Intercropping of Wheat and Pea as Influenced by Nitrogen Fertilization

The effect of sole and intercropping of field pea (Pisum sativum L.) and spring wheat (Triticum aestivum L.) on crop yield, fertilizer and soil nitrogen (N) use was tested on a sandy loam soil at three levels of urea fertilizer N (0, 4 and 8 g N m⁻²) applied at sowing. The ¹⁵ N enrichment and natural abundance techniques were used to determine N accumulation in the crops from the soil, fertilizer and symbiotic N₂ fixation. Intercrops of pea and wheat showed maximum productivity without the supply of N fertilizer. Intercropping increased total dry matter (DM) and N yield, grain DM and N yield, grain N concentration, the proportion of N derived from symbiotic N₂ fixation, and soil N accumulation. With increasing fertilizer N supply, intercropped and sole cropped wheat responded with increased yield, grain N yield and soil N accumulation, whereas the opposite was the case for pea. Fertilizer N enhanced the competitive ability of intercropped wheat recovering up to 90% of the total intercrop fertilizer N acquisition and decreased the proportion of pea in the intercrop, but without influencing the total intercrop grain yield. As a consequence, Land Equivalent Ratios calculated on basis of total DM production decreased from a maximum of 1.34 to as low as 0.85 with increased fertilizer N supply. The study suggests that pea–wheat intercropping is a cropping strategy that use N sources efficiently due to its spatial self-regulating dynamics where pea improve its interspecific competitive ability in areas with lower soil N levels, and vice versa for wheat, paving way for future option to reduce N inputs and negative environmental impacts of agricultural crop production.     

Pea–barley intercropping and short-term subsequent crop effects across European organic cropping conditions

Grain legumes are known to increase the soil mineral nitrogen (N) content, reduce the infection pressure of soil borne pathogens, and hence enhance subsequent cereals yields. Replicated field experiments were performed throughout W. Europe (Denmark, United Kingdom, France, Germany and Italy) to asses the effect of intercropping pea and barley on the N supply to subsequent wheat in organic cropping systems. Pea and barley were grown either as sole crops at the recommended plant density (P100 and B100, respectively) or in replacement (P50B50) or additive (P100B50) intercropping designs. In the replacement design the total relative plant density is kept constant, while the additive design uses the optimal sole crop density for pea supplementing with ‘extra’ barley plants. The pea and barley crops were followed by winter wheat with and without N application. Additional experiments in Denmark and the United Kingdom included subsequent spring wheat with grass-clover as catch crops. The experiment was repeated over the three cropping seasons of 2003, 2004 and 2005. Irrespective of sites and intercrop design pea–barley intercropping improved the plant resource utilization (water, light, nutrients) to grain N yield with 25–30% using the Land Equivalent ratio. In terms of absolute quantities, sole cropped pea accumulated more N in the grains as compared to the additive design followed by the replacement design and then sole cropped barley. The post harvest soil mineral N content was unaffected by the preceding crops. Under the following winter wheat, the lowest mineral N content was generally found in early spring. Variation in soil mineral N content under the winter wheat between sites and seasons indicated a greater influence of regional climatic conditions and long-term cropping history than annual preceding crop and residue quality. Just as with the soil mineral N, the subsequent crop response to preceding crop was negligible. Soil N balances showed general negative values in the 2-year period, indicating depletion of N independent of preceding crop and cropping strategy. It is recommended to develop more rotational approaches to determine subsequent crop effects in organic cropping systems, since preceding crop effects, especially when including legumes, can occur over several years of cropping.     

