Pore characteristics and hydraulic properties of a sandy loam supplied for a century with either animal manure or mineral fertilizers

Abstract Application of organic residues to soil is generally assumed to improve soil tilth. Only few studies have reported the long‐term effects on the more subtle aspects of soil porosity, and no reports have considered the potential effects of organic amendments on the pore system in the subsoil. We sampled undisturbed soil cores (100 cm³ and 6280 cm³) using metal cylinders in differently fertilized plots in the long‐term field experiment at Askov Experimental Station, Denmark. We selected the 0–60 cm soil layer of plots dressed for a century with either mineral fertilizers (labelled NPK) or animal manure (labelled AM) and unfertilized plots (UNF) as a reference. Both fertilization treatments were studied at two levels of nutrient application: ‘normal’ (labelled ‘1’) and 1.5 times ‘normal’ (labelled ‘1½’). Water retention, air permeability and air diffusivity were measured on the small cores, and we used the large cores for measuring near‐saturated and saturated hydraulic conductivity. In the plough layer, the AM and NPK soils displayed identical pore volumes in size fractions that were larger as well as smaller than 30 μm, while the UNF soil had a significantly smaller volume of pores < 30 μm. No clear trends were found in treatment effects on pore organization as calculated from air diffusivity and air permeability measurements. No significant differences in hydraulic conductivity were found in the plough layer. For the subsoil below ploughing depth, significantly larger macropore volumes and near‐saturated hydraulic conductivities were found for soil of plots receiving the larger (‘1½’) amount of nutrients compared with the ‘normally’ dressed soil. This effect was independent of fertilization system (AM or NPK). We attribute the larger volume of macropores to the improved root growth conditions in the soil with the higher nutrient level. We conclude that addition of animal manure at rates realistic in agriculture has only a modest effect on soil pore characteristics of the plough layer soil compared with the use of mineral fertilizers. For the subsoil below ploughing depth, a high level of nutrient application may increase soil macroporosity and near‐saturated hydraulic conductivity, but the origin of nutrients is of no significance.     

Comparative effect of human urine and ammonium nitrate application on maize (Zea mays L.) grown under various salt (NaCl) concentrations

The present study investigates the effect of urine and ammonium nitrate on maize (Zea mays L.) vegetative growth, leaf nutrient concentration, soil electrical conductivity, and exchangeable‐cations contents under various concentrations of NaCl in a soil substrate. The experiment was arranged in a completely randomized block design with eight replications under greenhouse conditions. The experimental soil substrate was made from a 1 : 1 : 1 volume‐ratio mixture of compost, quartz sand, and silty‐loam soil. Salinity was induced by adding 0, 15, and 30 mL of 1 M NaCl solution per kg of substrate to achieve an electrical conductivity (EC) of 1.3 (S0), 4.6 (S1), and 7.6 (S2) dS m^–1. Nitrogen sources were urine and ammonium nitrate applied at 180 and 360 mg N (kg soil substrate)^–1. Basal P and K were added as mono potassium phosphate in amounts equivalent to 39 mg P and 47 mg K (kg substrate)^–1, respectively. In the S0 treatment, a 3‐fold increase in EC was measured after urine application compared to an insignificant change in ammonium nitrate–fertilized substrates 62 d after sowing. Under saline conditions, application of 360 mg N (kg soil)^–1 as urine significantly decreased soil pH and maize shoot dry weight. At the highest salt and N dose (S2, N360) 50% of urine‐fertilized plants died. Regardless of salinity there was no significant difference between the two fertilizers for investigated growth factors when N was supplied at 180 mg (kg soil)^–1. Leaf N and Ca contents were higher after urine application than in ammonium nitrate–fertilized plants. At an application rate of 180 mg N (kg soil)^–1, urine was a suitable fertilizer for maize under saline conditions. Higher urine‐N dosages and/or soil salinity exceeding 7.6 dS m^–1 may have a deleterious effect on maize growth.     

