Green Manure Treatments Research Articles

Growth and yield response of wheat to EM (effective microorganisms) and parthenium green manure

Parthenium weed (Parthenium hysterophorus L.) is rapidly spreading in many countries around the world and has become a serious threat to nature as well as managed ecosystems. The present pot experiment was conducted in 2005 -2006 to study the effect of parthenium green manure (1, 2, 3 and 4% on fresh weight bases) and EM (effective microorganisms), a biofertilizer, on the growth and yield of wheat (Triticum aestivum L.). EM application was carried out by applying 1 L of 0.2% dilution of the commercial stock EM solution per pot at fortnight intervals throughout the experimental period. Plants were harvested at flowering and maturity stages. Shoot length and dry biomass were gradually increased by increasing the quantity of green manure. There was 272% increase in shoot dry biomass over control at maturity due to 4% green manure application as compared to 137% increase due to recommended dose of nitrogen-phosphorus-potassium (NPK) fertilizer. Highest root biomass was recorded in 3% green manure amended treatment. Spike length, number of grains per spike and grains yield was also gradually increased by increasing the quantity of green manure. There was 43 to 253% increase in grain yield over control due to various green manure treatments as compared to 96% increase due to NPK fertilizers over control. EM application in un-amended control, NPK fertilizers as well as in various green manure treatments either exhibited insignificant effect or significantly reduced various studied parameters. The present study concludes that parthenium weed has the potential to be used as green manure for wheat. Key words: Effective microorganisms, green manure, parthenium, wheat.

Ecological Relationships of Verticillium Wilt Suppression of Potato by Green Manures

Studies show that once a suppressive effect has been established, a green manure treatment for a single season is sufficient to either maintain or to re-establish the control of Verticillium wilt of potato. Verticillium wilt, caused by Verticillium dahliae Kleb., was controlled on the first years of Russet Burbank potato cropping following 2–3 successive years of green manure treatments. Following this control, yields were increased with the first year of potato cropping, but were reduced during the second consecutive year of cropping with potato. In the second year of continuous cropping with Russet Burbank, total yields were reduced by 10% and U.S. #1 tubers by 40%, and these yield reductions were accompanied by increased soil populations of V. dahliae by >5- fold. Yet, with a single season of an earlier–used green manure treatment (e.g. Austrian winter pea, sudangrass, Dwarf Essex rape, Bridger rape, oats, rye, or sweet corn), Verticillium wilt was again controlled and yields of Russet Burbank were increased to higher levels or to levels that were equivalent to those initially observed following either 2 or 3 successive seasons of green manure treatment. Green manures also demonstrated significant effects on microbial activities, which were inversely related to the incidence of Verticillium wilt. More specific effects on microbial activity and soilborne ecology were shown with increased populations of Fusarium spp. Verticillium wilt was negatively correlated with infections of potato feeder roots and stem-ends of potato tubers by F. equiseti. Exemplifying the effect of a green manure on fungal ecology, sudangrass treatments were shown to have lasting effects on Fusarium avenaceum populations with quantitative changes that extended 5 years beyond the time of soil incorporation with sudangrass.

The Effects of Green Manure (Sesbania rostrata) on the Growth and Yield of Rice

Green manuring with an N2-fixing legume crop can meet a substantial portion of rice N requirement and provide organic matter to wetland rice soils to maintain soil fertility. Organic-N fertilizers in the form of flood-tolerant, leguminous, stem-nodulating Sesbania rostrata can be useful alternatives to resource- poor rice farmers if applied as green manure. Therefore, the accumulation of fixed N by this green manure, their effect on the performance and yield of rice was examined. Firstly, root and/or stem nodulation, nitro- gen fixation (acetylene-reducing activity), growth and N accumulation of S. rostrata as affected by inocula- tion site were studied in a pot experiment. The growth and N accumulation of S. rostrata in stem inocula- tion treatment was the highest. Therefore, stem inoculation method was used for growing S. rostrata to incorporate into the rice soils for the second experiment. In the second experiment, the effects of S. ros- trata green manure application on the growth and yield of rice were studied. Green manure treatments (2 and 4 plants pot -1 ) were compared to urea treatments (40 and 80 kg N ha -1 ) and no application treatment. Green manure treatments increased dry matter weight and grain weight of rice significantly over urea and no application treatments. All green manure treatments increased N uptake of the plant. It can be con- cluded that incorporation of green manure legumes can add large amount of biologically fixed N to rice soils. The effective utilization of biomass produced by the stem-nodulating S. rostrata could be an eco- nomically viable component of integrated nutrient management for increasing the yield components and yield of rice per unit area.

