A SIMPLE AVAILABLE SOIL NITROGEN INDEX

Available soil-N values in commonly cultivated East African soils were determined in the laboratory by several methods, and correlated with one another. Mineralizable-N was correlated more with total-N than with organic-C. The values of mineralizable-N (Δ mineral-N) obtained on aerobic incubation were correlated with crop yield and nitrogen uptake in greenhouse experiments. The yield of dry matter and N uptake by the tomato crop in the absence of applied nitrogen were significantly correlated with Δ mineral-N in the soils; the degree of correlation decreased with increasing rates of fertilizer-N applied and Δ mineral-N and dry-matter yield were not correlated at the largest rate used. N uptake by the crop was significantly correlated with Δ mineral-N at all rates of applied nitrogen. The Δ mineral-N value determined on soil samples conditioned by 6 weeks incubation followed by 3 weeks air drying was considered to provide a good index to available nitrogen.     

不同施肥处理对连续三季作物氮肥利用率及其分配与去向的影响

采用室外盆栽试验系统研究了不同施肥处理对连续3个生长季作物生长状况、标记^15N利用率及其分配与去向的影响。结果表明,高量氮肥的施用能显著提高作物的生长和产量,而化肥配施玉米秸秆在第1生长季表现为抑制,第2、第3生长季则相反。作物体内来自标记氮肥的含量和比例随生长季的增加显著下降,高量氮肥和玉米秸秆的施用能显著提高其含量和比例（P〈0.05）。标记氮肥在土壤中的残留率随作物生长季的增加而降低,而标记氮肥的累积作物利用率和总损失率随着生长季的增加而增加,经过连续3季作物的吸收利用,标记氮肥在土壤中的残留率、累积作物利用率和总损失率分别平均为15．82％、61．11％和23．07％。标记氮肥的作物利用率和损失率主要发生在第1生长季内,高量氮肥的施用降低了标记肥料氮在土壤中的残留率,增加了氮素损失率;与单施化肥处理相比,化肥配施玉米秸秆能明显增加标记肥料氮在土壤和作物中的回收率,降低氮素损失率,提高比例为21．74％,从而说明在施肥当季,通过施入高C/N比有机物料玉米秸秆合理调节土壤中C源和N素营养的施用比例,可以达到增加氮肥在土壤中的残留率,提高氮肥利用率的目的。     

Effects of Organic and Inorganic Fertilizer on Growth,Yield, and Juice Quality and Residual Effects on Ratoon Crops of Sugarcane

ABSTRACT

Field experiments were carried out for three consecutive years (2003–2006) at Bangladesh Sugarcane Research Institute farm soil on plant (first crop after planting) and subsequent two ratoon crops of sugarcane. The main objectives of the study were to assess the direct and residual effects of organic and inorganic fertilizer on growth, yield, and juice quality of plant and ratoon crops. The plant crop consisted of four treatments. After harvesting of plant crop to evaluate the residual effects on ratoon crop the plots were subdivided except the control plot. Thus, there were seven treatments in the ratoon crop. Application of recommended fertilizer [nitrogen (N₁₅₀), phosphorus (P₅₂), potassium (K₉₀), sulfur (S₃₅), and zinc (Zn₃) kg ha^{? 1}] singly or 25% less of it either with press mud or farmyard manure (FYM) at 15 t ha^{? 1} produced statistically identical yield ranged from 67.5 to 69.0 t ha^{? 1} in plant crop. In the ratoon experiment when the recommended fertilizer was applied alone or 25% less of its either with press mud or FYM at 15 or even 7.5 t ha^{? 1} again produced better yield; it ranged from 64.8 to 69.2 in first ratoon and 68.2 to 76.5 t ha^{? 1} in second ratoon crops. Results showed that N, P, K, and S content in leaf progressively decreased in ratoon crops over plant crop. Juice quality parameters viz. brix, pol, and purity % remained unchanged both in plant and ratoon crops. Furthermore, organic carbon (C), available N, P, K, and S were higher in post harvest soils that received inorganic fertilizer in combination with organic manure than control and inorganic fertilizer treated soil. It may be concluded that the application of 25% less of recommended fertilizer (N₁₁₂, P₄₀, K₆₈, S₂₆, and Zn_2.2.5 kg ha^{? 1}) either with press mud or FYM at 15 t ha^{? 1} was adequate for optimum yield of plant crop. Results also suggest that additional N (50% extra dosage) keeping all other fertilizers at the same level like plant crop i.e. N₁₆₈, P₄₀, K₆₈, S₂₆, and Zn_2.25 kg ha^{? 1} either with press mud or FYM at 7.5 t ha^{? 1} may be recommended for subsequent ratoon crops to obtain good yield without deterioration in soil fertility.     