Total organic carbon and its composition in long-term field experiments in the Czech Republic

Abstract

Total organic carbon content and its composition have been evaluated in the topsoil in the selected plots of 13 long-term field experiments conducted in different soil and climate conditions. The altitude of the sites ranged from 225 – 670 m above sea level. Four variants of the organic and mineral fertilization were selected in each experiment: Nil, which did not receive any organic or mineral fertilizers since the beginning of the experiment, mineral fertilized variant NPK, organic fertilized (manured) variant FYM and both organic and mineral fertilized variant FYM + NPK. Total organic carbon (C) content in the topsoil differed as a result of the soil and climate conditions (it ranged from 0.96 – 1.80% C in the Nil variants) and due to the organic and mineral fertilization. The inert and decomposable part of the soil organic C content was calculated and the hot water soluble carbon content was determined. Relationships between the individual SOM fractions have shown a highly significant correlation, except for the decomposable C calculated as a difference to Nil variant.     

Phosphorus bioavailability of sewage sludge‐based recycled fertilizers in an organically managed field experiment

Recycled phosphorus (P) fertilizers from sewage sludge can contribute to the ongoing effort of closing the P cycle. Five recycled P fertilizers (Struvite SSL, Struvite AirPrex®, P‐RoC®, Pyrolysis coal, and Na‐SSA) were tested for their P availability in a two‐year field experiment with maize. The experiment was conducted on an organic certified research station at soil pH 6.5. Other P fertilizer treatments included: phosphate rock (PR), compost, and an unfertilized control. In addition, the rhizobacteria strain Bacillus sp. Proradix (Proradix®) was applied to test its ability to increase P bioavailability. Each year, shoot DM and P offtake of maize was measured and P use efficiency of the tested fertilizers was calculated. No significant differences in shoot DM were found among fertilized treatments and the unfertilized control in both years of experiment. Fertilization with recycled fertilizers increased P offtake by between 0% (Na‐SSA) and 27.5% (Struvite SSL) compared to the unfertilized control. Rhizobacteria application led to an increase in P offtake of maize from 25.9 to 38.7 kg P ha^?1 when combined with PR fertilization in the year of fertilizer application, while no significant effect was found for the recycled fertilizers. Some of the tested recycled fertilizers from urban waste water can be considered as effective fertilizers for their use in organic agriculture.     

Soil physical properties affected by long-term fertilization

According to the literature, soil physical properties are linked mainly with organic constituents that are often considered as the first indicator of soil fertility. But the use of fertilizers and amendments can change soil properties independently of the organic matter content. In a long‐term experiment at Versailles, fertilizers and amendments have been applied each year to uncultivated plots. After 70 years, the plots had the same low organic matter content except those which were treated with manure. However, the physico‐chemical environment had become strongly differentiated. Physical properties, especially soil water relations, were also greatly affected. The use of ammoniacal fertilizers strongly decreased soil pH and cation exchange capacity (CEC_soil). Plots treated in this way were more sensitive to the degradation of their hydraulic properties and became unstable in spite of the preservation of their porosity. Basic amendments (i.e. bases added as CO₃^2–, OH^–, O^2– or silicate anions) increased soil pH, CEC_soil and its saturation by exchangeable calcium. The increase in CEC_soil improved soil structural cohesion and water flow properties. After basic treatment, there is greater structural stability, and water moves faster through the soil. In potassic and sodic plots, K⁺ and Na⁺ affected water movement and increased the soil's sensitivity to degradation. Manure treatment increased water retention and soil stability. The cation exchange capacity, measured at soil pH, can be used as a good indicator of soil stability, in combination with the organic matter content and the kinds of exchangeable cation (especially K⁺ and Na⁺).     

Effect of buckwheat (Fagopyrum esculentum) on soil‐phosphorus availability and organic acids

As a cover crop, buckwheat (Fagopyrum esculentum) may increase soil‐P availability. Buckwheat was grown in low‐P and P‐fertilized field plots, and organic anions were measured in rhizosphere soil. Soil‐P availability was not affected by buckwheat, but the concentration of rhizosphere tartrate^2– was significantly higher (p < 0.005) in low‐P vs. P‐fertilized plots. This suggests that organic‐anion root exudation may have a role in buckwheat‐rhizosphere P dynamics.     

