Fertilizer market reforms and factors influencing fertilizer use by small-scale farmers in Bénin

Bénin, like other countries in sub-Saharan Africa, has initiated programs to reform agricultural input and output markets. While the impact of the reform programs has been different for each country, it is commonly observed that impact at the farm level has been less than anticipated. A central theme of this paper is to assess the impact of fertilizer market reforms on the fertilizer market structure and fertilizer use for both food and export (cotton) crop production in Bénin. This analysis of farm-level policy impact is based on data from 899 farm households randomly selected and interviewed in all six départements of Bénin in 1998/1999. Results of the study show that there have been only insignificant changes in the fertilizer market structure. Access to fertilizers has not improved; prices for fertilizer have risen in real terms, resulting in application rates lower than that recommended by extension agents. The effects of the reform programs are vital for investment decisions and provide lessons for introducing alternative approaches for improving soil fertility or management. Since 1992, 54% of farmers find maize (Zea mays L.) production more profitable, while 38% reported that cotton (Gossypium hirsutum L.) production has become more profitable. As a result of the mixed effects of the fertilizer market reform program on the level of fertilizer use and profitability, there is need to develop efficient soil fertility management strategies for small-scale farmers. Such strategies should incorporate the use of complementary inputs, such as seeds with a high level of response to the balanced nutrient package.     

Effects of soil properties, mulch and NPK fertilizer on maize yields and nutrient budgets on ferralitic soils in southern Benin

Four on-farm experiments examined whether modest applications of fertilizers in combination with prunings from native agroforestry trees would be an alternative to maintain the fertility of ferralitic soils in Benin. An application of about 1.9 t ha⁻¹ dry matter of mulch of Senna siamea combined with 30 kg N ha⁻¹, 22 kg P ha⁻¹ and 25 kg K ha⁻¹ as compound fertilizer was compared with (1) 60 kg N ha⁻¹, 43 kg P ha⁻¹ and 50 kg K ha⁻¹ as compound fertilizer alone, (2) mulch of S. siamea alone (about 3.2 t ha⁻¹ dry matter), and (3) a control treatment. Criteria were soil properties, yields, nutrient uptakes, and nutrient budgets. Application of sole mulch had no significant effects (P>0.05) on maize yields, while combined application of prunings and NPK fertilizers or sole NPK increased yields significantly (P<0.05). The most limiting nutrient was P. The local maize cultivar was efficient in P uptake, but not in internal nutrient utilization efficiency; mulch increased significantly the internal P utilization efficiency (P<0.05). Soil properties were interpreted with the QUEFTS (quantitative evaluation of the fertility of tropical soils) computer program. The predicted and measured yields were almost the same for maize without NPK. The measured responses to NPK were much lower than the responses calculated by QUEFTS. The calculated nutrient budgets were split into balances for available nutrients and for those not immediately available (NIA). Nutrient budgets were negative for the control and sole mulch treatments, and positive for the NPK treatments. Mulch improved the balances of NIA nutrients. The present experiment could not prove that combining NPK with mulch is the best option for sustainable agriculture. It may be more economical to apply lower rates of fertilizer to local maize than those applied in the two NPK treatments in the present study.     

Effect of P fertilizer application on N balance of soybean crop in the guinea savanna of Nigeria