Effect of rice straw management on nitrogen balance and residual effect of urea-N in an annual lowland rice cropping sequence

Two field experiments were conducted in 1999 (wet season) and 2000 (dry season) on a Ustic Endoaquerts in central Thailand to examine the impact of rice straw management practices on rice yield, N uptake and fertilizer-N use efficiency. Treatments included a combination of urea broadcast at a rate of 70 kg N ha^у with either straw or compost which were incorporated at a rate of 5 Mg ha^у. At maturity of the wet season rice, ¹⁵N recovery by the grain was low (11-14%) as well as straw-N derived from labeled N (5-7%). After harvest, 25-29% of applied N still remained in the soil, mainly in the 0 to 5-cm layer. Large amounts of fertilizer-N (53-55%) were lost (unaccounted for) from the soil/plant system during the first crop. Residual fertilizer-N recovery in the second rice crop was less than 3% from the original application. During both fallow seasons NO₃^m-N remained the dominant form of mineral N (NO₃^m + NH₄⁺) in the soil but its concentration was low. In the wet season grain yield response to N application was significant (P =0.05). Organic material sources did not significantly change grain yield and N accumulation in rice. In terms of grain yield and N uptake at maturity, there was no significant residual effect of fertilizer-N on the subsequent rice crop. These results indicated that the combined use of organic residues with urea did not decrease total N losses or increase crop yield or uptake of N compared to urea alone.     

太湖地区水稻季氮肥的作物回收和损失研究

在太湖地区水稻土上,采用田间微区15N示踪试验研究了不同氮磷肥配合下水稻季氮肥去向以及残留肥料氮在麦季的吸收利用。结果表明,水稻当季作物对肥料氮的回收率为29%～39%,土壤残留肥料氮的后效很低,后季冬小麦仅利用土壤残留肥料氮的2.4%～5.2%。经过连续两个稻麦轮作,0—60cm土壤中残留肥料氮占施氮量的11%～13%,绝大多数在0—20 cm表层土中。水稻季施用的肥料氮向耕层以下移动很少,20—60 cm土层中累积肥料氮仅占施氮量的0.6%～1.1%,主要发生在小麦季及水稻泡田时期,肥料氮损失占施氮量的47～54%,氨挥发和硝化反硝化气态损失是主要途径。高氮和高磷处理没有增加作物产量和氮肥利用率,过量施氮或施磷无益于作物增产和氮肥吸收利用。     

Cover‐crop seeding‐date influence on fall nitrogen recovery

Planting cover crops after corn‐silage harvest could have a critical role in the recovery of residual N and N from fall‐applied manure, which would otherwise be lost to the environment. Experiments were conducted at the University of Massachusetts Research Farm during the 2004–2006 growing seasons. Treatments consisted of oat and winter rye cover crops, and no cover crop, and four cover‐crop dates of planting. The earliest planting dates of oat and winter rye produced the maximum biomass yield and resulted in the highest nitrate accumulation in both cover‐crop species. The average nitrate accumulation for the 3 years in winter rye and oat at the earliest time of planting was 60 and 48 kg ha^–1, respectively. In 2004 where the residual N level was high, winter rye accumulated 119 kg nitrate ha^–1. While initially soil N levels were relatively high in early September they were almost zero at all sampling depths in all plots with and without cover crops later in the fall before the ground was frozen. However, in plots with cover crops, nitrate was accumulated in the cover‐crop tissue, whereas in plots with no cover crop the nitrate was lost to the environment mainly through leaching. The seeding date of cover crops influenced the contribution of N available to the subsequent crop. Corn plants with no added fertilizer, yielded 41% and 34% more silage when planted after oat and rye, respectively, compared with the no–cover crop treatment. Corn‐silage yield decreased linearly when planting of cover crops was delayed from early September to early or mid‐October. Corn‐ear yield was influenced more than silage by the species of cover crop and planting date. Similar to corn silage, ear yield was higher when corn was planted after oat. This could be attributed in part to the winter‐kill of oat, giving it more time to decompose in the soil and subsequent greater release of N, while the rapidly increasing C : N ratio of rye can lessen availability to corn plants. Early plantings of cover crops increased corn‐ear yield up to 59% compared with corn‐ear yield planted after no cover crop.     