Fate of 15N after combined application of rabbit manure and inorganic N fertilizers in a rice–wheat rotation system

The present study was carried out on pot experiments with rice (Oryza sativa L. cv. Wuyujing 7) and winter wheat (Triticum aestivum L. cv. Yangmai 6) rotation in a sandy and a clayey soil fertilized with ¹⁵N-labeled ammonium sulfate (AS) and ¹⁵N-labeled rabbit feces so as to study the mechanisms of reduction of fertilizer N loss by organic fertilizers. The treatments included: (1) control without any N fertilizer application; (2) fertilization with ¹⁵N-labeled AS (IF); (3) fertilization with labeled rabbit feces (OF); (4) fertilization with either 40% ¹⁵N-labeled rabbit feces and 60% unlabeled AS (IOF1) or (5) 40% unlabeled rabbit feces and 60% ¹⁵N-labeled AS (IOF2). In the rice season, the IOF treatments compared to the IF treatment decreased the percentage of lost fertilizer N from the sandy and clayey soils, whereas it increased the percentage of fertilizer N, present as mineral N and microbial biomass N (MBN). During the second season, when soils were cropped to winter wheat, the IOF treatments in comparison with the IF or OF treatment increased mineral N and MBN contents of soils sampled at tillering, jointing, and heading stages, and such increases were derived from the organic N fertilizer in the sandy soil and from the inorganic N fertilizer in the clayey soil. The increased MBN in the IOF treatments was derived from inorganic fertilizers applied both soils. Therefore, in the IOF treatment, during the rice season, the organic N increased the immobilization of inorganic N in MBN, while the inorganic N fertilizer applied to both soils stimulated the uptake of organic N and the organic N fertilizer increased the uptake of inorganic N by winter wheat; the inorganic N increased the recovery of organic N in the plant-soil system after harvesting the winter wheat.     

小麦-玉米-大豆轮作下黑土农田土壤呼吸与碳平衡

农田生态系统是陆地生态系统的重要组成部分,探讨农田生态系统的土壤呼吸与碳平衡对于科学评价陆地生态系统在全球变化下的源汇效应具有重要意义。基于中国科学院海伦农业生态实验站的长期定位试验,对不同施肥处理下黑土小麦-玉米-大豆轮作体系2005—2007年的作物固碳量与土壤CO2排放通量进行了观测,并对该轮作体系下黑土农田生态系统的碳平衡状况进行了估算。结果表明:在小麦-玉米-大豆轮作体系中,作物固碳量的高低表现为:玉米>大豆>小麦,平均值分别为6 513 kg(C).hm-2、4 025 kg(C).hm-2和3 655kg(C).hm-2。从作物生长季土壤CO2排放总量来看,3种作物以大豆农田生态系统的土壤CO2排放总量最高,平均值达4 062 kg(C).hm-2;其次为玉米,为3 813 kg(C).hm-2;而小麦最低,为2 326 kg(C).hm-2。3种作物轮作下NEP(净生态系统生产力)均为正值,表明黑土农田土壤-作物系统为大气CO2的"汇",不同作物系统的碳汇强度表现为玉米>小麦>大豆,三者的平均值分别为3 215 kg(C).hm-2、1 643 kg(C).hm-2和512 kg(C).hm-2。长期均衡施用氮、磷、钾化肥或氮、磷、钾化肥配施有机肥后,小麦、玉米和大豆农田生态系统的固碳量和土壤CO2排放总量均明显增加,并在氮、磷、钾配施有机肥处理下达到最高。不同的施肥管理措施将改变土壤-植物系统作为大气CO2"汇"的程度,总体表现为化肥均衡施用下NEP值较高,而化肥与有机肥配施下农田生态系统的NEP值较低。     

Soil organic carbon and physical properties as affected by long-term application of FYM and inorganic fertilizers in maize–wheat system

