Unbalanced nutrient ratios in pelleted compound recycling fertilizers

The aim of this study was to contribute to the development of pelleted compound recycling fertilizers with favourable handling and spreading characteristics and balanced nutrient ratios by combining nitrogen (N)‐ and phosphorus (P)‐rich waste resources (meat bone meal, fish sludge or food waste) with potassium (K)‐rich bottom wood ash. Pelleted compound recycling fertilizers with good durability and low dusting tendency were produced by roll‐pelleting preheated waste resources at a suitable moisture content. However, the nutrient ratios in the final products were insufficiently balanced, with too low N concentrations relative to P and K to meet crop demands. In a bioassay using barley (Hordeum vulgare ) and a nutrient‐deficient sand/peat mixture, the relative agronomic effectiveness (RAE ) of pelleted compound recycling fertilizers and reference recycling fertilizers was 22–42% of that of mineral compound fertilizer. Growth limitation was due to reduced N availability (mineral fertilizer equivalent ‐ MFE = 35–57%) or reduced P availability (MFE  = 20–115%), with the greatest P fertilizer value obtained for digestate based on dairy manure and fish sludge. Availability of K in bottom wood ash was masked by the experimental soil.     

Potential methods for estimating nitrogen fertilizer value of organic residues

New organic fertilizers based on waste products are continually being introduced in agriculture. Their nitrogen (N) fertilizer value of their total N and mineral N content varies widely, creating a demand for standardized laboratory methods. This study evaluated some potential methods for estimating the N fertilizer value of different kinds of organic fertilizers. The methods were evaluated against the N fertilizer value obtained from a ryegrass pot experiment. Fifteen fertilizers were tested, including different kinds of manure, powders from meat, bone, blood and feathers, rapeseed cake, lucerne pellets, sewage sludge, biogas residue, vinasse and mussel compost. Mineral fertilizer equivalents (MFE) were calculated as the fraction of total N (MFE) or organic N (MFE_org) out of total N that has the same availability to plants as inorganic N. Mineral N content (% of total N added with organic residue) after 4 weeks of incubation of soil was correlated to MFE (r² = 0.78), but was on average 17% lower. Warm water‐extractable N, amino acid N and crude fibre analysis all proved to be unsatisfactory as methods for estimating MFE or MFE_org. However, the carbon/nitrogen ratio accurately reflected short‐term plant‐available N through a negative linear relationship (r² = 0.83) and would thus be a very useful method for estimating MFE, with MFE decreasing by 5% per unit increase in C/N ratio. The results also indicated that the analysis of near infrared reflectance (NIR) spectra can be an even quicker and cheaper method to estimate MFE of organic residues, but this issue requires further research.     

Grain yield and crop N offtake in response to residual fertilizer N in long‐term field experiments

Organic inputs [e.g. animal manure (AM) and plant residues] contribute directly to the soil organic N pool, whereas mineral N fertilizer contributes indirectly by increasing the return of the crop residues and by microbial immobilization. To evaluate the residual effect of N treatments established in four long‐term (>35 yr) field experiments, we measured the response of barley (grain yield and N offtake at crop maturity) to six rates (0, 30, 60, 90, 120 and 150 kg N/ha) of mineral fertilizer N (N_new) applied in subplots replacing the customary long‐term plot treatments of fertilizer inputs (N_prev). Rates of N_prev above 50–100 kg N/ha had no consistent effect on the soil N content, but this was up to 20% greater than that in unfertilized treatments. Long‐term unfertilized plots should not be used as control to test the residual value of N in modern agriculture with large production potentials. Although the effect of mineral N_prev on grain yield and N offtake could be substituted by N_new within a range of previous inputs, the value of N_prev was not eliminated irrespective of N_new rate. Provided a sufficient supply of plant nutrients other than N, the use‐efficiency of N_new did not change significantly with previous mineral N fertilizer rate. The residual effect of mineral N fertilizer was negligible compared with the residual effect of N from AM and catch crop residues.     

