Model analysis of a straw mulch system for continuous wheat in an arid climate

Wheat (Triticum aestivum L.) production in some dryland regions is severely limited by the cereal cyst nematode (Heterodera avenae Woll.). Conventional fallow management during a wet period has been shown to allow hatching of the cysts during the fallow season and thereby sanitize the soil for the subsequent wheat crop. Recently a straw mulch (SM) management has been introduced into a long-term experiment in the Negev region of Israel. This management ameliorated the nematode damage and allowed continuous wheat production. Only three seasons of successful experimentation exist with the SM system so questions remain about its performance over seasons with differing weather conditions. A simple, mechanistic, wheat model was extended to simulate wheat development and growth when the crop is grown on nematode-infested soils. Incorporating statements describing inhibition of rooting depth as a result of nematode activity resulted in good agreement between simulations and 16 seasons of yield observations on continuous wheat. The effect of SM was simulated simply by decreasing soil evaporation and this resulted in higher levels of soil water and decreased nematode inhibition of rooting. Good agreement was obtained between the three seasons of experimental data and simulations of the SM system, with predicted grain yield within 10% of observations. Over 16 seasons, simulations of the SM system indicated substantial grain yield increases over continuous wheat in all but the highest-yielding season. Simulations in 14 seasons with conventional fallow management revealed that annual yields of SM were equivalent to biennial yields of the fallow system, resulting in a predicted doubling of wheat production for this dryland region of the Negev.     

Cereal cyst nematode effects on wheat water use,and on root and shoot growth

Wheat (Triticum aestivum L.) is grown in many arid regions using fallow management whereby no crop is grown in alternate cropping seasons. Although fallowing is important in increasing the availability of water and nitrogen to crops in many environments, experiments in Israel revealed that water carryover from the fallow season for wheat production was rare. This paper examines the possibility that improved water use, and improved root and shoot growth, result from soil sanitation of cereal cyst nematode (CCN, Heterodera avenae Woll.) in the fallow season. Pot experiments in controlled environments revealed a dramatic, negative effect of various populations of CCN on wheat root growth. The decrease in root growth was associated with decreased shoot growth and decreased rates of transpiration. Mechanical pruning of roots mimicked the effects of CCN infestation indicating that root pruning is probably the primary damage of CCN. In the field, dry weight yields of wheat were maintained even in continuous wheat management when a soil biocide was used to control CCN. It is proposed that the success of the fallow management is based on the fact that CCN cysts hatch in wet soil during rainy periods of the fallow year but fail to produce a new generation of cysts because no host plants are present.     

Critical precipitation period for dryland maize production

Grain yields for dryland maize (Zea mays L.) production in the semi-arid Great Plains of the United States can be unpredictable because of the erratic nature of growing season precipitation. Because of the high input costs for maize production, farmers need to have a tool that will help them assess the risk associated with dryland maize production. The objectives of this work were to determine the critical period for precipitation during the maize growing season and to develop a relationship between critical period precipitation and maize yield to use as a tool to quantify expected yield variability associated with dryland maize production in this region. Maize yield data were collected at Akron, CO from two dryland cropping systems experiments (1984–2009) in which maize was grown in a 3-year winter wheat (Triticum aestivum L.)–maize–fallow rotation. Yields were correlated with weekly precipitation amounts from planting to harvest in search of the period of time in which yield was most influenced by precipitation. Soil water contents at planting were measured either by gravimetric sampling or by neutron attenuation. Yields were found to be most closely correlated with precipitation occurring during the 6-week period between 16 July and 26 August. The data separated into two linear relationships defined by whether the sum of available soil water at planting and May precipitation was less than or greater than 250 mm. These two linear relationships between precipitation during this critical period and yield were used with long-term precipitation records to determine the probability of obtaining a maize yield of at least 2500 kg ha⁻¹ (generally considered to be a break-even yield) at three locations across the central Great Plains precipitation gradient. This analysis quantified the production risk associated with the highly variable corn yields that result from erratic summer precipitation in this region.     

