华北平原冬小麦-夏玉米轮作体系中标记15N的去向及残效

A field experiment was conducted to investigate the fate of ¹⁵N-labeled urea and its residual effect under the winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation system on the North China Plain. Compared to a conventional application rate of 360 kg N ha^-1 (N360), a reduced rate of 120 kg N ha^-1 (N120) led to a significant increase (P < 0.05) in wheat yield and no significant differences were found for maize. However, in the 0-100 cm soil profile at harvest, compared with N360, N120 led to significant decreases (P < 0.05) of percent residual N and percent unaccounted-for N, which possibly reflected losses from the managed system. Of the residual fertilizer N in the soil profile, 25.6%-44.7% and 20.7%-38.2% for N120 and N360, respectively, were in the organic N pool, whereas 0.3%-3.0% and 11.2%-24.4%, correspondingly, were in the nitrate pool, indicating a higher potential for leaching loss associated with application at the conventional rate. Recovery of residual N in the soil profile by succeeding crops was less than 7.5% of the applied N. For N120, total soil N balance was negative; however, there was still considerable mineral N (NH₄⁺-N and NO₃^--N) in the soil profile after harvest. Therefore, N120 could be considered agronomically acceptable in the short run, but for long-term sustainability, the N rate should be recommended based on a soil mineral N test and a plant tissue nitrate test to maintain the soil fertility.     

中国西北旱地小麦和玉米提高产量与水分利用率的氮肥管理效果

A field experiment with four treatments and four replicates in a randomized complete block design was conducted at the Changwu Experimental Station in Changwu County, Shaanxi Province, of Northwest China from 1998 to 2002. The local cropping sequence of wheat, wheat-beans, maize, and wheat over the 4-year period was adopted. A micro-plot study using ^15N-lahelled fertilizer was carried out to determine the fate of applied N fertilizer in the first year. When N fertilizer was applied wheat （years 1, 2 and 4） and maize （year 3） grain yield increased significantly （P 〈 0.05） （〉 30%）, with no significant yield differences in normal rainfall years （Years 1, 2 and 3） for N application at the commonly application rate and at 2/3 of this rate. Grain yield of wheat varied greatly between years, mainly due to variation in annual rainfall. Results of ^15N studies on wheat showed that plants recovered 36.6%-38.4% of the N applied, the N remained in soll （0-40 cm） ranged from 29.2% to 33.6%, and unaccounted-for N was 29.5%-34.2%. The following crop （wheat） recovered 2.1%- 2.8% of the residual N from N applied to the previous wheat crop with recovery generally decreasing in the subsequent three crops （beans, maize and wheat）.     

Application of controlled-release urea increases maize N uptake, environmental benefits and economic returns via optimizing temporal and spatial distributions of soil mineral N

The creation of controlled-release urea (CRU) is a potent substitute for conventional fertilizers in order to preserve the availability of nitrogen (N) in soil, prevent environmental pollution, and move toward green agriculture. The main objectives of this study were to assess the impacts of CRU''s full application on maize production and to clarify the connection between the nutrient release pattern of CRU and maize nutrient uptake. In order to learn more about the effects of CRU application on maize yields, N uptake, mineral N (N_min) dynamics, N balance in soil-crop systems, and economic returns, a series of field experiments were carried out in 2018–2020 in Dalian City, Liaoning Province, China. There were 4 different treatments in the experiments: no N fertilizer input (control, CK); application of common urea at 210 kg ha^-1 (U), the ideal fertilization management level for the study site; application of polyurethane-coated urea at the same N input rate as U (PCU); and application of PCU at a 20% reduction in N input rate (0.8PCU). Our findings showed that using CRU (i.e., PCU and 0.8PCU) may considerably increase maize N absorption, maintain maize yields, and increase N use efficiency (NUE) compared to U. The grain yield showed considerable positive correlations with total N uptake in leaf in U and 0.8PCU, but negative correlations with that in PCU, indicating that PCU caused excessive maize absorption while 0.8PCU could achieve a better yield response to N supply. Besides, PCU was able to maintain N fertilizer in the soil profile 0–20 cm away from the fertilization point, and higher N_min content was observed in the 0–20 cm soil layer at various growth stages, particularly at the middle and late growing stages, optimizing the temporal and spatial distributions of N_min. Additionally, compared to that in U, the apparent N loss rate in PCU was reduced by 36.2%, and applying CRU (PCU and 0.8PCU) increased net profit by 8.5% to 15.2% with less labor and fertilization frequency. It was concluded that using CRU could be an effective N fertilizer management strategy to sustain maize production, improve NUE, and increase economic returns while minimizing environmental risks.     

