Influence of modified forms of urea and nitrogen levels on weed growth and grain yield of lowland rice

The growth of weeds and their subsequent reduction of rice yield as affected by N source neem cake coated urea (NCU), dicyandiamide coated urea (DCU), rock phosphate coated urea (RPCU), urea supergranules (USG) and prilled urea (PU) was studied on a clay loam soil at Coimbatore, India. Experiments were conducted in northeast monsoon (NEM) 1981, summer 1982, and southwest monsoon (SWM) 1982 seasons.The crop was associated with eleven weed species, and the dominant weeds wereEchinochloa crus-galli, Cyperus difformis andMarsilea quadrifolia. The weed flora varied between seasons. Deep placement of USG reduced the dry weight of weeds in NEM and summer seasons at 60, 90 and 120 Kg N ha^–1 whereas it increased the dry weight at 60 and 90 but not 120 Kg N ha^–1 in SWM season. The dry weight of weeds decreased with increased N rates for all N sources during NEM and summer seasons. In SWM season, dry weight of weeds increased with increased N rates for all N sources except USG. The grain yield of rice was drastically reduced with the deep placement of USG at 60 but not 120 Kg N ha^–1 in SWM season. The differential effect of the N sources between seasons was due to the change of the weed flora. Dominance ofE. crus-galli during SWM season had greater influence on weed dry weight and grain yield of rice.Nitrogen uptake by weeds was frequently greater in unfertilized plots, particularly in NEM and summer seasons. In SWM season, the apparent fertilizer N recovery by weeds was high for USG. It decreased from 53% for 60 Kg USG-N ha^–1 to 4% for 120 Kg USG-N ha^–1.Contribution from the part of Ph.D. work of the first author at Department of Agronomy, Tamil Nadu Agricultural University, Coimbatore-641 003, Tamil Nadu, India.     

Nitrous oxide emissions as influenced by legume cover crops and nitrogen fertilization

In this study, we measured nitrous oxide (N₂O) fluxes from plots of fall-planted hairy vetch (HV, Vicia villosa) and spring-planted broadleaf vetch (BLV, Vicia narbonensis) grown as nitrogen (N) sources for following summer forage crabgrass (Digitaria sanguinalis). Comparisons also included 60 kg ha^?1 inorganic N fertilizer for crabgrass at planting (60-N) and a control without N fertilizer. Each treatment had six replicated plots across the slope. Fluxes were measured with closed chamber systems during the period between spring growth of cover crops and first-cut of crabgrass in mid-July. HV had strong stand and aboveground biomass had 185?±?50 kg N ha^?1 (mean?±?standard error, n?=?6) at termination. However, BLV did not establish well and aboveground biomass had only 35?±?15 kg N ha^?1. Ratio vegetation index of crabgrass measured as proxy of biomass growth was highest in HV treatment. However, total aboveground biomass of crabgrass was statistically similar to 60-N plots. Fluxes of N₂O were low prior to termination of cover crops but were as high as 8.2 kg N₂O ha^?1 day^?1 from HV plots after termination. The fluxes were enhanced by large rainfall events recorded after biomass incorporation. Rainfall enhanced N₂O fluxes were also observed in other treatments, but their magnitudes were much smaller. The high N₂O fluxes from HV plots contributed to emissions of 30.3?±?12.4 kg N₂O ha^?1 within 30 days of biomass incorporation. Emissions were only 2.0?±?0.7, 3.4?±?1.3 and 1.0?±?0.4 kg N₂O ha^?1 from BLV, 60-N and control plots, respectively.     

