Cereal yield losses caused by lepidopterous stemborers at different nitrogen fertilizer rates in Ethiopia

Abstract: Field trials were carried out at three locations in the cool‐wet western and one location in the semiarid eastern ecozones of the Amhara State of Ethiopia to determine the effects of nitrogen fertilizer on pest infestation and yield losses caused by lepidopterous stemborers in maize and sorghum. Three N fertilizer levels, i.e. 60, 120 and 180 kg/ha for maize, and 41, 64, and 87 kg/ha for sorghum, were compared with a zero N treatment. The dominant pest species were the noctuid Busseola fusca (Fuller) and the invasive crambid Chilo partellus (Swinhoe). Leaf N content was positively related to N fertilizer dosage. In general, pest density, parasitism, plant growth and borer damage variables increased with crop growth stage. On sorghum, in the cool‐wet western Amhara, increasing levels of N fertilizer also tended to increase pest density, plant growth and damage variables. In the semiarid ecozone, parasitism by the exotic parasitoid Cotesia flavipes Cameron tended to increase with N level. In the cool‐wet ecozone, sorghum yields increased by up to 74% because of fertilization; losses caused by stemborers decreased linearly with N dosage from 49% to 36%. In maize, because of low borer densities, there were no discernable trends for pest infestation and yield losses. In the cool‐wet ecozone, sorghum yields were positively related to insecticide application and plant height, and negatively to damage variables such as tunnelling and peduncle damage. In semiarid eastern Amhara, the effects of fertilizer on pest, damage and yield were low on both crops because of the higher soil fertility. The results indicate that the profitability of nitrogen fertilizer as an integrated pest management tactic in the control of cereal stemborers depends, among others, on the severity of borer damage and the soil fertility status prevailing in an area. It is concluded that N fertilizer helps minimize the impact of borers on grain yields, especially on sorghum and in the cool‐wet ecozone.     

Effect of nitrogen fertilizer level on infestations of lepidopterous stemborers and yields of maize in Zanzibar

The effect of nitrogen levels of 0, 60, 120, and 250 kg/ha and insecticide treatment (Furadan) on population densities and parasitism of lepidopteran stemborers, and maize yields were studied in Zanzibar during 2004/05. Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) dominated by 3-fold over Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and 42 fold over Chilo orichalcociliellus Strand (Lepidoptera: Crambidae). Stemborer density per plant and parasitism by Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) increased with nitrogen application level. Percentage of bored internodes per plant caused by stemborer decreased with N levels during the short rainy season. Pesticide application reduced densities of all stemborer species during the short rainy season, when infestations were high. Maize yield increased 2 to 8 times with N level, compared to the zero treatment, but the effect was less pronounced in the protected plots.     

Basal fertiliser application method, tuber initiation nitrogen, foliar NPK and the tolerance of potatoes to infection by the potato cyst nematodes Globodera rostochiensis and G. pallida

The effects of broadcast granular, placed liquid and foliar fertilisers on the tolerance of potatoes to infection by potato cyst nematodes were investigated. The tolerance of the potato cv. Pentland Dell was not significantly improved by fertiliser application type but placed liquid fertiliser, with or without foliar applications, increased the concentrations of N, P and K measured in whole plant dry matter of PCN infected plants. The tolerance of the potato cv. Sante was not statistically improved by altering the balance of fertiliser nitrogen applications between planting and tuber initiation or by applying foliar nitrogen. Nitrogen applications of 120 kg N ha^-1 at planting and a further 120 kg N ha^-1 at tuber initiation supplemented with foliar N, however, achieved a larger tuber yield than the same nitrogen programme without foliar N and gave a significantly greater yield than the application of 240 kg N ha^-1 at planting plus foliar N. The emergence of both cultivars was delayed in the absence of oxamyl. N, P and K concentrations within whole plant dry matter were significantly higher in plants from oxamyl treated plots and both N and K concentrations were significantly increased by increasing the quantity of N at planting, at 56 DAP. Splitting the fertiliser N between planting and tuber initiation appears to be important in maintaining the availability of this nutrient to PCN infected plants throughout the season.     

