The effect of managing improved fallows of Mucuna pruriens on maize production and soil carbon and nitrogen dynamics in sub-humid Zimbabwe

Mucuna pruriens has emerged as a successful forage or green manure legume for use in the smallholder animal-livestock systems of Zimbabwe. The efficiency of N recovery from mucuna residues in subsequent maize crops can be low and the loss of nitrate nitrogen from the soil profile prior to maize N demand is proposed as a reason for this. An experiment was established in the 1999–2000 wet season at seven on-farm sites in a communal farming district of Zimbabwe (average rainfall 650–900 mm) on acidic (pH < 5), and inherently infertile soils with texture ranging from sandy/sandy loam (n = 5) to clay (n = 2). Improved fallows of mucuna grown for 19 weeks produced between 4.7 and 8.5 t/ha dry matter (DM) at the sandy/sandy loam sites and between 9.5 and 11.2 t/ha DM at the clay sites. This biomass was then either cut and removed as hay, or ploughed in as a green manure. Weedy fallow treatments, which represent typical farmer practice, produced 3.3–6.3 t/ha DM. A maize crop was then grown on these same sites in the following 2000–2001 wet season and the dynamics of soil N and C and maize production were investigated. Where mucuna was green manured, a positive linear response (r² = 0.72) in maize yield to increasing mucuna biomass (containing 101–348 kg N/ha) was found. On the sandy sites, and where no P fertiliser was applied to the previous mucuna phase, a maize grain yield of 2.3 t/ha was achieved following the mucuna green-manure system; this was 64% higher than the maize yield following the weedy fallow and 100% higher than the maize yield following the mucuna removed hay system. Apparent nitrogen recoveries in the range of 25 to 53% indicate that there are large quantities of nitrogen not utilised by the subsequent maize phase. The loss of 73 kg/ha of nitrate N from the soil profile (0–120 cm) early in the wet season and prior to maize N demand is proposed as a reason for low N recovery. No change in labile C (measured with 333 mM KMnO₄) was detected through the soil profile at this time and it is suggested that labile C movement occurred between the sampling times.     

Initial and residual effects of nitrogen fertilizers on grain yield of a maize/bean intercrop grown on a Humic Nitosol and the fate and efficiency of the applied nitrogen

Initial and residual effects of nitrogen (N) fertilizers on grain yield of a maize/bean intercrop grown on a deep, well-drained Humic Nitosol (66% clay, 3% organic carbon) were evaluated. Enriched (¹⁵N) N fertilizer was used to study the fate of applied N in two seasons: using urea (banded) at 50 kg N ha^–1 in one season, and¹⁵N-enriched urea (banded), calcium ammonium nitrate (CAN, banded), and urea supergranules (USG, point placement) were applied in the other season (different field) at 100 kg N ha^–1. Nitrogen fertilizer significantly (P = 0.05) increased equivalent maize grain yield in each season of application with no significant differences between N sources, i.e., urea, CAN, and USG. Profitmaximizing rates ranged from 75 to 97 kg N ha^–1 and value: cost ratios ranged from 3.0 to 4.8. Urea gave the highest value: cost ratio in each season. Most (lowest measurement 81%) of the applied N was accounted for by analyzing the soil (to 150 cm depth) and plant material. Measurements for urea, CAN, and USG were not significantly different. The high N measurements suggest low losses of applied N fertilizer under the conditions of the study. Maize plant recovery ranged from 35 to 55%; most of this N (51–65%) was in the grain. Bean plant recovery ranged from 8 to 20%. About 34–43% of the applied N fertilizer remained in the soil, and most of it (about 70%) was within the top soil layer (0–30 cm). However, there were no significant equivalent maize grain increases in seasons following N application indicating no beneficial residual effect of the applied fertilizers.     

The availability of nitrogen from sugarcane trash on contrasting soils in the wet tropics of North Queensland

Sugarcane crop residues (‘trash’) have the potential to supply nitrogen (N) to crops when they are retained on the soil surface after harvest. Farmers should account for the contribution of this N to crop requirements in order to avoid over-fertilisation. In very wet tropical locations, the climate may increase the rate of trash decomposition as well as the amount of N lost from the soil–plant system due to leaching or denitrification. A field experiment was conducted on Hydrosol and Ferrosol soils in the wet tropics of northern Australia using ¹⁵N-labelled trash either applied to the soil surface or incorporated. Labelled urea fertiliser was also applied with unlabelled surface trash. The objective of the experiment was to investigate the contribution of trash to crop N nutrition in wet tropical climates, the timing of N mineralisation from trash, and the retention of trash N in contrasting soils. Less than 6% of the N in trash was recovered in the first crop and the recovery was not affected by trash incorporation. Around 6% of the N in fertiliser was also recovered in the first crop, which was less than previously measured in temperate areas (20–40%). Leaf samples taken at the end of the second crop contined 2–3% of N from trash and fertilizer applied at the beginning of the experiment. Although most N was recovered in the 0–1.5 m soil layer there was some evidence of movement of N below this depth. The results showed that trash supplies N slowly and in small amounts to the succeeding crop in wet tropics sugarcane growing areas regardless of trash placement (on the soil surface or incorporated) or soil type, and so N mineralisation from a single trash blanket is not important for sugarcane production in the wet tropics.     