Effects of transition season management on soil N dynamics and system N balances in rice–wheat rotations of Nepal

In the low-input rice–wheat production systems of Nepal, the N nutrition of both crops is largely based on the supply from soil pools. Declining yield trends call for management interventions aiming at the avoidance of native soil N losses. A field study was conducted at two sites in the lowland and the upper mid-hills of Nepal with contrasting temperature regimes and durations of the dry-to-wet season transition period between the harvest of wheat and the transplanting of lowland rice. Technical options included the return of the straw of the preceding wheat crop, the cultivation of short-cycled crops during the transition season, and combinations of both. Dynamics of soil N_min, nitrate leaching, nitrous oxide emissions, and crop N uptake were studied throughout the year between 2004 and 2005 and partial N balances of the cropping systems were established. In the traditional system (bare fallow between wheat and rice) a large accumulation of soil nitrate N and its subsequent disappearance upon soil saturation occurred during the transition season. This nitrate loss was associated with nitrate leaching (6.3 and 12.8 kg ha⁻¹ at the low and high altitude sites, respectively) and peaks of nitrous oxide emissions (120 and 480 mg m⁻² h⁻¹ at the low and high altitude sites, respectively). Incorporation of wheat straw at 3 Mg ha⁻¹ and/or cultivation of a nitrate catch crop during the transition season significantly reduced the build up of soil nitrate and subsequent N losses at the low altitude site. At the high altitude site, cumulative grain yields increased from 2.35 Mg ha⁻¹ with bare fallow during the transition season to 3.44 Mg ha⁻¹ when wheat straw was incorporated. At the low altitude site, the cumulative yield significantly increased from 2.85 Mg ha⁻¹ (bare fallow) to between 3.63 and 6.63 Mg ha⁻¹, depending on the transition season option applied. Irrespective of the site and the land use option applied during the transition season, systems N balances remained largely negative, ranging from −37 to −84 kg N ha⁻¹. We conclude that despite reduced N losses and increased grain yields the proposed options need to be complemented with additional N inputs to sustain long-term productivity.     

周年秸秆还田量对麦田土壤养分及产量的影响

为揭示周年秸秆还田量对小麦高产优质栽培的影响机理,在大田条件下,设置稻麦秸秆均不还田(CK)、25%稻麦秸秆均还田、50%稻麦秸秆均还田、75%稻麦秸秆均还田、100%稻麦秸秆均还田、100%麦季稻秸还田、100%稻季麦秸还田等7个秸秆处理,经过三年田间定位试验,分析了周年秸秆还田量对三年麦田土壤养分及小麦产量的影响。结果表明,周年秸秆还田后三年土壤养分和有机质含量均不同程度地提高,且随秸秆还田量的增加呈先增后减的趋势,效果最好的还田量主要集中在50%和75%。其中,第一年以50%秸秆还田量对土壤养分和有机质含量影响最明显;到第三年以75%还田量影响最显著,土壤全氮、有效磷、速效钾和有机质含量分别比CK提高了2.61%、4.05%、18.25%和5.90%。在前两年,不同秸秆还田处理对小麦均有增产效果,但在第三年,100%稻麦秸秆均还田和100%麦季稻秸还田处理略微减产。6个秸秆还田处理中只有50%稻麦秸秆均还田对小麦的增产效果在三年中均达到显著水平,增产幅度分别为11.23%、14.74%和14.29%。综合来看,50%稻麦秸秆均还田最适宜当地小麦高产栽培。     