Improving nitrogen efficiency: lessons from Malawi and Michigan

Two case studies are presented here of nitrogen (N) dynamics in potato/maize systems. Contrasting systems were investigated from (1) the highland tropics of Dedza, Malawi in southern Africa and (2) the northern temperate Great Lakes region of Michigan. Formal surveys were conducted to document grower perceptions and N management strategies. Survey data were linked with N budgets conducted by reviewing on-farm data from representative farms in the targeted agroecosystems and simulation modeling to estimate N losses. Potential N-loss junctures were identified. Interventions that farmers might accept are discussed. The Malawi system uses targeted application of very small amounts of fertilizer (average 18 kg N ha(-1)) to growing plants. This low rate is on the steep part of plant response to N curve and should serve to enhance efficiency; plant growth, however, is generally stunted in Malawi due to degraded soils and weed competition. Very limited crop yields reduce N efficiency from a simulated 60 kg grain per kg N to an actual of approximately 20 kg grain per kg N (at 40 kg N ha(-1) applied). Legume-intensified systems could improve growth potential and restore N use efficiency through amelioration of soil quality and transfer functions and from biological fixation N inputs. In the Michigan system, N efficiency is enhanced currently through multiple, split applications of N fertilizer tailored to plant growth rate and demand. Fertilizer N rates used by growers, however, averaged 32% higher than recommended rates and 40% higher than N removed in crop product. Application of 50 kg N ha(-1) to cover crops in the fall may contribute to the apparent high potential for N leaching losses. Careful consideration of N credits from legumes and residual soil N would improve N efficiency. Overall, N budgets indicated 0 to 20 kg N ha(-1) loss potential from the Malawi systems and tenfold higher loss potential from current practice in Michigan maize/potato rotations. Best management practices, with or without integration of legumes, could potentially reduce N losses in Michigan to a more acceptable level of about 40 kg N ha(-1).     

施钾量和施钾时期对小麦氮素和钾素吸收利用的影响

利用¹⁵N示踪技术,研究了施钾量和施钾时期对高产小麦氮素和钾素吸收利用的影响.结果表明： 0～20 cm土层土壤速效钾含量为118.5 mg·kg^-1时,一次性基施钾肥未提高植株的氮、钾积累量;速效钾含量为79.0 mg·kg^-1时,施钾显著提高了植株的氮、钾积累量.采用分期施钾时（1/2基施、1/2拔节期追施）,随施钾量增加,小麦吸收的肥料氮和土壤氮量及追施氮肥在土壤中的残留量均增加,肥料氮的损失量降低.分期施钾显著提高了植株的氮、钾积累量、吸收效率和生产效率,当施钾量为135 kg·hm^-2时,与一次性施钾相比,分期施钾促进了植株对追肥氮和土壤氮的吸收,提高了追施氮肥在土壤中的残留量.结果还表明：施钾提高了小麦的籽粒产量、蛋白质含量和湿面筋含量;分期施钾处理优于一次性施钾处理,以K45+45（45 kg·hm^-2基施、45 kg·hm^-2拔节期追施）处理最优.过多施钾使小麦产量和品质趋于降低.     

Relationships of soil fertility and stem borers damage to yield in maize-based cropping system in Cameroon

Field trials were designed to investigate the effect of direct nitrate fertilisation and mucuna fallow on maize yield and borer attacks in the humid forest zone of Cameroon. A traditional maizecassava- groundnut system (farmers’ practice) was compared with a maize-cassava + 120 Kg N ha-1, a rotation system in which maize-cassava followed a mucuna fallow as well as with a maize monocrop grown after mucuna fallow and with a maize monocrop grown with 120 Kg N ha-1. Average egg batch densities of Busseola fusca (Lepidoptera: Noctuidae) were lower by 35–55% in inter- than monocrops but the effect of nitrogen on B. fusca oviposition was not different from that of mucuna fallow. Highest larval infestations were found in sole maize with nitrogen and sole maize after mucuna. Yield losses were 4–10 times higher in the farmers’ practice compared to maize-cassava after mucuna and maizecassava with nitrogen. Mixed cropping systems including farmers’ practice yielded higher total gross and net benefits compared to sole maize crops. But, they were higher in maize-cassava intercrop + N than for farmer’s practice.     