Use of nitrification inhibitors (neem and DCD) to increase N efficiency in maize-wheat cropping system

A 2-year field experiment was conducted to study the effects of the nitrification inhibitors dicyandiamide (DCD) and neem cake on the efficiency of applied prilled urea nitrogen in a maize-wheat cropping system. Prilled urea (PU), neem cake coated urea (NCU) and DCD blended urea (DCDU) were applied to maize at two levels (60 and 120 Kg N ha^–1) and two methods (all preplant and split) of N application along with a no-nitrogen control and their relative residual effect was studied on succeeding wheat grown with three levels of N as PU.In 1990 maize responded well to N up to 60 kg N ha^–1; at this level PU increased maize yield by 1.03 t ha^–1, whereas NCU and DCDU increased maize yield by 1.55 and 1.18 t ha^–1 over the control, which was equivalent to an application of 127 and 94 kg N ha^–1 as PU, respectively. Furthermore, when the results were averaged over two years of study, residual N from the application of NCU and DCDU at 60 kg N ha^–1 left after maize cropping increased the grain yield of the succeeding wheat crop grown with 60 kg N ha^–1 as PU by 1.97 and 1.68 t ha^–1, respectively, over a no nitrogen control or 60 kg N ha^–1 as PU applied to the maize. This was equal to an application of 96 and 82 kg N ha^–1 as PU to wheat.Thus, neem cake increased the efficiency of urea N applied to maize and benefits were also seen in the succeeding wheat yield in the maize-wheat cropping system.     

Yield response of maize (Zea mays L.) to crop residue management on two major soil types Of Alemaya, Eastern Ethiopia: I. Effects of varying rates of applied and residual N and P fertilizers

Field trials were conducted on two soil types for seven years (1988–1994) to investigate grain yield response of maize to crop residue application as influenced by varying rates of applied and residual N and P fertilizers. Yearly application of N and P fertilizers at both one-half and full recommended rates resulted in grain yield increases of more than 500 and 1100 kg ha-1, respectively over application of only crop residue. Moreover, grain yield responses due to residual N and P fertilizers applied only during the first year were found to be comparable to the yearly applications of these fertilizers. Rainfall and soil type have exerted considerable influences on the grain yield response obtained in this study. Grain yield exhibited a corresponding decrease with decreasing rainfall. Grain yield increases on Typic Pellustert were relatively higher than on Typic Ustorthent.     

Effect of fertilization on organic and microbial biomass nitrogen using15N under corn (Zea mays L.) in two Quebec soils

Changes in soil organic N following fertilizer N applications are related to soil quality and subsequent N uptake by plants. Recovery of fertilizer N as organic N and soil microbial biomass N within two corn (Zea mays L.) fertilization systems was studied using¹⁵N on a Chicot soil (fine-loamy, mixed, frigid, Typic Hapludalf) and a Ste. Rosalie soil (fine, mixed, frigid, Typic Humanquept) in southwestern Quebec in 1989 and 1990. The two fertilization systems studied received a recommended rate of 170-44-131 kg (normal rate) and a high rate of 400-132-332 kg of N-P-K per hectare. Increasing fertilization rates above normal increased microbial biomass N immobilization with a subsequent greater N release. Higher fertilization rates significantly increased both the magnitude of soil microbial biomass N and microbial fertilizer N recovery in the soil microbial biomass.     

The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils

Field trials were carried out to study the fate of¹⁵N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha^–1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha^–1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha^–1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha^–1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.     

The influence of rate and time of nitrate supply on nitrogen fixation and yield in pea (Pisum sativum L.)