Soybean (Glycine max (L.) Merr.) is becoming increasingly important in the cereal-based cropping system of the Nigerian Guinea savanna zone and this justifies research on its effects on soil N. Although soybean can obtain 50% or more of its N requirement from the atmosphere, the N contribution of the crop to the system depends on the amount of N contained in roots, haulms, and fallen leaves after grain harvest. At four sites in the northern Guinea savanna, the effects on N balance of P fertilizer and soybean varieties of different duration were tested. The varieties received P fertilizer at the rates of 0, 30, and 60 kg P ha⁻¹. The total N accumulated aboveground at harvest averaged 104 kg N ha⁻¹ in the early and medium varieties, and 135 kg N ha⁻¹ in the late varieties. Across all varieties and sites, total N content was increased by 40–47% when P was applied. Apparent N harvest index averaged 85% but was not significantly affected by variety or P rate. When only grain was exported, the calculated N balance of the early and the medium varieties was −2.6 to −12.2 kg N ha⁻¹ while the longer duration varieties had positive N balances ranging from 2 to 10.9 kg N ha⁻¹. The N accrual was negative when P was not applied and ranged from 2.4 to 5.2 kg N ha⁻¹ with P application. The interaction of variety and site on the N balance was significant at P<0.05. N balance at the southernmost site was −14.2 kg N ha⁻¹ compared with 2.6–10 kg N ha⁻¹ at the northern sites where N₂ fixation was higher. The estimate of N balance is reduced when soybean haulms are exported. A positive N contribution by soybean is, therefore, possible in a soybean–cereal rotation when: (i) P is applied, (ii) the soybean variety is late maturing, and (iii) only grain is exported.     

Managing crop residues, fertilizers and leaf litters to improve soil C, nutrient balances, and the grain yield of rice and wheat cropping systems in Thailand and Australia

This paper reports on the influence that residue and fertilizer management have on nutrient balances, soil organic matter (SOM) dynamics, and crop yields of a flooded rice system in northeast Thailand (1992–1997) and a wheat–forage legume rotation in eastern Australia (1992–1998). Both soils had been subject to at least 18 years of cultivation and had lost up to 90% of the original labile (C_L) and 85% of the total carbon (C_T).For the rainfed rice cropping systems of northeast Thailand, a system is described in which small applications of leaf litter from locally grown trees are applied annually to rice paddy soils prior to transplanting. Annual applications of 1500 kg ha⁻¹ of leaf litter from different locally grown shrubs for five seasons resulted in increases in rice grain yield in 1997 of between 20 and 26% above the no-leaf litter control. Nutrient balances, determined by the difference between the inputs (fertilizer and added leaf litters) and outputs (grain and straw), indicated net positive balances of up to 457 kg N ha⁻¹, and 60 kg P ha⁻¹, after five seasons of leaf litter applications. Sulfur and potassium balances resulted in net deficits of up to −13 kg S ha⁻¹ and −52 kg P ha⁻¹, where no leaf litter was applied and rice straw was removed following harvest. Soil carbon (C) concentrations increased significantly only where higher fertilizer rate and rice stubble retention were combined.The poor management of fertilizers and crop residues, and excessive cultivation has also resulted in large soil fertility losses in the grain growing areas of Eastern Australia. After five wheat and two legume/fallow crops, negative N balances of up to −303 kg ha⁻¹ were calculated for the treatments where wheat stubble was not retained and bare fallow leys were used. The balance of nutrients such as K, which are contained in larger proportions in stubble, were found to be up to −362 kg ha⁻¹ on the straw-removed treatments and up to +29 kg ha⁻¹ on the straw-retained treatments. Forage legume leys resulted in short term increases in C_L and the carbon management index (CMI).Sustainable farming systems require that crop yields are stable through the maintenance of soil fertility and the balance of nutrients in the system. Increases in soil C levels require sustained periods of balanced fertilization and residue retention.     

PREP-PAC: a nutrient replenishment product designed for smallholders in western Kenya

