Soil properties and crop performance on a kaolinitic Alfisol after 15 years of fallow and continuous cultivation

A long-term field experiment was established on a kaolinitic Alfisol in Ibadan, Nigeria, in 1972. The land was cleared manually from secondary forest and used for (i) continuous no-till cropping with maize (Zea mays L.) and maize/cassava (Manihot esculenta Crantz) intercropping, (ii) planted fallow of guinea grass (Panicum maximum Jacq.), leucaena (Leucaena leucocephala de Wit), and pigeon pea (Cajanus cajan Millsp.), and (iii) natural bush regrowth in a randomized complete block design with three replications. At the end of 15 years, the fallow plots were cleared manually and cropped with maize for three years. The chemical and physical soil properties and crop performance of the newly-cleared plots were compared with those under 15 years of continuous cultivation. A total of 26 woody species were identified on the bush regrowth plots. Above-ground biomass accumulation of the bush plots was 157 Mg ha^-1 containing 1316 kg N ha^-1. Guinea grass, leucaena and natural bush regrowth plots had comparable organic C concentrations (approximately 20 g kg^-1) in the surface soil (0 to 10 cm) after 15 years. The organic C concentration in the surface soil under pigeon pea was the lowest (9.5 g kg^-1) among the four fallow treatments. Soil under 15 years of continuous no-till maize with and without residue mulch, respectively, contained approximately half (10 g kg^-1) and a quarter (5.7 g kg^-1) of the organic C under natural bush or guinea grass fallow. The levels of exchangeable Ca, K, Mg and effective cation exchange capacity (ECEC) were lower in the soils under continuous cultivation than in those under natural bush and planted fallow. Soil acidification occurred in soils under continuous cropping as depicted by the lower pH values and greater exchangeable Al and Mn concentrations compared to the fallow plots. Grain yield of maize (3 to 5 Mg ha^-1) without fertilizer application in the plots newly cleared from natural bush, guinea grass and leucaena fallow was comparable with that of continuous no-till maize with residue mulch and chemical fertilizer (N, P, K, Mg, Zn) applications. Among the four fallow treatments, maize grain and stover yields were the lowest in plots cleared from pigeon pea fallow.     

不同施肥制度下茬口对作物产量增益、土壤养分状况及施肥贡献率的影响

根据1991—2002年共12年的田间试验,研究了不同施肥制度下,茬口对作物产量增益、土壤养分状况及对施肥贡献率的影响。结果表明:与重茬相比,豆茬较有利于作物的高产和稳产;施用氮肥使其产量增益减小,并且施用氮肥愈多,产量增益愈小;增施有机肥情况下,产量增益的减小更为明显。在土壤养分方面,豆茬不仅能提高土壤的供氮能力,还能改善土壤的供磷、供钾量,有助于土壤养分状况的改善;施肥制度进步能够提高作物产量;施肥贡献率随着施肥制度的进步逐渐增大,但其增幅趋缓;随着施肥制度的进步,施肥贡献率在豆茬和重茬上所表现的差异逐渐缩小,最后趋同。     

Effects of nitrogen fertilization of grapefruit trees on soil acidification and nutrient availability in a Riviera fine sand

Nitrogen (N) fertilizer applied in the NH4+ form results in some degree of soil acidification, which could influence nutrient availability to plants and nutrient losses through leaching. Effects of various N rates (0 – 168 kg N ha-1 yr-1) on soil acidification and nutrient availability were investigated in a Riviera fine sand with 26-year-old white Marsh grapefruit (Citrus paradisi MacFadyen) trees. Soil pH significantly decreased with increasing NH4–N rates. Application of 112 kg N ha-1 yr-1 for four years decreased the pH by 0.7 to 1.7 unit. Soil acidification was greater when the NH4+ form of N fertilizer was applied as dry soluble granular material compared to fertigation or controlled release forms. The marked effect of NH4–N fertilization on the pH of the Riviera fine sand was due to its low buffering capacity. Soil acidification increased the concentration of extractable Fe and P but decreased that of K, Zn and Mn. Soil pH was positively correlated with concentration of Ca, but negatively with concentrations of Fe, Mn and Zn in six-month-old spring flush leaves of the grapefruit trees. Leaf P concentrations, however, were poorly correlated with soil pH. This study also demonstrated an increase in leaching of P and K below the grapefruit trees rootzone with a decrease in soil pH.     