不同的水稻品种产量及生理氮素利用效率的差异

Efficient use of N in agricultural practice can increase yield, decrease production costs and reduce the risk of environmental pollution. Effects of N fertilizer application rates on grain yield and physiological N use efficiency (PE) in relation to the accumulation and redistribution of biomass and N in rice (Oryza sativa L.) cultivars were studied at two experimental farms of Nanjing Agricultural University, Nanjing, China in 2004. Three high N use efficiency (NUE) rice cultivars (Wuyunjing 7, Nanguang and 4007) and one low NUE rice cultivar (Elio) with similar growth patterns were studied under seven N rates (0, 60, 120, 180, 240, 300 and 360 kg ha^-1). Grain yield increased with the N application rate and attained plateau at 180 kg N ha^-1 for rice cultivars at each site. Increasing N rate decreased PE for biomass and grain yield. Grain yield and PE of Elio were about 20% and 18% lower than those of high NUE cultivars. Differences in biomass, N accumulation and N redistribution were observed at the post-heading stage among rice cultivars with differing NUEs. The less reproductive tillers of Elio resulted in less demand for C and N during grain filling, thus leading to lower PE of Elio compared with the high NUE rice cultivars.     

磷和钾对巴基斯坦西北部向日葵生长、产量的交互效应

Potassium (K) and phosphorus (P) applications improve growth, increase yield and yield components of sunflower (Helianthus annuus L.) on K and P deficient soils in Northwest Pakistan. A field experiment was conducted using sunflower cv. Hysun-33 at the New Developmental Research Farm of KPK Agricultural University, Peshawar, Pakistan, during summer 2006. The experimental design was a randomized complete block in split plot arrangements, with six levels of K (0, 25, 50, 75, 100, and 125 kg K ha^-1) as main plots and four levels of P (0, 45, 90, and 135 kg P ha^-1) as sub-plots with three replications. Sunflower yield and yield components responded positively to K and P fertilization but the magnitude of response varied with the levels of K and P. Days to flowering and maturity, grains per head, 1000-grain weight, shelling percentage, and grain yield increased tremendously in the K and P-fertilized plots as compared to the control with no K and P applied. The combined application of 100 kg K and 45 kg P ha^-1 significantly increased yield components, grain yield, harvest index, and shelling percentage of sunflower, suggesting that 100 kg K ha^-1 in combination with 45 kg P ha^-1 could maximize productivity of sunflower planted after wheat on the K and P deficient soils in the study area.     

Assessing Nitrogen Fertilization Strategies in Winter Wheat and Cotton Crops in Northern Greece

The management of fertilizer application is crucial for agricultural production and environmental safety.The objective of this study was to assess the effciency of different fertilization strategies,applying fertilizers with and without nitrification inhibitors(NIs) in split application,in Greece.The assessment criteria used were based on crop yield,soil nitrogen(N)concentrations and economic effciency.For this purpose two crops(winter wheat and cotton)were seffected in order to explore the optimum fertilization strategy for each crop.Three treatments combining fertilizers with NIs were tested compared with conventional fertilization(CF).Slight differences in the quantity and the combination of fertilizers with NIs applied resulted in variable effects on crop yield,soil N and economic return.Split N application of 102 kg ha^-1,with half of the total amount applied at seeding,resulted in higher grain yield of winter wheat,lower NO₃^--N in soil and higher economic return.This result reveals the importance of N application at seeding in wheat crop.Fertilization strategy with 109.5 kg N ha^-1 and split P application resulted in higher cotton yield and higher economic profit.Split P application seemed to increase yield,even though it is not a common practise in the area.     