黄土区旱地覆盖对小麦养分吸收及水分利用的影响

为寻找适宜黄土区旱地小麦高效栽培的覆盖方式,通过田间试验研究了几个不同覆盖方式对黄土区旱地冬小麦产量、养分吸收以及水分利用效率的影响。结果表明,全年地膜全覆盖方式对提高小麦产量、养分吸收和水分利用效率效果最好,该处理下小麦籽粒产量较不覆盖、夏闲期地膜全覆盖和夏闲期地膜麦草行间覆盖等处理分别增加21.9%、21.2%和20.8%,水分利用效率提高17.54%、13.02%和15.65% ,同时籽粒吸收N、P、K总量较不覆盖增加45.7%、23.5%和21.4%,茎叶吸收N、P、K总量较不覆盖增加56.6%、172.9%和52.1%。夏闲期蓄水以夏闲期地膜麦草行间覆盖的效果最好,分别较不覆盖、夏闲期地膜全覆盖和全年地膜全覆盖等处理增加160.25%、39.3%和16.2%。综合考虑不同覆盖方式对小麦增产、养分吸收以及土壤蓄水保墒效果的影响,全年地膜全覆盖是黄土区旱作小麦较佳的栽培方式。     

Cropping sequence and tillage system influences annual crop production and water use in semiarid Montana,USA

Available water is typically the biggest constraint to spring wheat production in the northern Great Plains of the USA. The most common rotation for spring wheat is with summer fallow, which is used to accrue additional soil moisture. Tillage during fallow periods controls weeds, which otherwise would use substantial amounts of water, decreasing the efficiency of fallow. Chemical fallow and zero tillage systems improve soil water conservation, allowing for increased cropping intensity. We conducted a field trial from 1998 through 2003 comparing productivity and water use of crops in nine rotations under two tillage systems, conventional and no-till. All rotations included spring wheat, two rotations included field pea, while lentil, chickpea, yellow mustard, sunflower, and safflower were present in single rotations with wheat. Growing season precipitation was below average most years, resulting in substantial drought stress to crops not following fallow. Preplant soil water, water use, and spring wheat yields were generally greater following summer fallow than wheat recropped after wheat or alternate crops. Water use and yield of wheat following summer fallow was greater than for chickpea or yellow mustard, the only other crops in the trial that followed summer fallow. Field pea performed best of all alternate crops, providing yields comparable to those of recropped spring wheat. Chickpea, lentil, yellow mustard, safflower, and sunflower did not perform well and were not adapted to this region, at least during periods of below average precipitation. Following summer fallow, and despite drought conditions, zero tillage often provided greater amounts of soil water at planting compared to conventional tillage.     

Evaluating decision rules for dryland rotation crop selection

No-till dryland winter wheat (Triticum aestivum L.)-fallow systems in the central Great Plains have more water available for crop production than the traditional conventionally tilled winter wheat-fallow systems because of greater precipitation storage efficiency. That additional water is used most efficiently when a crop is present to transpire the water, and crop yields respond positively to increases in available soil water. The objective of this study was to evaluate yield, water use efficiency (WUE), precipitation use efficiency (PUE), and net returns of cropping systems where crop choice was based on established crop responses to water use while incorporating a grass/broadleaf rotation. Available soil water at planting was measured at several decision points each year and combined with three levels of expected growing season precipitation (70, 100, 130% of average) to provide input data for water use/yield production functions for seven grain crops and three forage crops. The predicted yields from those production functions were compared against established yield thresholds for each crop, and crops were retained for further consideration if the threshold yield was exceeded. Crop choice was then narrowed by following a rule which rotated summer crops (crops planted in the spring with most of their growth occurring during summer months) with winter crops (crops planted in the fall with most of their growth occurring during the next spring) and also rotating grasses with broadleaf crops. Yields, WUE, PUE, value-basis precipitation use efficiency ($PUE), gross receipts, and net returns from the four opportunity cropping (OC) selection schemes were compared with the same quantities from four set rotations [wheat-fallow (conventional till), (WF (CT)); wheat-fallow (no-till), (WF (NT)); wheat–corn (Zea mays L.)-fallow (no-till), (WCF); wheat–millet (Panicum miliaceum L.) (no-till), (WM)]. Water use efficiency was greater for three of the OC selection schemes than for any of the four set rotations. Precipitation was used more efficiently using two of the OC selection schemes than using any of the four set rotations. Of the four OC cropping decision methods, net returns were greatest for the method that assumed average growing season precipitation and allowed selection from all possible crop choices. The net returns from this system were not different from net returns from WF (CT) and WF (NT). Cropping frequency can be effectively increased in dryland cropping systems by use of crop selection rules based on water use/yield production functions, measured available soil water, and expected precipitation.     