Continuous cropping in the absence of external nutrient inputs to soils has led to the expression of poorly productive patches in farmers’ fields of western Kenya. Farmers attempting to correct these conditions are often confused by the spatial and symptomatic irregularity of affected plants and, until recently, no soil management product was commercially available that is specifically formulated to restore soil fertility to these patches. PREP-PAC consists of 2.0 kg of Minjingu rock phosphate (RP), 200 g of urea, seeds of various symbiotic nitrogen-fixing food legumes, rhizobial inoculant, gum arabic seed adhesive, lime for seed pelleting, and instructions for the use of these materials. It is intended for addition to 25 m² and produced at a cost of $ 0.56 per unit. The general principle is to apply slowly available RP sufficient for several cropping seasons with readily available nitrogenous fertilizer and to intercrop farmer’s maize (Zea mays) with a legume that provides residual fixed-nitrogen and organic inputs to the soil. This approach was tested in on-farm experiments conducted in collaboration with several grassroots rural development organizations. An experiment examined interactions between PREP-PAC components in a maize–soybean (Glycine max) intercrop in nutrient-depleted soils with sandy and clayey surface horizons. The treatments included ±RP, ±urea, and ±inoculants arranged as a 2³ factorial with four replicates at each location. Total value of the intercrops ranged between $ 0.83 in the unamended plots and $ 2.44 in plots treated with PREP-PAC. Significant positive effects were observed with the addition of RP (P<0.001), urea (P=0.04), and inoculant (P=0.01) and in interactions between RP and urea (P=0.02) or inoculant (P=0.07). The return ratio to PREP-PAC investment was 2.6 in the sandy soil and 3.7 in the clay. PREP-PACs were tested on-farm in 52 symptomatic patches containing maize–bean intercrops with and without an improved variety of climbing Phaseolus vulgaris cv. Flora. Unamended patches (25 m²=0.0025 ha) produced 1.6 kg maize and 0.08 kg bean. With addition of PREP-PAC containing Flora, yields increased to 4.1 kg maize and 1.1 kg bean (P<0.001 for both crops). Improvement in bean yield during the first cropping season nearly offset PREP-PAC’s investment costs. PREP-PAC is a strategic approach because all of its ingredients, except for urea, originate from East Africa, and are relatively inexpensive; the product is intended for distribution through existing retail and development networks.     

Rotation effects of grain legumes and fallow on maize yield,microbial biomass and chemical properties of an Alfisol in the Nigerian savanna

Understanding changes in soil chemical and biological properties is important in explaining the mechanism involved in the yield increases of cereals following legumes in rotation. Field trials were conducted between 2003 and 2005 to compare the effect of six 2-year rotations involving two genotypes each of cowpea (IT 96D-724 and SAMPEA-7) and soybean (TGx 1448-2E and SAMSOY-2), a natural bush fallow and maize on soil microbial and chemical properties and yield of subsequent maize. Changes in soil pH, total nitrogen (N_tot), organic carbon (C_org), water soluble carbon (WSC), microbial biomass carbon (C_mic) and nitrogen (N_mic) were measured under different cropping systems. Cropping sequence has no significant (P > 0.05) effect on soil pH and C_org, while WSC increased significantly when maize followed IT 96D-724 (100%), SAMPEA-7 (95%), TGx 1448-2E (79%) and SAMSOY-2 (106%) compared with continuous maize. On average, legume rotation caused 23% increase in N_tot relative to continuous maize. The C_mic and N_mic values were significantly affected by cropping sequence. The highest values were found in legume–maize rotation and the lowest values were found in fallow–maize and continuous maize. On average, C_mic made up to 4.8% of C_org and N_mic accounted for 4.4% of N_tot under different cropping systems. Maize grain yield increased significantly following legumes and had strong positive correlation with C_mic and N_mic suggesting that they are associated with yield increases due to other rotation effects. Negative correlation of grain yield with C_mic:N_mic and C_org:N_tot indicate that high C:N ratios contribute to nitrogen immobilization in the soil and are detrimental to crop productivity. The results showed that integration of grain legumes will reverse this process and ensure maintenance of soil quality and maize crop yield, which on average, increased by 68% and 49% following soybean and cowpea, respectively compared to continuous maize.     