Effects of NPK fertilizer combinations on yield and nitrogen balance in sorghum or pigeonpea on a vertisol in the semi-arid tropics

A long-term experiment was carried out on a Vertisol from 1986 to 1992 to examine the combined effects of NPK fertilizers on yield using sorghum (Sorghum bicolor L. Moench cv. CSH 5) and short-duration pigeonpea (Cajanus cajan L. Millsp. cv. ICPL 87). The fertilizer treatments were as follows: 0 (no fertilization), N (150 kg N ha^-1 ), P (65.5 kg P₂O₅ ha^-1), K (124.5 kg K₂O ha^-1), and all possible combinations (NP, NK, PK, and NPK). In this study we continued this experiment during the period 1993 to 1994 and analyzed the crop yield response to fertilizers and the N balance. The amount of N derived from the atmosphere and fertilizer was estimated by the ¹⁵N natural abundance method and ^l5N isotope dilution method, respectively. A combined application of Nand P fertilizers gave the highest grain yield for the two crops under the 8th and 9th continuous croppings, unlike the application of K fertilizer. The values of total N for the two crops were significantly higher in the NP and NPK plots. These crops took up N mainly from soil. There was a significant positive relationship between the uptake of N_dff and N_dfs by each crop. Pigeonpea or sorghum took up more N from the soil in the N fertilizer plots than in the plots without N, suggesting that soil N fertility was enhanced and the amount of N supplied from soil increased in the plots with consecutive application of N fertilizer for 7 y. Even pigeonpea, which fixes atmospheric N inherently, needed N fertilizer to achieve high grain yield, suggesting that N fixation by the nodules was not always sufficient to meet the N requirements of the crop under these conditions. Although fertilizer N exerted a beneficial effect on plant growth and yield in the two crops, the values of fertilizer N recovery (FNR) by the two crops were considerably low. Therefore, it is suggested that the development of N fertilizer management which could maximize FNR of each crop should be promoted.     

Relationships between nitrogen rate,plant nitrogen concentration,yield and residual soil nitrate‐nitrogen in silage corn

Abstract

Nitrogen (N) fertilizer is a key factor of yield increase but also an environmental pollution hazard. The sustainable agriculture system should have an acceptable level of productivity and profitability and an adequate environmental protection. The objectives of this study were to determine the relationships between N rate, DM yield, plant N concentration (NC) and residual soil nitrate‐nitrogen in order to improve the predicted N rate in corn (Zea mays L.) silage. The experiment was conducted over a period of three years in the province of Quebec on three soil series in a continuous corn crop sequence. Treatments consisted of six rates of N: O, 40, 80, 120, 160, and 200 kg N ha^‐1 as ammonium nitrate applied at planting: broadcast and side banded. Four optimum N rates were calculated using different models: (i) economic rate base on fertilizer and corn price using the quadratic model (E); (ii) economic rate based on fertilizer and corn price using the quadratic‐plus‐plateau model (QP); (iii) critical rate based on linear‐plus‐plateau model (P); (iv) lower than maximum rate (L) corresponding to 95% of maximum yield. The optimum plant NC at all growing stages and the N uptake at harvest were calculated depending on these N rates and yields.

The NC of whole plant at 8‐leaf stage (25–30 cm plant height) of ear leaf at tasselling and of whole plant at harvest stage, the N rate, the N uptake at harvest and the DM yield were all significantly intercorrelated and affected by soils and years, but not affected by N fertilizer application method. The DM yield was linearly and significantly related to NC of whole plant at 8‐leaf stage (rv = 0.932**). At this stage, the average NC corresponding to the optimum N rate and yield was of 3.71, 3.68, and 3.66% as calculated with E, L, and P model, respectively. Our data suggest that the NC of whole plant at 8‐leaf stage may be used to evaluate the N nutrition status of plant and the required optimum N fertilizer rate. The NC of ear leaf at tassel stage was also significantly correlated to corn yield (r = 0.994**). It may be used as an indicator to evaluate the near‐optimum N rate in the subsequent years.