The physical quality of the soil, which creates suitable environment for the availability and uptake of the plant nutrients, is generally ignored. Though the effect of organic manures on soil physical quality has been widely appreciated but that of inorganic fertilizers is studied to a lesser extent. The present study carried out during 2004–2005 aims to characterize the soil physical quality in relation to the long-term (32 years) application of farmyard manure (FYM) and inorganic fertilizers in maize (Zea mays L.) wheat (Triticum aestivum L.) cropping system. The treatments during both maize and wheat crops were (i) farm yard manure at 20 Mg ha⁻¹ (FYM), (ii) nitrogen at 100 kg ha⁻¹ (N₁₀₀), (iii) nitrogen and phosphorus at 100 and 50 kg ha⁻¹ (N₁₀₀P₅₀) and (iv) nitrogen, phosphorus and potassium at 100, 50 and 50 kg ha⁻¹ (N₁₀₀P₅₀K₅₀) in addition to (v) control treatment, i.e. without any fertilizer and/or FYM addition. The treatments were replicated four times in randomized block design in a sandy loam (Typic Ustipsament, non-saline, slightly alkaline). Bulk density, organic carbon content, structural stability of soil aggregates and water holding capacity of 0–60 cm soil layer were measured.The application of FYM to maize increased the organic carbon by 16% whereas N₁₀₀P₅₀K₅₀ increased it by 21%. The increased organic matter with both FYM and N₁₀₀P₅₀K₅₀ increased the total soil porosity and decreased soil bulk density from that in control plots. The mean weight diameter (MWD) was highest in FYM plots of both maize (0.160 mm) and wheat (0.172 mm) closely followed by that in N₁₀₀P₅₀K₅₀ plots. The effect of FYM in increasing the MWD decreased with soil depth. The average water holding capacity (WHC) was higher with FYM and N₁₀₀P₅₀K₅₀ application than that in control plots. The MWD, total porosity, OC content and WHC improved with the application of balanced application of fertilizers. The grain yield and uptake of N, P and K by both maize and wheat were higher with the application of FYM and inorganic fertilizers than in control plots. The uptake of N, P and K increased with the application of FYM and N₁₀₀P₅₀K₅₀.     

Nutrient management on crop productivity and changes in soil organic carbon and fertility in a four–year-old maize-wheat cropping system in Indo-Gangetic plains of India

The aim of this investigation was to prepare and evaluate organic manures (vermicompost, compost and FYM) and mineral fertilizers on crop productivity and changes in soil organic carbon (SOC) and fertility under a four-year-old maize-wheat cropping system. The results demonstrated that yields and nutrient uptake by crops increased significantly in plots receiving manures and mineral fertilizers either alone or in combination than unfertilized control. Application of manures and fertilizers also enhanced SOC, mineral N, Olsen-P and ammonium acetate-extractable K (NH₄OAc-K) after both the crops. Surface soil maintained greater build-up in SOC, mineral N, Olsen-P and NH₄OAc-K than sub-surface soil. Plots amended with manures at 5 t ha^?1 and 50% recommended dose of fertilizer (RDF) had pronounced impact on improving SOC and fertility after both the crops indicating that integrated use of manures and mineral fertilizers could be followed to improve and maintain soil fertility, increase crop productivity under intensive cropping system.     

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.     

Influence of land management on soil nutrients and microbial biomass in the central loess plateau,northwest China