Biofumigation with Brassica plants and its effect on the inoculum potential of Fusarium yellows of Brassica crops

The use of Brassica crops as green manure in the so-called biofumigation treatment has been successfully exploited for the management of soilborne pathogens and is gaining interest particularly in the case of less intensive agricultural systems. A study was undertaken to investigate possible negative side-effects of biofumigation in order to prevent possible damage caused by wilt pathogens able to attack both plants used for biofumigation as well as agricultural crops. To do so, firstly the response of different Brassicas, including some used in biofumigation, to the formae speciales of Fusarium oxysporum known for being pathogenic on Brassica crops was evaluated. Secondly, the effect of green manure treatments on yield, quality of crops, and inoculum densities, infection and survival of Fusarium oxysporum f. sp. conglutinans and F. oxysporum f. sp. raphani was evaluated. In the second part of the work, four Brassica crops, selected for their response (susceptibility or resistance) to F. oxysporum f. sp. conglutinans and to F. oxysporum f. sp. raphani were evaluated in order to determine their response to the two pathogens during subsequent crops grown in soil where plants were incorporated as green manure into the soil at the end of each cycle. Moreover, the dynamics of the populations of F. oxysporum f. sp. conglutinans and F. oxysporum f. sp. raphani in the soil after several biofumigation cycles was studied. Many of the Brassica crops used for biofumigation tested were susceptible to F. oxysporum f. sp. conglutinans and or to F. oxysporum f. sp. raphani. Green manure treatment, carried out by growing nine cycles of biocidal plants, with a short crop cycle of 30–35 days, did not reduce Fusarium wilts on susceptible Brassica hosts. The population of the pathogen was partially increased as a result of the incorporation of tissues of the susceptible plants. When Brassica crops grown were resistant to the two F. oxysporum pathogens used for soil infestation, green manure simulation did inhibit both pathogens, thus confirming its biocidal activity. The results obtained under our experimental conditions show that biofumigation treatment is not applicable for soil disinfestation on crops susceptible to the same formae speciales of F. oxysporum affecting Brassica species used for biofumigation. Brassica crops resistant to Fusarium yellows should be grown where biofumigation is applied. Moreover, alternation of crops used for biofumigation should be encouraged.

Optimal seeding rate for organic production of field pea in the northern Great Plains

Seeding rates have not been established for organic production of field pea in the northern Great Plains and producers must rely upon a recommended target stand of 88 plants m-2 for conventional production of this crop. This seeding rate may not be suitable as the two systems differ in the use of inputs and in pest management. The objective of this study was to determine an optimal seeding rate for organic production of field pea considering a number of agronomic factors and profitability. Field sites were established using a randomized complete block design with increasing seeding rates, summerfallow and green manure treatments. Seed yield increased up to 1725 kg ha-1 with increasing seeding rate. Weed biomass decreased with increasing seeding rate by up to 68%. Post-harvest soil phosphorus levels and soil water storage did not change consistently between treatments. Post-harvest soil inorganic nitrogen (N), however, was higher for the summerfallow and green manure treatments than for the seeding rate treatments. Field pea reached a maximum economic return at a seeding rate of 200 seeds m-2 and an actual plant density of 120 plants m-2. Organic farmers should increase the seeding rate of field pea to increase returns and provide better weed suppression. Key words: Pea (field), organic, seeding rate, weed suppression, profit, soil N