Effects of cropping history and phosphorus source on yield and nitrogen fixation in sole and intercropped cowpea–maize systems

Symbiotic N₂-fixation, N uptake efficiency, biomass- and crop production of cowpea and maize as affected by P source, sole- and intercropped, and introduction of break crops were studied on a farmer’s fields in semi-arid Tanzania. Cowpea fixed around 60% of its N from the atmosphere amounting to 70 kg N ha⁻¹ under sole and 36 kg N ha⁻¹ under intercropping as estimated by the ¹⁵N isotope dilution method around peak biomass production. The amount of N₂-fixed was 30–40% higher when P was applied as either TSP or MRP whereas cowpea yield were unaffected. Intercropped maize with 19,000 plant ha⁻¹ accumulated the same amount of N as 38,000 sole cropped maize plants although intercropping reduced the dry matter accumulation by 25%. The N uptake efficiency of the applied ¹⁵N labelled fertiliser was 26%, which equal a total pool of early available plant N of 158 kg N ha⁻¹. Under the N deficient conditions, P application did not increase the grain yield of maize. The LER indicate that sole cropping required 18% more area than intercropping in order to produce the same grain yield, and 35% more land when LER was based on N uptakes. Introduction of break crops in the maize systems, more than doubled accumulation of dry matter and N in the grain compared to continuous maize cropping. During maturation sole crop cowpea shedded leaves containing 41 kg N ha⁻¹. The current findings underline the importance of crop diversity in Sub Saharan Africa agriculture and emphasise the need for including all residues, including shedded leaves, in nutrient balance studies.     

Productivity of nitrogen fertilized plantain in intercropping systems

The investigation evaluated the productivity of plantain intercropped with cassava, cocoyam and yam, fertilized annually with 0, 320 and 480 kg N ha^–1 respectively. Yields from nitrogen fertilized intercrops were higher than those of unfertilized treatments. In plantain + cassava intercrop receiving 480 kg N ha^–1 plantain growth was suppressed. Plantain intercropped with yam and fertilized with 320 kg N ha^–1 matured early and produced better bunches than other treatments. Plantain + yam or cocoyam intercropping systems fertilized with 320 kg N ha^–1 were recommended because of improved plantain establishment and increased combined crop yields.     

Leaching loss of calcium,magnesium, potassium and nitrate derived from soil,lime and fertilizers as influenced by urea applied to undisturbed lysimeters in south-east Nigeria

Calcium hydroxide was applied to monolith lysimeters at Onne in south-east Nigeria. Eight lysimeters were cropped with maize followed by upland rice and four were uncropped. The cropped and two uncropped lysimeters received Mg, K and urea in the first season. Two uncropped lysimeters received no fertilizers. Drainage water was collected during the two growing seasons and analyzed for calcium, magnesium, potassium, sodium, nitrate and chloride. The fertilizer applied in the second season was not leached during the year of application.The cropped lysimeters lost 27 percent of the sum of the exchangeable Ca in the soil profile and the calcium added, and 29 percent of the corresponding sum for Mg. With no crop, the losses increased to 34 and 37 percent, respectively, but with no crop or fertilizer, the losses were similar to those from the cropped lysimeters. The loss of potassium ranged from 6 percent from the unfertilized lysimeters to 10 percent in the cropped lysimeters. The amounts of sodium leached ranged from 29 to 35 kg Na ha^–1. The bulk of the calcium and magnesium leached from calcium hydroxide and fertilizers occurred in the second season when the loss was in good agreement with the amount of nitrate lost giving (Ca + Mg)/NO₃ charge ratios of approximately one. Urea increased the amount of nitrate leached and led to a corresponding increase in the amounts of calcium and magnesium lost in the drainage water. The charge ratio remained unchanged when the cations were leached only with nitrate derived from the mineralization of soil organic matter. In the cropped lysimeters, this source accounted for about four times more nitrate in the drainage water than the fertilizer.     

Nitrogen dynamics of grass as affected by N input regimes, soil texture and climate: lysimeter measurements and simulations