Loss of soil organic matter under cropping systems is often considered one of the most serious forms of agriculturally induced soil degradation. Therefore, understanding how to improve or maintain soil fertility is of importance for sustainable systems of agriculture. This study deals with the effects of succession fallow and fertilization combined with crop rotation on the chemical properties and microbial biomass of soil in the central Loess Plateau, China. In order to create a more uniform experimental environment and avoid the influence of different crop residues, wheat/potato (W/P) rotation was selected as a fertilization treatment. The results showed that with increasing fallow time organic carbon (Corg) and total nitrogen (TN) slightly increased, microbial biomass carbon (MBC) and MBC/Corg gradually decreased, and microbial biomass nitrogen (MBN) remained unchanged. However, only MBC/Corg among all the microbial parameters measured showed significant differences at various stages of fallow. Although there was a decrease in organic carbon and total nitrogen in the fertilized plots, MBC was not significantly different in the various fallow and fertilized plots except for one‐year‐old fallows, which had the highest MBC. MBN, MBC/Corg and MBN/TN in fertilized plots were higher than for plots at different stages of fallow. Fertilization can increase organic carbon, total nitrogen, MBC and MBN content (compared to the control). It was concluded that appropriate land management, such as fertilization combined with crop rotation and reducing one‐year‐old fallow, would be useful ways to improve or maintain soil fertility. Copyright © 2005 John Wiley & Sons, Ltd.     

Biological and chemical properties of arable soils affected by long-term organic and inorganic fertilizer applications

 Using soils from field plots in four different arable crop experiments that have received combinations of manure, lime and inorganic N, P and K for up to 20 years, the effects of these fertilizers on soil chemical properties and estimates of soil microbial community size and activity were studied. The soil pH was increased or unaffected by the addition of organic manure plus inorganic fertilizers applied in conjunction with lime, but decreased in the absence of liming. The soil C and N contents were greater for all fertilized treatments compared to the control, yet in all cases the soil samples from fertilized plots had smaller C:N ratios than soil from the unfertilized plots. The soil concentrations of all the other inorganic nutrients measured were greater following fertilizer applications compared with the unfertilized plots, and this effect was most marked for P and K in soils from plots that had received the largest amounts of these nutrients as fertilizers. Both biomass C determined by chloroform fumigation and glucose-induced respiration tended to increase as a result of manure and inorganic fertilizer applications, although soils which received the largest additions of inorganic fertilizers in the absence of lime contained less biomass C than those to which lime had been added. Dehydrogenase activity was lower in soils that had received the largest amounts of fertilizers, and was further decreased in the absence of lime. This suggests that dehydrogenase activity was highly sensitive to the inhibitory effects associated with large fertilizer additions. Potential denitrification and anaerobic respiration determined in one soil were increased by fertilizer application but, as with both the microbial biomass and dehydrogenase activity, there were significant reductions in both N₂O and CO₂ production in soils which received the largest additions of inorganic fertilizers in the absence of lime. In contrast, the size of the denitrifying component of the soil microbial community, as indicated by denitrifying enzyme activity, was unaffected by the absence of lime at the largest rate of inorganic fertilizer applications. The results indicated differences in the composition or function of microbial communities in the soils in response to long-term organic and inorganic fertilization, especially when the soils were not limited. Received: 10 March 1998     

Nitrogen fertilizer–induced mineralization of soil organic C and N in six contrasting soils of Bangladesh

A 90‐day laboratory incubation study was carried out using six contrasting subtropical soils (calcareous, peat, saline, noncalcareous, terrace, and acid sulfate) from Bangladesh. A control treatment without nitrogen (N) application was compared with treatments where urea, ammonium sulfate (AS), and ammonium nitrate (AN) were applied at a rate of 100 mg N (kg soil)^–1. To study the effect of N fertilizers on soil carbon (C) turnover, the CO₂‐C flux was determined at nine sampling dates during the incubation, and the total loss of soil carbon (TC) was calculated. Nitrogen turnover was characterized by measuring net nitrogen mineralization (NNM) and net nitrification (NN). Simple and stepwise multiple regressions were calculated between CO₂‐C flux, TC, NNM, and NN on the one hand and selected soil properties (organic C, total N, C : N ratio, CEC, pH, clay and sand content) on the other hand. In general, CO₂‐C fluxes were clearly higher during the first 2 weeks of the incubation compared to the later phases. Soils with high pH and/or indigenous C displayed the highest CO₂‐C flux. However, soils having low C levels (i.e., calcareous and terrace soils) displayed a large relative TC loss (up to 22.3%) and the added N–induced TC loss from these soils reached a maximum of 10.6%. Loss of TC differed depending on the N treatments (urea > AS > AN >> control). Significantly higher NNM was found in the acidic soils (terrace and acid sulfate). On average, NNM after urea application was higher than for AS and AN (80.3 vs. 71.9 and 70.9 N (kg soil)^–1, respectively). However, specific interactions between N‐fertilizer form and soil type have to be taken into consideration. High pH soils displayed larger NN (75.9–98.1 mg N (kg soil)^–1) than low pH soils. Averaged over the six soils, NN after application of urea and AS (83.3 and 82.2 mg N (kg soil)^–1, respectively) was significantly higher than after application of AN (60.6 mg N (kg soil)^–1). Significant relationships were found between total CO₂ flux and certain soil properties (organic C, total N, CEC, clay and sand content). The most important soil property for NNM as well as NN was soil pH, showing a correlation coefficient of –0.33** and 0.45***, respectively. The results indicate that application of urea to acidic soils and AS to high‐pH soils could be an effective measure to improve the availability of added N for crop uptake.     