Effect of crop residue management on the yields of different crops and on soil properties

The effects of chopped (6–9 cm) and unchopped (long) crop residues of wheat (Triticum aestivum L.) and rice (Oryza sativa L.) in corn (Zea mays L.)— wheat and rice-wheat rotations on grain yield and soil properties were investigated in 27 field experiments during 9 years. Experiments on chopped wheat residue involved the treatments of two main plots with residue incorporation at 0 and 4 t/ha before sowing of corn and wheat and having subplots with 0, 40, 80 and 120 kg N/ha. The results obtained for 4 years showed that the incorporation of wheat residue not only improved the soil physicochemical properties but also increased the grain and stover yields of corn significantly. The yield obtained with 80 kg N in conjunction with 4 t/ha chopped wheat residue was identical to that with 120 kg N/ha alone. But the wheat yield was depressed significantly upon the incorporation of wheat residue before the sowing of wheat in all the years of investigation.The experiments on the management of unchopped wheat residue in corn-wheat rotation and of unchopped wheat (6 t/ha) and rice (12 t/ha) residues in rice-wheat rotation, involved three main treatments: physical removal, in-situ incorporation and in-situ burning of residues. Main treatments were tested at 60, 120 and 180 kg N/ha level over 5 years. Irrespective of N application, the residue management treatments had non-significant effects on the succeeding crop yield in all the years. Burning of residue improved the yield by about 0·2 t/ha, whereas residue incorporation did not affect the yield either of corn or rice. On the other hand, the wheat yield was depressed by 0·1–0·2 t/ha in both the rotations.The effect of applied N irrespective of residue management was significant in some years up to the level of 120 kg and in others, 180 kg N/ha.     

Establishment of phosphate-solubilizing strains of Azotobacter chroococcum in the rhizosphere and their effect on wheat cultivars under green house conditions

A pot experiment was conducted in the green house to investigate the establishment of phosphate solubilizing strains of Azotobacter chroococcum, including soil isolates and their mutants, in the rhizosphere and their effect on growth parameters and root biomass of three genetically divergent wheat cultivars (Triticum aestivum L.). Five fertilizer treatments were performed: Control, 90 kg N ha(-1), 90 kg N + 60 kg P2O5 ha(-1), 120 kg N ha(-1) and 120 kg N + 60 kg P2O5 ha(-1). Phosphate solubilizing and phytohormone producing parent soil isolates and mutant strains of A. chroococcum were isolated and selected by an enrichment method. In vitro phosphate solubilization and growth hormone production by mutant strains was increased compared with soil isolates. Seed inoculation of wheat varieties with P solubilizing and phytohormone producing A. chroococcum showed better response compared with controls. Mutant strains of A. chroococcum showed higher increase in grain (12.6%) and straw (11.4%) yield over control and their survival (12-14%) in the rhizosphere as compared to their parent soil isolate (P4). Mutant strain M37 performed better in all three varieties in terms of increase in grain yield (14.0%) and root biomass (11.4%) over control.     

The effect of stem and cob borers on maize subjected to different nitrogen treatments

The influence of four nitrogen levels (0, 60, 90 and 120 kg N/ha) on growth of maize and development of lepidopterous pests was investigatdd in a field trial. Nitrogen had a positive effect on both plant growth variables (plant height, stem diameter and yield), and development and survival ofSesamia calamistis andEldana saccharina, and thereby increased the incidence of dead hearts and stem tunneling. However, the percent yield loss due to artificial infestation decreased with increasing N application rate from 20% to 11% in the in the 0kg/ha and 120kg/ha treatment, respectively. Using a multiple regression analysis, plant height, plant diameter and stem tunneling were found to be the most important variables explaining the variability in maize yield.     