Effect of cropping systems on soil chemical characteristics,with emphasis on soil acidification*

The soil under intensive cultivation and low addition of crop residues is exposed to erosion and reduction of organic matter. Increases in soil organic matter, cation exchange capacity (CEC) and nutrient availability may occur in no-till systems with legumes and with large additions of organic residues. Nevertheless, some legumes may increase soil acidification through the carbon and nitrogen cycles. An experiment was carried out over 10 years, with 10 cropping systems on a Dark Red Podzolic soil (Paleudult) to evaluate the effect of no-till cropping systems on soil chemical characteristics. Legume cropping systems resulted in the greatest soil organic C gain and the highest ECEC to a depth of 17.5 cm. The increase was greatest at 0 - 2.5 cm layer. Clover systems resulted in the highest soil acidification at 2.5 - 7.5 and 7.5 - 17.5 cm depths. The rate of soil pH decrease at 2.5 - 7.5 cm depth under clover+ t Spergula/maize system was 0.1 unit year^-1. Differences in soil acidification affected soil ECEC. Soil exchangeable cation data indicate that nitrate leaching increased soil acidification. Maize yields were greatest in legume systems due to increased N supply.     

一次性施肥技术对水稻-油菜轮作系统氮素淋失特征及经济效益的影响

一次性施肥技术是指在作物根际附近只进行一次基施肥的新技术,具有简化施肥管理、降低劳动成本等优点,但其对环境的影响如氮素淋失等仍需进一步分析.本研究以长江中下游地区典型的水稻-油菜轮作模式为例,设置了空白对照(CK)、农民习惯施肥(FP)、优化施肥(OPT)、一次性基施尿素(UA)、一次性基施控释肥(CRF)5个处理,采用地下淋溶原位监测的方法,获取了不同处理下水稻-油菜轮作系统土壤90 cm深度处氮素(N)淋失特征,评估了一次性施肥技术对氮素淋失的影响,并综合分析了其经济效应.结果表明: 油菜季和水稻季土壤渗漏液中氮素的主要形态不同,油菜季渗漏液中以NO₃^--N为主,水稻季渗漏水中NO₃^--N和NH₄⁺-N各占约50%.从整个轮作周期看,氮素淋失主要发生在水稻季,与FP、OPT和UA相比,CRF氮淋失总量分别显著减少33.7%、20.8%和20.7%;但各施肥处理对油菜季氮素淋失影响不显著.在相同施氮量的条件下,与OPT相比,UA不仅保证油菜和水稻均稳产,而且使油菜季氮肥农学效率显著提高了15.1%,但是没能提高水稻季氮肥农学效率;CRF水稻产量和氮肥农学效率均差异不显著,但油菜产量和氮肥农学效率分别显著提高10.7%和18.9%.经济效益上,与OPT相比,UA和CRF处理油菜分别增收3660和3048 元·hm^-2,水稻分别增收3162和2220元·hm^-2.因此,对于长江中下游典型种植系统而言,综合考虑对氮素淋失、作物产量和经济效益的影响,一次性基施控释肥技术能在保证作物稳产或增产、提高农民经济效益的同时显著降低氮淋失量,是未来水稻-油菜轮作系统值得推荐的一种生产技术.     