The N uptake by whole above‐ground plant at harvest was quadratically related to corn yield. Data show that at high fertilizer N rate, the N uptake still increased without significantly increasing yield. The N uptake was of 176.5, 163.0, and 155.0 kg N ha^‐1 using the E, L and P rates of 146, 126, and 115 kg N applied ha^‐1, respectively. The optimum N rate and yield were affected by soil type and year, but not by the method of N fertilizer application. The yield increased rapidly up to a N rate of about 120 kg N ha^‐1 and then quite slightly to a maximum N rate of 192 kg N ha^‐1. The optimum N rate was of 115 and 126 kg N ha^‐1 using the P and L model respectively and as high as 146.8 kg N ha^‐1 using the E model. The L model, using a much smaller N rate, gave a reasonably high yield compared to E rate (12.2 and 12.5 Mg ha^‐1, respectively). The data show that a relatively much lower N rate than maximum did not proportionally diminish the yield. Thus, for a difference of 40.4% between maximum N rate and P rate a difference of only 7.4% in yield was observed. Using the L model the differences in rate and yield were of 34.4% and 4.7%, respectively. The QP model gave no significant difference compared to E model.

At harvest the residual soil NO₃‐N increased significantly with increasing N fertilizer rate in whole of the 100 cm soil profile, but mainly in the top 40 cm soil layer. The total NO₃‐N found in 0–100 cm profile at rate of 0, 120 and 200 kg applied N ha^‐1 at planting was as high as 33.7, 60.5, and 74.5 kg N ha^‐1 respectively in a light soil and 37.5, 97.5, and 145.5 kg N ha^‐1 in a heavy clay soil. The difference in NO₃‐N content in the 60–100 cm layer between different applied N rate suggests that at harvest, part of fertilizer N applied at planting was already leached below the 100 cm soil layer. Results, thus, show that reasonably high corn yields can be obtained using more adequate N fertilizer rates which avoid the overfertilization and are likely to reduce the air and ground water pollution.     

Effect of Micronutrient-Based Integrated Use of Nutrients on Crop Productivity,Nutrient Uptake,and Soil Fertility in Greengram and Fingermillet Sequence Under Semi-arid Tropical Conditions

To identify the best combinations of micronutrient-based fertilization treatments in terms of crop yield and nutrient uptake, three field experiments with greengram?fingermillet as the test sequence with 12 treatments on micronutrient-based fertilization [with recommended nitrogen (N)?phosphorus (P)?potassium (K) fertilizer] were conducted during 2005 to 2007 in a semi-arid Alfisol at Bangalore. The effects of treatments on available soil and plant uptake of nutrients [N, P, K, sulfur (S), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (B), and molybdenum (Mo)] and yield of crops were assessed based on standard analysis of variance procedure. Using the relationships of yield with soil and plant nutrient variables, regression models of yield through soil and plant variables were calibrated and effects of variables on crop yields were assessed. The models gave high and significant yield predictability in the range of 0.87 to 0.98 through different variables. The model of plant uptake through soil nutrients indicated that soil S, Fe, and Zn had significant positive effects, whereas soil N, K, B, and Mo had negative effects on plant nutrient status in greengram. Similarly, soil P, Mn, and Zn had significant positive effects, whereas soil N, K, and Fe had negative effects on plant uptake of nutrients in fingermillet. Based on a relative efficiency index (REI) criteria, T2 for plant uptake and T12 for maintaining soil nutrients were found to be superior in greengram, whereas T2 for plant uptake and T8 for maintaining soil nutrients were found to be superior in fingermillet over years based on REI. The combined REI over soil and plant nutrients for both crops indicated that application of T8 for greengram and T2 for fingermillet could be prescribed for attaining maximum plant uptake of nutrients and productivity of crops in sequence, apart from maintaining maximum soil fertility of nutrients under semi-arid Alfisols.     

