Soil carbon fractions in response to straw mulching in the Loess Plateau of China

Straw mulching has been used to conserve soil water and sustain dryland crop yields, but the impact of the quantity and time of mulching on soil C fractions are not well documented. We studied the effects of various amounts and times of wheat (Triticum aestivum L.) straw mulching on soil C fractions at 0–10- and 10–20-cm depths from 2009 to 2017 in the Loess Plateau of China. Treatments were no mulching (CK), straw mulching at 9.0 (HSM) and 4.5 Mg ha^?1 (LSM) in the winter wheat growing season, and straw mulching at 9.0 Mg ha^?1 in the summer fallow period (FSM). Soil C fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). All C fractions at 0–10 and 10–20 cm were 8–27% greater with HSM and LSM than FSM and CK. Both SOC and POC at 0–10 cm increased at 0.32 and 0.27 Mg ha^?1 year^?1 with HSM and at 0.40 and 0.30 Mg C ha^?1 year^?1 with LSM, respectively, from 2009 to 2017. Winter wheat grain yield was lower with HSM and LSM, but total aboveground biomass was greater with HSM than other treatments. All C fractions at most depths were correlated with the estimated wheat root residue returned to the soil and PCM at 0–10 and 0–20 cm was correlated with wheat grain yield. Wheat straw mulching during the growing season increased soil C sequestration and microbial biomass and activity compared with mulching during the fallow period or no mulching, regardless of mulching rate, due to increased C input, although it reduced wheat grain yield. Continuous application of straw mulching over time can increase soil C sequestration by increasing nonlabile C fractions while decreasing labile fractions. Straw mulching at higher rate and mulching during the summer fallow period had no additional benefits in soil C sequestration.     

<Emphasis Type="Italic">Trichoderma</Emphasis> inoculation and trash management effects on soil microbial biomass,soil respiration,nutrient uptake and yield of ratoon sugarcane under subtropical conditions

A field experiment was conducted during 2003–2005 and 2004–2006 at the Indian Institute of Sugarcane Research, Lucknow, India to study the effect of Trichoderma viride inoculation in ratoon sugarcane with three trash management practices, i.e. trash mulching, trash burning and trash removal. Trichoderma inoculation with trash mulch increased soil organic carbon and phosphorus (P) content by 5.08 Mg ha⁻¹ and 11.7 kg ha⁻¹ over their initial contents of 15.75 Mg ha⁻¹ and 12.5 kg ha⁻¹, respectively. Soil compaction evaluated as bulk density in 0- to 15-cm soil layer, increased from 1.48 Mg m⁻³ at ratoon initiation (in April) to 1.53 Mg m⁻³ at harvest (in December) due to trash burning and from 1.42 Mg m⁻³ at ratoon initiation (in April) to 1.48 Mg m⁻³ at harvest (in December) due to trash mulching. The soil basal respiration was the highest during tillering phase and then decreased gradually, thereafter with the advancement of crop growth. On an average, at all the stages of crop growth, Trichoderma inoculation increased the soil basal respiration over no inoculation. Soil microbial biomass increased in all plots except in the plots of trash burning/removal without Trichoderma inoculation. The maximum increase (40 mg C kg⁻¹ soil) in soil microbial biomass C, however, was observed in the plots of trash mulch with Trichoderma inoculation treatment which also recorded the highest uptake of nutrient and cane yield. On an average, Trichoderma inoculation with trash mulch increased N, P and K uptake by 15.9, 4.68 and 23.6 kg ha⁻¹, respectively, over uninoculated condition. The cane yield was increased by 12.8 Mg ha⁻¹ with trash mulch + Trichoderma over trash removal without Trichoderma. Upon degradation, trash mulch served as a source of energy for enhanced multiplication of soil bacteria and fungi and provided suitable niche for plant–microbe interaction.     