夏闲期施肥与覆盖处理对旱地冬小麦产量和土壤水分利用的影响

为给旱地夏闲期管理提供参考依据,采用大田试验,研究了夏闲期施肥与覆盖处理对旱地冬小麦土壤储水量、产量及水分利用效率的影响。结果表明,夏闲期施肥可明显提高播前0~100、100~200 cm土层储水量,增加了冬小麦穗数、籽粒产量和水分利用效率;不论施肥与否,地膜覆盖与纸覆盖均可提高播前底墒,增加小麦穗数和穗粒数,显著提高籽粒产量和水分利用效率,且地膜覆盖处理效果优于纸覆盖;施肥可增进覆盖的保水、增产及高效用水的作用。因此,旱地夏闲期可通过施肥与覆盖技术改善土壤水分状况,为旱地秋播作物高产创造条件。     

休闲期耕作对旱地小麦籽粒蛋白质形成及其相关酶活性的影响

为给旱地小麦高产优质栽培提供理论依据,通过大田试验研究了旱地小麦休闲期不同时间深翻、深松对0～300 cm土壤蓄水量、小麦籽粒蛋白质形成及其与氮代谢相关酶活性关系的影响.结果表明,休闲期深翻或深松均可提高旱地小麦播前0～300 cm土壤蓄水量,且欠水年效果明显,以前茬小麦收获后45 d深翻效果较好.休闲期耕作均显著提高了小麦蛋白质产量.耕作时间对籽粒蛋白质含量的影响因降雨年型不同而异,欠水年的休闲期耕作均显著降低了籽粒蛋白质含量;丰水年在麦收后15d耕作显著降低了籽粒蛋白质含量,而麦收后45 d耕作则显著提高了籽粒蛋白质含量,尤其显著提高了醇溶蛋白和麦谷蛋白含量,从而改善了品质.此外,丰水年麦收后45 d耕作可提高花后旗叶和籽粒谷氨酰胺合成酶(GS)活性、旗叶和籽粒谷氨酸合成酶(GOGAT)活性,降低花后旗叶和籽粒谷氨酸脱氢酶(GDH)活性;籽粒蛋白质的累积在麦收后15d耕作条件下与籽粒GDH活性关系密切,而麦收后45 d耕作条件下与旗叶GS和GOGAT活性相关性较大.总之,旱地小麦休闲期耕作在不同降雨年型下均可起到良好的蓄水保墒作用,且欠水年效果较明显;耕作时间对土壤水分、小麦氮代谢酶活性、籽粒蛋白质及其组分含量具有较大的调控效应,休闲期雨后耕作有利于籽粒蛋白质形成,且深翻效果较好.     

Simulated long-term effects of different soil management regimes on the water balance in the Loess Plateau, China