Nitrate leaching is often low from grasslands, primarily due to their long period of N uptake compared to arable crops. In the present paper we explore the combined effects of N input regime, soil type and climatic conditions through a combination of field lysimeter studies and simulation modeling of temporary grassland. A lysimeter consisting of eight 10 × 4 × 1 m individually drained cells was constructed in SW Norway, a region with a cool and wet marine climate. Six cells were filled with silty sand and two cells with coarse sand. The lysimeters were cropped first with barley for two years, followed by five years of grassland. Treatments included various combinations of N input (fertilizer, manure or both), and the results were analyzed by means of two coupled dynamic simulation models (CoupModel: a heat- and water transport model, and SOILN_–NO: a soil nitrogen model). The parameterized models were further used to assess a scenario with a more continental climate (somewhat cooler and drier). All treatments resulted in a net export of N, with N amounts removed at harvest ranging between 121 and 139% of that applied. Measured N yield from the treatment receiving manure only was almost as high as that from the treatment receiving fertilizer only, even though it received on average about 80 kg ha^–1 less inorganic N. Nitrogen losses through leaching were in the range of 5–23% of the N input, and soil type had a greater effect than source of N input. The inorganic N fraction of the leachate was 71–82% of the total N, and 98% of this was nitrate. The models gave reasonable simulation of N yields as well as of the timing and magnitude of nitrate leaching from the different treatments. They also clearly illustrated that the low nitrate leaching from the system is primarily attributable to a high plant N uptake. The scenario using weather data from a cooler and drier region showed a large decline in plant uptake of N outside the main cropping season, but simulated nitrate leaching was nevertheless significantly lower. With this scenario, precipitation was only 50% of that at the actual experimental site, and the lower temperatures during autumn and winter reduced net mineralization of soil organic N significantly. Thus, the reduction in precipitation and net mineralization of soil organic N apparently more than outweighed the effects of shorter growing season in the continental climate scenario.     

Timing of N fertilization on N2 fixation, N recovery and soil profile nitrate dynamics on sorghum/pigeonpea intercrops on Alfisols on the semi-arid tropics

Cropping systems and fertilizer management strategies that effectively use applied nitrogen (N) are important in reducing costs of N inputs. We examined the effect of time of N application on dry matter (DM) and grain yield (GY), N accumulation, the N budget in crop from soil, fertilizer and atmosphere, and the fertilizer N use efficiency (estimated by the conventional difference method, and the direct ¹⁵N recovery by the crops), in a sorghum/pigeonpea intercropping system on an Alfisol (Ferric Luvisols (FAO); or Udic Rhodustalf (USDA) in India. Fertilizer N was applied at planting (basal) and at 40 days after sowing (delayed). Nitrogen was applied only to the sorghum rows in the intercropping treatment. Nitrogen derived from air (N_dfa) was estimated by the¹⁵ N natural abundance method, and N derived from fertilizer (N_dff) was estimated by the ¹⁵N isotope dilution method. Delaying N fertilization till 40 days after sowing (DAS), rather than applying at sowing increased DM and GY of the sorghum, but not of pigeonpea. Delaying N fertilization to sorghum for 40 days significantly (p<0.001) increased ¹⁵N recovery in shoot from 15 to 32% in sole crop, and from 10 to 32% in intercrop. Similarly, there was a significant (p<0.001) increase in N recovery (by the difference method) from 43 to 59% in sole crop and from 28 to 71 % in intercrop sorghum. Fertilizer N recovery by sole crop pigeonpea (14%) was higher than intercrop pigeonpea (2–4%). Pigeonpea fixed between 120–170 kg ha-¹ of atmospheric N throughout the cropping season. Although there was a marked difference in nitrate-N (N0₃-N) concentrations between basal and delayed treatments at planting, no difference was observed in N0₃-N concentrations in soil solution between the treatments at 40 DAS. Our data on N accumulation by plants showed that the rate of N depletion or disappearance from the soil solution was 2–3 times faster than N accumulation by plants, suggesting that an appreciable amount of N0₃-N would disappear from soil solution in the top soil without being utilized by crops during the initial growth stage. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrogen dynamics following grain legumes and subsequent catch crops and the effects on succeeding cereal crops