Soil chemical and microbiological properties in hay production systems: residual effects of contrasting N fertilization of swine lagoon effluent versus ammonium nitrate

This study characterized soil chemical and microbiological properties in hay production systems that received from 0 to 600 kg plant-available N (PAN) ha⁻¹ year⁻¹ from either swine lagoon effluent (SLE) or ammonium nitrate (AN) from 1999 to 2001. The forage systems contained plots planted with bermudagrass (Cynodon dactylon L.) or endophyte-free tall fescue (Festuca arundinaceae Schreb.). In March 2004, the plots were sampled for measurements of a suite of soil chemical and microbiological properties. Nitrogen fertilization rates were significantly correlated with soil pH and K₂SO₄-extractable soil C but not with total soil C, soil C/N ratio, electrical conductivity, or Mehlich-3-extractable nutrients. Soil supplied with SLE had significantly lower Mehlich-3-extractable nutrients than the soil supplied with AN. Two indicators of soil N-supplying capacity (potentially mineralizable N and amino sugar N) varied with plant species and the type of N fertilizer. However, they generally peaked at an application rate of 200 or 400 kg PAN ha⁻¹ year⁻¹. Soil microbial biomass C also peaked at an application rate of 200 or 400 kg PAN ha⁻¹ year⁻¹. Nitrification potential was significantly higher in soil supplied with AN than in the unfertilized control but was similar between SLE-fertilized and unfertilized soils. Our results indicated that an application rate as high as 600 kg PAN ha⁻¹ year⁻¹ did not benefit soil microbial biomass, microbial activity, and N transformation processes in these forage systems.     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

Long-term effects of fertilizer managements on crop yields and organic carbon storage of a typical rice–wheat agroecosystem of China

The present paper summarizes the results from a long-term experiment setup in 1980 in the Taihu Lake region, China, to address the yield sustainability, the dynamic changes of soil organic carbon (SOC) storage, and soil fertility in the rice–wheat ecosystem. Treatments in three replicates comprising manure-treated and chemical fertilizer-treated groups (two factors), each having seven sub-treatments of different combinations of inorganic nitrogen (N), phosphorus (P), potassium (K), and rice straw, were randomly distributed. Results showed that the treatments of manure (pig manure from 1980 to 1996 and oil rape cake thereafter) + N + P + K (MNPK) and chemical fertilizer + N + P + K (CNPK) produced the highest and the most stable yields for both rice and wheat within the respective fertilizer treatment group. Potassium fertilization was necessary for yield sustainability in the ecosystem. Treatments of straw (as rice straw) + N (CRN) and manure + straw + N (MRN) produced more stable yield of rice but less stable of wheat. It was therefore recommended that straw should be only incorporated during the rice season. SOC contents in all treatments showed increasing trends over the period, even in the control treatment. Predicted SOC in chemical fertilizer-treated plots (mostly yet attainable) ranged from 16 to 18 g C kg⁻¹, indicating the high carbon (C) sequestration potential of the soil as compared to the initial SOC. SOC in manure- or straw-treated plots ranged from 17 to 19 g C kg⁻¹, which had been attained roughly 10 years after the experiment was initiated. Nutrient balance sheet showed that there was P surplus in all P-treated plots and a steady increase in Olsen-P over a 24-year period in 0–15 cm soil, which contributed little to crop yield increases. It was therefore suggested that P fertilization rate should be decreased to 30–40 kg P ha⁻¹ year⁻¹. Comparison of yields among the treatments showed that wheat was more responsive to P fertilizer than rice. Thus P fertilizer should be preferably applied to wheat. Soil pH decrease was significant over the 24-year period and was not correlated with fertilizer treatments. The overall recommendation is to incorporate straw at 4,500 kg ha⁻¹ year⁻¹ during the rice season only, with additional 190 kg N ha⁻¹ year⁻¹, 30–40 kg P ha⁻¹ year⁻¹ mainly during the rice season, and 150–160 kg K ha⁻¹ year⁻¹. Further research on the unusual P supply capacity of the soil is needed.     