Effects of nitrogen fertilizer application methods on growth and acetylene reduction activity ofAzolla pinnata and yield of rice

The influence of different methods of N fertilizer application-sub-surface placement (SS) and broadcast application (BC) as a single basal dose of 40 kg N ha^–1 of urea (U) and ammonium sulphate (AS)-on fresh weight (FW) and acetylene reduction activity (ARA) ofAzolla pinnata (Bangkok) and yield of rice was studied for consecutive three seasons. The FW, ARA and N yield ofAzolla were significantly superior with SS placement than with BC application. Of the two N sources, AS was superior to U in recording higher FW, ARA and N yield of Azolla irrespective of methods of N application. Crop yield and crop N uptake were higher with SS application alone and in combination with Azolla as compared to that of surface application of N fertilizers. The combined use of AS and Azolla recorded significantly higher crop yield and crop N uptake than that of U combined with Azolla, irrespective of methods of application.     

The effect of foliar supplements of potassium nitrate and urea on the yield of winter wheat

Winter wheat crops were grown with ostensibly adequate supplies of all soil nutrients in 1990 and 1991 with the aim of testing if late foliar supplements of K and N, applied at key development stages, could improve grain yield and grain N content. Foliar sprays of KNO₃ solution, supplying up to 40 kg K ha^–1 in total, at flag leaf unfolded, inflorescence completed and the watery-ripe stage of grain filling, had no effect on yield, yield components or grain N. Urea, supplying 40 kg N ha^–1 at flag leaf unfolded, had no effects on grain yield and grain N in 1990, but in 1991 grain N was increased by 0.14% whilst yield was reduced by up to 0.6 t ha^–1. Urea scorched flag leaf tips in both years. In 1990, the spring was very dry and foliar supplements might have been expected to have had an effect, but on this highly fertile soil all crop K and N requirements were met from the soil.     

Effect of the timing and rate of nitrogen fertilization on the growth and recovery of fertilizer nitrogen within the potato (Solanum tuberosum L.) crop

The effect of the timing of N fertilizer application on the uptake and partitioning of N within the crop and the yield of tubers has been studied in two experiments. In 1985 either none, 8 or 12 g N m^–2 was applied and in 1986 none, 12 or 18 g N m^–2. Fertilizer N was applied either at planting, around the time of tuber initiation or half at planting and the remainder in four foliar sprays of urea during tuber bulking.¹⁵N-labelled fertilizer was applied to measure the recovery of fertilizer N in the crops.There was an apparent pre-emergence loss of nitrate from the soil when N was applied at planting in 1986, thereby reducing the efficiency of fertilizer use. Applying the N at tuber initiation delayed and reduced the accumulation of N in the canopy compared with crops receiving all their fertilizer at planting. Foliar sprays of urea slightly increased both tuber yields and tuber N contents when compared to a single application at planting. The proportion of the fertilizer N recovered in the crop was little affected by the rate of N application, but a greater proportion of foliar-applied N was recovered than N broadcast at planting, due partly to pre-emergence losses of nitrate in 1986. It is suggested that late applications of N was foliar sprays can be of benefit to crops with a long growing season and reduce environmental losses of N.     

Yield and nitrogen uptake by rice as affected by variety,method of planting and new nitrogen fertilizers

A field experiment conducted for two years (1977 and 1978) at the Indian Agricultural Research Institute, New Delhi showed that yield and nitrogen uptake by rice was more in the case of medium duration (135 days) variety Improved Sabarmati than in the case of the short duration (105 days) variety Pusa-33. Highest yield and nitrogen uptake by rice was recorded when it was transplanted and lowest when rice was direct-seeded (drilled in moist soil). Broadcasting sprouted seeds on puddled seed bed gave yield and nitrogen uptake in between transplanting and direct-seeding and provides a reasonably acceptable method of planting. Rice responded well to nitrogen and the economic optimum dose was found to be 160–170 kg N ha^–1. Urea briquettes gave the highest yield and nitrogen uptake by rice and was superior to sulphur-coated urea or neem-cake-coated urea with respect to N-uptake. All these new nitrogen fertilizers were superior to urea and therefore hold considerable promise in rice culture.     