Comparison of growth, biomass and nutrient distribution in five promising clones of Populus deltoides under an agrisilviculture system

Variations in growth, above- and below-ground biomass and nutrient distribution were examined in five clones (G3, G48, 65/27, D121 and S7C1) of Populus deltoides grown under agrisilviculture system in sub-humid tropics of Central India. The monoclonal blocks were planted at 4x5 m in a randomized block design with three replications. Diameter at breast height (dbh) and tree height were consistently higher in clone 65/27 and lowest in clone S7C1. Mean annual increments (MAI) in dbh and height were 1.6 and 1.3 times higher in clone 65/27 compared to clone S7C1. Total biomass varied from 48.5 to 62.2 Mg ha(-1) in six-year-old clones. In rank order, the total biomass of clones was: 65/27>D121>G48>G3>S7C1. Stem wood accounted 60.4-68.9% to total biomass followed by coarse roots (12.2-18.9%), branches (12.3-15%), leaves (3.02-6.9%) and fine roots (1.5-2.7%). Root-shoot ratio ranged from 0.2 to 0.35. It was highest in clone G48 and lowest in clone S7C1. In six-year-old clones, total N ranged from 184.3 to 266.3 kg ha(-1), P from 16.8 to 31.1 kg ha(-1) and K from 81.9 to 128.7 kg ha(-1). Total N and P were highest in clone 65/27, while K in clone G48. Nutrients were lowest in clone S7C1. In general, maximum nutrients (N, P and K) were allocated to above-ground components (leaves>stem>branches) than below-ground components. Available N, P and K in the soil improved significantly after six years of planting. It was higher in 0-20 cm and decreased with soil depth. At 0-20 cm soil depth, N increased from 14.9% to 24.1%, P from 17.2% to 23.3% and K from 3.1% to 5.1% under different clones. The yield of both soybean and wheat reduced under poplar clones. Yield losses in soybean ranged from 10.1% to 33% and wheat from 15% to 30.3% under different clones. The management strategies for reducing tree-crop competition and nutrient export from the site under P. deltoides based agrisilviculture system for achieving sustainable production are discussed.     

黄土高原南部春玉米地膜栽培的水肥效应与氮肥去向

在黄土高原南部采用田间小区和微区试验,研究了春玉米地膜栽培下氮肥-水分-产量关系与氮肥去向。结果表明,相同施肥条件下地膜栽培(N120C)比平作栽培(N120UC)增产显著(46．7％),施用氮肥显著地发挥了地膜的增产潜力,处理N120(尿素氮120kg·hm^-2)、N180(尿素氮180kg·hm^-2)和N120M(尿素氮120kg·hm^-2+有机肥氮60kg·hm^-2),籽粒产量比对照CK(不施氮)分别增产41．8％、43．9％和34．7％,地膜栽培或施用氮肥都极大地改善了玉米水分生产效率(WUE)和降水利用率(RUE),试验中N120C比N120UC水分生产效率提高57．9％。降水利用效率提高54．5％;处理N120、N180和N120M比CK处理WUE分别提高38．4％、47．4％和32．4％,RUE分别提高42．3％、43．9％和34．7％,由于供试有机肥是半腐解的牛粪,比尿素氮素供给迟缓,所以对玉米产量和WUE提高幅度小,试验水分测定反映出,玉米利用的水分73．0％～83．7％来自降雨,表明决定春玉米产量的关键水分是生育期降水,玉米地膜栽培对氮肥去向有微弱影响,相对于平作玉米,氮肥总的回收率差异不大,但氮肥利用率下降7．3个百分点,土壤残留率上升6．4个百分点,土壤当季残留氮主要集中在0～20cm,不会发生向深层大量的淋溶和累积。     

Maize response to intermittent submergence,straw mulching and supplemental N-fertilization in subtropical region

Summary A 2-year field study was undertaken on a sandy loam in a tropical monsoon region to determine the growth and yield response of maize (Zea mays L.) to 10–11 day intermittent submergence at two growth stagesviz., 20 (stage 1) and 40 (stage 2) days after planting, in combination with two rates of rice straw mulch (0 and 6 t/ha) and three levels (0, 30 and 60 kg/ha) of soil-applied supplemental nitrogen. Intermittent submergence at both growth stages caused a severe oxygen stress in the root-zone. Compared with no-flooding, stage-1 flooding without additional N reduced the grain yield by 51 and 69%, stover yield by 16 and 45% and grain: stover ratio by 41 and 47% in the first and second year, respectively. Similar were the submergence effects on N, P, K and Zn concentrations in leaves, ears per plant and grain weight per ear. Relatively more adverse effects of stage-1 flooding in the second than the first year followed from the hotter soil and atmospheric environments in the former season. The stage-2 flooding produced practically no ill effects on growth and yield of the crop. Soil application of 60 kg N/ha after termination of stage-1 flooding recovered the grain yield by 77% in the first year and 65% in the second year. Additional nitrogen also benefited the growth and yield characters. The interactive effects of straw mulching with flooding were not distinct. Senior Scientist (Irrigation), formerly graduate student and Assistant Soil Physicsts, respectively.     