Effects of P,K, and liming on soil pH,Al, Mn,K, and forage barley dry matter yield and quality for a newly-cleared Cryorthod

Forage barley dry matter yield and quality, as well as soil pH, Al, and Mn were monitored in response to P, K, and lime application on a newly cleared Typic Cryorthod (Orthid Podzol). The overall yearly yield level was affected by precipitation. Without liming soil acidification occurred after three years of production. The liming rate of 2.2 Mg.ha⁻¹ was found optimal for maintaining initial pH levels (5.66) and increasing forage barley yields. It was also found optimum for K and P utilization for these first years of production. Soil pH dropped an average of 0.33 units over the three years on unlimed P plots and 0.46 units over 4 years on K plots. Phosphorus and K fertilization increased N utilization and resulted in decreased soil acidification. Phosphorus availability was greater in the first year of cropping than in subsequent years, this was likely due to the effects of higher available moisture, liming release of native P, and effects of initial fertilization. There was a 148% increase in total dry matter yield and an 85% increase in protein yield of forage barley with P application. Liming increased total forage barley yields an average of 69% and total protein yields 48%. Reduced barley yields in unlimed plots were due to low soil pH. After two years of cultivation, unlimed plots contained exchangeable Al and soluble Mn levels reported toxic for other soils. The higher liming rates of 4.4 and 6.6 Mg.ha⁻¹ reduced soluble Mn to near critically low levels. soil Al and Mn were highly correlated to pH. Soil exchangeable Al, Mn, and soluble Mn along with tissue Al were inversely correlated to percentage yield. The average yield respone to three levels of applied K, increased from zero initially to 67% by the fourth year. Total dry-matter production increased 32% and total protein yield increased an average of 32% and total protein yield increased an average of 15% with K fertilization over four years. About 60% of the yield response occurred between the 0 and 22kg K.ha⁻¹ rates. Initial soil exchangeable K levels were not maintained even at the highest 66kg K.ha⁻¹ treatment. Soil exchangeable Al and soluble Mn were elevated with dropping pH. Soil K reserves and resupply of exchangeable K in these soils over the long term will be an important factor in crop production.     

Effects of legumes on soil physical quality in a maize crop

The effect of intercropped legumes and three N fertilizer rates in a continuous maize (Zea mays L.) cropping system on the physical properties of two soils were investigated for three years. The legumes, being a mixture of alfalfa, clover and hairy vetch, had a significant cumulative effect on some physical properties of both soil. The lowest stability and smallest mean weight diameter of soil aggregates were associated with monoculture maize plots. Aggregate size and stability were not affected by N fertilization at any of the rates of 0, 70, and 140 kg ha^-1 in intercropped plots, except that aggregate stability was actually reduced by N fertilization in one soil, the Ste. Rosalie clay. In maize plots in both soils, stability and size of soil aggregates were significantly increased with increased added N. Intercropped legumes significantly decreased dry bulk density and soil penetration resistance. Added N had no measurable influence on these compaction factors. Soil water properties were not significantly affected by either intercropping or N fertilization. Positive effects noted on soil aggregation and other physical properties in intercropped plots are the result of enhanced root activity, or incorporation of legumes as green manure, or both. Improvement of soil structure in maize plots associated with increasing N application was the result of increased maize-root residues.     

北方冬小麦/夏玉米轮作体系土壤氨挥发的原位测定

采用通气法测定了北方冬小麦／夏玉米轮作体系田间土壤的原位氨挥发。结果表明,与冬小麦施用基肥相比,夏玉米追肥后土壤的氨挥发速率很快升高,但军发高峰期持续时间较短,最大氨挥发速率亦低于冬小麦,冬小麦拨节期追肥,氨挥发速率低且呈波动变化,未出现高峰值,从整个生长季节来看,冬小麦不施氮和每公顷施氮120、240、360kg时的累计挥发量分别为4．4、6．9、13．0、38．4kgN/hm^2,夏玉米为8．4、15．1、20．0、26．1kgN/hm^2。按我国北方冬小麦／夏玉米播种面积1864．4万hm^2计,每年由氨挥发向大气排放的氨素达23．8－120．2万t,其中17．2－96．4万t来自氮肥,相当于氮肥投入的2．1％－9．5％。     

Nitrogen mineralization and potential nitrification at different depths in acid forest soils