Nitrogen Dynamics and Losses in Direct‐Drilled Maize Systems

Abstract

The knowledge of nitrogen (N) losses in direct‐drilling agrosystems is essential to develop strategies to increase fertilizer efficiency and to minimize environmental damage. The objectives were i) to quantify the magnitude of N volatilization and leaching simultaneously as affected by different urea fertilization rates and ii) to evaluate the capacity of these specific plant–soil systems to act as a buffer to prevent nitrate leaching. Two experiments were conducted during 2001/02 and 2002/03 growing seasons in Alberti, Argentina. The crop was direct‐drilled maize and the soil a Typic Argiudoll. Ammonia losses, N uptake by crop at flowering and harvest, grain yield, N in previous crop residues, and soil nitrate content up to 2‐m depths were determined. Nitrogen availability, soil nitrate (NO₃)‐N up to 1 m plus fertilizer N, was linearly and highly associated with crop N uptake at flowering (R²=0.93, P<0.01) and at harvest (R²=0.852, P<0.01). Around 17.5% of fertilizer N was lost by volatilization in 10 days. The obtained values of residual nitrate N up to the 150‐cm depth were associated (R²=0.960, P<0.001) with those predicted by the nitrate leaching and economic analysis package (NLEAP) model. Maize in the direct‐drilling system was able to cycle N from the previous crop residues, N from soil organic matter, and N from fertilizers with few losses.     

基于土壤氮素平衡的旱地冬小麦监控施氮

提高作物产量,平衡土壤氮素携出,培肥土壤,避免过多肥料氮残留造成淋溶,是旱地作物施氮的主要目标。本研究通过1 m土层硝态氮监控,从土壤氮素的输入和携出平衡计算氮肥用量,并在陕西永寿不同肥力水平的地块上连续2年布置田间试验进行验证。结果表明,与习惯施肥相比,监控施肥的氮肥用量减少41.2%,籽粒平均增产17.0%,氮肥偏生产力平均增加188.3%,产投比平均提高28.9%。监控施肥处理在收获期1 m土层硝态氮残留量平均为37.0 kg/hm2,较习惯施肥（112.1 kg/hm2）降低66.9%。经过降雨集中的夏季休闲期后,监控施肥处理1 m土层的硝态氮平均增加15.4 kg/hm2,习惯施肥则减少27.4 kg/hm2。这说明通过对1 m土层硝态氮的监控,依据土壤养分平衡,计算旱地小麦氮肥用量,可以提高产量,有效减少氮肥投入,降低成本,增加农户收入,提高氮肥效率,减少旱地土壤硝态氮残留和淋溶。     

Dynamic model for the effects of K fertilizer on crop growth, K-uptake and soil-K in arable cropping. 2. Field test of the model

Abstract. The validity of the model described in Greenwood & Karpinets (1997) was tested against the results of single year, multi level K fertilizer experiments. Measurements of plant mass, %K in the plant and K activity ratio in soil had been made at harvest and at intervals during the growing season on spring wheat, summer cabbage and turnips. Reasonably good agreement was obtained between these measurements and simulated values when the two 'crop' parameters (defining the dependence of critical and maximum possible %K on plant mass) were adjusted for each crop. Also good agreement was generally obtained for plant weight and plant %K at harvest in less detailed experiments on 10 other crops. Values of the two 'crop' parameters for 12 of the crops were strongly correlated with one another suggesting that a single 'crop' parameter may be all that is required to define most inter-species differences in plant-K demand.
Simulations with the model indicate that, in central England, no response of 10 crops to K fertilizer would be likely on soils containing more than 170 mg of 1 M ammonium nitrate extractable-K/kg of soil and having clay contents of between 15 and 45%. Shortcomings of the model and opportunities for advance are discussed.
A simplified version of the model runs on the Internet at: http://www.qpais.co.uk/moda-djg/potass.htm     

Residue Decomposition and Fate of Nitrogen‐15 in a Wheat Crop under Different Previous Crops and Tillage Systems