Stabilization of carbon from maize in a sandy soil in a long-term experiment

The sequestration of carbon (C) in soil is not completely understood, and quantitative information about the amounts of organic carbon in the various fractions and their rates of turnover could improve understanding. We aimed (i) to quantify the amounts of C derived from maize at various depths in the soil in a long‐term field experiment with and without fertilization using ¹³C/¹²C analysis, (ii) to model changes in the organic C, and (iii) to compare measured and modelled pools of C. The organic C derived from the maize was measured in soil samples collected to a depth of 65 cm from four plots, two of which had been under continuous maize and two under continuous rye during long‐term field experiments with NPK and without fertilization. The fractionation procedures included particle‐size fractionation and extractions in water and in pyrophosphate solution. We used the Rothamsted Carbon Model to model the dynamics of the carbon from ¹³C data. The amounts of C derived from maize in the Ap horizon after 39 years of continuous maize cropping were 9.5% of the total organic C (where unfertilized) and 14.0% where NPK had been applied. Fertilization did not affect the residence time of carbon in the soil. The amounts of C derived from maize in water extracts were 21% of the total organic C (where unfertilized) and 22% where NPK had been applied. The extracts that were soluble in pyrophosphate and insoluble in acid were depleted in C from maize (the amounts were 5% and 7% of the total organic C, respectively). The results of the ¹³C natural abundance technique were used to model the dynamics of the organic C. Both the total organic C and the C derived from maize in the particle‐size fraction 0–63 μm agreed well with the total and maize‐derived sums of the model pools ‘inert organic matter’, ‘humified organic matter’ and ‘microbial biomass’. The model suggested that 64% (unfertilized) or 53% (NPK) of the organic C in the Ap horizon were inert. Only one of three published equations to determine the size of the inert pool agreed well with these model results.     

Agronomic effectiveness of rock phosphate combined with nitrogen sources in spot application: A pot experiment

Rock phosphate (RP) shows reduced dissolution in soils amended with limestone and when applied through spot application. A simple way to improve RP efficiency under these unfavorable conditions may be the combination with nitrogen (N) fertilizers which can increase the solubilization of apatite minerals and/or stimulate P uptake. In this context, we evaluated the agronomic effectiveness of a RP from Bayóvar, Peru (BY), combined with different N sources in spot application, in a clayey Oxisol (Typic Hapludox). The pot experiment consisted of a factorial scheme (3 × 2 × 2+4) in randomized block design with four replications. Treatments consisted of BY combined with three N sources (ammonium sulfate–BY+AS; urea–BY+U; potassium nitrate–BY+KN), in two forms (granulated or powdered), and in two N : P molar ratios (0.5 : 1.0 or 1 : 1) and four additional treatments [control: without P; monoammonium phosphate (MAP); powdered BY; granulated BY]. The products were incorporated into a 50 cm³ cylindrical soil volume (central and upper position in the pot: diameter 17 cm and height 15 cm) with three maize plants (Zea mays L.). Above‐ground biomass was sampled after 42 d after sowing, analyzed for N and P concentrations to calculate N and P uptake. Soil samples were taken from the cylindrical soil volume and measured for RP dissolution (ΔCa index), P availability (P‐resin index), and soil pH. Application of MAP increased soil P availability about 11 times compared with BY treatments. As a result, maize plants grew 3.8 times and absorbed 7.3 and 3.3 times more P and N compared to those fertilized with BY combined with N fertilizers. Compound fertilizers BY+AS and BY+KN had the same effect on N and P uptake, presenting an effectiveness about 12 and 19% greater than pure BY, respectively. Compound fertilizers with BY+AS were more effective in powdered form (with no N/P ratio effect), while BY+KN was more effective in granulated form and in 1 : 1 N : P ratio. BY+U combinations were less efficient in promoting plant P bioavailability than the other N sources. We conclude that Bayóvar RP has a low agronomic effectiveness for spot application, even when combined with N.     