Response of two okra (Abelmoschus esculentus L. Moench) varieties to fertilizers: Yield and yield components as influenced by nitrogen and phosphorus application

The response of two okra (Abelmoschus esculentus L. Moench) varieties (White velvet and NHAE 47-4) to fertilization in northern Nigeria was examined using four rates of nitrogen (0, 25, 50 and 100 kg ha^–1) and three rates of phosphorus (0, 13 and 26 kg ha^–1). Nitrogen application significantly increased green pod yield, pod diameter, number of fruits per plant, number of seeds per pod and pod weight. Application of phosphorus also significantly increased green pod yield, pod number and number of seeds per pod. The two varieties responded to nitrogen application differentially with respect to green pod yield. For optimum green pod yield of White velvet 35 kg N ha^–1 is suggested while for variety NHAE 47-4, N fertilization can be increased to 70 kg ha^–1. There was no differential response of varieties to phosphorus fertilization for green pod yield; however, the application of 13 kg ha^–1 enhanced the performance of both varieties.     

Yield and uptake response of lettuce to cadmium as influenced by nitrogen application

A screen house experiment was conducted to determine the effect of N (0, 50, 100 and 150 mg N kg^–1) and Cd (0, 5, 10, 25 and 50 mg Cd kg^–1) on growth and concentration and uptake of N and Cd in lettuce grown for 70 days. Nitrogen application increased significantly fresh yield, dry matter yield, N concentration and uptake, whereas these parameters were significantly decreased by Cd application at all levels of N. The concentration and uptake of Cd were significantly increased by Cd application at all levels of N. This increased Cd uptake was related to increased availability of Cd in soil. Application of N upto 100 mg N kg^–1 increased Cd uptake, whereas there was sharp reduction in Cd uptake at 150 mg N kg^–1 treatment at all levels of Cd. The plant dilution effects and reduced translocation of Cd from roots to tops or the competition at the root absorption sites at highest level of N seem to be the mechanisms responsible for N suppressed Cd uptake in this study.     

Residual fertilizer nitrogen as influenced by timing and nitrogen forms in a silty clay soil under sugarcane in Mauritius

A field study was initiated to investigate the influence of application time on the disposition of 100 kg N ha^–1 applied as¹⁵N-labelled NaNO₃ and (NH₄)₂SO₄ to a silty clay soil (a ustic eutropept) under sugarcane (Saccharum hybrid sp.) in Mauritius. The results showed that the vertical and lateral distribution of residual fertilizer N remaining in the soil 2 years after fertilization was not influenced by the chemical nature of N used nor by the time of application. On account of rapid biological immobilization more than 50% of the residual N in the soil remained in the surface 15-cm layer and less than 30% of fertilizer N had moved laterally more than 30 cm away from the zone of fertilization. There was however more residual fertilizer N in the soil when the N was applied in September (23 kg N ha^–1) than in December (16 kg N ha^–1) because fertilizer N applied during the active sugarcane growth in December was used more efficiently than similar applications in September when growth was slow. The present study provides further evidence to substantiate that N leaching is not of significant concern in soils located in a tropical environment similar to that of Mauritius.     

硫酸脲复合肥对玉米生长指标及产量的影响

通过田间试验方式研究硫酸脲复合肥、普通缓释肥、硫基肥、BB肥对玉米生长和产量的影响。结果表明,4种肥料处理均能促进玉米植株茎粗、穗粗和穗行数的增加,特别是硫酸脲复合肥处理,较CK分别增加了3.8%、3.6%和18.2%;而且4种肥料处理对玉米也有不同程度的增产效应,其中硫酸脲复合肥处理增产率最高,为21.09%。     

Growth,yield components and micronutrient nutrition of field-grown maize (Zea mays L.) as affected by nitrogen fertilization and plant density