Yield loss due to the stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) at different nitrogen application rates to maize

Field trials were conducted at Kibaha and Morogoro in eastern Tanzania during two seasons to evaluate the effect of nitrogen fertilization (0, 50, 75, 100 kg [N]/ha) on pest abundance, plant damage and yield loss of maize due to stemborers. In general, ear and grain weights increased linearly with nitrogen level. In the infested plot, grain weight increased 2.5 and 1.8 fold from 0 to 100 kg [N]/ha in the short and long rainy season, respectively, at Kibaha, and 1.4 and 1.6 times at Morogoro. Yield loss decreased with an increase in nitrogen application and the effect was stronger under high than low borer infestation levels. The results show the beneficial effect of nitrogen on the plant’s ability to compensate for borer damage. Analysis of economic benefits of applying fertilizer and insecticide treatment indicated that using insecticides is not profitable under high-pest-low-soil fertility conditions.     

Contribution of organic matter,N and P through roots and stubbles in irrigated rice culture

Summary A study was conducted on the quantities of crop residues (stubbles) recycled into the soil after harvest with 2 early and 3 medium duration varieties of rice under irrigated culture. The addition of crop residues depended linearly on the total dry matter production of the plants. Dry matter (DM) of stubbles and the N content of the same showed a linear trend. The relationship between grain yield and N contribution through stubbles fitted to a linear regression. In early types the maximum N recycled is 16 kg/ha at an yield range of 4 to 6 t/ha while in medium types a maximum of 26 kg N/ha is recycled at the same yield level. The relationships between DM of stubbles and ‘P’ content of the stubbles and between grain yield and ‘P’ content of stubbles also turned out to be linear. The P content varied from 1 to 4 kg/ha in early types and 1 to 2 kg/ha in medium group. More N was recorded in the stubbles of the medium group while more P was found in the early duration varieties. There were clear varietal variations and the results were discussed in the light of the current literature.     

Accumulation of biomass and mineral elements with calendar time by corn: application of the expanded growth model

The expanded growth model is developed to describe accumulation of plant biomass (Mg ha(-1)) and mineral elements (kg ha(-1)) in with calendar time (wk). Accumulation of plant biomass with calendar time occurs as a result of photosynthesis for green land-based plants. A corresponding accumulation of mineral elements such as nitrogen, phosphorus, and potassium occurs from the soil through plant roots. In this analysis, the expanded growth model is tested against high quality, published data on corn (Zea mays L.) growth. Data from a field study in South Carolina was used to evaluate the application of the model, where the planting time of April 2 in the field study maximized the capture of solar energy for biomass production. The growth model predicts a simple linear relationship between biomass yield and the growth quantifier, which is confirmed with the data. The growth quantifier incorporates the unit processes of distribution of solar energy which drives biomass accumulation by photosynthesis, partitioning of biomass between light-gathering and structural components of the plants, and an aging function. A hyperbolic relationship between plant nutrient uptake and biomass yield is assumed, and is confirmed for the mineral elements nitrogen (N), phosphorus (P), and potassium (K). It is concluded that the rate limiting process in the system is biomass accumulation by photosynthesis and that nutrient accumulation occurs in virtual equilibrium with biomass accumulation.     

