Nitrogen and potassium requirement of pineapple in relation to irrigation in Nigeria

The investigation studied the effect of fertilization with four nitrogen levels (0, 100, 150 and 200 kg/ha), four potassium levels (0, 100, 150 and 200 kg/ha) and four irrigation treatments (0, 3, 7 and 14-day interval) on the growth and yield of smooth Cayenne pineapples. Increasing irrigation frequency increased growth parameters of number of leaves, D-leaf length and days to 50% flowering. Fruit weight was highest at N = 150 kg/ha, K = 200 kg/ ha and irrigation once a week. Higher N levels (beyond 150 kg/ha) applied after the plant crop has been harvested did not further enhance yields of the ratoon crop. For K = 200 kg/ha potential and harvested yields were reduced in all irrigation treatments when N > 150 kg/ha.     

Efficiency of nitrogen fertilizer use under rainfed maize and irrigated wheat at Kadawa,northern Nigeria

Field trials were conducted at Kadawa, northern Nigeria, during 1975–77 to study the efficiency of nitrogen fertilizer use under maize (Zea mays L.)—wheat (Triticum aestivum L.) rotation; the study also examined the impact of continuous N use on some soil properties. Grain and straw dry matter yields, grain N content, crop N uptake and whole plant N concentration of wheat at different growth stages increased significantly with increasing levels of N application. Per cent increases in mean grain yield of N treated plots over control were 77, 131 and 141 for maize and 195, 308 and 326 for wheat at 60, 120 and 180 kg N per ha levels, respectively. The calculated N rates for maximum yield were 177.5 and 164.0 kg N per ha for maize and wheat, respectively. Short-term beneficial effect of dung on maize yield was ascribed to its additional N supply. Urea and calcium ammonium nitrate (CAN) were equally good for both maize and wheat; full and split N application gave no significant difference in yield. The values for mean fertilizer N recovery over all the crops were 64, 58 and 44% respectively, at 60, 120 and 180 kg N per ha levels.Nitrogen application at the highest rate (180 kg per ha) reduced the soil pH significantly in the top 40 cm of the soil profile. The magnitude of soil acidification at levels of N below 120 kg per ha was not appreciable in this study. High N application also depleted the soil of its cations at differential rates. Other factors such as N source, time of N application and addition of dung along with N fertilizer did not have much influence on the rate of short-term soil acidification due to N fertilizer use.     

Effect of nitrogen,phosphorus and soil and crop residues management practices on maize (Zea mays L.) yield in ultisol of eastern Cameroon

The shortening of fallow period in several areas in tropical Africa has reduced soil fertility and exposed soils to erosion and run-off. Fertilizer application and crop conservation practices are needeed to sustain high crop yield and to conserve the natural resource base for upland crop production in the continent. Field trials were carried out to evaluate the effect of fertilizer application and soil and crop residues management practices on yield of maize (Zea mays L.) planted on a Plinthudult soil at Bertoua, Eastern Cameroon. Maize yields increased significantly with nitrogen and phosphorus fertilizer application. Under the rainfall pattern prevailing in the area, the amount of nitrogen required for maximum yield was higher in the second season. On the other hand, the amount of phosphorus required for maximum yield appeared to decrease with time. The burning of crop residues and weeds prior to planting together with no-till practive gave higher yield of maize than other soil and crop residues management practices.     

Relationship between electroultrafiltration (EUF) extractable nitrogen,grain yield,and optimum nitrogen fertilizer rates for winter wheat

The objective of the investigation was to examine whether there exist relationships between the optimum nitrogen fertilizer rate for winter wheat and soil nitrogen fractions extracted by electroultrafiltration (EUF) from autumn samples of the upper soil layer (0–30 cm). Optimum nitrogen fertilizer rates were derived from grain yield curves of field trials carried out with increasing nitrogen fertilizer rates on 19 different sites in 1985/86 and 1986/87. Most soils were luvisols derived from loess, two soils were brown earths and one a pararendzina. Total Nitrogen fertilizer rates were 0, 40, 80, and 120 kg N/ha applied twice before ear emergence. The final nitrogen rate at ear emergence was the same for all treatments, namely 60 kg N/ha.Optimum nitrogen fertilizer rates were derived from the grain yield curve fitted to a modified Mitscherlich equation. The optimum nitrogen fertilizer rates were correlated with the nitrogen fractions extracted by EUF. The regression equation thus obtained showed that NO ₃ ^- , the organic N fraction (EUF Norg), and the EUF Norg-quotient each had a highly significant impact on the optimum nitrogen fertilizer rate. The higher the amounts of EUF-N extracted the lower the optimum nitrogen rate. Substituting the EUF Norg-fraction for total nitrogen concentration in the upper soil layer gave a poorer relationship between the optimum nitrogen fertilizer rate and the soil data. In absolute terms the EUF Norg-fraction had by far the greatest impact on calculating the optimum nitrogen fertilizer rate. The investigation shows that the EUF method is a suitable technique for the determination of available soil nitrogen from which optimum nitrogen fertilizer rates can be derived for winter wheat cultivated under soil and climatic conditions typical for cereal growing areas in central Europe.     