Growth and yield components in field-grown maize (Zea mays L.) were enhanced by nitrogen fertilization ranging from 50 to 200 kg N ha^–1. Ear diameter, kernel depth, grain: stover ratio, number of ears plant^–1, plant height and dry matter production increased as N fertilization rate was increased up to 100 or 150 kg N ha^–1. Tasselling in maize was hastened by N fertilization. Increasing plant density from 25000 to 75000 plants ha^–1 increased plant height, dry matter production and delayed tasseling but reduced ear diameter, kernel depth, grain: stover ratio and number of ears plant^–1. Increased N supply and plant density had no influence on the concentrations of Mn, Zn, Cu, and Fe in ear leaf; except that Mn concentration increased as N fertilization rate was increased up to 150 kg N ha^–1. Nitrogen × plant density interactions on the concentrations of the micronutrients in maize ear leaf were not significant.     

Late season nitrogen fertilization of soybeans: effects on leaf senescence, yield and environment

Nitrogen demand from soybean seeds during seed filling is very high and has been proposed as the cause of nitrogen remobilization and leaf senescence. Previous research has not shown consistent effects of late season fertilization on seed yield, while its effects on leaf senescence have not been evaluated. Two field experiments were performed to determine the effects of a late season N fertilization on leaf senescence and fall, seed yield and its components, and residual soil nitrate, and to evaluate the potential risk of groundwater contamination. Two rates of nitrogen (50 and 100 kg N ha^–1) were applied at the R3 and R5 development stages. Nitrogen fertilization, either at R3 or R5, increased soil nitrate availability during the seed-filling period. Seed yield, seed number and protein content were not affected by N fertilization. The addition of 100 kg N ha^–1 produced a small delay of 1–2 days in the leaf fall, and slightly increased seed size (3.6%). Our results suggest that increasing soil N availability during the seed-filling period is not an effective way to delay leaf senescence or to increase seed growth and yield of soybean. Nitrogen fertilization increased the level of residual nitrate in the top soil at one site (the one with lowest seed yield), increasing the risk of nitrate leaching during subsequent fallow.     

砂姜黑土区控释尿素与普通尿素掺混对小麦-玉米轮作定位产量及氮肥利用率的影响

在驻马店新坡村进行了小麦-玉米轮作制下的控释尿素与普通尿素掺混比例定位试验研究。结果表明:控释尿素与普通尿素掺混处理的小麦、玉米产量均以70%控释尿素+30%普通尿素处理最好,第1年和第2年的小麦产量分别比100%普通尿素处理增产17.0%和21.1%,玉米产量分别比普通尿素处理增产16.2%和16.2%;氮肥利用率与产量结果一致,均以70%控释尿素+30%普通尿素处理最高,分别为53.9%和54.5%。     

不同氮磷钾施肥水平对超级稻产量的影响

探讨各种土壤肥力状况下,不同氮磷钾施肥水平对超级稻(准两优1202)产量的影响,提出了超级稻合理的氮磷钾施肥水平和配比。     

Volatilization of ammonia from urea-ammonium nitrate solutions as influenced by organic and inorganic additives

Fertilizers containing urea can suffer from nitrogen (N) loss through ammonia volatilization, resulting in reduced effectiveness of the fertilizers. The loss of N may be reduced by use of organic or inorganic additives.Laboratory experiments were conducted on surface soil samples (0–15 cm) from two agricultural soils (St. Bernard and Ste. Sophie) to determine the impact of ammonium thiosulfate (ATS), boric acid, and a humic substance from leonardite, on NH₃ losses from surface-applied urea-ammonium nitrate (UAN) solutions. Experiments were carried out using moist soil samples in closed containers. Evolved NH₃ was carried out of the containers and trapped in boric acid solution using an ammonia-free humidified air flow.Total NH₃ losses in these experiments ranged from 12.1 to 21.3% of the N applied. The reduction in NH₃ volatilization (expressed as % of added N) due to additives ranged from 13.6 to 38.5% and 3 to 36.3% in St. Bernard and Ste. Sophie soils, respectively. More NH₃ volatilized from the boric acid or humic treated UAN solutions than from ATS-UAN solutions.Boric acid, ATS, and the humic substance, all significantly reduced urea hydrolysis in both soils in comparison to the untreated UAN solution. Further, the humic substance and boric acid treatment induced significant reduction in NO₃-formation. The results suggest that humic substance and to a lesser extent boric acid may function as urease and/or nitrification inhibitors. ATS treatment, particularly at higher levels increased NO₃-formation in both soils. The reason for this increase in nitrate formation is not clear.     