不同磷肥对砷超富集植物蜈蚣草修复砷污染土壤的影响

施肥是提高重金属污染土壤的植物修复效率的必要强化措施之一.通过研究农业生产中常用磷肥对砷超富集植物蜈蚣草生长、砷累积及氮磷钾吸收的影响,确定可提高蜈蚣草修复砷污染土壤能力的最佳磷肥类型.结果表明,与不施砷对照组相比.添加砷处理中施用相应磷肥的蜈蚣草总生物量中蜈蚣草均有所降低(除钙镁磷肥外);在添加砷的情况下,钙镁磷肥、磷酸二氢钙和磷酸二氢铵等3个施磷处理总生物量相对较高.显著高于其他磷肥处理和不施磷处理(0.83 g/pot);地上部砷累积量由大到小的顺序为:磷酸二氢钙>钙镁磷肥>磷酸二氢铵>磷酸二氢钾>磷酸二氢钠>不施磷>过磷酸钙;磷酸二氢钙处理的砷去除效率高达7.28%.由此可见,磷肥能一定程度提高砷超富集植物的修复能力,但不同磷肥对其砷去除效率的影响可达数倍之差,磷酸二氢钙是首选磷肥类型,综合考虑土壤pH、N、P和有效态砷等各种因子,磷酸二氢铵和钙镁磷肥也可作备选肥料类型.     

Can arbuscular mycorrhiza and fertilizer management reduce phosphorus runoff from paddy fields?

Our study sought to assess how much phosphorus (P) runoff from paddy fields could be cut down by fertilizer management and inoculation with arbuscular mycorrhizal fungi. A field experiment was conducted in Lalin River basin, in the northeast China: six nitrogen–phosphorus–potassium fertilizer levels were provided (0, 20%, 40%, 60%, 80%, and 100% of the recommended fertilizer supply), with or without inoculation with Glomus mosseae. The volume and concentrations of particle P (PP) and dissolved P (DP) were measured for each runoff during the rice growing season. It was found that the seasonal P runoff, including DP and PP, under the local fertilization was 3.7 kg/ha, with PP, rather than DP, being the main form of P in runoff water. Additionally, the seasonal P runoff dropped only by 8.9% when fertilization decreased by 20%; rice yields decreased with declining fertilization. We also found that inoculation increased rice yields and decreased P runoff at each fertilizer level and these effects were lower under higher fertilization. Conclusively, while rice yields were guaranteed arbuscular mycorrhizal inoculation and fertilizer management would play a key role in reducing P runoff from paddy fields.     

Cassava, maize and tree root development as affected by various agroforestry and cropping systems in Bénin, West Africa

Soil fertility levels, climate, aboveground interaction for light in plant canopies, and belowground interactions of the root systems for nutrients and water have an important influence on the performance of cropping systems. This study aims at identifying the impact of agroforestry treatments and fertilizer application on the root development of cassava-based cropping systems. At three sites in southern Bénin, the root development of intercropped maize (Zea mays) and cassava (Manihot esculenta) vs. sole-cropped cassava was monitored in an NPK fertilizer treatment and a no-fertilizer and no-mulch treatment. The latter represented local farmers’ practice. In addition, root development of sole-cropped cassava in three agroforestry systems was recorded at the same sites consisting of: (i) annually planted Cajanus cajan, (ii) perennial alleys, and (iii) a tree block of a Gliricidia sepium, Flemingia macrophylla, Parkia biglobosa, Millettia thonningii mixture. Soil monolith sampling was used to extract roots and generate data on the morphological development of root systems and their interactions. In general, intercropping reduced cassava root length density (RLD). Fertilizer applications significantly increased (P≤0.05) the RLD of intercropped maize and intercropped cassava at all sites. Annual alleys of C. cajan developed smaller RLD and root weight densities (RWD) than the perennial tree mixture, leading to less interference with cassava. Block arrangement of the tree mixture had detrimental effects on the cassava growth in the adjacent rows, indicated by high RLD and RWD of the tree mixture. However, the overall effect on cassava yield was positive, when the crop yield is calculated on an entire field basis.     

Water regime-nitrogen fertilizer incorporation interaction: Field study on methane and nitrous oxide emissions from a rice agroecosystem in Harbin, China

Water regime and nitrogen (N) fertilizer are two important factors impacting greenhouse gases (GHG) emission from paddy field, whereas their effects have not been well studied in cold region. In this study, we conducted a two-year field experiment to study the impacts of water regime and N fertilizer on rice yields and GHG emissions in Harbin, China, a cold region located in high latitudes. Our results showed that intermittent irrigation significantly decreased methane (CH₄) emission compared with continuous flooding, however, the decrement was far lower than the global average level. The N₂O emissions were very small when flooded but peaked at the beginning of the disappearance of floodwater. The N fertilizer treatments increased CH₄ emissions at low level (75kgN/ha). But both CH₄ and N₂O emissions were uninfluenced at the levels of 150kgN/ha and 225kgN/ha. Rice yields increased under intermittent irrigation and were highest at the level of 150kgN/ha. From our results, we recommended that the intermittent irrigation and 150kgN/ha as the ideal water regime-nitrogen fertilizer incorporation for this area to achieve low GHG emissions without impacting rice yields.     