Effects of timing of nitrogen and sulphur fertilizers on yield, nitrogen, and sulphur contents of Tef (Eragrostis tef (Zucc.) Trotter)

Nitrogen use efficiency (NUE) of tef, a major staple crop in Ethiopia, is very low, either caused by untimely use of nitrogen (N) fertilizers or lack of other essential nutrients like sulphur (S). The average grain yield of this crop is low, averaging <0.8 Mg ha⁻¹ in farmer’s fields of the semi-arid conditions. Therefore, the present study was conducted to see the effect of the timing of combined N and S fertilization on the yield, yield components, and N and S concentration in the plant parts of the crop. A factorial combination of three rates of N (0, 70, and 105 kg ha⁻¹) with four rates of S (0, 16, 32, and 48 kg ha⁻¹) was applied in randomized complete blocks in three replications. The experiment was carried out in the 2004 and 2005 cropping seasons in the Cambisols of the semi-arid area of Ethiopia. The crop responded significantly (P < 0.05) to both split (one-third at planting and two-thirds at late tillering) and whole (all at planting) N and S applications and years. Combined N and S fertilization increased the dry matter (DM) and grain yields on average by 1.7 and 0.3 Mg ha⁻¹, compared with the control. Similarly, S fertilization increased the NUE of the tef crop by 36%. Nitrogen concentration of shoots was found to significantly increase with S application (P < 0.05), with strong positive interactions both in the split and whole applications. The sulphur increase in grains was significant with N rates for both applications, with significant interaction effects observed for the split application in both cropping seasons. Split application resulted in 0.9 and 0.3 Mg ha⁻¹ significant increase in DM and grain yields, averaged for both years and treatments compared with the whole application. Similar significant increases were observed for panicle yield, NUE, and shoot and grain N and S concentrations. The average N:S ratio in grains was 10.6:1. Significant (P < 0.05) yearly variations were also observed. Dry matter and grain yields of 2005 were higher on average by 2.10 and 0.32 Mg ha⁻¹ than those of the 2004 cropping season. The percentage of N and S concentrations of grains, averaged for both applications, were higher by 13 and 9% in 2004; even though the N and S uptakes of 2005 were higher on average by 5.0 and 0.5 kg ha⁻¹ than those of the 2004 cropping season. This work showed that the yield response and NUE of the tef crop could be improved with split N and S fertilizer applications, with tef-producing farmers benefitting from the application of S-containing N fertilizers to soils deficient in these nutrients.     

Residual effectiveness of boron fertilizer for oilseed rape in intensively cropped rice-based rotations

Long-term field experiments (3–4 years) were conducted to evaluate the residual effect of boron (B) fertilizer for oilseed rape (Brassica napus L.) in an intensive crop rotation including two rice (Oryza sativa) crops per year. Experiments were conducted on four sites where the soil types were sandy, silty and clayey Inceptisols, and an Ultisol, located in the Zhejiang Province, Southeast China. Application of B fertilizer at rates of 1.1, 1.65 and 3.3 kg B/ha in the first year showed a different residual effect on oilseed yield in successive years, but had only small positive effects on the rice grain yield at two sites. The residual effect of 1.1 kg B/ha remained fully effective in correcting B deficiency in oilseed rape for 2 years in the Inceptisols, whereas the residual effect of 1.65 kg B/ha continued to correct B deficiency for at least 3 years in both the Inceptisols and the Ultisol. Foliar application of B fertilizer generally corrected B deficiency for oilseed rape but showed limited residual effect in the following years after application. The decline in residual values of B from a single fertilizer addition was closely related to the soil and leaf B concentration. Soil available B also decreased dramatically with the advance of rotation, but a larger decrease was found at a depth of 20–40-cm for the Inceptisols and the Ultisol. Thus, a more detailed understanding of the B cycling in the system is now needed to optimize management of B fertilizer.     