Abstract

Nitrogen (N) management may be improved by a thorough understanding of the nutrient dynamics during previous‐crop residue decomposition and its impact on fertilizer N fate in the soil–plant system. An experiment was conducted in the Argentine Pampas to evaluate the effect of maize and soybean as previouscrops and plow‐till and no‐till methods on N dynamics and ¹⁵N‐labeled fertilizer uptake during a wheat growing season. Maize and soybean residues released N under both tillage treatments, but N release was faster from soybean residues and when residues were buried by tillage. Net immobilization of N on decomposing residues was not detected. A regression model that accounted for 92% of remaining N variability included time, previous crop, and tillage treatment as independent variables. The rapid residue decomposition with N release was attributed to the high temperatures of the agroecosystem. The recovery of ¹⁵N‐labeled fertilizer in the wheat crop, soil organic matter, and decomposing residues was not statistically different between previous crop treatments or tillage systems. Crop uptake of fertilizer N averaged 52% across treatments. Forty percent of fertilizer N was removed in grains. Immobilization of labeled N on soil organic matter was substantial, averaging 34% of the ¹⁵N‐labeled fertilizer retained, but was very small on decomposing residues, averaging 0.2–3.0%. Fertilizer N not accounted for at harvest in the soil–plant system was 12% and was ascribed to losses. Previous crop or tillage system had no impact on wheat yield, but when soybean was the previous crop, N content of grain and straw+roots increased. Discussion is presented on the potential availability of N retained in wheat straw, roots, and soil organic matter for future crops.     

Productivity and nutrient use efficiency of maize,sorghum, and cotton in the West African Dry Savanna

Sustainable agricultural practices are needed to improve food security and support livelihoods in West Africa, where soil nutrient deficiencies and rainfed production systems prevail. The objective of this study was to assess the productivity and nitrogen (N) and phosphorus (P) use efficiencies of three dominant crops (maize, sorghum, and cotton) under different soil management strategies in the dry savanna of northern Benin. Data were collected for each crop in experiments with (1) an un‐amended soil as control, (2) a low use of external inputs, (3) an integrated soil–crop management practice, and (4) a high mineral fertilizer use, as treatments. Data were collected through researcher‐managed and farmer‐managed on‐farm trials in 2014 and 2015, and analyzed using linear robust mixed effects model and Pearson's correlation. Above‐ground biomass accumulation did not differ significantly among the control, integrated soil–crop management practice, and high mineral fertilizer use up to 30, 50, and 60 d after planting for maize, cotton, and sorghum, respectively. Thereafter, the differences in growth were substantial for each crop with highest biomass monitored with high mineral fertilizer use and lowest with the control. Biomass and economic yields at harvest were highest under high mineral fertilizer use and integrated soil–crop management practice, although the magnitude was crop‐specific. With the integrated soil–crop management practice and high mineral fertilizer use, N and P uptake by all crops was higher than for the un‐amended soil conditions. Inter‐seasonal changes in N uptake were higher for sorghum and cotton, but lower for maize. The highest agronomic efficiency and apparent recovery of N and P as well as positive N and P partial balances were obtained with the integrated soil–crop management practice for all three crops tested. The integrated soil–crop management strategy gave the highest yields and significantly improved N and P use efficiencies. The findings can contribute to formulating site and crop‐specific recommendations for sustainable agricultural practices in the Dry Savanna zone of West Africa.     

Responses of residual and recommended N,P, K,S nutrients and crops to six annual soil test-based fertilizer rates and seeding systems

Responses of residual and recommended nitrogen (N), phosphorus (P), potassium (K), sulfur (S) nutrient amounts and crops (yield, emergence, and height) to 0, 60, 100, and 140% soil test-based fertilizer rate applications on the same plots for six years under minimum tillage and direct seeding systems were assessed. Higher fertilizer rates increased residual nitrate (NO₃)-N, extractable K, and sulfate (SO₄)-S amounts after a low crop yield year, particularly NO₃-N, without temporal trend. Increase in residual available P level at higher fertilizer rates showed a positive temporal trend. Lower N, P, and S fertilizer rates were recommended to crops after higher residual NO₃-N, available P, and SO₄-S levels. Crops effectively used the residual nutrients. Compared to 0%, the relative seed yields at 60, 100, and 140% rates increased with years of fertilization. There were no clear responses of measured soil and crop parameters to seeding systems. Testing residual nutrients can optimize fertilizer use and crop yields.     