Nitrogen dynamics in paddy soil applied with various 15N-labelled green manures

The effects of 15N-labelled green manure (GM) application on rice yield and N uptake were investigated and compared with those of inorganic fertilizer (IF) and no fertilizer (NF) application. Nine GMs (white clover, Chinese milk vetch, hairy vetch, crimson clover, oats, rye, Italian ryegrass, white mustard, lacy phacelia) were either incorporated into or surface-applied on paddy soil. Among the nine GM treatments, the rice yield and N uptake tended to be higher in the white clover and hairy vetch treatments. The rice N uptake efficiency from the applied N source was highest in the incorporated hairy vetch (56%), followed by IF (52%), and incorporated white clover (44%), whereas for the other treatments there were no significant differences. The mineral fertilizer equivalent values of hairy vetch and white clover in case of the incorporation were 108% and 84%, respectively. Therefore, hairy vetch and white clover seem to be the most efficient organic N source as alternatives to inorganic N fertilizers. The N uptake efficiency of rice and residual N in soil derived from GM were higher in the incorporation treatments than that in the surface-applied treatments, indicating that N losses from the soil-plant system were lower with the incorporation.

Application of Rye Green Manure in Wheat Rotation System Alters Soil Water Content and Chemical Characteristics under Dryland Condition in Maragheh

This study was carried out with or without rye green manure along with 4 nitrogen fertilization treatments (0, 26, 103 and 337 (kg N ha(-1)) in 3 rotation system (green manure-wheat). Results showed that, although treatment effects on dryland wheat grain yield was not significant, but maximum grain yield (2484 kg ha(-1)) was obtained from application of rye green manure along with 26 kg N ha(-1); which is 22% more than check (without rye green manure) treatment. Green manure application with or without nitrogen increased EC (dS m(-1)), but decreased OC, P (av.), Cu (av.), Mn (av.), Zn (av.) and sand in the soil. In contrast to green manure, application of nitrogen along with green manure increased saturation and clay. In the stage of stem appearance, soil moisture content decreased 8% in green-manure application but with nitrogen application the moisture increased 6% compared with check in 0-20 cm depth. It can be concluded that, green manure application is useful along with nitrogen fertilizer application in long term. This treatment could increase soil moisture content, which leads to higher wheat grain yield in dryland areas. In addition, green manure application could change some soil characteristics such as soil TNV%, which decreases availability of some essential nutrients for dryland wheat.

The effects of pure and undersowing green manures on yields of succeeding spring cereals

A field experiment was conducted in 2004–2006 to investigate the effect of green manure treatments on the yield of oats and spring barley. In the experiment, different green manure crops with undersowing and pure sowing were compared for amounts of N, C, and organic matter driven into soil and their effect on cereal yield. The spring barley field had a total of 41.7–62.4 kg N ha−1 and 1.75–2.81 Mg C ha−1 added to the soil with straw, weed, and roots, depending on the level of fertilisation; with red clover, and both common and hybrid lucerne undersowing, with barley straw and roots, the values were 3.45–3.96 Mg C ha−1 and 139.9–184.9 kg N ha−1. Pure sowings of these three leguminous green manure crops had total applications of 3.37–4.14 Mg C ha−1 and 219.7–236.8 kg N ha−1. The mixed and pure sowing of bird's-foot trefoil provided considerably less nitrogen and carbon to the soil with the biomass than with the other leguminous crops. Application of biomass with a high C/N ratio reduced the yield of the succeeding spring cereals. Of the green manures, the most effective were red clover and both common and hybrid lucerne, either as undersowing or as pure sowing. Undersowings with barley significantly increased the N supply for the succeeding crop without yield loss of the main crop compared with the unfertilised variant. Compared with ploughing-in of green manure in autumn, spring ploughing gave a 0.2–0.57 Mg ha−1 larger grain yield.