Estimating the crop response to fertilizer nitrogen residues in long-continued field experiments

Knowledge of the cumulated effect of long-continued nitrogen (N) inputs is important for both agronomic and environmental reasons. However, only little attention has been paid to estimate the crop response to mineral fertilizer N residues. Before interpreting estimates for the crop response to previous N input rates, the experimental design for testing needs to be examined. Experimental designs that suspend the customary N inputs, leaving the test crop unfertilized, ignore any interaction between the rate of N applied in the past and the rate applied in the test year. We estimated the interaction using data from five long-continued field experiments on mineral and organic N input rates where the main plots were subdivided for incremental rates of mineral N fertilizer in the test year. The interaction between N applied in the past and in the test year significantly affected grain yield and N offtake when the residual effect originated from organic applications, but the interaction was not significant when mineral N fertilizer had been used in the past, making the residual effect of N applied in the past additive to the effect of N applied in the test year. The dry matter (DM) grain yield of spring barley decreased by an average of 5?kg?DM/ha and the grain N offtake by 46?g?N/ha for a decrease in the annual mineral N rate of 1?kg?N/ha applied for more than three decades. Although statistically significant, the crop response to mineral fertilizer N residues was of minor importance when compared with the residual effect of organic inputs.     

潮土区氮肥运筹对小麦产量和氮肥利用率的影响

研究了氮肥运筹对小麦产量和氮肥利用率的影响,结果表明:以控释BB肥处理最佳,达8070kg/hm2。控释尿素基肥处理和33.3%氮肥基肥+33.3%氮肥拔节+33.3%氮肥抽穗期处理产量分别为7796kg/hm2和7978kg/hm2,三处理之间没有达到1%极显著水平。在施用普通尿素的各个处理中,33.3%氮肥基肥+33.3%氮肥拔节+33.3%氮肥抽穗期处理的氮肥利用率最高,为36.8%,可见适当的施肥方式也能提高氮肥的利用率。控释尿素基肥处理和控释BB肥基肥处理的氮肥利用率分别为45.7%和47.3%,均高于施用普通尿素的各个处理,控释BB肥基肥处理的氮肥利用率高于控释尿素基肥处理的氮肥利用率。     

烤烟氯化铵肥效试验初报

在氯化铵小区定位试验的基础上，进行烤烟氯化铵肥效试验，结果证明，在我省气候条件下，当土壤氯离子含量在１３ｌｐｐｍ范围内，前作每亩施用氯化铵３４．８ｋｇ或当季作物每亩施用氯化铵１７．３２ｋｇ，对烤烟质量和产量无不良影响。     

Fate of urea applied to winter spinach in New Zealand

Field trials were conducted during three years (1996–1998) to follow the fate of N fertiliser applied to spinach (Spinacea oleracea L.) grown over winter (May–September) in New Zealand. Urea labeled with ¹⁵N was applied to the spinach at different rates (0, 200 or 400 kg N/ha), times (as two or three split applications) and placement methods (broadcast or banded). The results showed that the typical fertiliser practice of applying 350 kg N/ha near planting time followed by 50 kg N/ha 4 weeks later, resulted in leaching losses of 119–292 kg N/ha depending on the rainfall. Plants recovered only a small proportion of the fertiliser N (3–18% of the ¹⁵N). Better utilization of the fertiliser and lower leaching losses occurred when the fertiliser was applied strategically in split applications with only a small amount (10%) applied near sowing and the majority applied to match crop demand. For example, in 1998 applying 200 kg N/ha (20 kg N/ha initially+100 kg N/ha after 4 weeks and 80 kg N/ha after 8 weeks) resulted in twice the spinach yield (25 t/ha compared with 13 t/ha) and less than half the leaching loss (108 kg N/ha leached compared with 246 kg N/ha) compared with the typical fertiliser practice.     