Fate of N from Green Manures and Ammonium Sulfate

By means of ^15N tracer technique the fate of N in ammonium sulfate,milk vetch,sesbania and azolla,and the availability of their residual N were studied in a microplot experiment.Results showed that a) at the end of the first crop of early rice,both plant recovery and loss of N from ammonium sulfate were the highest whereas those from azolla were the lowest with those from milk vetch and sesbania in between;the sequence was reversed in terms of recovery of N in soil;the net residual N from ammonium sulfate was very low,about 1/7-1/4 of that from green manures,indicating that chemical N fertilizer contributes little to the soil N reserve;b) plant recovery of the residual N was low and it did not always decrease with time;the total plant recovery (from the second to the fifth crops) of the residual N from various test fertilizers was only 8-11% of the total N originally applied;c) the plant recovery of the residual N from ammonium sulfate was the highest,followed by those from milk vetch and sesbania,and that from azolla was the lowest,no matter in which cropping season (from the second to the fifth);N availability ratio showed the same trend,indicating that chemical N fertilizer helps renovate soil organic N,maintain and increase availability of soil N.     

旱地土壤中残留肥料氮的动向及作物有效性

氮素是作物生长最重要的必需元素之一。合理施用氮肥能促进作物生长并提高产量,但是,过多施用氮肥则抑制作物生长并导致大量的肥料氮残留在土壤中,这部分氮素不但会引起土壤养分不平衡,而且为生态环境带来潜在威胁,因此,研究残留氮的动向及作物有效性可为合理施用化肥氮、高效利用土壤残留氮素和减少残留氮素的损失提供依据。应用~(15)N示踪技术,通过4年定位试验,研究了黄土高原南部旱地冬小麦/夏玉米轮作过程中土壤残留肥料氮的变化及作物吸收利用。在冬小麦和夏玉米轮作的第一个周期,为了制造高肥料氮残留背景,于冬小麦播种前向微区施入240 kg hm~(-2)的~(15)N标记氮素;在夏玉米拔节期,为了研究氮肥施入对残留肥料氮的影响,设置0和120 kg hm~(-2)两个氮水平,以普通尿素施入微区。在第2至第4个轮作周期内,为了分析残留肥料氮的动向及其对作物的有效性,微区内不施任何肥料。结果发现,冬小麦播种前施用的~(15)N标记氮肥于收获期在0~200 cm土壤剖面中均有残留,但大部分累积在0~40 cm土层中,累积总量达到200.9 kg hm~(-2),占当季施入量的83.7%。在随后的夏玉米生长季残留的肥料氮迅速减少,之后随生长季的后移缓慢减少,然后保持相对稳定。经过4年的冬小麦/夏玉米轮作,0~300 cm土壤剖面仍残留大量的~(15)N肥料,后季不追施氮肥和追施氮肥处理的残留量分别为47.1 kg hm~(-2)和54.0 kg hm~(-2)。可见,有一部分肥料氮被固定在土壤有机质中。作物对残留氮的回收量逐年减少,且因后季追施氮肥与否而异,4年中作物对肥料氮的总利用率不追施氮肥和追施氮肥处理的分别为46.9%和50.4%,其中在第1个轮作周期中,小麦和玉米的总利用率分别41.6%和42.0%,后3年利用率分别仅有5.3%和8.4%;4年中残留~(15)N的损失率分别达38.1%和29.7%,其损失主要发生在第1个轮作周期的夏玉米生长季节。说明,在旱地土壤上,氮肥的残留是不可避免的,残留肥料氮的有效性较低,只有少量被作物逐年吸收,一部分以有机形态残留在土壤剖面中,另一部分发生了无效损失。后季追施氮肥可促进作物对土壤残留肥料氮的吸收且增加肥料氮在土壤中的保留,减少残留肥料氮的无效损失,但是以自身的大量损失为代价的。     

北京郊区冬小麦/夏玉米轮作体系中氮肥去向研究

采用田间微区15N示踪试验研究了肥料氮在冬小麦、夏玉米当季和后茬的去向。结果表明 ,在供试土壤的肥力水平和生产条件下 ,N 120kg/hm2 的施肥水平已经达到了较高产量 ,再增加氮肥施用量作物产量不再增加 ;其氮肥利用率和残留率均显著高于施氮量为N 360kg/hm2,损失率则远低于后者 ;在一季作物生长后仍有 20.9%～48.4%肥料氮残留于 0～100cm土层 ,这些残留的肥料氮在后茬的利用率不足 8% ,至施肥后第 2或第 3茬作物 ,仍有部分肥料氮残留于土壤。在低施氮量时 ,肥料氮以NO3--N残留的量很低 ,在高施氮量时 ,残留氮除以有机态、微生物态氮形式存在外 ,以NO3--N形式存在的比例也很高 ;在氮素损失途径中 ,淋洗损失可能占有相当重要的地位。     