Abundance, dispersion and parasitism of the stem borer Busseola fusca (Lepidoptera: Noctuidae) in maize in the humid forest zone of southern Cameroon

This study was conducted in the humid forest zone of Cameroon, in 2002 and 2003. The main objective was to investigate the effects of intercropping on infestation levels and parasitism of the noctuid maize stem borer Busseola fusca Fuller. Two trials were planted per year, one during the long and one during the short rainy season. Maize monocrops were compared with maize/legume or maize/cassava intercrops in two spatial arrangements: maize on alternate hills or in alternate rows. Spatial analyses showed that the stemborer egg batches were regularly dispersed in the maize monocrop and aggregated in the intercrops, as indicated by b, the index of dispersion of Taylor's power law. Depending on the crop association and planting pattern, intercrops reduced the percentage of plants with stem borer eggs by 47.4-58.4% and egg densities by 41.2-54.5% compared to monocropped maize. Consequently, larval densities were 44.4-61.5% lower in intercrops compared to monocrops. Intercropping maize with non-host plants did not affect larval parasitism. Up to two-fold higher levels of egg parasitism by scelionid Telenomus spp. were recorded in inter- compared to monocrops during the short rainy seasons of 2002 and 2003. No differences were found among the mixed cropping treatments and parasitism was lower during the long compared to the short rainy seasons. It was proposed that differences in levels of parasitism were due to density dependence effects rather than the effect of the presence of non-host plants in the system.     

Spatial and Temporal Variation of Roots, Arbuscular Mycorrhizal Fungi, and Plant and Soil Nutrients in a Mature Pinot Noir (Vitis vinifera L.) Vineyard in Oregon, USA

Soil and crop management practices may influence biomass growth and yields of cotton (Gossypium hirsutum L.) and sorghum (Sorghum bicolorL.) and sequester significant amount of atmospheric CO₂in plant biomass and underlying soil, thereby helping to mitigate the undesirable effects of global warming. This study examined the effects of three tillage practices [no-till (NT), strip till (ST), and chisel till (CT)], four cover crops [legume (hairy vetch) (Vicia villosa roth), nonlegume (rye) (Secale cerealeL), hairy vetch/rye mixture, and winter weeds orno covercrop], and three N fertilization rates (0, 60–65, and 120–130 kg N ha ^–1) on the amount of C sequestered in cotton lint (lint + seed), sorghum grain, their stalks (stems + leaves) and roots, and underlying soil from 2000 to 2002 in central Georgia, USA. A field experiment was conducted on a Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults). In 2000, C accumulation in cotton lint was greater in NT with rye or vetch/rye mixture but in stalks, it was greater in ST with vetch or vetch/rye mixture than in CT with or without cover crops. Similarly, C accumulation in lint was greater in NT with 60 kg N ha ^–1 but in stalks, it was greater in ST with 60 and 120 kg N ha ^–1 than in CT with 0 kg N ha ^–1. In 2001, C accumulation in sorghum grains and stalks was greater in vetch and vetch/rye mixture with or without N rate than in rye without N rate. In 2002, C accumulation in cotton lint was greater in CT with or without N rate but in stalks, it was greater in ST with 60 and 120 kg N ha ^–1 than in NT with or without N rate. Total C accumulation in the above- and belowground biomass in cotton ranged from 1.7 to 5.6 Mg ha ^–1 and in sorghum ranged from 3.4 to 7.2 Mg ha ^–1. Carbon accumulation in cotton and sorghum roots ranged from 1 to 14% of the total C accumulation in above- and belowground biomass. In NT, soil organic C at 0–10 cm depth was greater in vetch with 0 kg N ha ^–1 or in vetch/rye with 120–130 kg N ha ^–1 than in weeds with 0 and 60 kg N ha ^–1 but at 10–30 cm, it was greater in rye with 120–130 kg N ha ^–1 than in weeds with or without rate. In ST, soil organic C at 0–10 cm was greater in rye with 120–130 kg N ha ^–1 than in rye, vetch, vetch/rye and weeds with 0 and 60 kg N ha ^–1. Soil organic C at 0–10 and 10–30 cm was also greater in NT and ST than in CT. Since 5 to 24% of C accumulation in lint and grain were harvested, C sequestered in cotton and sorghum stalks and roots can be significant in the terrestrial ecosystem and can significantly increase C storage in the soil if these residues are left after lint or grain harvest, thereby helping to mitigate the effects of global warming. Conservation tillage, such as ST, with hairy vetch/rye mixture cover crops and 60–65 kg N ha ^–1 can sustain C accumulation in cotton lint and sorghum grain and increase C storage in the surface soil due to increased C input from crop residues and their reduced incorporation into the soil compared with conventional tillage, such as CT, with no cover crop and N fertilization, thereby maintaining crop yields, improving soil quality, and reducing erosion.     