Long‐Term Integrated Nutrient Management for Rice‐Based Cropping Pattern: Effect on Growth,Yield, Nutrient Uptake,Nutrient Balance Sheet,and Soil Fertility

Abstract

A 7‐year‐long field trial was conducted on integrated nutrient management for a dry season rice (Boro)–green manure (GM)–wet season rice (T. Aman) cropping system at the Bangladesh Rice Research Institute Farm, Gazipur during 1993–1999. Five packages of inorganic fertilizers, cow dung (CD), and GM dhaincha (Sesbania aculeata) were evaluated for immediate and residual effect on crop productivity, nutrient uptake, soil‐nutrient balance sheet, and soil‐fertility status. Plant height, active tiller production, and grain and straw yields were significantly increased as a result of the application of inorganic fertilizer and organic manure. Usually, the soil‐test‐based (STB) fertilizer doses for a high‐yield goal produced the highest grain yield of 6.39 t ha^?1 (average of 7 years) in Boro rice. Application of CD at the rate of 5 t ha^?1 (oven‐dry basis) once a year at the time of Boro transplanting supplemented 50% of the fertilizer nutrients other than nitrogen (N) in the subsequent crop of the cropping pattern. A positive effect of GM on the yield of T. Aman rice was observed. Following GM, the application of reduced doses of phosphorus (P), potassium (K), sulfur (S), and zinc (Zn) to the second crop (T. Aman) did not reduce yield, indicating the beneficial residual effect of fertilizer applied to the first crop (Boro rice) of the cropping pattern. The comparable yield of T. Aman was also observed with reduced fertilizer dose in CD‐treated plots. The total P, K, and S uptake (kg/ha/yr) in the unfertilized plot under an irrigated rice system gradually decreased over the years. The partial nutrient balance in the unfertilized plot (T₁) was negative for all the nutrients. In the fertilized plots, there was an apparent positive balance of P, S, and Zn but a negative balance of N and K. This study showed that the addition of organic manure (CD, dhaincha) gave more positive balances. In the T_4c treatment at 0–15 cm, the application of chemical fertilizers along with the organic manures increased soil organic carbon by (C) 0.71%. The highest concentration of total N was observed with T_4c followed by T_4d and T_4b, where CD was applied in Boro season and dhaincha GM was incorporated in T. Aman season. The sixfold increase in soil‐available P in T_4b‐, T_4c‐, T_4a‐treated plots was due to the addition of CD. Dhaincha GM with the combination of chemical fertilizer helps to mobilize soil‐available P by 3 to 6 ppm. The highest amount of soil‐available S was found in T_4c‐ and T_4a‐treated plots. It was 2.5 times higher than that of the initial soil. The application of CD and dhaincha GM along with chemical fertilizers not only increased organic C, total N, available P, and available S but also increased exchangeable K, available Zn, available iron (Fe), and available manganese (Mn) in soil.     