施用辐照处理的污水污泥对作物产量和土壤氮的影响

A field experiment was conducted to study the feasibility of irradiated and non-irradiated sewage sludge as a fertilizer for the growth of wheat and rice. The irradiated and non-irradiated sewage sludge were applied at rates of 0 (CK), 75, 150, 225 and 300 kg N ha^-1 for wheat, and 0 (CK), 112.5, 225, 337.5 and 450 kg N ha^-1 for rice, respectively. (NH₄)₂SO₄ at a rate of 150 kg N ha^-1 for wheat, and 225 kg N ha^-1 for rice were added to the control treatments. Additionally, 20 kg ¹⁵N ha^-1 in the form of (NH₄)₂SO₄ was added to each treatment for wheat to study the effect of sewage sludge on chemical nitrogen fertilizer recovery. The results showed that the irradiation of sewage sludge by gamma ray at a dosage of 5 kGy increased crop yield by 11%~27% as compared to the non-irradiated treatments. Irradiation stimulated mineralization of organic nitrogen in the sludge and improved seedling growth. It was found that addition of irradiated sludge could reduce the leaching loss of chemical nitrogen fertilizer. Both irradiated and non-irradiated sewage sludge could increase the content of soil total nitrogen. Based on the preliminary results, it was concluded that irradiated sewage sludge could partly substitute for chemical nitrogen fertilizer in crop production.     

有机无机肥长期配合施用对江苏小麦玉米两熟制作物产量和土壤肥力的影响

Winter wheat-maize rotations are dominant cropping systems on the North China Plain, where recently the use of organic manure with grain crops has almost disappeared. This could reduce soil fertility and crop productivity in the long run. A 20-year field experiment was conducted to 1) assess the effect of inorganic and organic nutrient sources on yield and yield trends of both winter wheat and maize, 2) monitor the changes in soil organic matter content under continuous wheat-maize cropping with different soil fertility management schemes, and 3) identify reasons for yield trends observed in Xuzhou City, Jiangsu Province, over a 20-year period. There were eight treatments applied to both wheat and maize seasons: a control treatment (C); three inorganic fertilizers, that is, nitrogen (N), nitrogen and phosphorus (NP), and nitrogen, phosphorus and potassium (NPK); and addition of farmyard manure (FYM) to these four treatments, that is, M, MN, MNP, and MNPK. At the end of the experiment the MN, MNP, and MNPK treatments had the highest yields, about 7 t wheat ha^-1 and 7.5 t maize ha^-1, with each about 1 t ha^-1 more than the NPK treatments. Over 20 years with FYM soil organic matter increased by 80% compared to only 10% with NPK, which explained yield increases. However, from an environmental and agronomic perspective, manure application was not a superior strategy to NPK fertilizers. If manure was to be applied, though, it would be best applied to the wheat crop, which showed a better response than maize.     

中国南方红壤上作物产量和土壤性质对长期施肥的响应

A 15-year fertilization experiment with different applications of inorganic N, P and K fertilizers and farmyard manure (M)was conducted to study the yield and soil responses to long-term fertilization at Qiyang, Hunan Province, China. Average grain yields of wheat and corn (1 672 and 5 111 kg ha^-1, respectively)for the treatment NPKM were significantly higher than those (405 and 310 kg ha^-1)of the unfertilized control and single inorganic fertilizer treatments. Compared with the corresponding initial values of the experiment, all treatments showed a yield decline of 9 to 111 kg ha^-1 year^-1 in wheat and 35 to 260 kg ha^-1 year^-1 in corn, respectively, and a significant pH decline of 0.07 to 0.12 pH year^-1, except for the treatments PK and NPKM. After long-term fertilization, the soil organic C, soil available P, exchangeable Ca²⁺ and Mg²⁺ and available Cu²⁺ and Zn²⁺ contents were higher in the treatment NPKM than in the treatments applied with inorganic fertilizer only. Compared to the treatment NPK, the treatment NPKM, where manure partially replaced inorganic N, had a positive impact on arresting the decline of soil pH. This improved grain yields of wheat and corn, suggesting that application of NPK fertilizer in combination with farmyard manure is important to maintain soil fertility and buffering capacity in red soil.     