Effects of sugarcane residue and green manure practices in sugarcane-ratoon-wheat sequence on productivity, soil fertility and soil biological properties

In a field experiment conducted during 2002 to 2004 in silty clay loam soil at Pantnagar, India, treatment of trash burning + Sesbania aculeata green manure (GM) incorporation gave the highest increases of 50.6 and 17.7% in ratoon cane yield and 15.0 and 19.4% in wheat grain yield over trash removal and trash burning treatments, respectively. Soil organic C and available N after ratoon and wheat crops were highest with trash removal + GM incorporation and available P and K with trash removal + GM mulch. The different treatments of trash and GM management were also superior to trash removal and trash burning in organic C and available N and P in soil at termination of the study. Soil microbial biomass C and dehydrogenase activity at the end were at a maximum with trash burning + GM mulch and trash removal + GM mulch treatments, respectively. Compared to trash removal and trash burning, counts of bacteria in soil after ratoon and wheat crops were significantly more only with different GM treatments; however, all GM and trash application treatments recorded significantly higher counts of fungi and actinomycetes. Irrespective of the treatments, population of total bacteria in soil decreased, while that of fungi and actinomycetes increased as compared to their initial counts following sugarcane-ratoon-wheat sequence.

Effects of Green Manure and Compost Of Pea Plant on Wheat

Cereal based cropping systems have been established for food security in many countries where farmers use plenty of chemical fertilizers, but adoption of leguminous crop in the system is not popular. Excessive use of fertilizers is responsible for health and environmental hazards. Adoption of legume in cereal based cropping systems and improvement of organic fertilizer are needed to reduce chemical fertilizer use. Pot experiments in the greenhouse were carried out with green manure (GM) and compost of green pea (Pisum sativum L.) plant residue (PP) with dried chicken manure (CM) and/or rapeseed (Brassica napus L.) oil residue (RR) at Gifu University, Japan during 2004-2007. The goal of the experiments was to assess: the effectiveness of GM and compost on growth and yield of wheat and ii) the efficiency of GM and compost to supply nutrients. After pod harvest, PP was mixed with CM or RR or half of CM plus half of RR, or nothing was mixed with PP for making GM and compost for wheat. Results of two pea-wheat cycles revealed that composts of PP with CM and CM plus RR were enriched by higher microbial activity; maintained the activity at a higher rate in the soil and supplied sufficient nutrients to wheat. As a result, wheat harvested higher amount of N P K with efficient recovery rate, which improved yield components and yield. Apparent nutrient recovery efficiencies of the composts could save fertilizer use and environment. Although higher value was found from compost than GM of similar organic materials, but among the GM treatments, PP with CM plus RR also gave higher yield. Moreover, instead of having enough nutrients, RR can not supply nutrients satisfactorily due to delay release but CM itself is efficient and stimulates RR to release nutrients. Therefore, pea compost with CM or CM plus RR is recommended for wheat.

Green manure effects on soil quality in relation to suppression of Verticillium wilt of potatoes

Verticillium dahliae is a major, persistent pathogen in soil but conventional control is becoming more difficult because of increasing costs and environmental impacts of pesticides. Organic amendments can naturally suppress plant diseases, but to be reliable, mechanisms and suppressive soil indicators need to be understood. Consequently, a 3 × 3 factorial experiment was conducted in two separate fields over 2 years with three green manure types (Austrian winter pea, Pisum sativum L.; broccoli Brassica oleracea L.; or Sudan grass, Sorghum vulgare), incorporated at three rates (6, 12, or 24 Mg ha−1 dry biomass). The relationship between soil chemical and microbiological properties and suppression of Verticillium wilt of potato was investigated using correlation and stepwise multiple-linear-regression (MLR) analysis. V. dahliae inoculum density (ID) were positively correlated with relative area under the senescence progress curve (RAUSPC) in both 2002 and 2003. In 2002, in addition to ID, low soil pH, low Ca, high K, high Mg, high total soil C, and low arylsulfatase activity were associated with low RAUSPC. Soil pH, Ca, K, and Mg were not impacted by green manure treatments, but rather indicated a pre-existing soil gradient at the 2002 site. In 2003, in addition to ID, high values of NO3−−N, total C, fluorescein diacetate hydrolysis (FDA), microbial respiration, and microbial biomass C were associated with low RAUSPC. These six factors were affected by green manure treatments. The best MLR model included terms for ID, FDA, and soil pH, and accounted for 70% of the variability in RAUSPC.