The quality of exogenous organic matter: short-term effects on soil physical properties and soil organic matter fractions

We examined the short-term effect of five organic amendments and compared them to plots fertilized with inorganic fertilizer and unfertilized plots on aggregate stability and hydraulic conductivity, and on the OC and ON distribution in physically separated SOM fractions. After less than 1 year, the addition of organic amendments significantly increased ( P  <   0.01) the aggregate stability and hydraulic conductivity. The stability index ranged between 0.97 and 1.76 and the hydraulic conductivity between 1.23 and 2.80 × 10⁻³ m/s for the plots receiving organic amendments, compared with 0.34–0.43, and 0.42–0.64 × 10⁻³ m/s, respectively, for the unamended plots. There were significant differences between the organic amendments (P <  0.01), although these results were not unequivocal for both soil physical parameters. The total OC and ON content were significantly increased ( P  <   0.05) by only two applications of organic fertilizers: between 1.10 and 1.51% OC for the amended plots versus 0.98–1.08% for the unamended and between 0.092 and 0.131% ON versus 0.092–0.098% respectively. The amount of OC and ON in the free particulate organic matter fraction was also significantly increased ( P  <   0.05), but there were no significant differences ( P  <   0.05) in the OC and ON content in the POM occluded in micro-aggregates and in the silt + clay-sized organic matter fraction. The results showed that even in less than 1 year pronounced effects on soil physical properties and on the distribution of OC and ON in the SOM fractions occurred.     

Contribution of organic amendments to soil organic matter detected by thermogravimetry

Sustainable soil management requires reliable and accurate monitoring of changes in soil organic matter (SOM). However, despite the development of improved analytical techniques during the last decades, there are still limits in the detection of small changes in soil organic carbon content and SOM composition. This study focused on the detection of such changes under laboratory conditions by adding different organic amendments to soils. The model experiments consisted of artificially mixing soil samples from non‐fertilized plots of three German long‐term agricultural experiments in Bad Lauchstädt (silty loam), Grossbeeren (silty sand), and Müncheberg (loamy sand) with straw, farmyard manure, sheep faeces, and charcoal in quantities from 3 to 180 t ha^?1 each. In these mixtures we determined the organic carbon contents by elemental analysis and by thermal mass losses (TML) determined by thermogravimetry. The results confirmed the higher reliability of elemental analysis compared to TML for organic carbon content determination. The sensitivity of both methods was not sufficient to detect the changes in organic carbon content caused by small quantities of organic amendments (3 t ha^?1 or 0.1–0.4 g C kg^?1 soil). In the case of elemental analysis, the detectability of changes in carbon content increased with quantities of added amendments, but the method could not distinguish different types of organic amendments. On the contrary, the based on analysis of degradation temperatures, the TML allowed this discrimination together with their quantitative analysis. For example, added charcoal was not visible in TML from 320 to 330°C, which is used for carbon content determination. However, increasing quantities of charcoal were reflected in a higher TML around 520°C. Furthermore, differences between measured (with TML_110–550) and predicted mass loss on ignition using both organic carbon (with TML₃₃₀) and clay contents (with TML₁₄₀) were confirmed as a suitable indicator for detection of organic amendments in different types of soils. We conclude that thermogravimetry enables the sensitive detection of organic fertilizers and organic amendments in soils under arable land use.     

Maize Inbreds' Response to Riecito Phosphate Rock and Triple Superphosphate on an Acidic Soil

Abstract

Tropical acidic soils require large inputs of nitrogen (N) and phosphorus (P) fertilizers to sustain crop production. Attempts to use phosphate rock (PR) as a cheaper P source have shown limited success because of low rock solubility. The objective of this study was to evaluate growth and P nutrition of aluminum (Al)‐tolerant maize inbreds fertilized with PR. Twelve Al‐tolerant inbreds from CIMMYT were planted in 2‐kg pots filled with an acidic soil very low in available P and fertilized with 0, 40, or 100 mg kg^?1 of Riecito PR or triple superphosphate (SP). Plant shoots were harvested 35 days after planting, and biomass, root length, P uptake, and soil residual P were determined. Inbreds were able to sustain growth when fertilized with PR. There was indication that various mechanisms were involved in the responses to PR fertilization. Cultivars combining high uptake and conversion efficiencies should improve maize utilization of PR.