Nitrogen fertilizer equivalencies of organics of differing quality and optimum combination with inorganic nitrogen source in Central Kenya

Decline in crop yields is a major problem facing smallholder farmers in Kenya and the entire Sub-Saharan region. This is attributed mainly to the mining of major nutrients due to continuous cropping without addition of adequate external nutrients. In most cases inorganic fertilizers are expensive, hence unaffordable to most smallholder farmers. Although organic nutrient sources are available, information about their potential use is scanty. A field experiment was set up in the sub-humid highlands of Kenya to establish the chemical fertilizer equivalency values of different organic materials based on their quality. The experiment consisted of maize plots to which freshly collected leaves of Tithonia diversifolia (tithonia), Senna spectabilis (senna) and Calliandra calothyrsus (calliandra) (all with %N>3) obtained from hedgerows grown ex situ (biomass transfer) and urea (inorganic nitrogen source) were applied. Results obtained for the cumulative above ground biomass yield for three seasons indicated that a combination of both organic and inorganic nutrient source gave higher maize biomass yield than when each was applied separately. Above ground biomass yield production in maize (t ha^–1) from organic and inorganic fertilization was in the order of senna+urea (31.2), tithonia+urea (29.4), calliandra+urea (29.3), tithonia (28.6), senna (27.9), urea (27.4), calliandra (25.9), and control (22.5) for three cumulative seasons. On average, the three organic materials (calliandra, senna and tithonia) gave fertilizer equivalency values for the nitrogen contained in them of 50, 87 and 118%, respectively. It is therefore recommended that tithonia biomass be used in place of mineral fertilizer as a source of nitrogen. The high equivalency values can be attributed to the synergetic effects of nutrient supply, and improved moisture and soil physical conditions of the mulch. However, for sustainable agricultural production, combination with mineral fertilizer would be the best option.     

Major nutrient balances in small-scale vegetable farming systems in peri-urban areas in China

Balances of major nutrients such as nitrogen (N), phosphorus (P), and potassium (K) in small-scale farming systems are of critical importance to nutrient management and sustainable agricultural development. Mass balances of N, P, and K and some of their influencing factors were studied for two years from July 2003 to July 2005 on small-scale vegetable-farming systems in two contrasting peri-urban areas (Nanjing and Wuxi) of the Yangtze river delta region of China. This balance approach considered organic fertilizer inputs (cow manure, pig manure, and human biosolids), inorganic fertilizer inputs (urea, composite fertilizer, and phosphates), irrigation water, and atmospheric deposition; and considered outputs by vegetables. Input via organic fertilizers was significant for all element balances in the Nanjing area. Inorganic and organic fertilizer, particularly inorganic fertilizer, contributed major nutrient inputs to the system in the Wuxi area. Compared with nutrient output by vegetables, there were significant surpluses of N and P on two vegetable farm systems. Furthermore, N surplus in the Nanjing area was higher than that in the Wuxi area with an inverse relationship to P surplus. In contrast, the general trend of K balances was negative on both sites; hence, the nutrient use efficiency was significantly lower for N and P than K. The nutrient imbalance may be attributed to the differences between fertilizer types and management modes driven by social economic status differences among farmer households. The large N and P net excess creates an environmental threat because of potential losses to ground or surface waters, whereas negative K balance creates soil fertility risks. The results highlight researchers’ and farmers’ need to develop rational fertilization technology to optimize nutrient management on vegetable farmlands to promote sustainable agricultural development in peri-urban areas.     

Evaluation of current fertilizer practice and soil fertility in vegetable production in the Beijing region

A survey on current fertilizer practices and their effects on soil fertility and soil salinity was conducted from 1996 to 2000 in Beijing Province, a major vegetable production area in the North China Plain. Inputs of the major nutrients (NPK) and fertilizer application methods and sources for different vegetable species and field conditions were evaluated. Excessive N and P fertilizer application, often up to about 5 times the crop requirement in the case of N, was very common, especially for high-value crops. Potassium supply may have been inadequate for some crops such as leafy vegetables. Urea, diammonium orthophosphate ((NH₄)₂HPO₄) and chicken manure were the major nutrient sources for vegetable production in the region. Over 50% of N, 60% of P and nearly 90% of K applied originated from organic manure. Total N application rate for open-field Chinese cabbage from organic manure and inorganic fertilizers ranged from 300 to 900 kg N ha^–1 on 78% of the farms surveyed. More than 35% of the surveyed greenhouse-grown tomato crops received > 1000 kg N ha^–1 from organic and inorganic sources. A negative K balance (applied K minus K removed by the crop) was found in two-thirds of the surveyed fields of open-field Chinese cabbage and half of the surveyed fields of greenhouse-grown tomato. Plant-available N, P and K increased with increasing length of the period the greenhouse soils had been used for vegetable production. Similarly, soil salinity increased more in greenhouse soils than in open-field soils. The results indicate that balanced NPK fertilizer use and maintenance of soil quality are important for the development of sustainable vegetable production systems in this region.     