Leaching of soil organic carbon and nitrogen in sandy soils after cultivating grass-clover swards

Several studies have focused on the formation and losses of dissolved organic matter in forest systems, whereas a limited number have dealt with this aspect in agricultural soils. The purpose of this study was to estimate the leaching of dissolved organic carbon (DOC) and nitrogen (DON), with focus on the period after cultivating grass-clover swards. Grass-clovers were ploughed in the spring prior to sowing cereals followed by either catch crops or bare soil. The concentrations of DOC and DON decreased with soil depth and ranged at 90-cm soil depth between 7 and 21 mg C L⁻¹ and between 1 and 3 mg N L⁻¹, respectively, in a sandy loam soil, and between 16 and 63 mg C L⁻¹ and between 1 and 10 mg N L⁻¹, respectively, in a coarse sandy soil. The resulting DOC/DON ratios were in the range between 2 and 42, with higher values in the coarse sandy soil than in the sandy loam soil. The total percolation was 218 mm in the sandy loam soil and 596–645 mm in the coarse sandy soil, which resulted in an annual leaching of 22–40 kg DOC ha⁻¹ year⁻¹ and 3–4 kg DON ha⁻¹ year⁻¹ in the sandy loam soil, and 174–310 kg DOC ha⁻¹ year⁻¹ and 10–31 kg DON ha⁻¹ year⁻¹ in the coarse sandy soil. It was shown that higher amounts of DOC were lost by leaching under the catch crops than from bare soil, that losses of DON were higher from bare soil than from soils with catch crops and that DON contributed significantly to the total N loss. Thus, DON needs to be taken into account in N-balance calculations.     

长期秸秆覆盖对免耕稻-麦产量、土壤氮组分及微生物群落的影响

为探究长期秸秆覆盖对免耕区作物产量、土壤氮素组分及微生物群落特征的影响,以稻–麦定位免耕试验为研究对象,选取了其中免耕且秸秆移除和免耕且秸秆覆盖2个处理,于试验开展第12年（2018年）小麦收获后,统计分析近五年产量数据,并采集各处理0～5、5～10、10～20、20～30 cm的土壤样品,测定土壤全氮及活性氮组分,利用磷脂脂肪酸（PLFA）方法表征土壤微生物群落。结果表明：（1）秸秆覆盖显著提高了小麦产量（增幅为6.49%）,对水稻产量影响不显著。（2）秸秆覆盖对土壤氮组分的影响略有差异：它显著提高了土壤0～5 cm全氮、硝态氮和铵态氮以及0～10 cm颗粒有机氮、0～5 cm和10～20 cm可溶性有机氮含量,对微生物生物量氮无显著影响;它提高了0～5 cm和10～20 cm可溶性有机氮占全氮的比例,对其他组分占全氮比例无显著影响。（3）秸秆覆盖显著提高了土壤微生物总PLFA和细菌PLFA丰度,对真菌PLFA和放线菌PLFA无影响,降低了土壤真菌/细菌比;微生物生物量氮、土壤全氮、颗粒有机碳/颗粒有机氮比是显著影响土壤微生物群落组成的关键土壤环境因子。（4）无论秸秆覆盖与否,土壤全...     

Microbiological and chemical changes in two arable soils after long-term sludge amendments

 Sludge amendments increase the input of carbon and nutrients to the soil. However, the soil concentrations of heavy metals and xenobiotica can also increase due to sludge amendments, with possible effects on soil microorganisms and soil fertility. Therefore, we studied the effects on soil microorganisms and soil chemistry in two arable soils after 12 and 16 years of sewage sludge amendment (0, 1 and 3 dry matter ha^–1 year^–1). The sludge amendments were combined with nitrogen addition at three rates according to crop requirements, and all combinations were replicated 4 times, giving a total number of 36 parcels at each experimental site in a non-randomised block design. Univariate data evaluation as well as principal component analysis and discriminant function analysis (DFA) were used to identify differences between treatments in microbial and chemical parameters. The DFA showed that acid and alkaline phosphatase, potential ammonium oxidation and total nitrogen were the most important parameters to discriminate between a priori defined groups of sludge treatments. Among the heavy metals, copper showed the highest increase in soil concentration with sludge amendments, but this increase was still not high enough to have a significant influence on the measured parameters. None of the xenobiotica investigated was found in high soil concentrations. In conclusion, the present study showed that the sewage sludge affected several of the biological and chemical parameters investigated. However, no severe negative effects on soil microorganisms were detected at these moderate levels of sludge amendment. Received: 3 December 1998     