A soil management regime that improves water use efficiency (WUE) is urgently required to increase the sustainability of the winter wheat-summer fallow system in the Loess Plateau, China. However, the long-term partitioning of the water balance must be understood in order to evaluate the viability of possible soil management regimes. Therefore, an ecosystem model (CoupModel) was used to explore the effects on components of the water balance of five types of soil management regimes: conventional practice, wheat straw mulching, incorporation of high organic matter contents, compaction, and use of a harvested fallow crop. Three variants of the fallow crop approach were also considered, in which the crop was harvested 15, 30 and 45 days before sowing the wheat (designated Fallow-15d, Fallow-30d and Fallow-45d, respectively). Simulations were used to identify the relative magnitude of soil evaporation, wheat transpiration and deep percolation and to elucidate the temporal variability in these components for a selected location using climate records spanning 45 years. However, the soil management regime significantly influenced the magnitude of every component of the water balance (in terms of minimum, maximum and mean values) over the long periods considered. Consequently, wheat yield and WUE differed significantly among the simulated treatments. Mulching led to significantly lower soil evaporation, higher transpiration, and more frequent and extensive deep percolation than other regimes, thereby improving fallow efficiency (percentage of rainfall stored in the soil during the fallow period at the end of the fallow period), wheat yields and WUE. In contrast, soil compaction gave the opposite results, leading to the most unfavourable partitioning of the water balance reflected in the lowest wheat yield and WUE values of all the regimes. In 90% of the years no deep percolation occurred in the soil compaction simulations. Use of a fallow crop with optimal harvest timing (Fallow-30d) improved partitioning of the water balance (decreased soil evaporation) and did not significantly reduce wheat yield compared with conventional practice. High organic matter contents in the soil also had a positive influence on the water balance and improved wheat yield and WUE relative to conventional practice. Therefore, mulching appears to be the best management practice for the winter wheat-summer fallow system in the Loess Plateau, according to the simulations. Increasing soil organic matter may be the best option if mulching cannot be implemented. The ideal time for harvesting a fallow crop for use as green manure or fodder appears to be ca. 30 days before sowing the winter wheat.     

Effects of tillage,crop rotation and nitrogen fertilization on wheat-grain quality grown under rainfed Mediterranean conditions

The grain quality of wheat is influenced by the protein content, which in turn depends on environmental conditions and cropping practices. We carried out a 3-year field study in a rainfed Mediterranean region on the effects of tillage, crop rotation and nitrogen fertilization on the grain quality of hard red spring wheat (Triticum aestivum) in terms of protein content, test weight and alveogram indices. Tillage treatments were no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower (Helianthus annus L.) (WS), wheat–chickpea (Cicer arietinum L.) (WCP), wheat–fababean (Vicia faba L.) (WFB), wheat–fallow (WF) and continuous wheat (CW). Fertilizer nitrogen was used at three different rates: 50, 100 and 150 kg N ha⁻¹. A split–split plot design with four replicates was used. Grain protein content was found to be inversely proportional to rainfall during the growing season. The tillage method was also found to affect grain protein content, test weight and some grain quality indices. Through its effect on moisture and nitrate in the soil. The crop rotations that included a legume (WCP and WFB) had marked effects on wheat quality. The increased grain protein content and resulted in improved rheological properties of the dough (viz. a higher alveogram index and a more balanced tenacity/extensibility ratio). However, no differences due to N dilution in the plant were observed in the wettest year studied, which was also the highest yielding. Increasing the fertilizer N rate increased the grain protein content; this variable had the most marked influence on grain quality indices, though in the year that gave the highest yield the N dilution effect was observed. The many significant interactions among experimental variables reveal a close relationship among grain yield, protein content, grain quality and the wheat growth conditions. Specifically, the amount of rainfall and its distribution in the growing season strongly influenced N availability and uptake by the crop, as well as wheat-grain quality indices.     