肥料二次加工新技术的研究进展概述

概述了肥料二次加工的必要性,详述了利用农业、工业、畜牧业等的废弃资源作为肥料二次加工的原料来源,不仅可克服施肥中存在的问题,而且可"变废为宝"保护环境。指出了肥料二次加工中应注意的问题,即有机与无机相结合,大量元素与中、微量元素相结合,速效与缓效相结合,农药与肥料相结合,营养元素的配置上注重土壤养分与不同农作物的养分需求相结合。今后肥料二次加工应向高效化、液体化、缓效化、复合化及复混化、功能化、生态环保化发展,只有重视科技创新,才能从根本上提升肥料的竞争力。     

腐植酸聚失肥的研制与开发

利用黄腐酸为载体研制开发腐植酸聚失肥是在低碳经济、可持续农业、有机农业、生态农业大环境下发展的新肥源和新型肥料产业。该肥料的主要特点和功能：聚合土壤中养分,控制养分流失;提高肥料利用率,补充化肥的不足;改良土壤,增强作物抗逆性;提高作物产量,改善产品品质;科技含量高,生产工艺先进。     

Fly ash—a potential source of soil amendment and a component of integrated plant nutrient supply system

In sub-tropical climate the high rainfall and high temperature is responsible for low soil productivity due to losses of bases and low organic matter content in soil. In acid lateritic soil low availability of P and high content of Al and Fe posses nutritional imbalance which is generally corrected by lime materials. Alkaline fly ash can be used in such problematic soil as an amended material and also it acts as source of plant nutrition for crop production. An attempt was made to develop an integrated plant nutrient supply system utilizing the fly ash along with other organic wastes like paper factory sludge, farm yard manure, crop residue and chemical fertilizers for rice-peanut cropping system. Direct and residual effects of fly ash were assessed based on crop yield, nutrient uptake and changes in soil characteristics. The application 10 t ha⁻¹ of fly ash in combination with organic sources and chemical fertilizer increased the grain yield and nutrient uptake of rice, and pod yield of peanut compared to chemical fertilizers alone. The heavy metal contents in plant and soil system was analyzed and found to remain below the permissible level. The results indicated that fly ash could be applied safely to tropical agro eco-systems for retaining productivity of acid lateritic soil.     

有机中微肥在沃土工程建设中的作用

围绕沃土工程建设,分析了肥料的生产和应用中存在的“三重三轻”的问题。笔者认为:测土平衡施肥是沃土工程建设的关键;土壤营养元素的丰缺是肥料二次加工的理论依据;必需元素的有效性是优质配方肥料质量的重要指标;活性必需元素的生产成本是配方肥能否推广的重要因素;肥料生产企业应把提高肥料利用率作为研究的课题。有机中微肥在肥料生产,尤其是二次加工中扮演了重要角色,是沃土工程建设中必不可少的要素。     

Soil fertility status and nutrient input–output flows of specialised organic cropping systems: a review

The management of specialised organic crops for vegetable and fruit production require the use of imported fertilizers. A wide range of fertilizers is currently available to organic farmers. These include bulky organic materials with a relatively low nutrient concentration commonly used as base dressing (e.g. composts, solid animal manures) and complementary commercial organic fertilizers with relatively high nutrient concentrations to adjust nutrient supply to crop requirements (e.g. feather meal, hoof and horn meal, vinasse, meat and bone meal, etc.). Nutrient imbalances are a major threat affecting the long term sustainability of horticultural and fruit cultivation systems. Major reasons for these imbalances are the biased element composition of base as well as complementary fertilizers in relation to the nutrient offtakes via harvested products. Gaseous nitrogen losses during manure management and gaseous as well as leaching nitrogen losses after application are major reasons for such nutrient imbalances, as they lead to a relative increase in the concentration of other elements. Conceptual weaknesses in the fertilizer approach in organic farming exist, namely the preferred application of slow release nitrogen fertilizers often rich in phosphorus. This review suggests that the current soil fertility approaches based on application of solid fertilizers and simultaneously a low rate of N inputs via N₂ fixation do not foster balanced nutrient levels. The key challenge is to design cropping systems with a higher share of N inputs via biological N₂ fixation, and to find fertilizers with a nutrient stoichiometry better suited to match the overall specific offtakes of fertilized crops.     