The influence of nitrate N supply on dry matter production, N content and symbiotic nitrogen fixation in soil-grown pea (Pisum sativum L.) was studied in a pot experiment by means of¹⁵N fertilizer dilution. In pea receiving no fertilizer N symbiotic nitrogen fixation, soil and seed-borne N contributed with 82, 13 and 5% of total plant N, respectively. The supply of low rates of nitrate fertilizer at sowing (starter N) increased the vegetative dry matter production, but not the seed yield significantly. Nitrogen fixation was not significantly decreased by the lower rates of nitrate but higher rates supplied at sowing reduced the nitrogen fixation considerably. Applying nitrate N at the flat pod growth stage increased the yield of seed dry matter and N about 30% compared to pea receiving no nitrate fertilizer. Symbiotic nitrogen fixation was reduced only about 11%, compared with unfertilized pea, by the lowest rate of nitrate at this application time. The pea very efficiently took up and assimilated the nitrate N supplied. The average fertilizer N recovery was 82%. The later the N was supplied the more efficiently it was recovered. When nitrate was supplied at the flat pod growth stage 88% was recovered, and 90% of this N was located in the seeds.     

Influence of dry season supplementation for cattle on soil fertility and millet (Pennisetum glaucum L.) yield in a mixed crop/livestock production system of the Sahel

An experiment was conducted in 1996 and 1997 in semi-arid Niger, to determine the influence of supplementation (no supplement, supplemented with millet bran + simple superphosphate + blood meal) of cattle and mulching (0 or 3 t ha⁻¹ of Aristida sieberiana straw) on soil fertility and millet yield. Manure was applied through corralling at a rate of 3 t faecal dry matter (FDM) ha⁻¹ alone or associated to mulching. The residual effects of the treatments were measured on a second millet crop in 1997. Compared to control, the association of mulching and corralling of supplemented as well as non supplemented cattle increased soil pH (KCl) (P < 0.01), Bray1-P (P < 0.05) and NH₄-N (P < 0.05); grain by 136% (P < 0.01) stover yeild by moer than 150% (P < 0.05); and N and P uptake (P < 0.01) during the two cropping seasons. The association of mulching and corralling increased soil NH₄-N (P < 0.01) and soil pH (P < 0.01), compared to the sole corralling. The improvement of soil chemical properties resulted in grain yield increases of 54% (P < 0.01) and stover increases of 42% (P < 0.01). The effect of mulching and corralling association on grain and stover yeilds was higher when cattle were supplemented (67 and 50%) than when they were not supplemented (30 and 26%). The effects of the supplementation on grain and stover yields, and N and P uptake by millet, were restricted, when animals were corralled on bare soil (no mulching). The residual effects of supplementation were minimal. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of tree foliage of locust bean (Parkia biglobosa) and neem (Azadirachta indica) on soil fertility and productivity of maize in a savanna alfisol

Organic matter (OM) management is key to sustainable fertility and productivity of tropical soil systems. Short-term evaluation of the potentialsof foliage of neem and locust bean in soil fertility improvement, as measured by the productivity of maize, was carried out on a savanna Alfisol from 1995 to1997. The trees are indigenous to the savanna, and common in farms and homesteads in the region. The objective was to determine the effects of theseeasily renewable and cheap OM sources on maize response to applied inorganic fertilizer and soil chemical properties. Treatments consisted of three sourcesof organic matter: no-OM, neem and locust bean, and three rates of inorganic fertilizer, applied at 0, and of the recommended rate of120–27–50 NPK for maize, which in addition served as check. Results obtained over the three seasons were consistent, and revealed that neem wassuperior to locust bean by a factor of 2 and also to no-OM treatments, but were all inferior to the recommended fertilizer rate (with a maximum yield of 3.75t/ha). Isolated relative effects for neem and locust bean only in the third year were 138% and 86% respectively, and declined progressively withincreasing levels of applied inorganic fertilizer. This trend was consistent for the three years, during which soil productivity (relativity index) clearlyappreciated. Results also revealed that P and organic C accumulation was greater with locust bean, but neem decomposed faster and depressed pH less, a clearindication that indices of soil productivity may not always be tied to OM or absolute values of soil properties alone in savanna soil systems. The studyalso revealed that the effects of the tree foliages, the inorganic fertilizer rates and the interactions were significant at various levels of probability forgrain, stover, plant height, available P, OM and pH. There was the possibility of better crop performance with combinations of OM and inorganic fertilizer levels for the soils. Integrated fertility management systems using 3 tons of neem foliage and recommended inorganic fertilizer rate produced a goodmaize crop, and offers an economically viable option for the resource poor maize farmers of the Nigerian savanna.     