On-farm assessment of soil erosion and non-point source pollution in a rain-fed vegetable production system at Dianchi lake’s catchment, southwestern China

Vegetable is important cash crop in Dianchi lake’s catchment, but the non-point source (NPS) pollution from the intensive agricultural production systems is a critical hurdle on the alleviation of serious eutrophication in Dianchi lake. Our objectives were to quantify soil erosion and NPS pollution in rain-fed vegetable production systems at the area. The experiment was a randomized complete factorial design with two plastic mulch treatments (narrow vs. wide plastic mulch) and two rotation treatments (broccoli–zucchini–winter wheat vs. broccoli–zucchini–fallow). The narrow-plastic-mulch system has significantly (P < 0.05) increased runoff and soil loss than wide-plastic-mulch system. Results indicated that plastic mulch substantially accelerated runoff generation and soil erosion at vegetable seedling stages, whereas runoff and soil loss were apparently alleviated in furrow with residue mulch. The sediment transport played a predominant role in soil nitrogen (N) and phosphorus (P) movement by surface runoff. The annual losses of N and P via surface runoff in the vegetable field were ranged from 2.0 to 5.1 kg/ha and 0.3 to 1.1 kg/ha respectively in the three considerably drier rain season, but their losses never exceeded 1 % of the annual fertilizer application. Removal of crop residues was the major causes of N and P export from the soil in the vegetable fields, which exceeded 20 and 8 % of the annual nitrogen and phosphorus fertilizer application respectively. This implicated that inappropriately discarding of the residues would pose serious consequences for water contamination of Dianchi lake. As under appropriate discarding of residues, the wide-plastic-mulch system could improve NPS pollution control and crop production in vegetable field at Dianchi lake’s catchment.     

The effect of nitrogen source and crop rotation on the growth and yield of processing tomatoes

Four crop rotation and management systems were studied in 1994 and 1995 in relation to growth and yield of irrigated processing tomatoes (Lycopersicon esculentum Mill.). The four treatments were three four-year rotation systems [conventional (conv-4), low input and organic] and a two-year rotation system [conventional (conv-2)]. The four-year rotation was tomato-safflower-corn-wheat(or oats+vetch)/beans, and the two-year rotation was tomato-wheat. Purple vetch (Vicia sativa L.) was grown as a green manure cover crop preceeding tomatoes in the low input and organic systems. Nitrogen was supplied as fertilizer in the conventional systems, as vetch green manure plus fertilizer in the low input system and as vetch green manure plus turkey manure in the organic system. Tomato cv. Brigade was direct-seeded in the conventional systems and transplanted to the field in the low input and organic systems. In both years the winter cover crop was composed of a mixture of vetch and volunteer oats with N contents of 2.2% in 1994 and 2.7% (low input) or 1.8% (organic) in 1995. In 1994 yields were higher in conventionally grown tomatoes because a virus in the nursery infected the transplants used in the low input and organic systems. In 1995 tomatoes grown with the low input and conv-4 systems had similar yields, which were higher than those of tomatoes grown with the conv-2 and organic systems. N uptake by the crop was greater than 200 kg N ha^–1 for high yield (> 75 t ha^–1) and uptake rates of 3 to 6 kg N ha^–1 day^–1 during the period of maximum uptake were observed. The lower yield with the organic system in 1995 was caused by a N deficiency. The main effect of the N deficiency was a reduced leaf area index and not a reduction of net assimilation rate (NAR) or radiation use efficiency (RUE). Nitrogen deficiency was related to low concentration of inorganic N in the soil and slow release of N from the cover crop + manure. A high proportion of N from the green manure but only a low proportion of N from the manure was mineralized during the crop season. In the conventional systems, the estimated mineralized N from the soil organic matter during the crop season was around 85 kg ha^–1. A hyperbolic relationship between N content and total dry weight of aboveground biomass was observed in procesing tomatoes with adequate N nutrition. Lower yields with the conv-2 than with the conv-4 system were due to higher incidence of diseases in the two year rotation which reduced the NAR and the RUE. Residual N in the soil in Oct. (two months after the incorporation of crop residues) ranged between 90 and 170 kg N ha^–1 in the 0–90 cm profile.Department of Vegetable Crops.     

A short communication on the effect of nitrogen fertilization of willow on yield,combustion emissions and greenhouse gas balance

Nitrogen fertilizer was applied to willow after harvest in 2011, two levels of nitrogen were applied (75; 150 kg N/ha) in addition to a control. The trial was harvested in January 2013, biomass from each treatment was burnt and emissions from combustion were quantified. Nitrogen application increased leaf nitrogen and plant height although there was no difference between the nitrogen treatments. Plant height and maximum stem diameter increased with applied nitrogen at final harvest. Nitrogen fertilization significantly increased yield by 35 % although there was no difference between the two nitrogen treatments. Stem nitrogen content did not differ significantly between treatments and there was no significant difference in NO_x emissions between treatments. A life cycle assessment showed that nitrogen fertilization significantly increased net greenhouse gas benefit by up to 30 % depending on the fuel replaced. The study demonstrated that the application of relatively low levels of nitrogenous fertilizer to willow can significantly improve greenhouse gas mitigation without affecting other aspects of the environment such as air quality.     