Soil nutrient depletion by agricultural production in Southern Mali

The degree of soil mining by agricultural production in Southern Mali is assessed by calculating nutrient balances: differences between the amount of plant nutrients exported from the cultivated fields, and those added to the fields. Export processes include extraction by crops, losses due to leaching, to erosion, and to volatilization and denitrification. Inputs include applications of fertilizer and manure, restitution of crop residues, nitrogen fixation, atmospheric deposition of nutrients in rain and dust, and enrichment by weathering of soil minerals. Nutrient balances are calculated for N, P, K, Ca, and Mg. Both pessimistic and optimistic estimates are given.The resulting figures indicate, even when the most optimistic estimates are used, large deficits for nitrogen, potassium and magnesium. For the region as a whole, the calculated deficits are -25 kg N/ha,-20 kg K/ha, and -5 kg Mg/ha. Further, acidification is to be expected, in particular in areas where cotton is grown. The deficits are caused by traditional cereal crops, but also by cotton and especially by groundnut. The latter two crops are fertilized, but insufficiently. It is important to note, that the negative figures are not automatic recommendations for application of a specific amount of additional fertilizer. For phosphorus and calcium the balance of the region as a whole appears to be about in equilibrium, but locally large variations may occur.Erosion and denitrification are important causes of nutrient loss, accounting respectively for 17 and 22% of total nitrogen exports. Atmospheric deposition and weathering of minerals in the soil are still important nutrient inputs that contribute as much as nutrients as organic and mineral fertilizer combined. Nutrient depletion is very large in comparison to the amount of fertilizer applied. Drastic options, such as doubling the application of fertilizer or manure, or halving erosion losses, even if feasible, would still not be enough to make up for the calculated deficits.The annual value of withdrawn nutrients, if related to prices of fertilizers, varies between 10,000 and 15,000 FCFA/ha (40-60 US $/ha). Since the estimated average gross margin from farming in this area is 34,000 FCFA/ha (123 US $/ha), soil mining appears to provide an amount equal to 40% of farmers' total income from agricultural activities.     

The role of inorganic fertilizers and their management practices

Nutrient management is the key issue in sustainable soil fertility. N, P, K fertilization aims not only for a high economic return of the investment through optimized yield and quality, but also for minimum environmental hazards. The basic concept underlying integrated plant nutrition systems, is the maintenance and possible increase of soil fertility for sustaining enhanced crop productivity through optimal use of all sources of plant nutrients, particularly inorganic fertilizer, in an integrated manner and as appropriate to each specific ecological, social and economic situation. Much research has established the importance of fertilizers in increasing the fertility of soil and in influencing its productivity. It has been observed that applying fertilizers causes many changes in the soil, including chemical changes, that can positively or negatively influence its productiveness. Only a fraction of the fertilizer applied to the soil is taken up by the crop, the rest either remains in the soil or is lost through leaching, physical wash-off, fixation by the soil, or release to the atmosphere through chemical and microbiological processes. The critical information on the relative merits of different fertilization practices such as method of fertilizer placement, time and rate of application and type of fertilizers, is essential. Results from different field and laboratory experiments which helped to achieve maximum efficiency, in the most economical and sustainable way of fertilizer use to reduce the nutrient losses and production costs to the farmers and prevent environmental pollution are presented in the paper.     

提高化肥利用率 发展低碳农业

提高肥料利用率、创新肥料生产技术是发展低碳经济的需要。提高农作物吸收养分能力、测土平衡施肥、开发新型肥料、利用有机废弃资源生产有机肥、加速秸秆应用研究是提高肥料利用率的有效途径,不仅可减轻化肥对环境的污染,而且还可以增强农作物的抗病、抗寒、抗高温的能力,提高农业投入产出比,进而实现农业低碳经济。     

Nutrient evolution in soil and cereal yield under different fertilization type in dryland