Studi Serapan Hara N, P, K dan Potensi Hasil Lima Varietas Padi Sawah (Oryza sativa L.) pada Pemupukan Anorganik dan Organik

The objective of the research was to study the nutrition uptake (nitrogen, phosphorus, and potassium,) and the grain production of five rice varieties representing modern, new plant type and local varieties under application of inorganic, organic and combined inorganic-organic fertilization. Five rice varieties were Way Apoburu and IR-64 (modern varieties), Midun and Sarinah (local varieties from Sukabumi and Garut, respectively), and Fatmawati (new plant type variety). Five fertilizer treatments were (1) full recommendation dosage of inorganic fertilizer (250 kg urea/ha, 100 kg SP-36/ha, and 100 kg KCl/ha), (2) ¼ recommendation dose of inorganic fertilizer + rice straw, (3) ½ recommended dose of inorganic fertilizer + rice straw, (4) rice straw, and (5) green manure from Crotalaria juncea biomass. The results showed that there was no specific response of rice varieties to the fertilization treatments, even though there was specific nutrient uptake pattern and yield of each variety, and there was significant effect of fertilizer treatment to nutrient uptake and rice yield. Nutrient uptake and grain yield indicated that nutrient imobilisation occurred at 1 st season, however the availability of N, P, K nutrients increased at 2 nd and 3 rd season on rice straw and green manure treatments. Rice straw application caused lower nutrient uptake and grain yield than full dosage inorganic fertilizer at 1 st season but both were not significantly different at 2 nd and 3 rd season. Application of rice straw with ½ dosage of inorganic fertilizers was not significantly different from full dosage of inorganic fertilizers in nutrient uptake and grain yield. Modern varieties showed higher level of N absorption than that of new type variety although it was not significantly different with that of local varieties, whereas the P and K uptake of modern varieties was lower than that of local and new plant type varieties. The modern varieties also showed higher level of dry grain per hill than that of local and new plant type varieties. However yield per ha of all varieties tended to be similar. Key words: uptake, efficiency, mineral nutrition, variety, lowland rice

Legume–maize rotation and nitrogen effects on weed performance in the humid and subhumid tropics of West Africa

A long-term trial was established in 1998. The objectives among others were to assess the impact of nitrogen, natural bush fallow, and legume−maize rotations on weed growth and species composition in the forest/savanna transition zone (Ibadan) and northern Guinea savanna (Zaria) in Nigeria. At both locations, the experiment was arranged as a split-plot design. The main plots were green manure legumes ( Pueraria phaseoloides [Roxb.] Benth in Ibadan and Aeschynomene histrix Poir. in Zaria), a forage legume ( Stylosanthes guianensis [Aubl.] Sw.), grain legumes (cowpea [ Vigna unguiculata {L.} Walp ‘IT-90K-284-2’ or soybean [ Glycine max {L.} Merr ‘TGx 1864 and TGx 1485-1 D’), natural bush fallow, and continuous cropping with maize [ Zea mays L.]/cassava [ Manihot esculenta Crantz] ‘82/00058’ at Ibadan and maize at Zaria. Grain legumes were either double-cropped in one season by growing short-duration soybean with cowpea varieties sequentially, or by growing long-duration cultivars within one growing season. Nitrogen levels (0 and 30 kg N ha −1) were the subplot treatments. Weed data were collected in 2000 and 2003 after 2 years of continuous cropping or rotation with natural fallow or legumes. Weed density was significantly higher at Zaria (177 plants m −2) than at Ibadan (149 plants m −2). Weed dry matter was higher at Ibadan than at Zaria. Weed density and dry matter were lower in the green manure and forage legume treatments in both years at Ibadan. At Zaria, the forage legume treatment had the lowest weed density and dry matter in 2003 only. In 2003 at Ibadan, per capita weed population growth rate (WPGR) decreased in the green manure and forage legume treatments. There was an increase in WPGR in continuous cropping, double-cropping with cowpea and soybean, and natural bush fallow treatments. At Zaria, WPGR was not affected by fallow type or nitrogen ( P>0.05). Redundancy analysis showed significant differences in species composition among the various treatments. Nitrogen level did not affect density, dry matter, or the composition of weeds.