氮气及Si3N4＋BN＋SiO2埋粉对ZrO2相组成的影响

本文研究了在１７７０℃－１８００℃，保温一小时的烧成条件下，氮气及ＳｉｅＮ４＋ＢＮ＋ＳｉＯ２埋粉对工业ＺｒＯ２和Ｙ－ＴＺＰ相组成的影响。实验结果发现：氮对纯工业ＺｒＯ２和Ｙ－ＴＺＰ均有稳定作用。     

Effect of Substrate Composition (C/N/P ratio) on Microbial Community and Membrane Fouling Tendency of Biomass in Membrane Bioreactors

In this study, biomass characteristics including bacterial community, extracellular polymeric substances (EPS) production, and membrane fouling propensity were examined when the membrane bioreactors (MBRs) were fed with different substrates (i.e., different C/N/P ratios). Denaturing gradient gel electrophoresis (DGGE) analysis revealed that significant shifts of bacterial communities happened when increasing nitrogen or phosphorus loading in the MBRs, which followed in an almost similar way. At steady state, the biomass from the low C/N- and C/P-MBRs had comparable concentrations and produced similar EPS levels as those in the control MBR. However, the median particle size increased when the MBRs fed with low C/N- or C/P- substrate, possibly associated with the filamentous bacteria propagating in the MBRs. Increasing nitrogen or phosphorus loading 1-fold could not induce more serious membrane fouling compared to the control MBR.     

The Effects of Ozonation,Biological Filtration and Distribution on the Concentration of Easily Assimilable Organic Carbon (AOC) in Drinking Water

The concentration of easily assimilable organic carbon (AOC) as determined with growth measurements using wo bacterial cultures, increased linearly with ozone dosage at values below 1 mg O₃/mg of C. Moreover, a linear relationship was found between AOC increase and the decrease of UV absorbance of water after ozonation with various dosages. Biological filtration in water treatment reduced AOC concentrations, but the remaining values were above the AOC concentration before ozonation. This AOC removal was attended with an increased colony count in the filtrate. The AOC concentration of drinking water produced by the application of ozone in water treatment decreased during distribution. The greatest decrease was observed with the highest AOC concentration. Also in this situation, the highest colony counts were found. To date, ozonation is applied in seven water treatment plants in the Netherlands.     

Continuous production of poly(3-hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-3-hydroxyvalerate): Effects of C/N ratio and dilution rate on HB/HV ratio

Ralstonia eutropha was cultivated in a continuous stirred fermenter with various C/N ratios (20, 30, and 40), dilution rates, and organic salt substrates (sodium propionate or sodium valerate) to explore the microbial growth and the poly(3HB-co-3HV) accumulation. When sodium propionate was used as the secondary carbon source, the HB/HV molar ratio at various C/N ratios and dilution rates did not change appreciably (approximately 90: 10). The highest poly(3HB-co-3HV) content in biomass (41.8%) and poly(3HB-co-3HV) productivity (0.100 g/(L·h)) occurred under the condition with a C/N ratio of 20 and dilution rate of 0.06 h⁻¹. When sodium valerate was used as the secondary carbon source, the productivity of poly(3HB-co-3HV) increased with increasing dilution rate for the C/N ratio of 30 and 40. The average HB/HV molar ratio ranged from 48: 52 to 78: 32. The feeding of sodium valerate promoted the accumulation of HV better than feeding sodium propionate did. This study shows that a potential strategy of manipulating by both C/N ratio and dilution rate could be used to control the HV unit fraction in poly(3HB-co-3HV) in a continuous cultivation.     

Nitrogen rhizodeposition from soybean (<Emphasis Type="Italic">Glycine max</Emphasis>) and its impact on nutrient budgets in two contrasting environments of the Guinean savannah zone of Nigeria

Nitrogen (N) rhizodeposition by grain legumes such as soybean is potentially a large but neglected source of N in cropping systems of Sub-Saharan Africa. Field studies were conducted to measure soybean N rhizodeposition in two environments of the Guinean savannah of Nigeria using ¹⁵N leaf labelling techniques. The first site was located in Ibadan in the humid derived savannah. The second site was in Zaria in the drier Northern Guinean savannah. Soybean N rhizodeposition in the top 0.30 m of soil varied from 7.5 kg ha⁻¹ on a diseased crop in Ibadan to 33 kg ha⁻¹ in Zaria. More than two-thirds of soybean belowground N was contained in the rhizodeposits at crop physiological maturity, while the rest was found in the recoverable roots. Belowground plant-derived N was found to constitute 16–23% of the total soybean N. Taking rhizodeposited pools into account led to N budgets close to zero when all residues were removed. If residues were left in the field or recycled as manure after being fed to steers, soybean cultivation led to positive N budgets of up to +95 kg N ha⁻¹. The role and potential of grain legumes as N purveyors have been underestimated in the past by neglecting the N contained in their rhizodeposits.