Nitrogen dynamics and crop growth on an Alfisol and a Vertisol under a direct-seeded rainfed lowland rice-based system

Rice (Oryza sativa L.) followed by chickpea (Cicer arietinum L.) or a fallow is one of the predominant cropping systems in the rainfed lowlands of India. Crop rotation experiments over 3 years (1996–1998) to quantify N supply and demand under rainfed lowland rice–chickpea and rice–fallow cropping systems on a loam Alfisol and a clay Vertisol in Raipur, India were conducted under direct-seeded rice culture. The rice growth, yield, development and N accumulation were affected most by N rates (0, 40, 80, 120 kg ha⁻¹) followed by cropping system (rice–chickpea, rice–fallow) and soil types (Alfisol, Vertisol). The incorporation of chickpea in the cropping system helped in accumulating a greater amount of soil N than fallow. The rice yield, dry matter and N accumulated were significantly higher in rice–chickpea than rice–fallow systems on both soils and in all years. The lowest rice yields were recorded in 1997 due to unfavorable rainfall distribution. The total rainfall was the highest in this season, but most of it occurred during a short period at an early growth stage. The post-heading rains were lowest in this season and resulted in the lower rice yield as compared with that of 1996 and 1998. This indicates the significance of rainfall distribution in controlling yield in a rainfed environment. The rice yields were lower on Vertisol than Alfisol during periods of drought. The performance of chickpea was also better in Alfisol as compared with that in the Vertisol due to its better soil physical attributes. The residual effect of N applied to the preceding rice crop was non-significant on all yield, growth and N accumulation parameters of chickpea. The N balance computed from the top 70 cm soil layers indicated less N loss in the rice–chickpea system as compared with that in rice–fallow. The recovery efficiency at the highest N rate (120 kg N ha⁻¹) was higher for the rice–chickpea (57–61%) than that of rice–fallow (49–53%) system. The improved N balance for rice–chickpea system from third year onwards was due to switch to dry seeding and improved soil N status. The inclusion of legume and the effective capture of biologically fixed N and soil N through direct-seeded rice system in rainfed lowlands may help in improving the rice yield of resource poor farmers.     

休闲期不同耕作模式对旱地麦田土壤水分、养分及产量的影响

为探索适宜晋南旱地小麦高效生产的耕作模式,以晋麦92为试验材料,设置休闲期深翻/深翻、深松/深翻、深松/深松、常规耕作(对照)4个耕作模式,研究其对土壤水分及养分、作物生长和水分利用效率的影响。结果表明,深翻/深翻、深松/深翻、深松/深松模式较对照休闲末期3m内土壤蓄水量和土壤蓄水效率显著提高,土壤蓄水效率提高达52.5%~91.3%,以深松/深松模式较好;越冬-孕穗期3m内土壤蓄水量提高,且深松/深松模式与对照差异显著;各生育时期单株干物质积累量提高,且越冬-拔节期深松/深松、深松/深翻模式与对照差异显著,孕穗-成熟期各耕作模式与对照差异均显著;穗数、千粒重、产量和水分利用效率显著提高,其中穗数提高22.7%~29.9%,水分利用效率提高15.1%~21.6%,产量提高39.4%~60.3%,以深松/深松模式较好;收获后0~40cm土层土壤有机质平均含量提高2.5%~8.7%,速效磷含量提高11.1%~34.4%,碱解氮含量提高5.1%~20.2%,以深松/深松模式较好。总之,深翻/深翻、深松/深翻、深松/深松模式均能提高土壤蓄水保墒能力,改善养分供应状况,有利于促进小麦干物质积累,最终提高产量和水分利用效率,以深松/深松模式最佳。     

Rice establishment method affects nitrogen use and crop production of rice–legume systems in drought-prone eastern India