Long-term effect of varying nutrient management practices on the distribution of native iron and manganese in various chemical pools under rice – wheat cropping

A long-term experiment under a rice – wheat system was used to investigate the effect of organic manures and chemical fertilizers application on the distribution of Fe and Mn in various soil fractions. The cultivation of rice – wheat continuously for seven years without any fertilization did not deplete the amounts of Fe and Mn in various fractions from their original levels. Application of farmyard manure, press mud and green manure along with chemical fertilizers increased the Fe content by 37.5, 56.3 and 75.0% in water-soluble plus exchangeable fraction, respectively compared to chemical fertilizer only treatment (N150P75K75Zn25). In organically bound Fe fractions, the increases due to corresponding treatments over fertilizer-only treatment were 16.4, 20.7 and 10.3%, respectively. The water-soluble plus exchangeable Mn registered an increase of 84.6, 46.2 and 46.2% with N150P75K75Zn25 + farmyard manure, N150 + press mud and N150P37.5K37.5Zn25 + green manure treatments, respectively, compared to N150P75K75Zn25 treatment. The organically bound Mn fraction was almost 2.6 times greater in organic manures + inorganic fertilizers treatments than fertilizer alone treatment. The amounts of both Fe and Mn in water-soluble plus exchangeable, organically bound and Mn-oxide fractions were significantly higher after rice than after wheat harvest.

Effects of Green Manure Type and Amendment Rate on Verticillium Wilt Severity and Yield of Russet Burbank Potato.

Increasing restriction of agrochemicals is motivating development of ecology-based cropping systems, including green manures, to manage soilborne diseases. Green manures have shown promise in suppressing Verticillium dahliae, but information about effect of different green manures and optimal application rates remains limited. Therefore, we conducted two single-year field experiments comparing effects of Austrian winter pea (Pisum sativum 'Melrose'), broccoli (Brassica oleracea var. botrytis 'Excelsior'), and Sudan grass (Sorghum vulgare var. sudanense 'Monarch'), amended at 6, 12, or 24 Mg ha-1, on soil populations and root infection by V. dahliae, wilt severity, and yield of Russet Burbank potato. Inoculum density was reduced relative to the nonamended, infested control by all broccoli treatments, Austrian winter pea applied at 12 and 24 Mg ha-1, and Sudan grass applied at 12 Mg ha-1. Root infection was not reduced by any green manure treatment. Median wilt severity was reduced approximately 70% by all green manures applied at 24 Mg ha-1 and 74% by Austrian winter pea applied at 12 Mg ha-1. Tuber yield was reduced approximately 20% in nonamended, V. dahliae-infested controls relative to the noninfested controls. No green manure treatment improved yield relative to the nonamended, infested control.

Effects of Green Manures on Growth, Yield and Quality of Green Okra (Abelmoschus esculentus L.) Har Lium Cultivar