Changes in soil phosphorus pools of grasslands following 17 yrs of balanced application of manure and fertilizer

Limiting the use of phosphorous (P) in intensive agriculture is necessary to decrease losses to surface waters. Balanced fertilizer application (P supply equals P offtake by the crop) is a first step to limit the use of P. However, it is questioned whether this balance approach is sufficient to maintain soil fertility. A long‐term field experiment (17 yr), on grazed grassland, has been conducted on sandy soil, marine clay soil and peat soil to obtain insight into the effects of balanced P fertilizer application on soil test P values and to explain the results by changes in P pools in the soil. The balance approach led to a gradual decline in plant available P, measured as P‐AL, in the topsoil (<0.10 m deep). This decline was accompanied by a decline in oxalate extractable P, dithionite extractable P and inorganic P (0.5 m H₂SO₄). The decline in these mineral P pools in the topsoil was (partly) compensated by an increase in the amount of organic P. There was evidence for the accumulation of P in an occluded form, especially at one of sites which received P as Gafsa rock phosphate [Ca₃(PO₄)₂].     

Phosphorus availability of sewage sludge‐based fertilizers determined by the diffusive gradients in thin films (DGT) technique

The plant‐availability of phosphorus (P) in fertilizers and soil can strongly influence the yield of agricultural crops. However, there are no methods to efficiently and satisfactorily analyze the plant‐availability of P in sewage sludge‐based P fertilizers except by undertaking time‐consuming and complex pot or field experiments. We employed the diffusive gradients in thin films (DGT) technique to quantify the plant P availability of various types of P fertilizers with a novel focus on sewage sludge‐based P fertilizers. Mixtures of fertilizer and soil were incubated for 3 weeks at 60% water holding capacity. DGT devices were deployed at the beginning of the incubation and again after 1, 2, and 3 weeks. Two weeks of incubation were sufficient for the formation of plant‐available P in the fertilizer/soil mixtures. In a pot experiment, the DGT technique predicted maize (Zea mays L.) biomass yield and P uptake significantly more accurately than standard chemical extraction tests for P fertilizers (e.g ., water, citric acid, and neutral ammonium citrate). Therefore, the DGT technique can be recommended as a reliable and robust method to screen the performance of different types of sewage sludge‐based P fertilizers for maize cultivation minimizing the need for time‐consuming and costly pot or field experiments.     

Effects of organic matter addition on phosphorus availability to flooded and nonflooded rice in a P‐deficient tropical soil: a greenhouse study

Addition of organic matter (OM) to flooded soils stimulates reductive dissolution of Fe(III) minerals, thereby mobilizing associated phosphate (P). Hence, OM management has the potential to overcome P deficiency. This study assessed if OM applications increases soil or mineral fertilizer P availability to rice under anaerobic (flooded) condition and if that effect is different relative to that in aerobic (nonflooded) soils. Rice was grown in P‐deficient soil treated with combinations of addition of mineral P (0, 26 mg P/kg), OM (0, ~9 g OM/kg as rice straw + cattle manure) and water treatments (flooded vs nonflooded) in a factorial pot experiment. The OM was either freshly added just before flooding or incubated moist in soil for 6 months prior to flooding; blanket N and K was added in all treatments. Fresh addition of OM promoted reductive dissolution of Fe(III) minerals in flooded soils, whereas no such effect was found when OM had been incubated for 6 months before flooding. Yield and shoot P uptake largely increased with mineral P addition in all soils, whereas OM addition increased yield and P uptake only in flooded soils following fresh OM addition. The combination of mineral P and OM gave the largest yield and P uptake. Addition of OM just prior to soil flooding increased P uptake but was insufficient to overcome P deficiency in the absence of mineral P. Larger applications of OM are unlikely to be more successful in flooded soils due to side effects, such as Fe toxicity.     

Short‐term and residual availability of nitrogen after long‐term application of organic fertilizers on arable land

Knowledge on short‐term and long‐term availability of nitrogen (N) after application of organic fertilizers (e.g., farmyard manure, slurry, sewage sludge, composts) provides an important basis to optimize fertilizer use with benefits for the farmer and the environment. Nitrogen from many organic fertilizers often shows little effect on crop growth in the year of application, because of the slow‐release characteristics of organically bound N. Furthermore, N immobilization after application can occur, leading to an enrichment of the soil N pool. However, this process finally increases the long‐term efficiency of organic fertilizers. Short‐term N release from organic fertilizers, measured as mineral‐fertilizer equivalents (MFE), varies greatly from 0% (some composts) to nearly 100% (urine). The most important indicators to be used for predicting the short‐term availability of N are total and NH ‐N contents, C : N ratio (especially of the decomposable organic fraction), and stability of the organic substances. Processing steps before organic fertilizers are applied in the field particularly can influence N availability. Composting reduces mineral‐N content and increases the stability of the organic matter, whereas anaerobic fermentation increases NH ‐N content as well as the stability of organic matter, but decreases the C : N ratio remarkably, resulting in a product with a high content of directly available N. Nevertheless, long‐term effects of organic fertilizers rather slowly releasing N have to be considered to enable optimization of fertilizer use. After long‐term application of organic fertilizers, the overall N‐use efficiency is adequate to a MFE in the range of 40%–70%.     

