, while Eucampia zodiacus and the cryptophyte Cryptomonas spp. dominated in spring and autumn, respectively, comprising more than 75% of the community at most stations. In the bioassay experiments the phytoplankton biomass increased by 30–600% in the +N (added nitrogen) and +NP (added nitrogen and phosphorus) treatments relative to the control and the +P (added phosphorus) treatments, indicating that phytoplankton growth can respond rapidly to pulsed nitrate loading events. Based on the algal bioassay and the field survey, the abrupt input of high nutrient levels following rainfall stimulated the growth of diatom assemblages including the Skeletonema genus. Our results demonstrate that the growth of centric diatoms was enhanced by inputs of N and Si, and that the concentrations of these nutrients may be among the most important factors controlling phytoplankton growth in Gwangyang Bay.

Impacts of Agricultural Management Practices on the Risk of Nitrogen and Phosphorus Losses at Catchment Scales by Using GIS and Index Models

The unreasonable agricultural management measure is the main cause of the risk of nitrogen and phosphorus losses. The objective of this paper was to evaluate the impacts of agricultural management practices on the risk of nitrogen and phosphorus losses at catchment scales based on GIS and integrated index models. The results showed that 93.1% of the catchment was no risk and low risk area, while 6.9% for medium and high risk of nitrogen and phosphorus losses. Spatial analysis of risk index indicated that different agricultural management practices lead to number and proportion of grids are different. At very high risk area, about 599 of grid number is only for the actual management practice, accounting for 0.22% of the total, while at very low risk area, 165884.00 and 60.51% for river buffer zone respectively. Control effect of different agricultural management practices for risk of nitrogen and phosphorus losses is better, which very low and low risk areas of based fertilizer applied deeply and buffer zone construction accounted for 98% and 95.6%, and the control effect sorted as follows: base fertilizer applied deeply&gt; construction of river buffer zone&gt; reduced nitrogen application&gt; reduced phosphorus application.