The inclusion of grain legumes in rainfed lowland rice farming systems provides an opportunity to increase food production, household income, and human nutrition of impoverished rice farmers in Asia. We examined the effect of rice establishment method on the performance of wet season rice (Oryza sativa L.) and post-rice crops of either chickpea (Cicer arietinum L.) or moong [Vigna radiata (L.) Wilczek] on an Udic Haplustalf in the drought-prone, rainfed lowlands of eastern India. Rice was either direct seeded in lines on moist soil immediately after the onset of wet season rain or transplanted after sufficient rainwater accumulated for soil submergence. Crop establishment method had no effect on rice performance in a season (2001) with normal rainfall. In a drought season (2002), direct seeding resulted in mean rice grain yield of 2.3 t ha⁻¹, whereas the transplanted rice crop failed. The agronomic efficiency of N fertilizer applied to direct-seeded rice was comparable for the 2 years (18 and 24 kg grain per kg N applied). Topsoil inorganic N was markedly higher following chickpea and moong than following a post-rice fallow. Direct-seeded rice had higher yield and accumulation of N following a post-rice legume than following fallow, but transplanted rice derived no such benefit from the legume. Direct-seeded rice was established 1–2 months before transplanted rice, and direct-seeded rice matured before transplanted rice by 8 days in the favorable season and by 26 days in the drought season. The soil nitrate present after legumes and fallow rapidly disappeared, presumably by denitrification, following the onset of rains and soil flooding prior to transplanting. A portion of this accumulated soil nitrate was taken up by the direct-seeded rice before it could be lost. But transplanted rice did not benefit from this inorganic N derived from legumes because virtually all soil nitrate was lost before transplanting. Direct seeding of rice ensured better use of residual and applied N, reduced risk due to drought, and favored intensification with post-rice legumes in drought-prone lowland systems.     

休闲期覆膜与施氮量对旱地小麦水氮利用效率和籽粒产量的影响

为探寻旱地小麦休闲期覆盖下的适宜施氮量,在旱地小麦休闲期覆盖与不覆盖条件下,分别设置75、150和225kg·hm-2三个施氮量,分析了休闲期覆盖配施氮肥对旱地小麦水氮利用效率和籽粒产量的影响。结果表明,休闲期覆盖显著提高播种至孕穗期0~300cm土壤蓄水量,其中播种期土壤水分增加70~81mm,其蓄水保墒效果可延续至孕穗期,进而提高了小麦产量和水分利用效率。休闲期覆盖促进了小麦植株对氮素的吸收和积累,增加了植株花前氮素转运量、花后氮素积累量以及籽粒氮素积累量,提高了氮素收获指数和氮素生产效率。休闲期覆盖配施氮素150kg·hm-2时,蓄水、增产和水分高效利用、氮素积累与转运的效果最好。     

Weed and disease incidence in no-till facultative wheat in the Pacific Northwest,USA

Weeds and diseases are major problems in the tillage-based winter wheat (Triticum aestivum)/summer fallow (WW/SF) cropping system of the low precipitation zone (≤300 mm) of the Pacific Northwest. Computer models have estimated that no-till spring crops may reduce soil erosion susceptibility by 95%. However, these annual cropping systems were not economically viable alternatives to the WW/SF rotation. Late-planted WW, also examined as an alternative, was similarly not viable with 35% lower grain yields than WW planted at the normal seeding date for the area. In 2002, two facultative wheat (FW) rotations were incorporated into a long-term, multidisciplinary field study to compare weed and disease incidence with a WW/reduced tillage summer fallow (WW/RSF) system for 4 years. Facultative wheat, not synonymous with late-planted WW, is often derived from SW by WW crosses and exhibits strong photosensitivity and partial sensitivity to vernalization. The two FW systems compared with WW/RSF were no-till FW/no-till spring wheat (FW/SW) and no-till FW/chemical fallow (FW/ChF). Facultative wheat was planted in early-November compared to WW planted in early-September and SW in the following March. Although 16 weed species were present during the study, Bromus tectorum and Salsola tragus were the most pervasive weeds and were found at the highest densities in FW following SW (FW_(SW)). Populations of B. tectorum were often 90% higher in FW_(SW) than in either WW or FW following ChF. The FW/ChF, WW/RSF, and SW following FW had similarly low weed populations when averaged over 4 years. Facultative wheat had less root disease than WW throughout the study. Stripe rust (Puccinia striiformis) was severe in SW in 2005, but did not affect either FW. Based on the low weed and disease incidence coupled with the no-till planting of FW, the FW/ChF system showed promise as an alternative sustainable system to WW/SF.     