Contribution of decomposing harvest residues to nutrient cycling in a second rotation Eucalyptus globulus plantation in south-western Australia

Amounts of nutrients in harvest residues and their contribution to nutrient cycling were quantified following logging of a Eucalyptus globulus plantation in south-western Australia. An estimated 64 t ha^–1 of leaf, bark and branch material less than 3 cm in diameter was deposited on the forest floor during harvesting. Leaves contributed about one-third of the residue dry weight but accounted for almost three-quarters of residue-N stores (299 of 428 kg N ha^–1) and 36% to 52% of P, K, Ca, and Mg stores. Stores of nutrients in slash were significant in comparison to amounts in surface soil (0–20 cm). Residue-N amounted to 11% of total surface soil N and cations stored in residues were equivalent to 23–114% of surface soil exchangeable cations. Decomposition of the leaf fraction of slash was rapid with more than 90% of dry weight released during the 105-week study. Bark and branch fractions of diameters 0.5, 1 and 2 cm lost 39%, 37%, 32% and 29% of dry weight, respectively, during the same period. Single and double exponential decay models fitted to the data indicated half lives ranging from 20 weeks for leaves and from 3 to 4 years for bark and the branch fractions. During decomposition, K was leached rapidly from all residue fractions, Mg and P were released at similar rates to dry weight, and Ca and N were released more slowly than dry weight. In the 105-week study period, 250 kg ha^–1 of N, 20 kg ha^–1 of P, 213 kg ha^–1 of Ca, 298 kg ha^–1 of K, and 63 kg ha^–1 of Mg were returned to the soil from decomposing harvest slash. The leaf fraction was the major contributor to nutrient cycling, accounting for almost all of the N and Ca release and from half to three-quarters of the K, Mg and P released. Amounts of nutrients released from residues in the year following logging greatly exceeded quantities likely to be taken up by the newly established tree crop.     

Long-term yield trend and sustainability of rainfed soybean–wheat system through farmyard manure application in a sandy loam soil of the Indian Himalayas

A long-term (30 years) soybean–wheat experiment was conducted at Hawalbagh, Almora, India to study the effects of organic and inorganic sources of nutrients on grain yield trends of rainfed soybean (Glycine max)–wheat (Triticum aestivum) system and nutrient status (soil C, N, P and K) in a sandy loam soil (Typic Haplaquept). The unfertilized plot supported 0.56 Mg ha⁻¹ of soybean yield and 0.71 Mg ha⁻¹ of wheat yield (average yield of 30 years). Soybean responded to inorganic NPK application and the yield increased significantly to 0.87 Mg ha⁻¹ with NPK. Maximum yields of soybean (2.84 Mg ha⁻¹) and residual wheat (1.88 Mg ha⁻¹) were obtained in the plots under NPK + farmyard manure (FYM) treatment, which were significantly higher than yields observed under other treatments. Soybean yields in the plots under the unfertilized and the inorganic fertilizer treatments decreased with time, whereas yields increased significantly in the plots under N + FYM and NPK + FYM treatments. At the end of 30 years, total soil organic C (SOC) and total N concentrations increased in all the treatments. Soils under NPK + FYM-treated plots contained higher SOC and total N by 89 and 58% in the 0–45 cm soil layer, respectively, over that of the initial status. Hence, the decline in yields might be due to decline in available P and K status of soil. Combined use of NPK and FYM increased SOC, oxidizable SOC, total N, total P, Olsen P, and ammonium acetate exchangeable K by 37.8, 42.0, 20.8, 30.2, 25.0, and 52.7%, respectively, at 0–45 cm soil layer compared to application of NPK through inorganic fertilizers. However, the soil profiles under all the treatments had a net loss of nonexchangeable K, ranging from 172 kg ha⁻¹ under treatment NK to a maximum of 960 kg ha⁻¹ under NPK + FYM after 30 years of cropping. Depletion of available P and K might have contributed to the soybean yield decline in treatments where manure was not applied. The study also showed that although the combined NPK and FYM application sustained long-term productivity of the soybean–wheat system, increased K input is required to maintain soil nonexchangeable K level.     