The effects of faba bean, lupin, pea and oat crops, with and without an undersown grass-clover mixture as a nitrogen (N) catch crop, on subsequent spring wheat followed by winter triticale crops were determined by aboveground dry matter (DM) harvests, nitrate (NO₃) leaching measurements and soil N balances. A 2½-year lysimeter experiment was carried out on a temperate sandy loam soil. Crops were not fertilized in the experimental period and the natural ¹⁵N abundance technique was used to determine grain legume N₂ fixation. Faba bean total aboveground DM production was significantly higher (1,300 g m^?2) compared to lupin (950 g m^?2), pea (850 g m^?2) and oat (1,100 g m^?2) independent of the catch crop strategy. Faba bean derived more than 90% of its N from N₂ fixation, which was unusually high as compared to lupin (70–75%) and pea (50–60%). No effect of preceding crop was observed on the subsequent spring wheat or winter triticale DM production. Nitrate leaching following grain legumes was significantly reduced with catch crops compared to without catch crops during autumn and winter before sowing subsequent spring wheat. Soil N balances were calculated from monitored N leaching from the lysimeters, and measured N-accumulation from the leguminous species, as N-fixation minus N removed in grains including total N accumulation belowground according to Mayer et al. (2003a). Negative soil N balances for pea, lupin and oat indicated soil N depletion, but a positive faba bean soil N balance (11 g N m^?2) after harvest indicated that more soil mineral N may have been available for subsequent cereals. However, the plant available N may have been taken up by the grass dominated grass-clover catch crop which together with microbial N immobilization and N losses could leave limited amounts of available N for uptake by the subsequent two cereal crops.     

Effect of K on nitrogen fixation of intercrop groundnut and the competition between intercrop groundnut and maize

Application of adequate level of K has shown to improve the competitive ability of the legume in legume/grass mixtures. However, the effect of K on the competitive ability of grain legumes in legume/cereal intercropping systems has not been adequately studied. Hence, studies were made to ascertain if the effects of K could be exploited in improving the performance of groundnut (Arachis hypogaea L.) cv. No. 45 when intercropped with maize (Zea mays L.) cv. Badra. The study was conducted at the Faculty of Agriculture, University of Ruhuna, Kamburupitiya, Sri Lanka in 1988 in basins filled with 36 kg of soil. It involved establishing maize and groundnut as monocrops and as intercrops at three K levels viz. 0, 20 and 40 mg of K kg^–1 of soil. Monocrop maize and groundnut had 2 and 5 plants/basin, respectively while the intercrop had 1 maize plant and 3 groundnut plants/basin. The soil used was Red Yellow Podzolic which was tagged by incorporating¹⁵N-labelled plant material. When grown as a monocrop, K had no effect on the percent N derived from atmosphere, amount of N₂ fixed, dry matter production, pod yield and total N content of groundnut. However, when intercropped with maize lack of K application affected the above parameters significantly which was overcome by improving K level. Thus, the optimum level of K for groundnut was greater when intercropped than monocropped. A significant interaction between K level and cropping system was evident with regard to N₂ fixation, pod yield and total dry matter production of groundnut. Intercrop maize derived 30–35% of its N content from the associated groundnut plants which amounted to 13–22 mg N/plant. The amount of N supplied by groundnut to associated maize plant was not affected by K level. It appears that there is scope for alleviating growth depression of the legume component in legume/cereal intercropping systems by developing appropriate K fertilizer practices.     

Calculated rates of soil acidification of intensively used grassland in the Netherlands

The major processes involved in acidification of soils under intensively managed grassland are the transformation and subsequent leaching of applied nitrogen (N), assimilation of excess cations in herbage and acidic atmospheric deposition. Carbonates from fertilizers and excess cations in purchased concentrates are the most important proton (H⁺) neutralizing agents applied to grassland. In this study, the effects of grazing, cutting and N application on the net proton loading from each of the main processes were calculated, using a simple model.On mown swards, simulated excess cation uptake by the sward released 4.5–9.3 kmol_c H⁺ ha^–1 yr^–1. The total proton loading on mown grassland decreased from about 8.0 to 5.3 kmol_c ha^–1 yr^–1 when fertilizer N input as CAN-27 increased from 0 to about 400 kg ha^–1 yr^–1. Contributions from atmospheric deposition ranged from 2.2 kmol_c ha^–1 yr^–1 when herbage yield exceeded 10 Mg ha^–1 yr^–1 to 3.0 kmol_c ha^–1 yr^–1 when herbage production was only 5.5 Mg ha^–1 yr^–1.On grazed swards, transformation of organically bound N from urine and dung to nitrate (NO ₃ ^- ) and the subsequent leaching of excess NO ₃ ^- was the main source of protons. Application of 400 kg N ha^–1 yr^–1 to grazed swards increased the proton loading from transformed N from 3.9 to 16.9 kmol_c ha^–1 yr^–1. The total proton loading on grazed swards exceeded that of mown swards when the input of fertilizer N exceeded 150 kg ha^–1 yr^–1.Underestimation of the amount of N immobilized in the soil biomass and lost by denitrification may have resulted in a slight overestimation of the amount of N lost by leaching and thereby also the simulated total proton loading.     