Determination of organic materials quality based on nutrient recovery,mineral fertilizer equivalency and maize (Zea mays L.) allometry

Crop production in Sub-Saharan Africa is primarily limited by soil fertility decline. In view of this, the fertilizer value of locally available organic materials (OMs) was assessed for their nutrient release to crop growth. Crop residues and farmyard manure (FYM) were evaluated along with mineral fertilizers to grow a test crop maize variety – Gibe 2. The maize allometric parameters, nutrient ratios (NRs), nutrient recovery (NRy) and mineral fertilizer equivalency (MFE) were used to assess the mineral fertilizer value (MFV) of OMs. MFE of OMs was estimated as the available mineral N and P out of the fraction of total nitrogen and phosphorus applied relative to mineral fertilizers supply. The results revealed that maize allometry, NRy and MFE were significantly influenced by fertilizer sources. OM amendment resulted in poor maize allometry and low NRy. Interestingly, MFE of OM amended ranged from ?201% with chickpea (CHP) residue to 63% with FYM. The results demonstrate that CHP has the poorest quality, while FYM is a good-quality OM as a fertilizer source.     

Nitrogen availability of various biogas residues applied to ryegrass

Biogas plants in Germany are producing an increasing amount of biogas residues to be recycled via agricultural crop production. To test whether the wide range of various substrates used in the anaerobic digestion can affect the chemical composition and nutrient availability, seven biogas residues derived from different substrates were investigated with respect to their N supply to ryegrass. Both the short‐term and the long‐term N availability were studied in a 309‐d pot experiment lasting for five successive growth cycles each starting with a fertilizer application. The organic fertilizers were applied based on an equal amount of ammonium‐N (300 mg N per pot) and compared to mineral N from ammonium nitrate of equal dosage. Biogas residues varied greatly in their chemical composition (ammonium‐N 0.20% to 0.51%, N_total 0.36% to 0.75%, and C_org 1.85% to 4.75% in fresh matter). After the first growth cycle, the N availability of the biogas residues applied based on ammonium‐N was at least equal to that from ammonium nitrate. Differences in N offtake after one fertilizer application were negatively correlated to the C_org : N_org ratio of the organic fertilizers. After five successive fertilizer applications, the N utilization of most of the organic fertilizers was increased compared to that of the mineral fertilizer. It is concluded that biogas residues provide plant‐available N at least corresponding to their ammonium content and that the accumulation of organic N in soil through repeated application of biogas residues contributes to N release.     

Anaerobic co‐digestion of perennials: Methane potential and digestate nitrogen fertilizer value

Co‐digestion of crop biomass improves the traditional manure‐based biogas yield due to an increased content of easily degradable carbon compounds. In this study, the methane potential of three perennials (grass, legumes, and grass+legume) was determined using various amounts together with animal manure. The nitrogen (N) mineralization dynamics in soil and the N‐fertilizer value of the derived digestates were subsequently tested in both a soil incubation study and a pot experiment with spring barley. Digestion of all tested perennials together with a manure‐based inoculum increased the cumulative methane yield four to five times compared to digestion of the inoculum alone, with the highest increases observed with pure grass. However, the methane potential decreased along with increasing grass biomass concentration. In the plant pot experiment, all tested digestates increased barley shoot biomass by 40–170%, to an extent statistically comparable to mineral N fertilizer. However, the application of the digestate originating from fermentation with pure grass resulted in lower plant growth and a more fluctuating soil mineral N content throughout the incubation study compared to the other digestates. Considering the high dry matter and methane yield ha^?1, the possibility to substitute mineral N fertilizer inputs by leguminous biological N₂ fixation capacity, and the digestate fertilizer value, the integration of grass–legume mixtures or sole legumes into anaerobic digestion systems as co‐substrate for manure seems to be promising. This could furthermore contribute to the diversification of cropping systems for bioenergy production.     