Effects of mulching on soil physical properties and runoff under semi-arid conditions in southern Spain

Application of crop residues to soil and reduced or no tillage are current management practices in order to achieve better water management, increase soil fertility, crop production and soil erosion control. This study was carried out to quantify the effect of wheat straw mulching in a no tilled Fluvisol under semi-arid conditions in SW Spain and to determine the optimum rate in terms of cost and soil protection. After a 3-years experiment, mulching application significantly improved physical and chemical properties of the studied soil with respect to control, and the intensity of changes was related to mulching rate. The organic matter content was generally increased, although no benefit was found beyond 10 Mg ha⁻¹ year⁻¹. Bulk density, porosity and aggregate stability were also improved with increasing mulching rates, which confirmed the interactions of these properties. Low mulching rates did not have a significant effect on water properties with respect to control, although the available water capacity increased greatly under high mulching rates. After simulated rainfall experiments (65 mm h⁻¹ intensity), it was found that the mulch layer contributed to increase the roughness and the interception of raindrops, delaying runoff generation and enhancing the infiltration of rain water during storms. Mulching contributed to a reduction in runoff generation and soil losses compared to bare soil, and negligible runoff flow or sediment yield were determined under just 5 Mg ha⁻¹ year⁻¹ mulching rate. It was observed that during simulations, the erosive response quickly decreases with time after prolonged storms (30 min) due to the exhaustion of available erodible particles. These results suggest that the erosive consequences of intermediate intensity 5-years-recurrent storms in the studied area could be strongly diminished by using just 5 Mg ha⁻¹ year⁻¹ mulching rates.     

Effects of long-term mineral fertilization on microbial biomass,microbial activity,and the presence of <Emphasis Type="Italic">r</Emphasis>- and <Emphasis Type="Italic">K</Emphasis>-strategists in soil

Long-term effects of mineral fertilization on microbial biomass C (MBC), basal respiration (R _B), substrate-induced respiration (R _S), β-glucosidase activity, and the r–K-growth strategy of soil microflora were investigated using a field trial on grassland established in 1969. The experimental plots were fertilized at three rates of mineral N (0, 80, and 160 kg ha⁻¹ year⁻¹) with 32 kg P ha⁻¹ year⁻¹ and 100 kg K ha⁻¹ year⁻¹. No fertilizer was applied on the control plots (C). The application of a mineral fertilizer led to lower values of the MBC and R _B, probably as a result of fast mineralization of available substrate after an input of the mineral fertilizer. The application of mineral N decreased the content of C extracted by 0.5 M K₂SO₄ (C _ex). A positive correlation was found between pH and the proportion of active microflora (R _S/MBC). The specific growth rate (μ) of soil heterotrophs was higher in the fertilized than in unfertilized soils, suggesting the stimulation of r-strategists, probably as the result of the presence of available P and rhizodepositions. The cessation of fertilization with 320 kg N ha⁻¹ year⁻¹ (NF) in 1989 also stimulated r-strategists compared to C soil, probably as the result of the higher content of available P in the NF soil than in the C soil.     