Residual benefits of promiscuous soybean to maize (Zea mays L.) grown on farmers’ fields around Minna in the southern Guinea savanna zone of Nigeria

Biological nitrogen fixation (BNF) by promiscuous cultivars of soybeans (Glycine max (L.) Merr.) in cereal-based cropping systems of Nigeria’s moist savanna zone offers a potential for minimizing the investment made by resource-poor farmers on nitrogen fertilizers. A 3-year trial was conducted on five farmers’ fields in the southern Guinea savanna zone of Nigeria to assess the residual effects of two successive crops of promiscuous soybean cultivars on the yield of a following maize (Zea mays L.) crop. The soybean cultivars, TGX1456-2E (medium maturity) and TGX1660-19F (late maturity), were grown in 1996 and 1997. Treatments, imposed only in the first year of the trial, were: (i) uninoculated, (ii) inoculated with a mixture of two Bradyrhizobium strains, and (iii) fertilized with 60 kg N ha⁻¹. A fourth treatment was a plot left to fallow. In 1998, all the previous soybean and fallow plots were sown to maize without any fertilizer application. Results in 1996 and 1997 showed a soybean response to inoculation in the first year, but differences due to the residual effect of inoculation in the second year were not significant. Both cultivars showed a similar response to inoculation but responses at the five sites were varied. Soybean cultivar 1456-2E fixed 43–52% of its N amounting to 56–70 kg N ha⁻¹ and cultivar 1660-19F derived 39–54% of its N from N₂-fixation which amounted to 51–78 kg N ha⁻¹. Both cultivars had a high N harvest index resulting in a net removal of 52–95 kg N ha⁻¹ when both grain and stover were exported. Even when the stover was returned, there was a depletion of 23–65 kg N ha⁻¹, with 1456-2E removing more N than 1660-19F. Arbuscular-mycorrhizal infection on maize roots was 11–27% and dependent on previous soybean treatments and farmers’ fields. Plant height, shoot biomass, grain yield, and N uptake of maize were significantly greater in plots previously sown to soybean than in the fallow plots. In general, plots sown to the late maturing cultivar 1660-19F exhibited better residual effect, producing larger yield parameters than the plots planted with medium maturing 1456-2E.     

长期施肥和耕作下紫色土坡耕地土壤C、N、P和K化学计量特征

阐明长期施肥和耕作对坡耕地土壤C、N、P和K含量及其化学计量比的影响,将有助于深刻理解土壤C和养分元素循环过程及其相互作用机制,对施肥管理及农业面源污染防治具有重要意义.在紫色土坡耕地(坡度为15°)建立15个小区(长8 m×宽4 m),设置5个处理(每个处理3次重复):顺坡无施肥处理(对照,CK)、顺坡复合施用有机肥和化肥处理(T1)、顺坡单施化肥处理(T2)、顺坡单施化肥增量处理(T3)和横坡单施化肥处理(T4),比较各处理0～10 cm及10～20 cm土层的C、N、P和K含量及其化学计量变化特征.结果表明,各处理土壤C、N和P差异显著(P <0. 05),均表现为T1> T3> T4> T2>CK,施肥处理下K含量差异不显著(P> 0. 05),但均显著高于对照处理(P <0. 05),表现为T4> T3> T2> T1> CK.各处理土壤的C∶N在10～20 cm土层中差异显著(P <0. 05),表现为T4> T3> T1> CK> T2;而C∶P则在0～10 cm土层差异显著(...     