Fertilizer value of nitrogen in hen and broiler manure after application to spring barley using different application timing

The nitrogen (N) fertilizer effect of layer hen and broiler manure applied at different times on spring barley yield was studied in seven Swedish field experiments during 2005–2008. Two experiments had parallel field incubations to study N release after fertilizer application. The effect of total N in manure on N offtake was 30–40% that of mineral N, except in a dry year, when the effect was very low. Although the relative proportions of ammonium N, uric acid N and other N differed between the hen and broiler manure, the effect of total N was similar for both. In field incubations, mineral N decreased from 75 to 60% of total N applied in hen manure, whereas it increased from 20 to 50% in broiler manure, because of net immobilization and release, respectively. The limited fertilizer nitrogen replacement value, corresponding to only 30–40% of total N, could be as a result of ammonia volatilization after rather shallow incorporation with harrow. Net N release from broiler manure lasted for 6–8 weeks after application, after which it generally ceased. In some cases, manure application in early spring gave better yield effects than application at sowing, probably because of better synchronization of the N release with crop N requirements. The residual N effect on the N offtake in crop in the year after manure application was on average 3% of the total N applied, equivalent to a fertilizer replacement value of about 6%.     

Long‐term effects of animal manure and mineral fertilizers on phosphorus availability and silage maize growth

A better appraisal of the plant availability of soil phosphorus (P) added with animal manure is crucial to alleviate environmental impacts from over‐application of P. This study compares the availability of P to maize in the Askov long‐term experiments using unmanured plots and plots receiving corresponding rates of nitrogen (N), P and potassium (K) in mineral fertilizers or manure. Total‐P and water extractable P (Pw) in soil, and plant height, dry weight, P concentration and P uptake were determined in early August. Final yields were determined in late October. Soil Pw was similar for plots receiving corresponding rates of P in mineral fertilizer or manure form. With a strong relationship between Pw, and maize growth and final yields, Pw was a reliable indicator of P availability to maize. Plant dry weight, P concentration and P uptake in early August were 23%, 8% and 31% higher, respectively, for maize grown on soil receiving manure compared with mineral fertilizer, while final maize yield in late October was 13% higher. Plant height and dry weight determined in early August suggested that maize development at this growth stage defined final maize yield. We conclude that the availability of P was similar after long‐term application of corresponding rates of P in animal manure and mineral fertilizers, and that animal manure improves the growth of maize compared to mineral fertilizers. This is ascribed to micronutrients and residual N effects from previous additions of manure.     

Characterizing phosphorus availability in waste products by chemical extractions and plant uptake

Background: The fertilizer value of phosphorus (P) in waste products relies heavily on its availability to the subsequent crop. Aim: We studied the link between extractable P in waste products and apparent P recovery (APR, i.e., difference in plant P uptake between P amended and un‐amended soils divided by the amount of P added) using spring barley grown on three sandy soils. Methods: The products included sewage sludge, biomass ash, struvite, compost, meat and bone meal, biochar from sewage sludge, and industrial sludge. Soft rock phosphate and triple‐superphosphate (TSP) were included for comparison. Availability of P was characterized by extraction with water and solutions of sodium bicarbonate, citric acid, oxalic acid, hydrochloric acid, ammonium acetate, ammonium fluoride and anion exchange resin membranes. TSP was used to establish mineral‐fertilizer‐equivalents (MFE). Water and bicarbonate extractions were also applied to products incubated with soil before extraction. Results: The APR ranged 26 to 31% for TSP and 0 to 30% for waste products. APR correlated most strongly with bicarbonate extractable P. The correlation increased when products were incubated with soil before extraction. Conclusions: We conclude that bicarbonate extraction is a good indicator of potential P availability. However, interactions between waste products and soil properties modify P availability.     