Recovery of nitrogen by spring barley from ammonium nitrate,urea and sulphur-coated urea as affected by time and method of application

The objective of this study was to increase the efficiency of fall-applied N either by placement in bands or by using a slow-release fertilizer. Four field experiments were conducted in north-central Alberta to determine the influence of N source, time of application and method of placement on the recovery of fall-applied N as soil mineral N in May, and on yield and recovery of N in grain of spring-sown barley. The recovery in soil of mineral N by May from the fall-applied fertilizers varied among treatments. More specifically, the recovery was lowest with topdressed application, highest with banding, and tended to be less with incorporation application as compared to banding. Recovery of mineral N was least for sulphur-coated urea (SCU) compared with A.N. and urea, regardless of method of application. The loss of fall-applied N was substantial, but leaching did not go beyond 60 cm deep.Yield and recovery of N in barley grain were much greater with spring application than with fall application at the 4 sites for ammonium nitrate (A.N.) and at 3 sites for urea. The SCU treatments were inferior. The A.N. and urea had greatest yield and N recovery with banding, followed by incorporation and then with topdressing for both fall- and spring-applied N. Method of application had little effect on yield and N uptake with SCU. In all, the greatest yield or crop N uptake was obtained with spring banding of A.N. or urea, while SCU did not function well as a fall- or spring-applied N fertilizer.(Contribution No. 680)     

不同施肥方式对水稻生长、养分吸收和品质的影响

研究不同施肥方式对田间水稻生长、养分吸收和品质的影响。结果表明,施肥能显著提高水稻产量,增产幅度在7.62%~41.90%,NPK与有机肥配合施用、施用控释肥分别增产31.75%和41.90%,氮磷钾对水稻增产作用NKP。氮肥农学利用率以缓控释肥处理最高,达11.08 kg/kg,氮肥利用率最高与最低相差31.10%;氮磷钾施肥+有机肥处理和控释肥处理田面水中速效氮含量显著低于其他处理,稻米品质最好。     

Cotton fertilization with composts of (sugarbeet) vinasse and agricultural residues

A concentrated depotassified beet vinasse was mixed with each of ten solid agricultural residues. The ten mixtures were composted for 7 months. The composts obtained after this period were used to fertilize a cotton crop. A mineral treatment was used for comparison and a treatment without fertilization was used as control. The nitrate content of petiole determined before the first top dressing revealed significant differences between treatments. All treatments produced higher yields than the control. Analysis of fibre quality did not show significant differences between treatments.     

Growth response,yield and yield components of upland cotton (Gossypium hirsutum L) as affected by rates and time of nitrogen application in the Nigerian savannah

Effects of rate and time of nitrogen fertilization on growth, yield and yield components of upland cotton (Gossypium hirsutum L) were studied in two years (1975–76). Four rates of nitrogen application (0, 26, 52 and 78 kg ha^–1) timed at 3 or 8 weeks after sowing were compared. Seed cotton yield components increased significantly with increased N application at least up to 52 kg N ha^–1, with yield increases between 49% and 73%. Seed cotton yield was influenced by treatments mainly through boll number. Both crop growth rate and fruiting were enhanced by nitrogen fertilization. Applying N at 8 weeks (flowering) favoured yield only slightly over that at 3 weeks (thinning), but improved crop growth and fruiting by about 64% and 24%, respectively. There were significant N rate × time interactions in favour of fertilization at flowering. Applying 52 kg N ha^–1 at 8 weeks seems best for cotton in the Nigerian savannah.