钾肥对镉的植物有效性的影响

采用室外盆栽模拟试验,研究了在镉单一污染及镉、铅复合污染的土壤中,钾肥（K₂SO₄）的施用及其施用水平对镉的植物有效性的影响.结果表明,施用钾肥可显著(p<0.05)促进小麦干重的增长,缓解重金属镉及镉、铅复合污染对小麦的毒害作用.不同施用水平的钾肥均减少了小麦对镉的吸收,降低了镉的植物有效性.随着钾肥施用水平的增加,小麦植株不同部位（根、茎叶和籽实）镉的浓度先逐渐降低而后上升,小麦植株不同部位的富集系数也呈现先降低而后上升的趋势,并且钾肥在K2水平时对镉的缓解效果最佳.施用钾肥降低了根际、非根际土壤交换态镉的含量,钾肥主要影响了小麦根际、非根际土壤中交换态、碳酸盐态镉的含量,而对铁锰氧化物结合态、有机质硫化物态和残渣态镉的影响较小.镉、铅复合处理与镉单一处理相比较,铅可促进小麦对镉的吸收,提高镉的植物有效性.     

Seasonal exports of phosphorus from intensively fertilised nested grassland catchments

We carried out a one year (2002) study of phosphorus (P) loss from soil to water in three nested grassland catchments with known P input in chemical fertilizer and animal liquid slurry applications. Chemical fertilizer was applied to the grasslands between March and September and animal slurry was applied over the twelve months. The annual chemical P fertilizer applications for the 17 and 211 ha catchments were 16.4 and 23.7 kg P/ha respectively and the annual slurry applications were 10.7 and 14.0 kg P/ha, respectively. The annual total phosphorus (TP) export in stream-flow was 2.61, 2.48 and 1.61 kg P/ha for the 17, 211 and 1524 ha catchments, respectively, compared with a maximum permissible (by regulation) annual export of ca. 0.35 kg P/ha. The export rate (ratio of P export to P in land applications) was 9.6% and 6.6% from the 17 and 211 ha catchments, respectively. On average, 70% of stream flow and 85% of the P export occurred during the five wet months (October to February) indicating that when precipitation is much greater than evaporation, the hydrological conditions are most favourable for P export. However the soil quality and land use history may vary the results. Particulate P made up 22%, 43% and 37% of the TP export at the 17, 211 and 1524 ha catchment areas, respectively. As the chemical fertilizer was spread during the grass growth months (March to September), it has less immediate impact on stream water quality than the slurry applications. We also show that as the catchment scale increases, the P concentrations and P export decrease, confirming dilution due to increasing rural catchment size. In the longer term, the excess P from fertilizer maintains high soil P levels, an antecedent condition favourable to P loss from soil to water. This study confirms the significant negative water quality impact of excess P applications, particularly liquid animal slurry applications in wet winter months. The findings suggest that restricted P application in wet months can largely reduce the P losses from soil to water.     

Mercury in some chemical fertilizers and the effect of calcium superphosphate on mercury uptake by corn seedlings(Zea mays L.)

Mercury (Hg) contents in ten chemical fertilizers were determined, and the effect of calcium superphosphate (CSP) on the uptake and translocation of Hg in corn seedlings was investigated by pot experiments. CSP was applied at the levels of 0, 66.7, and 133.4 mg P2O5/kg to Hg-treated (2 mg/kg) and untreated soils. CSP had the highest Hg content (5.1 mg/kg), followed by the NPK compound fertilizer 15-5-5 (15% N, 5% P2O5, 5% K2O) (1.2 mg/kg), then by nitrogen fertilizers (except for ammonia sulfate) and potassium fertilizers. Application of CSP did not obviously iuence the biomass of corn roots, but it significantly increased the biomass of corn shoots in Hg-treated soil. Application of CSP at the levels of 66.7 and 133.4 mg P2O5/kg did not obviously iuence the uptake of Hg by corn seedlings on soils without Hg treatment, but it decreased the Hg uptake of corn seedlings significantly on Hg-treated soils. The transfer coefficient of Hg in corn seedlings improved slightly on soils without Hg treatment, but decreased slightly on Hg-treated soils with the application of CSP. These results implied that CSP could ameliorate Hg toxicity to corn seedlings by inhibiting the uptake and the translocation of Hg in plants on Hg-polluted soils.     