Potential phosphorus leaching from sandy topsoils with different fertilizer histories before and after application of pig slurry

This study investigated the effects of historical long‐term and recent single applications of pig slurry on phosphorus (P) leaching from intact columns of two sandy topsoils (Mellby and Böslid). The soils had similar physical properties, but different soil P status (ammonium lactate‐extractable P; P‐AL) and degree of P saturation (DPS‐AL). Mellby had P‐AL of 220–280 mg/kg and DPS‐AL of 32–42%, which was higher than for Böslid (P‐AL 140 mg/kg and DPS 21%). The study investigated the effects since 1983 of four treatments with different fertilizer histories, in summary high (HighSlurryMellby) and low (LowSlurryMellby) rates of pig slurry and mineral P (MinMellby) applications at Mellby and mineral P application at Böslid (MinBöslid). The columns were irrigated in the laboratory five times before and five times after a single application of pig slurry (22 kg P/ha). Concentrations of dissolved reactive P (DRP), dissolved organic P and total‐P (TP) in leachate and loads were significantly higher (P < 0.005) from the treatments at Mellby than those at Böslid. TP concentrations followed the trend: HighSlurryMellby (0.57–0.59 mg/L) > MinMellby (0.41–0.49 mg/L) > LowSlurryMellby (0.31–0.36 mg/L) > MinBöslid (0.14–0.15 mg/L), both before and after the single slurry application. DRP concentrations in leachate were positively correlated with DPS‐AL values in the topsoil (R² = 0.95, P < 0.0001) and increased with greater DPS‐AL values after the single slurry application (R² = 0.79, P < 0.0001). Thus, DPS‐AL can be an appropriate indicator of P leaching risk from sandy soils. Moreover, the build‐up of soil P because of long‐term repeated manure applications seems to be more important for potential P losses than a single manure application.     

Enhancing phosphorus availability,soil organic carbon,maize productivity and farm profitability through biochar and organic–inorganic fertilizers in an irrigated maize agroecosystem under semi‐arid climate

Biochar amendments offer promising potential to improve soil fertility, soil organic carbon (SOC) and crop yields; however, a limited research has explored these benefits of biochar in the arid and semi‐arid regions. This two‐year field study investigated the effects of Acacia tree biomass‐derived biochar, applied at 0 and 10 t ha^?1 rates with farmyard manure (FYM) or poultry manure (PM) and mineral phosphorus (P) fertilizer combinations (100 kg P ha^‐1), on maize (Zea mays L.) productivity, P use efficiency (PUE) and farm profitability. The application of biochar with organic–inorganic P fertilizers significantly increased soil P and SOC contents than the sole organic or inorganic P fertilizers. Addition of biochar and PM as 100% P source resulted in the highest soil P (104% increase over control) and SOC contents (203% higher than control). However, maize productivity and PUE were significantly higher under balanced P fertilizer (50% organic + 50% mineral fertilizer) with biochar and the increase was 110%, 94% and 170% than 100%‐FYM, 100%‐PM and 100% mineral fertilizer, respectively. Maize productivity and yield correlated significantly positively with soil P and SOC contents These positive effects were possibly due to the ability of biochar to improve soil properties, P availability from organic–inorganic fertilizers and SOC which resulted in higher PUE and maize productivity. Despite the significant positive relationship of PUE with net economic returns, biochar incorporation with PM and mineral fertilizer combination was economically profitable, whereas FYM along biochar was not profitable due to short duration of the field experiments.     

Long‐term fertilization impacts on corn yields and soil organic matter on a clay‐loam soil in Northeast China

A long‐term fertilization experiment with monoculture corn (Zea mays L.) was established in 1980 on a clay‐loam soil (Black Soil in Chinese Soil Classification and Typic Halpudoll in USDA Soil Taxonomy) at Gongzhuling, Jilin Province, China. The experiment aimed to study the sustainability of grain‐corn production on this soil type with eight different nitrogen (N)‐, phosphorus (P)‐, and potassium (K)–mineral fertilizer combinations and three levels (0, 30, and 60 Mg ha^–1 y^–1) of farmyard manure (FYM). On average, FYM additions produced higher grain yields (7.78 and 8.03 Mg ha^–1) compared to the FYM0 (no farmyard application) treatments (5.67 Mg ha^–1). The application of N fertilizer (solely or in various combinations with P and K) in the FYM0 treatment resulted in substantial grain‐yield increases compared to the FYM0 control treatment (3.56 Mg ha^–1). However, the use of NP or NK did not yield in any significant additional effect on the corn yield compared to the use of N alone. The treatments involving P, K, and PK fertilizers resulted in an average 24% increase in yield over the FYM0 control. Over all FYM treatments, the effect of fertilization on corn yield was NPK > NP = NK = N > PK = P > K = control. Farmyard‐manure additions for 25 y increased soil organic‐matter (SOM) content by 3.8 g kg^–1 (13.6%) in the FYM1 treatments and by 7.8 g kg^–1 (27.8%) in the FYM2 treatments, compared to a 3.2 g kg^–1 decrease (11.4%) in the FYM0 treatments. Overall, the results suggest that mineral fertilizers can maintain high yields, but a combination of mineral fertilizers plus farmyard manure are needed to enhance soil organic‐matter levels in this soil type.     