Yield decline of cereals grown in monoculture may be alleviated with alternative crop management strategies. Crop rotation and optimized tillage and fertilizer management can contribute to more sustainable food and fiber production in the long-term by increasing diversity, maintaining soil organic matter (SOM), and reducing adverse effects of excessive N application on water quality. We investigated the effects of crop sequence, tillage, and N fertilization on long-term grain production on an alluvial, silty clay loam soil in southcentral Texas. Crop sequences consisted of monoculture sorghum (Sorghum bicolor (L.) Moench,) wheat (Triticum aestivum L.), and soybean (Glycine max (L.) Merr), wheat/soybean double-crop, and rotation of sorghum with wheat/soybean. Grain yields tended to be lower with no tillage (NT) than with conventional tillage (CT) early in the study and became more similar after 11 years. Nitrogen fertilizer required to produce 95% to maximum sorghum yield was similar for monoculture and rotation upon initiation of the experiment and averaged 16 and 11 mg N g^-1 grain with NT and CT, respectively. After 11 years, however, the N fertilizer requirement became similar for both tillage regimes, but was greater in monoculture (17 mg N g^-1 grain) than in rotation (12 mg N g^-1 grain). Crop sequences with double-cropping resulted in greater land use efficiency because similar or lower amounts of N fertilizer were required to produce equivalent grain than with less intensive monoculture systems. These more intensive crop sequences produced more stover with higher N quality primarily due to the inclusion of soybean in the rotation. Large quantities of stover that remained on the soil surface with NT led to greater SOM content, which increased the internal cycling of nutrients in this soil. In southcentral Texas, where rainfall averages nearly 1000 mm yr^-1, more intensive cropping of sorghum, wheat, and soybean with moderate N fertilization using reduced tillage can increase grain production and potentially decrease N losses to the environment by cycling more N into the crop-SOM system.     

中药渣蚓粪对玉米生长及土壤肥力特性的影响

采用盆栽试验,研究了中药渣蚓粪对玉米生长及土壤肥力的影响.结果表明: 随着蚓粪施用量的增加,玉米的株高、茎粗、叶面积、叶绿素含量均显著增加;生长60 d收获时,多数蚓粪处理的土壤容重显著降低;蚓粪处理的土壤pH显著高于对照和相应的化肥处理.蚓粪处理的土壤全氮、有机质含量也明显高于化肥处理,且随蚓粪施用量的增加,效果越趋显著.中药渣蚓粪可作为一种高效有机肥,其合理施用有助于改善土壤物理结构,缓解土壤的酸化进程,提高土壤有机质和氮素含量,有效促进作物生长.     

Prediction of long-term fertilizer nitrogen requirements of maize in the tropics using a nitrogen balance model

A simple N balance model was used to calculate fertilizer requirement for a target N uptake by maize. Nitrogen uptake from soil sources and target uptake of N with fertilizer N additions were obtained from fertilizer trials in Africa and Latin America. Most experiments had data for only one cropping period, although some from Latin America had data for four to six crops. The transfer coefficient of fertilizer N to the crop was adjusted to realize maximum recovery of fertilizer N under best methods of fertilizer application. The time constants of transfer of soil N to the crop were allowed to vary and were affected mainly by soil texture. Where 4 to 6 cropping periods were available good agreement between actual and predicted fertilizer N requirements was obtained. With this approach long-term fertilizer N requirements for 14 sites were predicted using first cropping period N uptake. This study showed that pools of organic N in more coarse-textured soils were usually smaller and declined more rapidly than in fine-textured soils. Labile organic N pools declined with time under all simulations, but approached equilibrium within 10 croppings seasons. Equilibrium N uptake from the soil organic N pool was predicted to be 31 kg ha^–1 for the more coarse-textured soils and 36 kg ha^–1 for the fine-textured soils. Long-term projections of fertilizer requirements using input data of the field experiments were reasonable, and effects of legume green manures and other amendments could be clearly evaluated.     