Response of the soil microbial biomass and nematode population to a wetting event in nitrogen-amended Negev desert plots

 Water and N availability are the major limiting factors of primary production in desert ecosystems, and the response of soil biota to these two factors is of great importance. We examined the immediate response of soil nematodes and the microbial biomass to a single pulse of water amendment in N-treated plots in the Israeli Negev desert. Plots were treated with 0, 50 and 100 kg NH₄NO₃ ha^–1 in December 1992, and at the end of the summer period (August 1993) the plots were exposed to a 15 mm water. Soil samples from the 0–10 cm layer were collected daily and analysed soil moisture, total soluble N, nematode populations and microbial biomass. Soil moisture increased to 8.5%, then gradually decreased to 2% during the 11 days of the study. Microbial biomass, soil respiration and metabolic quotient values did not exhibit any significant correlation with soil N levels. Free-living nematode population levels in the different plots were found to increase from a mean level of 45 500 to a mean level of 92 300 individuals m^–2. N treatment was found to affect the patterns of free-living nematode population dynamics. The results of this study demonstrated the importance of moisture availability levels and the ability to mobilize previous N inputs into available N which, occurring in pulses, can affect the microbial ecophysiological status, nematode population dynamics and the interrelationship between these two important components in the desert soil milieu. Received: 5 November 1998     

Evaluation of press mud cake as a source of nitrogen and phosphorus for rice–wheat cropping system in the Indo-Gangetic plains of India

Press mud cake (PMC) is an important organic source available for land application in India. Adequate information regarding availability of nitrogen and phosphorous contained in PMC to rice–wheat (RW) cropping system is lacking. In field experiments conducted for 4 years to study the effect of PMC application to rice as N and P source in RW system, application of 60 kg N ha⁻¹ along with PMC (5 t ha⁻¹) produced grain yield of rice similar to that obtained with the 120 kg N ha⁻¹ in unamended plots. In the following wheat, the residual effects of PMC applied to preceding rice were equal to 40 kg N and 13 kg P ha⁻¹. Immobilization of soil and fertilizer N immediately after the application of PMC was observed in laboratory incubation. The net amount of N mineralized from the PMC ranged from 16% at 30 days to 43% at 60 days after incubation. Available P content in the soil amended with PMC increased by about 60% over the unamended control within 10 days of its application. The P balance for the no-PMC treatment receiving recommended dose of 26 kg P ha⁻¹ year⁻¹ was −13.5 kg P ha⁻¹ year⁻¹. The P balance was positive (+42.3 to 53.5 kg P ha⁻¹ year⁻¹) when PMC was applied to rice. Application of PMC increased total N, organic carbon, and available P contents in the soil.     

Nitrogen conservation in soil and crop residues as affected by crop rotation and soil disturbance under Mediterranean conditions

We investigated conservation and cycling of N under oat–oat and lupine–oat rotations in disturbed and undisturbed soil, when roots or roots plus aboveground residues were retained. Crop residues were labelled with ¹⁵N in Year 1, and differential soil disturbance was imposed after harvest. In Year 2, plant growth, N transfer from residue into the various sinks of the second crop (plant, soil, and residual residues), and changes in microbial activity and numbers were determined. Oat biomass was greater after lupine than after oat due to differences in supply of N from these residues. Buried residues of both crops appeared to decompose faster than when left on the soil surface. Lupine residues decomposed faster than oat residues. Oat biomass was not affected by soil disturbance if grown after lupine but decreased when oat straw was buried in the soil. More residue N was recovered from soil than from the crop. Most ¹⁵N was recovered from disturbed soil, which also had greater dehydrogenase activity and more culturable fungi. At the end of the oat–oat rotation, 20 and 5 kg N ha⁻¹ were derived from the roots of the first crop in undisturbed or disturbed soil, respectively. Equivalent values for the lupine–oat rotation were 18 and 44 kg N ha⁻¹. Returning aboveground residues provided an extra 52–80 kg N ha⁻¹ for oat and 61–63 kg N ha⁻¹ for lupine relative to treatments where they were removed. Over a year, lupine contributed 9 to 20 kg N ha⁻¹ more to the agroecosystem than did oat.     