Phosphorus balances for arable soils in Southern England 1986–1999

The behaviour of P in a range of English arable soils was examined by plotting the change in resin P in the topsoil (ΔPres) at the end of a 3‐ to 5‐year period, against the P balance over the same period (fertilizer P applied minus offtake in crops, estimated from farmers’ reported yields and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops are valid averages, 20–60% of ΔPres was explained by the balance. Applying excess P fertilizer increased Pres, and reducing P fertilizer use decreased it; typically 3–4 kg P ha^?1 was required for each mg L^?1ΔPres (6–8 kg ha^?1 for each mg L^?1 of Olsen P). About half the P balance seems to be resin extractable and this differed little between soil groups, except in cases of very low P (index 0) in which the P buffering was stronger, and on very high P soils (index 4/5) when buffering was less. However, on calcareous soils and red soils, when fertilizer was applied in accord with offtake, Pres fell by up to 4 mg L^?1 year^?1 (2 mg L^?1 yr^?1 olsen P) and to prevent this an extra 3–10 kg P ha^?1 year^?1 fertilizer was required. But on most non‐calcareous soils, replacing offtake maintained Pres, with perhaps slight rises on soils of low clay content or greater organic matter content. In soils under arable rotations, the apparent recovery of P from fertilizer was often around 100%, falling to 85% on Chalk soils and 75% on medium–heavy soils on limestone or Lower Chalk. The fate of the ‘missing’ P needs clarification. The case for corrections to current P fertilizer recommendations in the UK on certain soil types is discussed.     

Effect of organic,inorganic, and combined organic and inorganic P fertilization on plant P uptake and soil P pools

Phosphorus (P) is a limited resource, and its efficient use is a main task in sustainable agriculture. In a 6‐year field experiment on a loamy‐sand soil poor in P, the effects of organic, inorganic, and combined organic‐inorganic fertilization on crop yield, P uptake into grain, and soil properties (organic matter [OM] content, pH, water‐extractable P [P_w], double lactate–extractable P [P_dl], oxalate‐extractable P [P_ox], P‐sorption capacity [PSC], and degree of P saturation [DPS]) were investigated for the maritime climate in northeast Germany. Nine treatments were compared: a control treatment without fertilizer application, two organic fertilizers (cattle manure [CM] and biowaste compost [BC]; applied at a rate of 30 t ha^–1 in autumn 1998 and 2001), application of triple‐superphosphate (TSP; applied once a year either in autumn or in spring to evaluate the effects of application date), and combinations of organic and inorganic fertilizations. Several winter and spring crops (oilseed rape, barley, wheat) were cultivated according to good agricultural practice. The 6 year–average yield and P uptake were significantly higher for fertilized plots than for nonfertilized plots. Although the combination of organic × inorganic fertilizers resulted in higher soil P contents, significant yield increases were only found when organic fertilization was combined with TSP in spring. Small effects of P supply on yield in some years indicate that plant‐available soil P (despite of low P_dl values) was sufficient for crop growth. Phosphorus supply affected soil P_dl and P_w more than the parameters measured in the oxalate extract (P_ox, PSC, DPS). In general, periodically applied cattle manure and biowaste compost had the same effect on yield, P uptake, and soil P status as annually applied soluble mineral P.     