Under semiarid conditions the response of crops to synthetic fertilizers is often reduced. Organic fertilizers can be used to provide a continuous source of nutrients for the crops. The soil nitrogen and crop yield in a rotation of durum wheat (Triticum durum)–fallow-barley (Hordeum vulgare)–vetch (Vicia sativa) were studied during 4 years when synthetic fertilizer (chemical), compost (organic) or no fertilizer (control) were applied in a field with high initial contents of soil NO₃–N (> 400 kg N ha⁻¹), phosphorus (22 mg kg⁻¹) and potassium (> 300 mg kg⁻¹). Changes in soil organic matter, phosphorus and potassium were also measured. During the crop period, chemical fertilization significantly increased the content of soil NO₃–N in the first 0.30 m of soil with respect to organic fertilization and the control. The yield of wheat and barley was not increased after applying chemical or organic fertilizer with respect to the unfertilized plots. The estimated losses of nitrogen were similar for the three types of fertilization, as well as the uptake of nitrogen for the total biomass produced. The initial levels of organic matter and phosphorus were maintained, even in the plots that were not fertilized, while the potassium decreased slightly. Thus, the rotation and burying of crop residues were enough to maintain the crop yield and the initial content of nutrients.     

Effects of long-term fertilization and mulch on soil fertility in contour hedgerow systems: A case study on steeplands from the Three Gorges Area,China

The use of contour hedgerows is widely advocated to sustain crop production and reduce soil loss on steeplands in the Three Gorges Area of China. However, little is known about the effects of soil management on soil fertility within these systems, or about the spatial gradients in soil nutrients that may develop in terraces formed behind the vegetative barriers. Therefore, we carried out a study on the effects of various long-term soil management practices on soil fertility and spatial variation of fertility between hedgerows. At a site in the Three Gorges Area, China, we applied five treatments to a contour hedgerow system: control (no fertilizer and manure); chemical fertilizer (CF); chemical fertilizer and mulch (CF + MU); pig manure (PM); and mulch, pig manure, and chemical fertilizer (CF + PM + MU). Soil samples were collected from the topsoil horizon (0–20 cm) of the selected five treatments in 2006 after 11 crop cycles, and physical and chemical properties were analyzed. The results showed that chemical fertilizer clearly improves nutrient status of the topsoil, while pig manure also increased the amount of soil organic matter. This increase in organic matter was associated with an increase in soil aggregate stability, a reduction in bulk density, and reduced penetration resistance of the soil. Mulch with pig manure and chemical fertilizer was the best management practice for improving soil quality and crop yields in the Three Gorges Area. Further, mulch and pig manure addition also decreased the magnitude of the spatial variation, but did not offset the soil fertility gradients because tillage resulted in significant movement of soil. More favorable soil properties were found at the lower positions within each alley, regardless of the management practice applied.     

不同种类填料对复合肥肥效的影响

简要介绍了复合肥生产中对填料的要求,测定了不同填料对复合肥中氮、磷、钾养分释放速率的影响。通过盆栽和多点大田试验,研究了8种不同填料对复合肥养分释放以及不同区域肥效的影响,为区域配方肥生产提供技术支撑。     

浅析山西省土壤肥力动态变化趋势

根据近年来山西省土壤肥力动态监测数据,土壤中有机质呈不断下降的趋势,而全氮、碱解氮、速效磷、速效钾则表现上升趋势。土壤养分的这种变化趋势反映出近年来许多农民都以施用化肥为主,施有机肥的数量在逐年减少,长此下去,这将会导致土壤肥力整体贫瘠化,值得引起大家的重视。     

Additional effects of fertilizing on several foliar nutrient concentrations and ratios inEucalyptus grandis

The interaction responses to N, P, K fertilizing and limimg in four experiments withEucalyptus grandis are described. Inclusion of the N—P and P—K relationships gives a clearer understanding of the nutrient requirements of this species. Phosphorus and nitrogen supply is of great importance, but must be well balanced when either or both are adequately supplied in specific circumstances. Potash supply is also of importance, especially in conjunction with phosphorus, although no direct benefit has been found in these experiments. Increased soil pH reduces the uptake of these latter two nutrients. Magnesium is of greater importance and more readily taken up than calcium inE. grandis. Zinc seems to be the most important of the micro-nutrients and its interactions make it evident that Zn-enriched fertilizers should be used. Manganese levels are generally high where growing conditions are adverse. The great importance is indicated of the foliar N/P and P/K ratios as diagnostic criteria for evaluating fertilizer needs inE. grandis.     

Comparing the effectiveness of fertilizers

The effectiveness of different sources of the same nutrient should be compared using plots of yield versus fertilizer applied to find how much more of the less-effective source is needed to provide the same yield. This gives the same result as measuring the relative response to the two fertilizers — provided response is defined as the instantaneous slope of the yield-fertilizer curve rather than the yield produced by a given amount of fertilizer. In most cases, and especially for immobile nutrients, the relative effectiveness, measured as suggested, will not be affected by the level of application. It is reasonable to assume this simple case until this assumption can be disproved — rather than assuming a more complicated case in the first instance.     