This green manure experiment with the use of okra crop as indicator plant was carried out at Mahasarakham University Experimental Farm, Mahasarakham province, Northeast Thailand during May to September 2005 to investigate four types of green manure legume crops on growth, yield and quality of edible fresh pods of okra crop when grown on Roi-Et soil series (Oxic Paleustults). The four types of green manure plants include Jack bean, Cowpea, Green gram, and Giant sensitive plant. The experiment consisted of five treatments, i.e., T1 (Control), T2 (Jack bean), T3 (Cowpea), T4 (Green gram) and T5 (Giant sensitive plant). The experiment was laid in a Completely Randomized Design (CRD) with four replications. The results showed that Roi-Et soil series (Oxic Paleustults) contained some considerable mean values of organic matter (1.64-1.66%) but soil available phosphorus and exchangeable potassium were relatively low, particularly potassium. Green manures of the four legume plants slightly improved soil property of the Roi-Et soil series (tested at the end of the experimental period). The most effective green manure on stem diameter, bushy diameter, leaf numbers plant(-1) and leaf area of the fifth leaf of the okra plants, in most cases, was found with Jack bean and Cowpea ranked the second. However, in most cases, Cowpea gave a similar effect as that of Green gram and Giant sensitive plant. Pod length and weight pod(-1), pod diameter and edible fresh pod yields (5941.86 kg ha(-1)) were highest with Jack bean green manure treatment (T2), whilst the rest, in most cases, were similar. Green manure treatments gave highly significant effect on total soluble solids of pods over the control treatment, whilst total acidity, fibre and pectin contents were unaffected by green manure treatments. Green manure of Jack bean was the best legume crop for green manure to be used in improving soil fertility, particularly for Roi-Et soil series (Oxic Paleustults).

Soil enzyme activities, microbial community composition and function after 47 years of continuous green manuring

Green manuring practices can influence soil microbial community composition and function and there is a need to investigate the influence compared with other types of organic amendment. This study reports long-term effects of green manure amendments on soil microbial properties, based on a field experiment started in 1956. In the experiment, various organic amendments, including green manure, have been applied at a rate of 4 t C ha −1 every second year. Phospholipid fatty acid analysis (PLFA) indicated that the biomass of bacteria, fungi and total microbial biomass, but not arbuscular mycorrhizal (AM) fungi, generally increased due to green manuring compared with soils receiving no organic amendments. Some differences in abundance of different microbial groups were also found compared with other organic amendments (farmyard manure and sawdust) such as a higher fungal biomass and consequently a higher fungal/bacterial ratio compared with amendment with farmyard manure. The microbial community composition (PLFA profile) in the green manure treatment differed from the other treatments, but there was no effect on microbial substrate-utilization potential, determined using the Biolog EcoPlate. Protease and arylsulphatase activities in the green manure treatment were comparable to a mineral fertilized treatment receiving no additional C, whereas acid phosphatase activity increased. It can be concluded that green manuring had a beneficial impact on soil microbial properties, but differed in some aspects to other organic amendments which might be attributed to differences in quality of the amendments.

Long-term effect of organic/inorganic input on the distribution of zinc and copper in soil fractions under a rice – wheat cropping system

A long-term experiment under a rice – wheat system was used to investigate the effect of organic and inorganic fertilizer application on the zinc (Zn) and copper (Cu) in various soil fractions. Levels of Zn and Cu in the different fractions were comparable to the initial levels after 7 years of continuous cropping without any fertilization. However, addition of organic manures in the absence of inorganically applied Zn or Cu increased the water-soluble plus exchangeable, organic fraction and the manganese oxide and amorphous iron oxide fractions of Zn and Cu over their initial levels. Application of N150P75K75Zn25 + farmyard manure (FYM) or N75P37.5K37.5Zn25 + green manure lowered the Zn content in the carbonate and crystalline iron oxide fractions, with a concomitant increase in Zn associated with the water-soluble plus exchangeable, organic fraction and the manganese oxide and amorphous iron oxide fractions compared to the N150P75K75Zn25 treatment alone. Levels of Cu in the water-soluble plus exchangeable, organic fraction and the manganese oxide and amorphous iron oxide fractions were significantly higher in the N150P75K75Zn25 + FYM, N150 + press mud and N75P37.5K37.5Zn25 + green manure treatments than in the N150P75K75Zn25 treatment alone. A maximum increase in Cu of 1.4 – 1.5-fold was observed in the organic fraction. The residual fraction, and amorphous and crystalline iron oxide fractions constituted the major proportion of total Zn and Cu in soil.