Environmental factors affecting nitrogen efficiency in flooded tropical rice

How environmental factors modify the effect of time of nitrogen application on grain yield and yield components of rice (Oryza sativa L.) were studied under field experiments during the 1975 dry and wet seasons on a fertile Maahas clay soil (an isothermic clayey mixed Aquic Tropudalf). Two rice varieties, one early maturing (IR28) and one medium maturing (IR26), which are highly responsive to nitrogen fertilizer, were tested. These varieties were planted monthly from January through December. Three nitrogen levels were applied in a single or in split doses to examine the maximum nitrogen efficiency under different climatic conditions.Low solar radiation values during the reproductive growth periods of both varieties reduced the spikelet number per unit area. IR26 rice, with an excessive number of spikelets per panicle, was more sensitive to solar radiation. It produced a high percentage of unfilled spikelets at low solar radiation.Nitrogen levels higher than 120 kg N ha^–1 were required to obtain maximum grain yields from both varieties under high solar radiation values during the reproductive growth periods. At low solar radiation levels, 60 kg N ha^–1 was adequate to get an optimum grain yield with high fertilizer efficiency.Increased grain yields greater than 1.0 t ha^–1 were obtained when the nitrogen fertilizer was applied at appropriate times. Proper application minimized the adverse effects of low solar energy.     

Phosphorus availability to irrigated lowland rice as affected by sources,application level and green manure

To evaluate alternative fertilizer phosphorus (P) sources in lowland rice, two field experiments were conducted under irrigated conditions in Quezon Province, Philippines during 1990–1991 crop year. In another field experiment fertilizer P recycling through a green manure crop applied in the succeeding rice, was studied. Addition of fertilizer P increased grain yield by 1.5–2.0 t/ha (46%) in 1990 wet season (WS) and by 1.6–2.1 t/ha (56%) in 1991 dry season (DS). However, fertilizer P source and application level did not effect grain yield significantly. Results indicated that the less water-soluble and less expensive partially acidulated phosphate rock (PAPR), phosphate rock (PR) and less reactive PR were as effective as the more soluble but more expensive triple superphosphate (TSP). The relative effectiveness (RE) of local guano was significantly lower than that of other sources of fertilizer P. Fertilizer P applied to a pre-rice Sesbania rostrata green manure increased rice grain yield by 1.5–1.9 t/ha during 1991 DS. Further, S. rostrata fertilized with Morocco phosphate rock (MPR) gave significantly higher rice grain yield than did rice fertilized with MPR applied alone. In the P source experiments Olsen method and Pi correlated better with growth attributes than Bray 2 P. Phoshours uptake did not differ significantly among P sources and levels. Results suggest that P uptake was improved with green manuring. Correlation analyses revealed a close correlation between P uptake and dry matter yield and P uptake and grain yield.     

Outlook on fertilizer use efficiency in the tropics

In this paper efficiency of applied fertilizers under tropical conditions is examined. Understanding of the fertilizer efficiency is particularly important for the developing countries mainly because there is need for enhancement of crop yields at a reduced cost. Many of the soil, plant and climatic factors of the tropical regions that contribute to the efficiency of the applied fertilizers have been discussed. Many of the tropical soils are acidic in nature and in these soils efficiency of applied fertilizer is relatively poor, mainly because plant roots are unable to grow and function to their fullest extent in utilizing the soils available nutrients. To enhance yield potentials there is need for understanding of interaction between crop species and soil and climatic variables. Incorporation and adoptation of a suitable application time can greatly enhance efficiency of urea form of nitrogen. Research findings in tropical soils have shown that an initial broadcast application of P and subsequent band treatment is more effective than either method of application alone. Current crop yields in tropical countries are far below the known yield potentials. Such low production potentials are attributed to the lack of suitable crop germplasms and understanding of improved agronomic practices. Intensification of research activities in fertilizer use efficiency in tropical countries is suggested.Senior author formerly was a Research Advisor to EMBRAPA/IICA/World Bank Program in Brazil.     

Effects of different nitrogen doses on thymoquinone and fatty acid composition in seed oil of black cumin (Nigella sativa L.)