玉米追氮对玉米∥大豆间作体系产量和土壤硝态氮的影响及其后茬效应

【目的】明确玉米条带不同追施氮量对间作作物产量、 吸氮量和土壤硝态氮动态变化的影响,并阐明间作系统不同施氮量的后茬农学效应和环境效应。【方法】玉米和大豆播种时均施用相同的基肥(其中氮肥用量为N 45 kg/hm2),根据大喇叭口期玉米条带追施氮量的不同(N 0、 75、 180 kg/hm2)设置三个处理(N0、 N75、 N180),并且大豆生育期间均不追施氮肥,然后实时监测玉米和大豆各个关键生育期的生物量和土壤硝态氮动态变化,并对比分析各处理的后茬冬小麦产量和土壤硝态氮残留量。【结果】随着玉米条带追施氮量的增加,玉米条带生物量、 产量和吸氮量均无显著变化,而且玉米追施氮量的多少对大豆生物量、 产量和吸氮量没有明显影响。间作种植系统土壤硝态氮含量受到追施氮量的影响,氮肥追施后,020 cm土壤硝态氮含量显著上升,但2040 cm土壤硝态氮含量变化不大。追施氮量越多,玉米条带和大豆条带的土壤硝态氮含量也越高,作物收获后土壤硝态氮残留量也越高,玉米条带追施N 180 kg/hm2的间作系统作物收获后土壤硝态氮含量高出其他两个处理12%~25%。此外,后茬作物冬小麦产量、 吸氮量并未随着前茬间作系统施氮量的增加而增加,但小麦收获后的0100 cm土壤硝态氮残留却随着前茬间作系统施氮量的增加而增大,相对仅施用基肥而不追施氮肥的间作系统,前茬间作系统追施氮肥导致后茬小麦收获后土壤(0100 cm)硝态氮残留量增加了22.38%~70.18%。【结论】针对玉米与大豆间作种植模式,只施用玉米基肥(其中氮肥用量为N 45 kg/hm2)而不追肥,或者在施用基肥的基础上,仅在玉米条带上追施少量氮肥(N 75 kg/hm2),不会影响间作体系产量,还可降低后茬小麦0100 cm土壤中的硝态氮残留。     

Effect of N supply on apparent recovery of fertilizer N as crop N and Nmin in soil during and after cultivation of winter cereals

Field trials were conducted over two years to investigate the effect of increasing N supply on apparent fertilizer N recovery by winter cereal crops (4 × wheat and 2 × barley) and on non‐recovered N. Apparent fertilizer N recovery was calculated by comparing N in fertilized and unfertilized crops. Non‐recovered N is defined as N which was neither found in crops nor soil mineral N (N_min = NH₄‐N + NO₃‐N). At N supply levels according to common farming practice (N_cfp = 190 to 220 kg N/ha), 60— 93% of the fertilizer N was recovered in crops at harvest, while at high N supply levels of 265 to 273 kg N/ha 58—76% of fertilizer N was recovered. There were small differences in soil N_min in 0—200 cm between N_cfp and unfertilized plots, but substantial increases in N_min occurred at the highest N supply. Amounts of non‐recovered N differed substantially between sites (maximum value of 84 kg N/ha). Non‐recovered N increased with increasing N rate on only 3 out of the 6 sites, indicating that N immobilization was not necessarily dependent on N rate. The fate of non‐recovered N was studied for a further year by growing catch crops on the sites after cereal harvest. N re‐mineralization deduced from changes in catch crop N and in N_min indicated that non‐recovered N had been immobilized in the soil. At three sites, crop N uptake was found between milk‐ripe stage and harvest (19 to 60 kg N/ha) suggesting substantial uptake of N mineralized from soil. However, grain yields were lower with N rates below N_cfp, indicating that late net soil N mineralization could not compensate for reductions in N fertilizer rate in these trials.