Effects of green manure use on sweet corn root length density under reduced tillage conditions

A green manure (GM) is a crop grown primarily as a nutrient source and soil amendment for subsequent crops. In environments such as Florida, combined use of GM and reduced tillage may improve soil water and nutrient retention and reduce potential groundwater pollution. In the first 3 years of a long-term experiment, use of GM in a reduced-tillage system on a sandy Florida soil benefited the season-long growth of sweet corn (Zea maysL. var. Rugosa) much more than final ear yields. To help understand these patterns, we evaluated response of sweet corn roots when in rotation with GM of sunn hemp (Crotalaria junceaL.; summer) and cahaba white vetch (Vicia sativaL.; winter 2002–2003) and a multi-species mixture of hairy vetch (V. villosaRoth.) and cereal rye (Secale cerealeL.; winter 2003–2004). Treatments included sweet corn with combinations of 0 or 133 kg chemical N ha−1(as NH4NO3) and with or without GM. A highly fertilized treatment (267 kg chemical N ha−1) without GM was also included. Soil cores were sampled from three depths (0–15, 15–30 and 30–60 cm) both between and within corn rows. Data from two experiments showed that use of GM increased sampled corn root length density (RLD) by 44–54%, although only within the upper 15 cm of soil in one of the two experiments. Corn following GM plus 133 kg chemical N ha−1produced up to 44% greater RLD than corn with 267 kg chemical N ha−1. Sampled RLD decreased with distance away from corn plants (from in-row to between-row positions, and from shallow to deeper depth), with roughly 85–95% of sampled RLD existing in the top 30 cm of soil across all treatments. During the 2004 experiment, we found that broadcast, as opposed to banded (placed along corn row only), chemical N application resulted in more even distribution of corn RLD between in-row and between-row positions during late-season without regard to GM crop. Although GM permitted optimal sweet corn growth with a 50% reduction in chemical N application, ear fill during the final 1–2 weeks before harvest may have been reduced in GM treatments. GM effects on the amount and spatial distribution of sweet corn RLD may help explain these trends. Provision of greater N from GM residues and/or altered distribution of supplementary chemical N and irrigation may be required to achieve greater ear yield benefit from GM.

Influence of Fertilizers Applied to a Paddy−Upland Rotation on Characteristics of Soil Organic Carbon and Humic Acids

The qualitative and quantitative characteristics of soil organic carbon (SOC) and related humic acids (HAs) extracted from the soils of field plots were investigated after 8 years of annual paddy (Oryza sativa L.) and upland maize (Zea mays L.) rotation with various fertilizations. Seven fertilization treatments were selected: Ck (no inputs); Chem (chemical fertilizer of NPK); Comp (swine compost); Comp + 33% of Chem N rate; Comp + 67% of Chem N rate; GM (legume green manure) + 33% of Chem N rate; and peat + 33% of Chem N rate. Organic and inorganic nitrogen inputs of six treatments were equivalent with respect of nitrogen content, but Comp, GM, and peat treatments were complemented with various amounts of inorganic N. After harvest of the eighth paddy crop, surface soil samples collected from the plots were subjected to soil characterizations and extraction of humic substances, which were used for chemical, spectroscopic (FTIR, 13C NMR, ESR, X-ray diffractometry), delta13C, and 14C dating analyses. The yields of HAs extracted from the seven treatments were significantly different. Treatment containing persistent organic compound such as the peat + 33% N treatment increased the humification process in topsoils and produced higher yield of HA. Spectroscopic analyses revealed that fertilization treatments changed the functional groups, alkyl C, crystalline characteristics, and delta13C ratios of HAs and turnover rate of SOC considerably. The SOC of the peat + 33% N treatment had the highest mean residence time of 3100 years. Various fertilizer treatments are correlated with turnover rate of SOC and related HAs, which are associated with concerned carbon sequestration as well as mitigation of CO2 emission in the soil environment.