种植模式和施肥对黄土旱塬农田土壤团聚体及其碳分布的影响

本研究以长武黄土高原农业生态试验站33年长期定位试验处理为研究对象,选取撂荒(R)、小麦连作(CK/W)、小麦玉米轮作(L),小麦连作选取单施氮肥(N)、单施磷肥(P)、施氮磷肥(NP)、单施有机肥(M)、氮肥配施有机肥(NM)、磷肥配施有机肥(PM)、氮磷肥配施有机肥(NPM)共10种不同种植模式和施肥田间处理,运用干湿筛法和TOC法,分析长期不同施肥和种植模式下黄土旱塬农田土壤力稳性和水稳性团聚体数量、稳定性、各粒级团聚体中全碳和有机碳的分布特征,以及各粒级团聚体对碳分布的贡献。结果表明: 力稳性团聚体以>0.25 mm大团聚体为主,含量>67%,施肥使其减少;连作减少了微团聚体,而轮作增加了微团聚体且其效果大于施肥处理。水稳性团聚体以<0.25 mm微团聚体为主,含量>61%;施肥和耕作均减少了水稳性微团聚体。不同施肥方式和种植模式均降低了团聚体破坏率(PAD),增加了大团聚体(R_0.25)含量。施用有机肥显著提高了力稳性团聚体各粒级中全碳和有机碳含量;连作和轮作增加了各粒级团聚体中全碳含量,但轮作显著降低了有机碳含量。单施氮、磷肥使土壤全碳含量降低,而氮磷复合肥和有机肥使土壤全碳含量显著增加;种植模式对全碳的影响较施肥处理小,连作和轮作使土壤全碳增加。除单施氮、磷肥外,复合施肥和施用有机肥使土壤有机碳显著增加;不同种植模式对土壤有机碳的影响小于施肥处理,轮作使有机碳含量降低。微团聚体对土壤全碳和有机碳的贡献率最大,可达21.2%~33.6%;不同施肥和种植模式使微团聚体全碳的贡献率增加,施肥处理中NP和NPM显著增加了微团聚体的全碳和有机碳贡献率,轮作对微团聚体全碳和有机碳的增加趋势贡献最显著。     

Crop rotation

Crop rotation has been used for thousands of years. During the 1950s and early 1960s, it was felt that synthetic fertilizers and pesticides could forever replace crop rotation without loss of yield, but that opinion has changed. The current consensus is that crop rotation increases yield and profit and allows for sustained production. For example, maize, in a 2‐year rotation with soybean, yields 5 to 20% more than continuous maize, and no amount of fertilizer or pesticide can compensate completely for that difference. It is not well understood what causes the rotation effect, but improvements in soil physical properties and soil organic matter probably play a beneficial role in rotations that include multiple years of sod, pasture, or hay. Short rotations such as maize‐soybean actually result in a degradation in those same factors, yet the rotation effect still is realized. Recent information suggests that soilborne pathogens may be responsible for the yield depression seen with continuous monoculture.     

耕作和培肥对豫中区小麦-玉米轮作系统土壤氮平衡和温室气体排放的影响

豫中区作为黄淮海平原粮食的主产地,节能、减排和增效是该区农业发展的重要方向。本研究基于2010年耕作与培肥定位试验,在2018—2019年探究了3种耕作方式(深耕、浅耕和免耕)和2种培肥模式(氮肥和氮肥+有机肥)对土壤氮平衡和温室气体排放的影响。结果表明: 增施有机肥能增加土壤全氮积累量;在小麦和玉米成熟期,0～60 cm土层土壤全氮积累量在浅耕+有机肥处理下最高,分别为8058.53和8299 kg N·hm^-2,较其他处理高3.2%～27.4%和4.3%～7.2%。分析土壤氮素投入与输出可知,增施有机肥处理氮素均表现为盈余,浅耕+有机肥处理盈余量最高,为13.57 kg N·hm^-2,比深耕+有机肥和免耕+有机肥分别高9.52和0.18 kg N·hm^-2;氮损失以硝态氮淋溶为主,占总损失的73.4%～76.9%,其中深耕+有机肥处理硝态氮淋溶量最高,为48.37 kg N·hm^-2,较其他处理高18.9%～35.1%。2018—2019周年全球增温潜势在深耕+有机肥处理下最高,为33070 kg N·hm^-2,较其他处理高6.6%～26.8%;增施有机肥增加了N₂O和CO₂的排放,降低了CH₄的吸收。作物周年产量在深耕+有机肥处理下最高,较其他处理高5.0%～17.1%;但作物收获指数在浅耕+有机肥处理下最高。综上,在保证作物产量、维持氮素平衡和降低温室气体排放方面,推荐的种植模式为浅耕+增施有机肥。     