保护地蔬菜轮作体系中两种不同复合肥对产量的影响及其氮素动态特征

Yield and N uptake of tomato (Lycopersicum esculentum Mill.) and pepper (Capsicum annuum L.) crops in five successive rotations receiving two compound fertilizers (12-12-17 and 21-8-11 N-P₂O₅-K₂O) were studied to determine 1) crop responses, 2) dynamics of NO₃-N and NH₄-N in different soil layers, 3) N balance and 4) system-level N efficiencies. Five treatments (2 fertilizers, 2 fertilizer rates and a control), each with three replicates, were arranged in the study. The higher N fertilizer rate, 300 kg N ha^-1 (versus 150 kg N ha^-1), returned higher vegetable fruit yields and total aboveground N uptake with the largest crop responses occurring for the low-N fertilizer (12-12-17) applied at 300 kg N ha^-1 rather than with the high-N fertilizer (21-8-11). Ammonium-N in the top 90 cm of the soil profile declined during the experiment, while nitrate-N remained at a similar level throughout the experiment with the lower rate of fertilizer N. At the higher rate of N fertilizer there was a continuous NO₃-N accumulation of over 800 kg N ha^-1. About 200 kg N ha^-1 was applied with irrigation to each crop using NO₃-contaminated groundwater. In general, about 50% of the total N input was recovered from all treatments. Pepper, relative to tomato, used N more efficiently with smaller N losses, but the crops utilized less than 29% of the fertilizer N over the two and a half-year period. Local agricultural practices maintained high residual soil nutrient status. Thus, optimization of irrigation is required to minimize nitrate leaching and maximize crop N recovery.     

Response of low-nitrogen tolerant maize genotypes to nitrogen application in a tropical Alfisol in northern Nigeria

In the dry savannas of west and central Africa, where low soil fertility is major constraint to maize production, the development of tropical maize genotypes with high and stable yield under low-nitrogen condition is very important, since access to these improved genotypes may be the only affordable alternative to many small scale farmers.

Field trials were conducted at Samaru (Typic Haplustalfs) to investigate the response of low-N tolerant maize cultivars to nitrogen (N) fertilizer. Nitrogen application rates were 0, 30, 60, 90 kg N ha⁻¹ and four maize cultivars (Low-N pool C2, ACR 8328 BN C7, Super Oba II and TZR-SR). Maize leaf area index, intercepted radiation, leaf area and stover weights were increased due to nitrogen application at flowering. For most of the parameters, 60 kg N ha⁻¹ appeared to have the significantly high values. However, there was no significant difference between application rates of 60 and 90 kg N ha⁻¹ in stem weight, stover weight, grain yield and shelling percent at harvest. Genotypic variation observed in the maize agronomic traits were not significant except in leaf weight and grain yield. The amount of nitrogen taken by maize increased with increase in fertilizer rates. Application of 30 and 90 kg N ha⁻¹ to soil increased the maize grain N concentration and total N uptake. About 45.3 kg ha⁻¹ and 8.8 g N kg⁻¹ nitrogen uptake was obtained in maize shoot and grain, respectively, at the application of 90 kg N ha⁻¹. Low-N pool C2 genotype had the highest grain N concentration and shoot uptake significantly higher than TZB-SR. Nitrogen fertilizer applied accounted for 97% variation in soil nitrate. There existed a positive and significant correlation between maize grain yield and leaf nitrogen uptake (r = 0.33, P < 0.01). Averagely, nitrogen fertilizer applied accounted for 86% variations in maize grain yield.     