The impact of historic land use and modern forestry on nutrient relations of Central European forest ecosystems

In the past forests in Central Europe were not only sources of timber and fuelwood but also sources of nutrients to sustain the human population. The use of forests as pastures is still common in some areas while other formerly widespread practices such as litter raking or pollarding have been abandoned. Harvesting of wood, a material of extremely low mineral nutrient content and of wide C/N-ratio depletes nutrients and acid neutralizing capacity at only moderates rates, harvesting of other biomass fractions has a much more severe impact on forest ecosystems. Soil acidification from intensive biomass harvesting of historic land use equaled or exceeded present soil acidification due to the deposition of air pollutants. As a result of historic land use the majority of Central European forest ecosystems was severely depleted of nutrients and acid neutralizing capacity when modern long-rotation forestry became the dominant form of forest land use. At present high deposition rates of acidifying air pollutants prevent the recovery of forest ecosystems in Central Europe. It has to be noted that ecosystem degradation due to excessive biomass harvesting led to systems which were depleted both in nitrogen and acid neutralizing capacity, while high nitrogen deposition rates from Central European air pollution cause a novel combination of progressive soil acidification and concurrent nitrogen saturation. This combination has a high potential for aggravating mineral nutrient deficiencies and nutritional disorders in forest ecosystems.     

Multiple benefits of manure: The key to maintenance of soil fertility and restoration of depleted sandy soils on African smallholder farms

Manure is a key nutrient resource on smallholder farms in the tropics, especially on poorly buffered sandy soils, due to its multiple benefits for soil fertility. Farmers preferentially apply manure to fields closest to homesteads (homefields), which are more fertile than fields further away (outfields). A three-year experiment was established on homefields and outfields on sandy and clayey soils to assess the effects of mineral nitrogen (N) fertilizer application in combination with manure or mineral phosphorus (P) on maize yields and soil chemical properties. Significant maize responses to application of N and manure were observed on all fields except the depleted sandy outfield. Large amounts of manure (17 t ha⁻¹ year⁻¹) were required to significantly increase soil organic carbon (SOC), pH, available P, and base saturation, and restore productivity of the depleted sandy outfield. Sole N as ammonium nitrate (100 kg N ha⁻¹) or in combination with single superphosphate led to acidification of the sandy soils, with a decrease of up to 0.8 pH units after three seasons. In a greenhouse experiment, N and calcium (Ca) were identified as deficient in the sandy homefield, while N, P, Ca, and zinc (Zn) were deficient or low on the sandy outfield. The deficiencies of Ca and Zn were alleviated by the addition of manure. This study highlights the essential role of manure in sustaining and replenishing soil fertility on smallholder farms through its multiple effects, although it should be used in combination with N mineral fertilizers due to its low capacity to supply N.     

Profitability of agro-forestry based soil fertility management technologies: the case of small holder food production in Western Kenya

Persistent food insecurity accompanied by low and declining farm household incomes are a common feature of many small holder maize and bean producers in western Kenya. This has been largely attributed to soil nutrient depletion, among other factors. One way of addressing soil fertility problems in many maize-based cropping systems is the use of agro-forestry based technologies. We carried out a survey in western Kenya (Vihiga and Siaya districts) aimed at analyzing the financial and social profitability of use of agroforestry based (improved tree fallows) and other soil fertility management technologies among smallholder farmers. The Policy Analysis Matrix (PAM) was used to determine the financial and social profitability of different production systems, which were categorized on the basis of the technology used to address soil fertility. Farm budgets were first prepared and in turn used to construct the PAMs for six production systems namely: maize–bean intercrop without any soil fertility management inputs; maize–bean intercrop with chemical fertilizers only; maize–bean intercrop with a combination of chemical fertilizers and improved fallows; maize–bean intercrop with improved fallows only; maize–bean intercrop with a combination of improved fallows and rock phosphate; and maize–bean intercrop with Farm Yard Manure (FYM) only. Results revealed that use of chemical fertilizers with improved fallows was the most profitable technology and thus the study recommended that farmers be encouraged to intensify the use of chemical fertilizers. To make chemical fertilizers more accessible to farmers, the study also recommended that good linkages be made between farmers and micro credit institutions so that small scale farmers are not actually biased against due to lack of collateral when credit is being advanced to clients.