Integrated nutrient management and waste recycling for restoring soil fertility and productivity in Japanese mint and mustard sequence in Uttar Pradesh, India

Supplementing the nutrient requirement of crops through organic manures plays a key role in sustaining soil fertility, and crop productivity and reducing use of fossil fuels. Field experiments were conducted for 2 years at two different locations (i.e. Lucknow and Pantnagar) in Uttar Pradesh, India. The objectives of the study were to assess the herb and essential oil yields of Japanese mint (Mentha arvensis cv. Hy 77), and its nutrient accumulation under single and combined applications of organic manures and inorganic fertilizers (NPK). Changes in physical and chemical characteristics of the soils (Fluvisols, Mollisols) were also determined. Eight treatments comprising different combinations of NPK through inorganic fertilizers and farm yard manure (FYM) were compared. The distilled waste of mint after extraction of essential oil was recycled to soils in the plots to supplement the nutritional requirement of the succeeding mustard crop (Brassica juncea cv. Pusa Bold). Herb and essential oil yield of mint were significantly higher with combined application of organic and inorganic sources of nutrients as compared to single applications. Accumulation of N and P was at par under full inorganic and combined supply whereas, K accumulation was higher with the former. Soil organic C and pH after harvest of mint did not significantly differ among the treatments, but the level of mineralizable N, Olsen-P and NH₄OAc extractable K were higher in soil with integrated supply of nutrients. Significant increase in soil water stable aggregates, organic C, available NPK and microbial biomass, and decrease in soil bulk density were observed with waste recycling over fertilizer application. These benefits were reflected in the seed and stubble yield of mustard which succeeded mint. This study indicates that combined application of inorganic fertilizers with organics helps in increasing the availability of nutrients and crop yield and provides a significant effect to the succeeding crop. Similarly, recycling crop residues reduces the need for fossil fuel based fertilizer, and helps in sustaining and restoring soil fertility in terms of available nutrients and major physical and chemical characteristics of the soil.     

含钛高炉渣合成复合肥料及大豆栽培实验研究

以含钛高炉渣为原料采用加热法制备肥料,以提高其溶解性能,使其中的营养元素转化为易被植物吸收利用的形式,并通过栽培实验研究了肥料对大豆生长状况、性状、产量和营养成分的影响。结果表明:炉渣中Mg、Ti、Fe的溶出率分别为88%、84%和75%,肥料中可被植物有效利用的元素有氮、硅、硫、钙、镁、铁和钛。该肥料可以使大豆产量、百粒重和叶片叶绿素含量明显增加;生育期缩短2 d;籽粒的氮、磷和钾含量显著增加,蛋白质和淀粉含量增加。施用该固态复合肥并未导致钒和铬等重金属元素在大豆体内的富集。     

Rice mill waste as organic manure on a degraded Alfisol

In much of sub-Saharan Africa (SSA), the lack of organic soil amendments constitutes one of the principal causes for declining soil fertility in intensifying farming systems. The challenge, therefore, remains to increase the availability of organic inputs and to develop recommendations for their combination with inorganic fertilizers. An on-farm experiment was conducted in the northern Guinea savanna of Nigeria to evaluate the fertilizer effect of rice (Oryza sativa L.) mill waste (RMW) on a degraded Alfisol. The decomposition and nutrient (N and P) release patterns of RMW were studied using the litterbag technique, and the effect on maize yield and soil properties was determined. The RMW was applied at rates of 0, 5, 10, and 15 Mg DM ha⁻¹ and was applied either unburnt or burnt (farmers’ practice). In both years, compound fertilizer was broadcast during land preparation on all plots at rates of 40 kg N ha⁻¹, 17 kg P ha⁻¹, and 33 kg K ha⁻¹.Results obtained in the litterbag study showed that, at maize harvest, more than 90% of the P had been released from the decomposing RMW. However, around 60% of the organic C and 45% of the N still remained. Compared to the control treatment (0 Mg ha⁻¹ RMW), which yielded 0.55 Mg ha⁻¹, maize (Zea mays L.) grain yields were increased by 95% when 10 Mg ha⁻¹ of unburnt RMW was applied, and by 147% with 15 Mg ha⁻¹ (mean of 2 years). In contrast, burnt RMW did not result in significant yield increases. The cumulative application of 30 Mg ha⁻¹ of unburnt RMW significantly increased the soil organic carbon in the surface soil from 0.7% (0 Mg ha⁻¹ RMW) to 1.3%.The results of this investigation indicate that RMW constitutes a valuable organic input in the Guinea savanna if applied unburnt at rates of 10–15 Mg ha⁻¹ in combination with inorganic fertilizer. The repeated application of unburnt RMW may contribute to the rehabilitation of degraded soils through the buildup of soil organic matter.     