Nitrogen mineralization from an organically managed soil and nitrogen accumulation in lettuce

The potential of an organically managed Cambic Arenosol to supply nitrogen (N) from either an applied commercial organic fertilizer (granulated hen manure), a compost produced on‐farm, or four different mixtures of both fertilizers was studied in a laboratory incubation and a pot experiment with lettuce. In the incubation experiment, a significant higher apparent N mineralization occurred after hen‐manure application (53.4% of the organic N applied) compared to compost (4.5%) or mixed‐fertilizer application (8.7% to 16.7%). The apparent N mineralization in a mixed treatment consisting of compost and half rate of hen manure (15.4% of the organic N applied) was significantly higher than that estimated based on the N mineralization for compost and hen‐manure treatments (7.6%), proving that a combined application of both fertilizers enhanced organic‐N mineralization when compared to separate fertilizer supply. In the pot experiment, a higher lettuce fresh‐matter yield was obtained with hen manure (1.9 kg m^–2) than with compost (1.7 kg m^–2) or unfertilized control treatment (1.3 kg m^–2). Combined application of compost with only a half rate of hen manure led to yields (2.0 kg m^–2) equal to those obtained with only hen manure. A good correlation was observed between the N‐mineralization incubation data and the N accumulated by lettuce plants in the pot experiment (r = 0.983). Hence, in the organic production of baby‐leaf lettuce, a mixture of compost and hen manure appears to be a good fertilization alternative, since it allows a reduction by half of the typical amount of commercial fertilizer usually applied (granulated hen manure), cutting fertilization costs, and providing an amount of available N that allows maintaining lettuce yields.     

Long‐term effects of manure and fertilization on soil organic matter and quality parameters of a calcareous soil in NW China

Long‐term applications of inorganic fertilizers and farmyard manure influence organic matter as well as other soil‐quality parameters, but the magnitude of change depends on soil‐climatic conditions. Effects of 22 annual applications (1982–2003) of N, P, and K inorganic fertilizers and farmyard manure (M) on total organic carbon (TOC) and nitrogen (TON), light‐fraction organic C (LFOC) and N (LFON), microbial‐biomass C (MB‐C) and N (MB‐N), total and extractable P, total and exchangeable K, and pH in 0–20 cm soil, nitrate‐N (NO ‐N) in 0–210 cm soil, and N, P, and K balance sheets were determined using a field experiment established in 1982 on a calcareous desert soil (Orthic Anthrosol) at Zhangye, Gansu, China. A rotation of irrigated wheat (Triticum aestivum L.)‐wheat‐corn (Zea mays L.) was used to compare the control, N, NP, NPK, M, MN, MNP, and MNPK treatments. Annual additions of inorganic fertilizers for 22 y increased mass of LFON, MB‐N, total P, extractable P, and exchangeable K in topsoil. This effect was generally enhanced with manure application. Application of manure also increased mass of TOC and MB‐C in soil, and tended to increase LFOC, TON, and MB‐N. There was no noticeable effect of fertilizer and manure application on soil pH. There was a close relationship between some soil‐quality parameters and the amount of C or N in straw that was returned to the soil. The N fertilizer alone resulted in accumulation of large amounts of NO ‐N at the 0–210 cm soil depth, accounting for 6% of the total applied N, but had the lowest recovery of applied N in the crop (34%). Manure alone resulted in higher NO ‐N in the soil profile compared with the control, and the MN treatment had the highest amount of NO ‐N in the soil profile. Application of N in combination with P and/or K fertilizers in both manured and unmanured treatments usually reduced NO ‐N accumulation in the soil profile compared with N alone and increased the N recovery in the crop as much as 66%. The N that was unaccounted for, as a percentage of applied N, was highest in the N‐alone treatment (60%) and lowest in the NPK treatment (30%). In the manure + chemical fertilizer treatments, the unaccounted N ranged from 35% to 43%. Long‐term P fertilization resulted in accumulation of extractable P in the surface soil. Compared to the control, the amount of P in soil‐plant system was surplus in plots that received P as fertilizer and/or manure, and the unaccounted P as percentage of applied P ranged from 64% to 80%. In the no‐manure plots, the unaccounted P decreased from 72% in NP to 64% in NPK treatment from increased P uptake due to balanced fertilization. Compared to the control, the amount of K in soil‐plant system was deficit in NPK treatment, i.e., the recovery of K in soil + plant was more than the amount of applied K. In manure treatments, the recovery of applied K in crop increased from 26% in M to 61% in MNPK treatment, but the unaccounted K decreased from 72% in M to 37% in MNPK treatment. The findings indicated that integrated application of N, P, and K fertilizers and manure is an important strategy to maintain or increase soil organic C and N, improve soil fertility, maintain nutrients balance, and minimize damage to the environment, while also improving crop yield.