Nitrate leaching in temperate agroecosystems: sources, factors and mitigating strategies

Nitrate (NO₃ ^–) leaching from agriculturalproduction systems is blamed for the rising concentrations ofNO₃ ^– in ground- and surface-waters around the world.This paper reviews the evidence of NO₃ ^– leachinglosses from various land use systems, including cut grassland, grazed pastures,arable cropping, mixed cropping with pasture leys, organic farming,horticultural systems, and forest ecosystems. Soil, climatic and managementfactors which affect NO₃ ^– leaching are discussed.Nitrate leaching occurs when there is an accumulation ofNO₃ ^– in the soil profile that coincides with or isfollowed by a period of high drainage. Therefore, excessive nitrogen (N)fertilizer or waste effluent application rates or N applications at the wrongtime (e.g. late autumn) of the year, ploughing pasture leys early in the autumn,or long periods of fallow ground, can all potentially lead to highNO₃ ^– leaching losses. N returns in animal urine havea major impact on NO₃ ^– leaching in grazed pastures.Of the land use systems considered in this paper, the potential for causingNO₃ ^– leaching typically follow the order: forest< cut grassland < grazed pastures, arable cropping < ploughing ofpasture < market gardens. A range ofmanagement options to mitigate NO₃ ^– leaching isdescribed, including reducing N application rates, synchronizing N supply toplant demand, use of cover crops, better timing of ploughing pasture leys,improved stock management, precision farming, and regulatory measures. This isfollowed by a discussion of future research needs to improve our ability topredict and mitigate NO₃ ^– leaching.     

Effect of climate change on greenhouse gas emissions from arable crop rotations

The DAISY soil–plant–atmosphere model was used to simulate crop production and soil carbon (C) and nitrogen (N) turnover for three arable crop rotations on a loamy sand in Denmark under varying temperature, rainfall, atmospheric CO₂ concentration and N fertilization. The crop rotations varied in proportion of spring sown crops and use of N catch crops (ryegrass). The effects on CO₂ emissions were estimated from simulated changes in soil C. The effects on N₂O emissions were estimated using the IPCC methodology from simulated amounts of N in crop residues and N leaching. Simulations were carried out using the original and a revised parameterization of the soil C turnover. The use of the revised model parameterization increased the soil C and N turnover in the topsoil under baseline conditions, resulting in an increase in crop N uptake of 11 kg N ha^–1 y^–1 in a crop rotation with winter cereals and a reduction of 16 kg N ha^–1 y^–1 in a crop rotation with spring cereals and catch crops. The effect of increased temperature, rainfall and CO₂ concentration on N flows was of the same magnitude for both model parameterizations. Higher temperature and rainfall increased N leaching in all crop rotations, whereas effects on N in crop residues depended on use of catch crops. The total greenhouse gas (GHG) emission increased with increasing temperature. The increase in total GHG emission was 66–234 kg CO₂-eq ha^–1 y^–1 for a temperature increase of 4°C. Higher rainfall increased total GHG emissions most in the winter cereal dominated rotation. An increase in rainfall of 20% increased total GHG emissions by 11–53 kg CO₂-eq ha^–1 y^–1, and a 50% increase in atmospheric CO₂ concentration decreased emissions by 180–269 kg CO₂-eq ha^–1 y^–1. The total GHG emissions increased considerably with increasing N fertilizer rate for a crop rotation with winter cereals, but remained unchanged for a crop rotation with spring cereals and catch crops. The simulated increase in GHG emissions with global warming can be effectively mitigated by including more spring cereals and catch crops in the rotation.     