Biological nitrogen fixation in faba bean (Vicia faba L.) in the Ethiopian highlands as affected by P fertilization and inoculation

 N₂ fixation by leguminous crops is a relatively low-cost alternative to N fertilizer for small-holder farmers in developing countries. N₂ fixation in faba bean (Vicia faba L.) as affected by P fertilization (0 and 20 kg P ha^–1) and inoculation (uninoculated and inoculated) with Rhizobium leguminosarium biovar viciae (strain S-18) was studied using the ¹⁵N isotope dilution method in the southeastern Ethiopian highlands at three sites differing in soil conditions and length of growing period. Nodulation at the late flowering stage was significantly influenced by P and inoculation only at the location exhibiting the lowest soil P and pH levels. The percentage of N derived from the atmosphere ranged from 66 to 74%, 58 to 74% and 62 to 73% with a corresponding total amount of N₂ fixed ranging from 169 to 210 kg N ha^–1, 139 to 184 kg N ha^–1 and 147 to 174 kg N ha^–1 at Bekoji, Kulumsa and Asasa, respectively. The total N₂ fixed was not significantly affected by P fertilizer or inoculation across all locations, and there was no interaction between the factors. However, at all three locations, N₂ fixation was highly positively correlated with the dry matter production and total N yield of faba bean. Soil N balances after faba bean were positive (12–58 kg N ha^–1) relative to the highly negative N balances (–9–44 kg N ha^–1) following wheat (Triticum aestivum L.), highlighting the importance of rotation with faba bean in the cereal-based cropping systems of Ethiopia. Received: 13 January 2000     

Impacts of 22-year organic and inorganic N managements on soil organic C fractions in a maize field,northeast China

Impacts of 22-year organic and inorganic N managements on total organic carbon (TOC), water-soluble organic C (WSOC), microbial biomass C (MBC), particulate organic C (POC) and KMnO₄ oxidized organic C (KMnO₄-C) concentrations, C management index (CMI), and C storage in surface soil (0–20 cm) were investigated in a maize (Zea may L.) field experiment, Northeast China. The treatments included, CK: unfertilized control, M: organic manure (135 kg N ha^− 1 year^− 1), N: inorganic N fertilizer (135 kg N ha^− 1 year^− 1) and MN: combination of organic manure (67.5 kg N ha^− 1 year^− 1) and inorganic N fertilizer (67.5 kg N ha^− 1 year^− 1). TOC concentration and C storage were significantly increased under the M and MN treatments, but not under the inorganic N treatment. The organic treatments of M and MN were more effective in increasing WSOC, MBC, POC and KMnO₄-C concentrations and CMI than the N treatment. The M treatment was most effective for sequestrating SOC (10.6 Mg ha^− 1) and showed similar increase in degree of grain yield to the N and MN treatments, therefore it could be the best option for improving soil productivity and C storage in the maize cropping system.     

Improving quality of sugarcane-growing soils by organic amendments under subtropical climatic conditions of India

A field trial was conducted on an inceptisol to assess the effect of different bio-manures on sugarcane yield, cane quality, and changes in soil physico-chemical and microbial properties in plant–ratoon system. Seven treatments, viz. control, vermicompost, farmyard manure (FYM), biogas slurry, sulphitation pressmud cake (SPMC), green manuring with intercropped Sesbania, and recommended dose of NPK (150:60:60 kg ha⁻¹), were randomized within a block and replicated three times. Improvement in bulk density and infiltration rates was recorded after the addition of various bio-manures. The highest organic C was recorded in the vermicompost (0.54%) and pressmud (0.50%) treatments. The highest increase in soil microbial biomass C (185.5%) and soil microbial biomass N (220.2%) over its initial value was recorded with the addition of FYM. Dry matter production in plant, as well as ratoon crop, was significantly higher by bio-manure application over the control. Plant N uptake was highest in the pressmud treatment (227.7 kg ha⁻¹), whereas P and K uptake were highest (41.4 and 226.50 kg ha⁻¹) in vermicompost treatment. The highest number of millable canes (95.6 and 101.0 thousand ha⁻¹) in plant and ratoon crop were obtained with the addition of pressmud. The highest yield (76.7 t ha⁻¹) was recorded in planted cane with vermicompost application, whereas ratoon yield was highest (78.16 t ha⁻¹) with pressmud application. In both planted and ratoon crop, organic amendments produced yields statistically similar to those with recommended NPK (76.1 and 78.1 t ha⁻¹ for plant and ratoon cane).     