紫色丘陵区玉米/大豆套作系统土壤磷吸附-解吸动力学

利用田间小区试验研究了玉米/大豆套作(M/S)、玉米单作(M)、大豆单作(S)3种栽培模式下施磷对土壤磷吸附解吸特征的影响.结果表明： 在不施磷处理下,M/S系统产量较M、S分别提高9.8%、79.1%,土地当量比为1.58;在施磷处理下,M/S系统产量较M、S分别提高10.4%、80.3%,土地当量比为1.62.与不施磷处理相比,施磷使M/S、M、S 3种栽培模式下的系统总产量分别提高12.7%、12.2%、17.6%.无论施磷与否,3种栽培模式下土壤最大缓冲容量(SBC)值均表现为M/S>M>S;但与施磷处理相比,不施磷处理下M/S、M、S栽培模式下土壤SBC值分别降低19.6%、30.3%、12.0%.各栽培模式在施磷处理下土壤单位吸附量的解吸量b值大小为M/S>M>S;与不施磷处理相比,施磷使M/S、M、S模式下b值分别增加10.9%、39.1%、-9.6%.土壤最大吸磷量(Q_m)及土壤磷解吸率也表现出相同的趋势.     

Nitrogen cycling in leucaena (Leucaena leucocephala) alley cropping in semi-arid tropics

In an alley cropping system, prunings from the hedgerow legume are expected to supply nitrogen (N) to the associated cereal. However, this may not be sufficient to achieve maximum crop yield. Three field experiments with alley-cropped maize were conducted in a semi-arid environment in northern Australia to determine: (1) the effect of N fertilizer on maize growth in the presence of fresh leucaena prunings; (2) the effect of incorporation of leucaena and maize residues on maize yield and the fate of plant residue¹⁵N in the alley cropping system; and (3) the¹⁵N recovery by maize from¹⁵N-labelled leucaena, maize residues and ammonium sulphate fertilizer.Leucaena residues increased maize crop yield and N uptake although they did not entirely satisfy the N requirement of the alley crop. Additional N fertilizer further increased the maize yield and N uptake in the presence of leucaena residues. Placement of leucaena residues had little effect on the availability of N to maize plants over a 2 month period. The incorporation of leucaena residues in the soil did not increase the recovery of leucaena¹⁵N by maize compared with placement of the residues on the soil surface. After 2 months, similar proportions of the residue¹⁵N were recovered by maize from mulched leucaena (6.3%), incorporated leucaena (6.1%) and incorporated maize (7.6%). By the end of one cropping season (3 months after application) about 9% of the added¹⁵N was taken up by maize from either¹⁵N-labelled leucaena as mulch or¹⁵N-labelled maize residues applied together with unlabelled fresh leucaena prunings as mulch. The recovery of the added¹⁵N was much higher (42.7%) from the¹⁵N-labelled ammonium sulphate fertilizer at 40 kg N ha^-1 in the presence of unlabelled leucaena prunings. Most of the added¹⁵N recovered in the 200 cm soil profile was distributed in the top 25 cm soil with little leached below that. About 27–41% of the leucaena¹⁵N was apparently lost, largely through denitrification from the soil and plant system, in one cropping season. This compared with 35% of the fertilizer¹⁵N lost when the N fertilizer was applied in the presence of prunings. ei]H Lambers     