Wheat Responses in Semiarid Northern Ethiopia to N2 Fixation by Pisum Sativum Treated with Phosphorous Fertilizers and Inoculant

Nitrogen fixation (N₂) by leguminous crops is a relatively low-cost alternative to N fertilizers for smallholder farmers in Africa. Nitrogen fixation in pea (Pisum sativum L. cv. Markos) as affected by phosphorus (P) fertilization (0, 30 kg P ha⁻¹) and inoculation (uninoculated and inoculated) in the semiarid conditions of Northern Ethiopia was studied using the ¹⁵N isotope dilution method and locally adapted barley (Hordeum vulgare L. cv. Bureguda) as reference crop. The effect of pea fixed nitrogen (N₂) on yield of the subsequent wheat crop (Triticum aestivum L.) was also assessed. Phosphorus and inoculation significantly influenced nodulation at the late flowering stage and also significantly increased P and N concentrations in shoots, and P concentration in roots, while P and N concentrations in nodules were not affected. Biomass, pods m⁻² and grain yield responded positively to P and inoculation, while seeds pod⁻¹ and seed weights were not significantly affected by these treatments. Phosphorus and inoculation enhanced the percentage of N derived from the atmosphere in the whole plant ranging from 53 to 70%, corresponding to the total amount of N₂ fixed varying from 55 to 141 kg N ha⁻¹. Soil N balance after pea ranged from − 9.2 to 19.3 kg N ha⁻¹ relative to following barley, where barley extracted N on the average of 6.9 and 62.0 kg N ha⁻¹ derived from fertilizer and soil, respectively. Beneficial effects of pea fixed N₂ on yield of the following cereal crop were obtained, increasing the average grain and N yields of this crop by 1.06 Mg ha⁻¹ and 33 kg ha⁻¹, respectively, relative to the barley–wheat monocrop rotation. It can be concluded that pea can be grown as an alternative crop to fallow, benefiting farmers economically and increasing the soil fertility.     

Nitrogen cycling assessment in a hedgerow intercropping system using 15N enrichment

Nitrogen (N) cycling was determined in monocultures of Sorghumbicolor (L.) Moench and alley cropped sorghum with Acaciasaligna (Labill.) H. Wendl. in semiarid Northern Kenya. N inputthrough biological N₂ fixation of the acacia, N transfer from thelegume to the intercrop and losses of applied N through harvest and leachingwere estimated using ¹⁵N enrichment. The biological N₂fixation and N transfer estimates clearly demonstrated the limitations of¹⁵N enrichment techniques in field experiments showing even highertransfer than actually fixed N. Therefore, N transfer in the hedgerowintercropping system could not be determined by the ¹⁵N dilutionmethodology. The ¹⁵N balance approach, however, yielded reliableresults even 1.5 years after ¹⁵N application. 74 to 88% of theapplied ¹⁵N was recovered after three cropping cycles, most of it inthe soil (0–1.2 m). Only about 10% of the¹⁵N was taken up by the above-ground vegetation of both monocultureand agroforestry. The trees took up more of the applied ¹⁵N(8.4%) than the sorghum (1.3%) in the agroforestry system,indicating nutrient competition between tree and crop. Leaching losses below 1.2m depth were low in this semi-arid environment with 3 and 6%of the applied ¹⁵N in the monoculture and agroforestry system,respectively. ¹⁵N losses from leaching were 2.5 times higher in thealley than under the tree row. Incorporating the leguminous tree into thesorghum cropping system had no effect on total leaching and total uptake ofapplied ¹⁵N in above-ground biomass.     