Weed management systems based on animal-drawn cultivators for maize production in the Southern Highlands of Tanzania

Experiments on weed management techniques for maize production were carried out at the Uyole Agricultural Centre and on farmer's fields in Mbozi district, Tanzania, using the inter-row cultivator (Cossul), over-the-row cultivator (MOP) and hand-weeding. There were no significant differences in field capacities between the two cultivators, although the MOP cultivator tended to have slightly higher capacities. Field capacities tended to be higher when the maize was 45 cm high. The use of cultivators alone reduced labour inputs for weeding by 80%, and the use of cultivators combined with hand-weeding reduced labour by 40%, compared with hand-weeding alone. Hand-weeding alone, or in combination with cultivator weeding gave the best control of weeds, and similar high maize yields (5 t ha⁻¹ compared with 2 t ha⁻¹ with no weeding). The use of cultivators alone gave significantly poorer weed control and a yield of 3.3 t ha⁻¹. The use of cultivators plus within-row hand-weeding gave marginal rates of return greater than 1.0, indicating a reasonable return on the investment in labour. The results emphasize the importance of weeding for higher maize yields in the Southern Highlands of Tanzania. Higher yields can be obtained by manual weeding alone but at the cost of high labour inputs, representing high levels of family drudgery or high labour hiring costs. Those farmers who have access to ox-drawn systems are advised to arrange additional within-row manual weeding to ensure higher yields. Ox-drawn cultivators alone for weeding are only suitable for situations where labour is scarce.     

Influence of nitrogen and weed management on the productivity of upland rice

Nitrogen and weeds are two important factors that influence the productivity of rainfed upland rice (Oryza sativa L.) in tropical Asia. A low recovery of applied fertilizer N in rainfed uplands is generally associated with high nitrate leaching losses and weed interferences. Field experiments were conducted during the wet seasons of 2002 and 2003 at the research farm of Central Rainfed Upland Rice Research Station, Hazaribag, Jharkhand, India, to determine the response of upland rice to nitrogen applied at 60 kg N ha^–1 as different forms of urea (single pre‐plant application of controlled‐release urea, single pre‐plant application of urea supergranules, and split application of prilled urea with or without basal N) against no N application under three weed‐control regimes (unweeded, pre‐emergence application of butachlor at 1.5 kg a.i. ha^–1 supplemented with one single hand weeding or two hand weedings). The response of rice to applied N varied greatly among the three weed‐control regimes. Across the different N treatments, the application of 60 kg N ha^–1 resulted in a grain‐yield increase above the unfertilized control of only 0.24 Mg ha^–1 in unweeded treatments, whereas yields increased by 1.07 Mg ha^–1 when butachlor application was supplemented with a single hand weeding and by 1.28 Mg ha^–1 with two hand weedings. Among the weed‐control measures, hand weeding twice produced highest grain yield in both years. The comparison of different forms of urea showed that a single pre‐plant application of controlled‐release urea resulted in average grain yields of 1.57 and 1.87 Mg ha^–1 compared to 1.32 and 1.30 Mg ha^–1 in the case of the recommended practice of split‐applied prilled urea in the years 2002 and 2003, respectively. The highest agronomic N use efficiency of 15–20 kg grain per kg N applied and the highest apparent N recovery of 39%–45% were attained with controlled‐release urea, suggesting that this N form is particularly beneficial for upland‐rice cultivation under variable rainfall conditions, provided weeds are controlled.     

Effects of density of planting and time of nitrogen application on maize varieties in different ecological zones of West Africa

Abstract

Field experiments were conducted in 1992 on soils which have been classified as Alfisols ranging from Paleustalf to Oxic Paleustalf which represent three different ecological zones of West Africa. This research was conducted to determine the effect of density of planting on yield and yield components at 53,333, 66,666, and 79,999 plants‐ha^‐1 and time of nitrogen (N) fertilizer application [50% at planting and 50% at four weeks after planting (4WAP), entire N application at two weeks after planting (2WAP), and 50% at planting and 50% at anthesis]. The experiment was a factorial arrangement fitted to randomized complete block design and replicated three times. The maize (Zea mays L.) varieties used in this study gave increased yields at population density up to 53,333 plants‐ha^‐1 in Ikenne and Mokwa, while a response of 79,999 plants‐ha^‐1 was obtained at Kaduna. The results also showed that a split application of N at planting and 4 WAP appeared to be the best for Ikenne, while the entire application at 2WAP appeared to be the best in savanna ecologies. The results indicate increase yield with increasing latitude suggesting that the higher solar radiation in the savanna ecologies increase the photosynthetic capacity of the maize plants used in the study. Maize genotypes used in this study did not respond to density beyond 53,333 plants‐ha^‐1 at Ikenne and Mokwa, though a response was obtained up to 79,999 plants‐ha^‐1 at Kaduna. Thus, it can be concluded that density response is location dependent and that farmers should plant maize at highest optimum plant population density as determined by experimental results in each ecological zone of West Africa. The results also showed that a split application of N at planting and 4WAP appeared to be the best for Ikenne, while the entire N application at 2WAP appeared to be the best for the savanna ecologies.     