Intercropping Enhances Productivity and Maintains the Most Soil Fertility Properties Relative to Sole Cropping

Yield and nutrient acquisition advantages are frequently found in intercropping systems. However, there are few published reports on soil fertility in intercropping relative to monocultures. A field experiment was therefore established in 2009 in Gansu province, northwest China. The treatments comprised maize/faba bean, maize/soybean, maize/chickpea and maize/turnip intercropping, and their correspoding monocropping. In 2011 (the 3^rd year) and 2012 (the 4^th year) the yields and some soil chemical properties and enzyme activities were examined after all crop species were harvested or at later growth stages. Both grain yields and nutrient acquisition were significantly greater in all four intercropping systems than corresponding monocropping over two years. Generally, soil organic matter (OM) did not differ significantly from monocropping but did increase in maize/chickpea in 2012 and maize/turnip in both years. Soil total N (TN) did not differ between intercropping and monocropping in either year with the sole exception of maize/faba bean intercropping receiving 80 kg P ha⁻¹ in 2011. Intercropping significantly reduced soil Olsen-P only in 2012, soil exchangeable K in both years, soil cation exchangeable capacity (CEC) in 2012, and soil pH in 2012. In the majority of cases soil enzyme activities did not differ across all the cropping systems at different P application rates compared to monocrops, with the exception of soil acid phosphatase activity which was higher in maize/legume intercropping than in the corresponding monocrops at 40 kg ha⁻¹ P in 2011. P fertilization can alleviate the decline in soil Olsen-P and in soil CEC to some extent. In summary, intercropping enhanced productivity and maintained the majority of soil fertility properties for at least three to four years, especially at suitable P application rates. The results indicate that maize-based intercropping may be an efficient cropping system for sustainable agriculture with carefully managed fertilizer inputs.     

Dryland residue and soil organic matter as influenced by tillage, crop rotation, and cultural practice

Novel management practices are needed to increase dryland soil organic matter and crop yields that have been declining due to long-term conventional tillage with spring wheat (Triticum aestivum L.)-fallow system in the northern Great Plains, USA. The effects of tillage, crop rotation, and cultural practice were evaluated on dryland crop biomass (stems + leaves) yield, surface residue, and soil organic C (SOC) and total N (STN) at the 0?C20?cm depth in a Williams loam (fine-loamy, mixed, superactive, frigid, Typic Argiustolls) from 2004 to 2007 in eastern Montana, USA. Treatments were two tillage practices [no-tillage (NT) and conventional tillage (CT)], four crop rotations [continuous spring wheat (CW), spring wheat-pea (Pisum sativum L.) (W-P), spring wheat-barley (Hordeum vulgaris L.) hay-pea (W-B-P), and spring wheat-barley hay-corn (Zea mays L.)-pea (W-B-C-P)], and two cultural practices [regular (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and ecological (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height)]. Crop biomass and N content were 4 to 44% greater in W-B-C-P than in CW in 2004 and 2005 and greater in ecological than in regular cultural practice in CT. Soil surface residue amount and C and N contents were greater in NT than in CT, greater in CW, W-P, and W-B-C-P than in W-B-P, and greater in 2006 and 2007 than in 2004 and 2005. The SOC and STN concentrations at 0?C5?cm were 4 to 6% greater in CW than in W-P or W-B-P in NT and CT from 2005 and 2007. In 2007, SOC content at 10?C20?cm was greater in W-P and W-B-P than in W-B-C-P in CT but STN was greater in W-B-P and W-B-C-P than in CW in NT. From 2004 to 2007, SOC and STN concentrations varied at 0?C5?cm but increased at 5?C20?cm. Diversified crop rotation and delayed planting with higher seed rates and banded N fertilization increased the amount of crop biomass returned to the soil and surface residue C and N. Although no-tillage increased surface residue C and N, continuous nonlegume cropping increased soil C and N levels at the surface layer compared with other crop rotations. Continued return of crop residue from 2004 to 2007 may increase soil C and N levels but long-term studies are needed to better evaluate the effect of management practices on soil C and N levels under dryland cropping systems in the northern Great Plains.     