Soil microbial activity,aggregation and nutrient responses to straw pulping liquor in corn cropping

The cereal and grass seed cropping systems of the Pacific northwestern USA generate a valuable fiber source for papermaking. Pulping straw with KOH produces black liquor, an organic waste effluent with potential as a K source and soil amendment. The objectives of this study were to determine if black liquor from wheat straw pulping with KOH improves soil quality including soil aggregation, microbial biomass and microbial activity, and corn yield. A 2-year field trial with a randomized complete block design was conducted with black liquor or KCl applied at 168 and 336 kg K ha⁻¹ at two sites, respectively, planted to corn in Central Washington. Black liquor applied at rates of 168 and 336 kg K ha⁻¹ slightly increased soil pH by 0.2 to 1.4 units and electrical conductivity by 0.0 to 0.8 dS m⁻¹ at both sites, and significantly increased soil test K compared to the nonamended control by 199 to 368 mg K kg⁻¹ soil in the top 5 cm at Paterson and by 44 to 200 mg K kg⁻¹ soil in the top 5 cm at Prosser. Corn had no yield response to the application of either K sources, black liquor, or KCl applied at both rates at both sites. Generally, black liquor applied at these rates increased soil dehydrogenase, β-glucosidase, and arylsulfatase activities, microbial biomass C, and soil wet stable macroaggregates in the top 5-cm soil at both sites. The results of this study suggest that the organic-rich waste liquor from wheat straw pulping with KOH may improve soil quality and soil test K without reducing crop productivity.     

Litterfall, litter decomposition and nutrient release patterns in four native tree species raised on coal mine spoil at Singrauli, India

 Litterfall, leaf litter decomposition and N and P release were studied in four tree species (Dalbergia sissoo, Azadirachta indica, Pongamia pinnata and Shorea robusta) planted on a mine spoil habitat. Annual litterfall varied from 1220 kg ha^–1 in the S. robusta stand to 3620 kg ha^–1 in the A. indica stand. The fast-growing species A. indica and D. sissoo exhibited higher litter production in comparison to the other two slow-growing species. The total N returned to the soil through litterfall ranged from 8.6 kg ha^–1 year^–1 in the S. robusta stand to 36.5 kg ha^–1 year^–1 in the D. sissoo stand. The annual percent leaf litter mass loss was distinctly greater in A. indica (73%) and D. sissoo (69%) in comparison to P. pinatta (59%) and S. robusta (47%). The mean relative decomposition rates of leaf litter material were maximum in the rainy season and minimum in summer. Rainfall and its associated variables exhibited greater control over litter docomposition than temperature. Lignin and water-soluble compounds were better predictors of annual mass loss rates accounting for 90% variability. Mass loss was positively correlated with N and P mineralization rates. Lignin was the best predictor of annual N and P mineralization rates. Nutrient release pattern differed; constant release occurred in A. indica, initial release followed by delayed immobilization and release occurred in D. sissoo and P. pinnata, and initial immobilization followed by gradual release was noticed in S. robusta. A. indica and D. sissoo, showing high litterfall and rapid litter decomposition rate, hold promise for the rehabilitation of nutrient-poor coal mine spoils. On the other hand, S. robusta with less litterfall and a slow decomposition rate may prove disadvantageous. Received: 10 March 1998