Maize productivity and soil carbon storage as influenced by wheat residue management

Wheat (Triticum aestivum L) residue removed, burnt, or incorporated with or without 0, 60, and 120 kg nitrogen (N) ha^?1 effects on maize (Zea mays L) hybrids (Pioneer-3025, Pioneer-30P45, and Kiramat) were assessed at University of Agriculture, Peshawar, Pakistan during 2010 and 2011 for maize production and soil carbon (C) storage. Pioneer-30P45 had higher grain yield, leaf area, and delayed maturity. Residue burning combined with 120 kg N ha^?1 produced higher grain yield. The leaf area, leaf area ratio, grain N content, and solar radiation interception were improved with N + residue burnt/incorporated over control. The grain yield was positively correlated with yield parameters. Soil organic carbon (SOC) content were in order of incorporated > burnt > removed at all growth stages (i.e., sowing, tasseling, maturity, and harvesting). Conclusively, wheat residue burnt/incorporated into the soil with 120 kg N ha^?1 was best for maize production of Pioneer-30P45; however residue incorporation into the soil improved SOC.     

Zinc bioavailability in maize grains in response of phosphorous–zinc interaction

Phosphorous (P) and zinc (Zn) are plant nutrients that interact with each other in soil–plant systems. Such interactions may cause deficiency of one of the nutrients interacting with each other if interactions are antagonistic. In the present trial, a field experiment was conducted to investigate the interactive effect of Zn (0 and 16 kg ha^?1) and P (0 and 60 kg ha^?1) on growth, yield and grain Zn concentration of two maize (Zea mays L.) genotypes, i.e., Neelam (local) and DK‐6142 (hybrid). Growth and yield of both maize genotypes were increased by the application of Zn and P treatments compared with control, but Zn+P was more effective than their sole application. When compared to control, combined application of Zn+P increased grain Zn and P concentrations by 52% and 32%, respectively, averaged for the two genotypes. Single application of P decreased grain Zn concentration by 10% over control. Application of P and Zn particularly in combination decreased the grain [phytate] : [Zn] ratio and increased the estimated human Zn bioavailability in grains based on a trivariate model of Zn absorption in both maize genotypes. Conclusively, combined Zn+P application appeared more suitable for enhancing grain yield and agronomic Zn biofortification in maize grains. However, Zn fertilization aiming at increasing grain yield and grain Zn concentration should consider the genotypic variations and P rate.     

Grain yield response of Zea mays (hybrid AE 703) to Azotobacter chroococcum H23

Summary Field experiments were conducted during 1985 and 1986 to examine the effect of Azotobacter chroococcum on the grain yield of maize. Application of 40 kg N ha^–1 plus A. chroococcum caused a significant increase in maize yield. Azotobacter inoculation was more efficient at lower doses (40 kg N ha^–1) than at high doses (80 kg N ha^–1) of urea.     

Nitrogen topdressing at the jointing stage affects the nutrient accumulation and translocation in rainfed waxy maize

Timely and fitting nitrogen (N) application decreases costs and pollution risk in maize cultivation. To explore the accumulation and remobilization of dry matter (DM), N, phosphorus (P), and potassium (K) in waxy maize under various N topdressings (0?kg ha^?1, LN; 150?kg ha^?1, MN; 300?kg ha^?1, HN) at the jointing stage, a field trial involving two waxy maize varieties (Suyunuo 5 and Yunuo 7) was conducted in 2013–2016. The highest grain yield was obtained under MN mainly due to the highest grain numbers and grain weight. The increase in grain yield under MN was mainly due to the high DM accumulation post-silking, as well as high N, P, and K accumulation and remobilization pre-silking. Generally, the plants had high harvest index (HI) of DM (N, P, and K), partial N fertilizer productivity, and moderate N utilization efficiency (NUE) under MN.     