Genotypic variations in the accumulation of Cd exhibited by di erent vegetables

It is an important approach to use the Cd-contaminated soils properly by growing low accumulator or excluder plants for Cd to produce safe foods. To find the suitable vegetable species for growing in Cd-contaminated soils, in the present study the variations in the Cd accumulation for twenty eight vegetable species and several cultivars of five common vegetables (cowpea, kidney pea, bitter gourd, cucumber and squash) were investigated in two soil Cd levels (1 and 2 mg/kg Cd). Experimental results showed that highly significant di erences in Cd concentration were evident among 28 vegetables. For example, spinach Cd concentrations were 110-fold and 175-fold higher than that of sweet pea under the 1 and 2 mg/kg Cd exposures, respectively. For Cd accumulation, the order of vegetable species was: leafy vegetables > solanaceous vegetables > kale vegetables > root vegetables > allimus > melon vegetables > legumes. Distinctive di erences were also identified when comparing di erent cultivars of the five common vegetables with an average range of 0.003–0.094 mg/kg Cd. Our results indicated that a large genotypic variation existed among vegetable species or cultivars when subjected to Cd exposure. Therefore, it is important and feasible to elect/breed vegetable species/cultivars with low accumulation of Cd, especially in mildly Cd-contaminated soils.     

Soil quality response to long-term nutrient and crop management on a semi-arid Inceptisol

The soil quality concept provides a tool to help quantify the combined biological, chemical and physical response of soil to crop management practices. Our objective was to quantify effects of 10 fertilizer and farm yard manure (FYM) treatments applied for 31 years to a rotation that included maize (Zea mays), pearl millet (Pennisetum americanum), wheat (Triticum aestivum) and cowpea (Vigna unguiculata) on an Inceptisol at the Indian Agricultural Research Institute in New Delhi, India. A soil quality index (SQI) based on six soil functions (i.e. the soil's ability to: accommodate water entry, facilitate water movement and storage, resist surface degradation, resist biochemical degradation, supply plant nutrients and sustain crop productivity) was derived for each treatment using bulk density, water retention, pH, electrical conductivity (EC), plant-available nutrients, soil organic matter (SOM), microbial biomass, soil enzymes and crop yield. SQI ratings ranged from 0.552 (unfertilized control) to 0.838 for the combined NPK fertilizer plus manure treatment. Comparisons among treatments indicated that SQI increases associated with the combined (NPK + manure) treatment were distributed as follows: N (7.1% increase), P (7.8%), K (14.4%), Zn (4.8%) and manure (15%). The control (−11.4%) and N alone (−5.1%) resulted in degradation compared to a reference soil (no fertilizer/manure, no crop), and NP alone or sub-optimal rates of NPK were on the verge of degradation. Hand weeding and sulphur application had no measurable effect on SQI. High K fixing capacity was a limiting factor for these soils, even when FYM was applied. The lower SQI rating associated with N or NP-only treatments suggests that two of the most common fertilizer management practices in India may not be sustainable. The SQI was calculated without the weighting factors too, which revealed that the weighting factors did not affect the relative ranks of individual treatments.