Early phosphorus nutrition,mycorrhizae development,dry matter partitioning and yield of maize

We conducted a field experiment to test the hypothesis that improved phosphorus nutrition occurs in maize plants with rapid arbuscular (AM) mycorrhizae development at early developmental stages and that this also is reflected in dry matter allocation and final yield. A split-split plot design was used with previous crop (Zea mays L.-maize and Brassica napus L.-canola), tillage practices (no-tillage or conventional tillage) and P fertilization (5 levels) as factors chosen to modify mycorrhizae development at early developmental stages of maize. Previous cropping with canola resulted in decreased shoot-P concentration and shoot growth of maize at early stages. No-tillage resulted in higher shoot-P concentration but lower shoot weight than conventional tillage. Greater shoot-P uptake was related to a rapid intraradical development of mycorrhizae (previous crop of maize) or rapid connection to a mycorrhizal mycelium network (no-tillage treatments). Maize yield and harvest index were lower after cropping with canola. The yield for conventional tillage was higher than that for no-tillage but the harvest index was lower. The hypothesis was supported at early stages of maize growth by the effect of previous crop but not by results of tillage, because an unknown factor reduced growth in the no-tillage system. The hypothesis was supported at maturity by increased biomass allocation to grain relative to total shoot weight in treatments with greater shoot-P concentration at early stages.     

旱地小麦不同栽培条件对土壤硝态氮残留的影响

在陕西渭北旱塬进行了2a田间试验,研究不同栽培模式、施氮量和小麦种植密度对旱地硝态氮残留的影响。结果表明,种植小麦2a后0~200 cm土壤剖面中残留硝态氮58.6~283.9 kg/hm2,数量可观,短期内在渭北旱塬深厚的土壤中不会对地下水造成威胁,但夏季休闲期间容易下迁至作物无法吸收的土壤深度。与常规无覆盖模式相比,地膜覆盖和垄沟种植显著提高了作物对氮素的吸收,但同时也增加了土壤0~200 cm的硝态氮残留,这与地膜覆盖导致有机氮矿化增加有关;秸秆覆盖对作物氮素吸收和硝态氮残留均没有明显影响。施氮量低于120 kg/hm2时,各种栽培模式土壤剖面残留硝态氮的分布差异较小,只有地膜覆盖和垄沟种植处理在土壤表层有少量硝态氮累积;施氮量为240 kg/hm2时,无覆盖和秸秆覆盖土壤60~120 cm深度都有明显累积峰,地膜覆盖和垄沟种植土壤残留硝态氮则在60 cm以上土层累积较多。小麦种植密度也影响了各种栽培模式土壤硝态氮及其分布特点。垄沟种植条件下,从土壤表层到200 cm的深层,垄上土壤残留硝态氮均显著高于沟内土壤;上层差异最大,随着土壤深度的增加其差异逐渐降低;随着施氮量的增加,这种差异显著增大;随小麦种植密度的增加则显著降低。随着施氮量增加,小麦吸氮量和土壤中残留硝态氮量均显著提高;施氮增加的残留硝态氮占施氮量的0.3%~44.6%。垄沟种植模式施氮增加的残留硝态氮最多,地膜覆盖处理次之,垄沟种植处理垄上土壤增加量远远高于沟内土壤。施氮量提高1倍,增加的残留硝态氮量平均提高了3倍多。提高小麦种植密度,施氮增加的残留硝态氮平均减小13.2 kg/hm2。由于种植密度增加显著提高了小麦对氮素的吸收,因此硝态氮残留有降低的趋势。其中,秸秆覆盖模式80~140 cm土层降低显著;地膜覆盖条件下高密与低密残留硝态氮的差异主要在深层;垄沟模式中,低密度种植硝态氮残留量在整个土壤剖面都高于高密度处理;而无覆盖条件下,残留硝态氮则随种植密度的提高呈增加趋势。