Nitrogen application and underground water contamination in some agricultural soils of South Western Nigeria

The effect of nitrogen fertilizer application on nitrate leaching and contamination of underground and surface waters in a continuously cropped lowland area of South Western Nigeria has indicated a high potential for nitrate leaching.It was estimated that with 100 kg N ha^–1 applied, as much as 29.5 kg N ha^–1 could be lost through leaching below the root zone of a maize crop, Over a 3 year period the applied nitrogen contributed to nitrate pollution of underground water significantly in excess of the maximum level accepted for potable water. This was particularly high in valley bottoms where the nitrate nitrogen content ranged from 12.8 to 24.6 mg L^–1. Contribution to adjacent stream was, however, not significant.     

Movement of bromide as a tracer for nitrate in an Alfisol of the Indian Semi-Arid Tropics under rainfed condition

The variable responses of crops to added nitrogen (N) in Alfisols of the Indian semi-arid tropics are partly due to variable rainfall and partly due to variable losses of available-N. To measure the losses of N through leaching, which can be appreciable under some circumstances, a field experiment was conducted during the rainy season (June-September) of 1992, using bromide (Br) as a tracer for NO ₃ ^- . Bromide (as NaBr) was applied to bare fallow soil at a rate of 200 kg ha^–1 in microplots (2 m × 2 m) and its vertical movement was monitored periodically. Data on rainfall and Br^– distribution in the soil profile on different dates of soil sampling clearly indicated that the movement of Br^– was strongly dependent on rainfall. During the first month (15 June-15 July) after Br^– application, with scattered and light rainfall about 90% of the added Br^– remained in the soil profile (0.6 m). After continuous heavy rainfall in early August more than 90% Br^– had moved beyond 0.6 m depth. This indicates a very high risk of NO ₃ ^- leaching in this soil, and it is unavoidable without special measures to protect the applied N.     

Phosphorus status of soil and leaching losses: results from operating and dismantled lysimeters after 15 experimental years

The objectives of the present study were: (1) to evaluate the predicting value of the most important European soil P tests for P leaching losses; and (2) to investigate how these soil P tests reflect the development of P depth profiles in original homogeneous soils of lysimeters. The study included more than 100 lysimeters, located at the Lysimeter Station Falkenberg/Saxony-Anhalt, UFZ-Centre for Environmental Research Leipzig-Halle GmbH, Germany. Soil textures were sand, sandy loam, loam and silt. The management forms were arable land, grassland and fallow with various variation in fertilisation, crop rotation and irrigation. Samples were collected from the A-horizons and from the whole profiles of eight set-aside and dismantled lysimeters at 10-cm sections. The concentrations of total P were determined monthly in the leachates and evaluated for a three-year period. The concentrations of P extracted by ammonium acetate lactate (AL-P), double lactate (DL-P), sodium bicarbonate (Olsen-P) and ammonium oxalate (OX-P) as well as P_t were significantly correlated with each other (P<0.05–P<0.001) for arable soils. The relevant regression coefficients were strongly influenced by soil texture, soil use and management. The mean annual P concentrations of the leachates were in the range 0.4–1.2 mg l^–1 for sands and <0.001–0.1 mg l^–1 for the textures sandy loam, loam and silt. These corresponded to P leaching losses of 0.001–2846 g ha^–1 yr^–1. Mean annual and maximum P concentrations and leaching losses were significantly (r>0.954, P<0.001) predicted by the OX-P concentrations of arable topsoils in lysimeters filled with sand. For sandy loam under grass the agronomic soil P tests (AL-P, DL-P and Olsen-P) enabled reasonable predictions of P in leachate. Under arable use, factors such as fertilisation, management intensity, depth of tillage and irrigation resulted in weak correlations between soil P concentrations and P in leachate. It was shown for the first time that all P extractants reflected P enrichments in topsoils and subsoils and the development of distinct depth profiles. Influence of soil use on the depth distribution of P was more pronounced in the 0–20 cm layer than in the subsoils. Here, the original homogeneous substrate had oscillating P concentrations at 10-cm increments under all soil uses. These could not be explained by Al_ox and Fe_ox but were significantly correlated with the C_t contents and bulk density. This indicates that vertical movement of P containing organic matter along with differences in porosity contributed to the heterogeneous P distribution in the lysimeter subsoils. This new evidence must be considered if data sets from long-term lysimeter experiments are used to calibrate and validate P leaching models.     