Response of Acala cotton to nitrogen rates in the San Joaquin Valley of California

The responses of Acala cotton (Gossypium hirsutum L.) in California to a range of applied nitrogen (N) treatments were investigated in a 5-year, multisite experiment. The experiment's goals were to identify crop growth and yield responses to applied N and provide information to better assess the utility of soil residual N estimates in improving fertilizer management. Baseline fertilizer application rates for the lowest applied N treatments were based on residual soil nitrate-N (NO3-N) levels determined on soil samples from the upper 0.6 m of the soil collected prior to spring N fertilization and within 1 week postplanting each year. Results have shown positive cotton lint yield responses to increases in applied N across the 56 to 224 kg N/ha range in only 41% (16 out of 39) of test sites. Soil NO3-N monitoring to a depth of 2.4 m in the spring (after planting) and fall (postharvest) indicate most changes in soil NO3- occur within the upper 1.2 m of soil. However, some sites (those most prone to leaching losses of soluble nutrients) also exhibited net increases in soil NO3-N in the 1.2- to 2.4-m depth zone when comparing planting time vs. postharvest data. The lack of yield responses and soil NO3-N accumulations at some sites indicate that more efforts should be put into identifying the amount of plant N requirements that can be met from residual soil N, rather than solely from fertilizer N applications.     

Short-term effects on soil properties and wheat production from secondary paper sludge application on two Mediterranean agricultural soils

This study was conducted under greenhouse conditions to evaluate the potential use of SPS as a fertilizer, amendment and/or liming agent for wheat (Triticum aestivum L.). Two representative Mediterranean agricultural soils, a Cambic Arenosol (cmAR) and a Cromic Cambisol (crCM) were used. Treatments included four sludge rates ranging from 0 to 40 g kg(-1) (equivalent of 0, 38, 88 and 120 Mg ha(-1)). A significant increment in soil pH, organic carbon, N total, available P and exchangeable K were observed in both soils. Sludge application significantly increased N and decreased Zn, Mn and Cu concentrations in wheat. Wheat grain yields were reduced by 33% and 37% when 120 Mg SPS ha(-1) was applied to cmAR and crCM soils, respectively, due apparently to unavailability of Mg. However, straw yields, with much lower Mg requirements, increased significantly with SPS rates. Secondary pulp mill sludge seems to be a potential source of organic matter, N, P, K and a potential soil amendment liming agent for acid soils, when appropriate supplemental fertilizer was provided. For grain crops grown in these soils, addition of Mg is required for proper nutrient balance.     

Reversal of adverse effects of heavy ammonium sulphate application on growth and nutrient status of a kikuyu pasture

Summary Adverse effects resulting from fertilization with high rates of ammonium sulphate were determined on a kikuyu grass (Pennisetum clandestinum) pasture grown on a krasnozem in a sub-tropical environment. Corrective fertilizer practices using lime and phosphorus were evaluated.Ammonium sulphate application (336 kg N/ha/annum for 4 years followed by 672 kg N/ha/annum for 2 years) decreased soil pH from 5.0 to 4.0. Under these conditions, soluble Al in the soil increased, while exchangeable Ca, Mg, and K decreased. Concentrations of Ca, Mo, and P in the kikuyu tops were lowered, while concentrations of Mn were raised. Liming to pH 5.5 promoted growth more at 672 kg N/ha/annum than at 134 kg N/ha/annum, while generally little further yield response occurred as soil pH was raised to about 6.0. Liming increased the concentrations of P, Ca, N, and Mo but decreased Mn in kikuyu tops.Phosphorus application decreased soluble aluminium in the soil in all nitrogen treatments, but only increased kikuyu yield where 672 kg N/ha/annum was applied. It did not alter plant chemical composition, except for an increase in P concentration.Yield increases to liming and P were attributed to the alleviation of Al toxicity in the high N treatments. Lime responses in low N treatments were due to improved N nutrition resulting from mineralization of organic N.Lime application reduced the amount of N fertilizer required for maximum growth of kikuyu from 672 kg N/ha/annum on the unlimed soil to 134 kg N/ha/annum, while maintaining an adequate level of nutrients in the herbage and avoiding the problems of excess soil acidity. re]19760622