Black cumin, Nigella sativa L. belonging to Ranunculaceae, is a valuable medicinal plant because of the curative effects of seed and oil. Despite studies on black cumin, there are few studies on the effects of nitrogen on fatty acid composition, no records on thymoquinone yield, and the thymoquinone content of the seed oil. In this study, the effects of different nitrogen doses on the seed oil yield, thymoquinone ratio/yield, and fatty acid compositions were investigated. Field studies with nitrogen doses (0, 40, 60, 80, and 100 kg/ha) were studied using the randomized plot design. As a result of the research, nitrogen doses significantly affected the oil and thymoquinone yields while insignificant on the thymoquinone ratio. The highest oil yield with 501.6 kg/ha was obtained from 80 kg/ha of the nitrogen doses, while the highest thymoquinone yield with 10.24 kg/ha was obtained from the control plots. Thymoquinone yields were in the same statistical group with other nitrogen doses, except for means of 100 kg/ha nitrogen doses. Linoleic, oleic, and palmitic acids were major fatty acids of black cumin, and their variations were insignificant in nitrogen applications. The values of butyric, capric, and linolenic acids varied significantly in different nitrogen doses. As a result of the study, it was determined that the highest oil yield was obtained from 80 kg/ha nitrogen application. It has been determined that nitrogen doses above 60–80 kg/ha should be avoided for the seed oil and thymoquinone yields in black cumin.     

Assessing internal crop nitrogen use efficiency in high-yielding irrigated cotton

Improving the efficiency of nitrogen (N) fertiliser use is one means of reducing greenhouse gas emissions, particularly in irrigated crops such as cotton (Gossypium hirsutum L.). Internal crop N use efficiency (iNUE) was measured within two N fertiliser rate experiments that covered a wide range of N fertility over six cropping seasons. Crop iNUE was determined by dividing lint yield by crop N uptake. No nutrients other than N limited cotton growth or yield and the crops were irrigated to avoid drought stress. The optimal N fertiliser rates were determined from fitted quadratic functions that related lint yields with N fertiliser rates for each cropping system in each year. When the optimal N fertiliser rate was applied, crop iNUE averaged 12.5 ± 0.2 kg lint/kg crop N uptake. The crop iNUE was then used to determine the degree to which N fertiliser was under or over-applied, with respect to the economic optimum N fertiliser rate. Low iNUE values were associated with excessive N fertiliser application. Crop iNUE was determined in 82 commercial cotton crops in six valleys over the final 4 years of this study. The crop iNUE value was high in 8 fields (10%), optimal in 9 fields (11%) and low in 65 fields (79%). Crop N uptake averaged 247 kg N/ha, yield 2,273 kg lint/ha and crop iNUE 10.1 kg lint/kg crop N uptake for these sites. Averaged over all sites and years, about 49 kg N/ha too much N fertiliser was applied. Apparent N fertiliser recovery by cotton in the N rate experiments ranged from <20% in N-fertile treatments where legume crops had been grown, to more than 60% following winter cereal crops. Information on crop iNUE will enable cotton producers to assess their N fertiliser management and adjust N fertiliser rates for future crops. This study has demonstrated that there is scope to substantially reduce N fertiliser inputs to Australian cotton fields without reducing yields.     

Leaching of nitrate,calcium and magnesium under maize cultivation on an oxisol in Togo

In tropical regions, crop yields generally decrease with time, partly due to a decline in the levels of exchangeable bases linked to acidification of the upper layers of the soil. Nitrogen, calcium and magnesium balances were studied on an oxisol in southern Togo under continuous maize cropping with mineral fertilization and crop residue return, by measuring inputs and outputs.The balance was near equilibrium for nitrogen (urea dressing, 120 kg N ha^–1 y^–1) and negative for calcium and magnesium. Leaching represented between 29% and 85% of the total output for nitrogen and accounted for practically all the calcium and magnesium outputs.In the upper horizons, nitrate, calcium and magnesium contents in the soil solution were correlated. This was interpreted as an exchange between the calcium and magnesium ions adsorbed on the soil and the protons released by the transformation of ammonium into nitrate. The nutrient content of the soil solution increased in the case of no potassium fertilization, probably because of a lower nitrogen immobilization by microorganisms, the crop residue yield being reduced by the induced deficiency. An insufficient potassium fertilization increases leaching losses of calcium, magnesium and nitrogen.In the deeper horizons, the nitrate content of the soil solution was not correlated with the calcium and magnesium contents. Nitrogen was probably taken up by roots and some calcium and magnesium ions exchanged during their transport through the soil.     

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.