The effects of a nitrification inhibitor on leaching losses and recovery of mineralized nitrogen by a wheat crop after ploughing-in temporary leguminous pastures

The effect of a nitrification inhibitor on the accumulation of ammonium (NH ₄ ⁺ -N) and nitrate (NO ₃ ^- -N) in the profile was investigated in two field experiments in Canterbury, New Zealand after the ploughing of a 4-year old ryegrass/white clover pasture in early (March) and late autumn (May). Nitrate leaching over the winter, and yield and N uptake of a following wheat crop were also assessed.The accumulation of N in the soil profile by the start of winter was greater in the March fallow (76–140 kg N ha^–1) than in the May fallow treatment (36–49 kg N ha^–1). The nitrification inhibitor dicyandiamide (DCD) did not affect the extent of net N mineralization, but it inhibited nitrification when applied to pasture before ploughing, especially at its depth of incorporation (100–200 mm). Nitrification inhibition in spring was greater when DCD was applied in May rather than in March due to its reduced degradation over the winter.Cumulative nitrate leaching losses were substantial from the March fallow treatment in both years (about 100 kg N ha^–1). A delay in the cultivation of pasture and the application of DCD both reduced nitrate leaching losses. When leaching occurred early in the winter (in 1991), losses were less when pasture was cultivated in May (2 kg N ha^–1) than when DCD was applied to pasture cultivated in March (68 kg N ha^–1). When leaching occurred late in the winter (in 1992), similar losses were measured from pasture cultivated in May (49 kg N ha^–1) and from DCD-treated pasture cultivated in March (57 kg N ha^–1).Grain harvest yield and N uptake of the following spring wheat crop were generally unaffected by the size of the N leaching loss over the winter. This was due to the high N fertility of the soil after four years of a grazed leguminous pasture.     

Leaching losses of urea-N applied to permeable soils under lowland rice

Application of 120 kg urea-N ha^–1 to lowland rice grown in a highly percolating soil in 10 equal split doses at weekly intervals rather than in 3 equal split doses at 7, 21 and 42 days after transplanting did not significantly increase rice grain yield and N uptake. Results suggest that leaching losses of N were not substantial. In lysimeters planted with rice, leaching losses of N as urea, NH ₄ ⁺ , and NO ₃ ^- beyond 30 cm depth of a sandy loam soil for 60 days were about 6% of the total urea-N and 3% of the total ammonium sulphate-N applied in three equal split doses. Application of urea even in a single dose at transplanting did not result in more N leaching losses (13%) compared to those observed from potassium nitrate (38%) applied in three split doses. Nitrogen contained in potassium nitrate was readily leached during the first week of its application. More N was lost from the first dose of N applied at transplanting than from the second or third dose. Data pertaining to yield, N uptake and per cent N recovery by rice revealed that the performance of different fertilizer treatments was inversely related to susceptibility of N to leaching.     

Nitrogen leaching and plant uptake from controlled-release fertilizers

Controlled-release N fertilizers are commonly used in the production of container-grown ornamental crops, yet the relative effects of various nutrient sources on N leaching are not well known. A 27-week experiment was conducted to evaluate N leaching loss and plant growth following two applications of six controlled-release N fertilizers and one soluble N fertilizer to container-grownEuonymus patens Rehd. The controlled-release fertilizers evaluated were (noncoated) isobutylidene diurea, oxamide, urea formaldehyde, and (coated) Osmocote, Prokote Plus, and sulfur-coated urea. Of the fertilizers tested, the coated fertilizers generally out-performed the noncoated fertilizers in reducing N leaching losses, stimulating plant growth, and increasing tissue N concentrations. Low N concentrations in the leachate of some treatments indicated efficient nutrient use by the plant. In other treatments, low N concentrations in the leachate merely reflected incomplete N release from the fertilizer. A daily application of NH₄NO₃ resulted in a constant rate of N loss but was not the most effective in promoting growth. Plant growth, tissue N concentrations, and N leaching losses were all increased by doubling the fertilizer application rate from 1 kg N m^–3 to 2 kg N m^–3.