Liming and Nitrogen Effects on Maize Yield and Nitrogen Use Efficiency

ABSTRACT

The study was aimed to determine the appropriate nitrogen (N) rate to combine with liming for enhanced maize yield and nitrogen use efficiency (NUE). Two maize varieties [Ikom White (IKW) and Obatanpa-98 (Oba-98)], two lime rates (0 kg ha^?1 and 500 kg ha^?1) and three N rates (0, 90 and 180 kg ha^?1) were used. The treatments were laid as a split-split plot in a randomized complete block design with three replications. The growth attributes, photosynthetically active radiation (PAR), harvest index, dry matter, and grain yield increased (P ≤ 0.05) with increases in N rates, especially in plots amended with lime. Oba-98 was better yielding (2.12 versus (vs) 1.88 t ha^?1) and absorbed more (P ≤ 0.05) radiation (442.06 vs 409.54 μmol m^?2s^?1) than IKW. The efficiency indices and partial factor productivity were best optimized at the 90 kg ha^?1 N rate with Oba-98 having higher values than IKW. Therefore, liming (500 kg ha^?1) plus N at 180 kg ha^?1produced the best yield of the hybrid maize, Oba-98.     

Effect of tillage and fertilizer levels on wheat yield, nitrogen uptake and their correlation with carbon isotope discrimination under rainfed conditions in north-west Pakistan

Appropriate cultural practices need to be determined for enhancing crop yields with low inputs under rainfed conditions. A field experiment was conducted to study the effect of tillage practices and fertilizer levels on yield, nitrogen (N) uptake and carbon (C) isotope discrimination in wheat (Triticum aestivum L.) grown under semi-arid conditions at three sites in north-west Pakistan: NIFA, Urmar and Jalozai. Two fertilizer levels, 60 kg N ha⁻¹+30 kg P ha⁻¹ (L1) and 60 kg N ha⁻¹+60 kg P ha⁻¹ (L2), were applied to wheat grown under conventional tillage (T1) and no-tillage (T0) practices. Labeled urea having 1% ¹⁵N atom excess at 60 kg N ha⁻¹ was applied as aqueous solution in microplots within each treatment plot. A pre-sowing irrigation of 60 mm was applied and during the growing season, the crop relied entirely on rainfall (268 mm). Biomass yield, N uptake and stable C isotope composition (δ¹³C) of plants were determined at maturity. Yield of wheat was improved by tillage at two sites (Sites 1 and 2), while at the third site yield was reduced by tillage as compared with the no-tillage treatment. At Sites 1 and 2, nutrient addition (L2, 60 kg N ha⁻¹+60 kg P ha⁻¹) increased the yield of all plant parts (straw, grain and root) in contrast to Site 3 where only grain yield was increased significantly. Maximum grain yield of wheat was observed with tillage under nutrient level L2 at all sites. Generally, the tillage treatment did not affect the N content in plant parts compared with no-tillage (T0) treatment at all three sites. However, fertilizer N uptake by wheat was variable under different fertilizer levels and tillage practices. Nitrogen derived from fertilizer (Ndff) for grain at Site 2 was higher in tilled plots but was not affected by tillage practice at the other sites. The C isotope (δ¹³C) values varied from −28.96 to −26.03‰ under different treatments at the three sites. The δ¹³C values were less negative indicating more effective water use at Sites 2 and 3 compared to Site 1. The C isotope discrimination (Δ) values were positively correlated with yield of wheat straw (r=0.578^*), grain (r=0.951^**) and root (r=0.583^*). Further, the Δ in grain had significant negative relationship (r=0.912^**) with Ndff (%). The tillage practice exerted a positive effect on yield, N uptake and plant N derived from fertilizer by wheat compared to no-tillage. The positive correlation of Δ with grain, straw and root yields and negative correlation with the Ndff (%) by wheat suggest that this value (Δ) could be used to predict these parameters. However, further studies on different crops under varied environmental conditions are necessary.