北部冬麦区旱地小麦品种的演变规律

为了给北部冬麦区旱地小麦育种提供参考,利用1986-2015年国家北部冬麦区旱地小麦长治区试点参试品种的试验资料,研究其演变规律,并对产量和主要农艺性状进行相关和通径分析。结果表明,28年间北部冬麦区旱地小麦品种产量呈逐年递增趋势,年平均遗传进展分别为68.163kg·hm~(-2)或1.57%。主要农艺性状演变的总趋势是,有效穗数和千粒重增加,穗粒数略有减少,株高降低,抽穗期和成熟期提前,灌浆期延长,其年平均遗传进展分别为0.18%、0.26%、-0.03%、-0.26%、-0.12%、-0.05%、0.17%。从产量及主要农艺性状变化趋势和变异情况及区域布局、气候条件和育种现状分析,选育抗旱节水性好、高产稳产适应性广的品种是北部冬麦区旱地小麦育种面临的挑战和最终目标。为了适应当前耕作制度、生产条件和气候变化的影响,北部冬麦区旱地品种选育应在加强品种抗旱节水性选择的基础上,通过适当降低株高增强抗倒性来进一步增加穗数,通过选育穗子较大、小穗数适中、结实性好的品种来提高穗粒数,通过选择灌浆期长且灌浆速率高的品种来提高品种的千粒重。     

秸秆带状覆盖对旱地冬小麦产量及土壤水分的影响

为探讨西北半干旱雨养条件下秸秆带状覆盖麦田水分利用特征和增产效果,通过田间试验,以露地条播为对照(CK),研究了3种不同覆盖处理[秸秆带状覆盖常规条播(SM1)、秸秆带状覆盖宽幅条播(SM2)和全膜覆土穴播(PM)]对旱地冬小麦田土壤含水量、小麦产量和水分利用效率的影响。结果表明,秸秆带状覆盖和全膜覆土穴播均可显著改善小麦全生育期0~20cm以及开花前20~90cm土壤墒情,但开花后20~90cm以及全生育期90~200cm土壤墒情普遍不如CK。3种覆盖处理均能促进冬小麦对土壤贮水的利用,显著提高开花至成熟阶段的耗水量及其占总耗水量的比例。秸秆带状覆盖和全膜覆土穴播生育期耗水量分别比CK增加4.6%和7.6%。秸秆带状覆盖在孕穗前0~200cm土壤墒情与全膜覆土穴播无显著差异,孕穗期开始则好于全膜覆土穴播;全膜覆土穴播0~200cm土壤贮水消耗量显著高于秸秆带状覆盖,而开花至成熟阶段的耗水量及其占总耗水量的比例则略低于秸秆带状覆盖。3种覆盖处理均显著提高产量和水分利用效率,PM、SM1和SM2较CK分别增产36.8%、29.7%和27.5%,水分利用效率分别提高27.3%、23.9%和22.7%。产量与生育期耗水量呈显著正相关(r=0.97*)。覆盖处理中,全膜覆土穴播产量虽最高,但从产量、水分利用效率和经济效益角度综合考虑,秸秆带状覆盖优于全膜覆土穴播。因此认为,秸秆带状覆盖是一种更加高产高效、适宜在西北半干旱雨养区推广的覆盖种植方式。     

Remote sensing assessment of regional yield losses due to sub-optimal planting dates and fallow period weed management

New tools in agricultural research are needed for improved assessment of agronomic practices and their impacts on crop production. Remote sensing data acquired by satellite sensors offers great promise to complement field-based approaches, which generally suffer from small sample sizes. In this study, we used Landsat data from the Yaqui Valley, a prominent spring wheat (Triticum aestivum L.) growing region in Northwest Mexico, to investigate the effect of planting date and fallow period weeds on wheat yields. Three crops cycles were analyzed for the planting date study, while 2 years were investigated for the weed study.