不同水肥耦合条件下水稻干物质积累与分配特征

2009年5—9月在湖北省灌溉试验中心站以优质水稻新两优香4为材料,采用长期淹灌和间歇灌溉2种灌溉模式,结合3种施肥(氮及磷肥)水平F1、F2、F3,研究了不同水肥耦合条件下水稻产量形成过程和干物质积累与分配特征。结果表明,不同水肥处理下水稻各生育期干物质积累的动态变化相似,分蘖前期水稻干物质的积累量随施肥的增加而上升,到一定程度则会下降,不同灌溉模式间的差别不明显。从分蘖后期到抽穗开花期,不同水肥处理水稻干物质的积累总量均明显增大,且不同处理间差异显著,F1、F2、F3处理抽穗开花期间歇灌溉模式干物质积累量比淹灌模式分别大12.1%、22.1%、61.9%。间歇灌溉模式水稻干物质净积累量(NDMA)和群体生长速率(CGR)峰值随施肥量的增加发生改变,由出现在低肥水平(F1)的抽穗开花期至乳熟期转变为高肥水平(F2,F3)的分蘖后期至拔节孕穗期,且NDMA和CGR显著增大。不同水肥处理水稻黄熟期干物质在各器官间的分配不同,但均表现出相同趋势,即由高到低依次为籽粒、茎、叶、根。不同灌溉模式水稻的收获指数随施肥量的增加而下降,淹灌模式下收获指数下降明显,相对F1处理,F2、F3处理下分别下降12.4%、17.9%。干物质积累过程的拟合结果表明,三次曲线模型比Logistic模型的拟合精度高。     

Exploring options for water savings in lowland rice using a modelling approach

Water-saving irrigation regimes are needed to deal with a reduced availability of water for rice production. Two important water-saving technologies at field scale are alternately submerged–nonsubmerged (SNS) and flush irrigated (FI) rice. SNS allows dry periods between submerged soil conditions, whereas FI resembles the irrigation regime of an upland crop. The effects of these regimes on the water balance and water savings were compared with continuously submerged (CS) and rainfed (RF) regimes.The crop growth model ORYZA2000 was used to calculate seasonal water balances of CS, SNS, FI, and RF regimes for two locations: Tuanlin in Hubei province in China from 1999 to 2002 during summer seasons and Los Baños in the Philippines in 2002–2003 during dry seasons. The model was first parameterized for site-specific soil conditions and cultivar traits and then evaluated using a combination of statistical and visual comparisons of observed and simulated variables. ORYZA2000 accurately simulated the crop variables leaf area index, biomass, and yield, and the soil water balance variables field water level and soil water tension in the root zone.Next, a scenario study was done to analyse the effect of water regime, soil permeability, and groundwater table depth on irrigation requirement and associated rice yield. For this study historical weather data for both sites were used.Within seasons, the amount of irrigation water application was higher for CS than for any of the water-saving regimes. It was found that groundwater table depth strongly affected the water-yield relationship for the water-saving regimes. Rainfed rice did not lead to significant yield reductions at Tuanlin as long as the groundwater table depth was less than 20 cm. Simulations at Los Baños with a more drought tolerant cultivar showed that FI resulted in higher yields than RF thereby requiring only 420 mm of irrigation.The soil type determined the irrigation water requirement in CS and SNS regimes. A more permeable soil requires around 2000 mm of irrigation water whereas less permeable, heavy soil types require less than half of this amount. We conclude that water savings can be considerable when water regimes are adapted to soil characteristics and rainfall dynamics. To further optimize water-saving regimes in lowland rice, groundwater table dynamics and soil permeability should be taken into account.     

以土水势为灌溉指标的水稻节水灌溉研究

2002年5月～10月在河南省惠北试验站进行大田试验,以土水势为灌水下限控制指标,研究了不同水分胁迫条件下的中稻生物效应和水分生产率。结果表明:水分胁迫通过对不同生长阶段根、茎、叶等器官生长发育的影响和降低有效分蘖数而最终影响水稻产量。与传统灌溉相比,以土水势-30kPa为灌水下限控制指标,对产量无显著影响,且可以大大节约灌水量,提高水分生产率,是该地区中稻较为适宜的灌水制度。     

干旱环境下春小麦最优调亏灌溉制度确定

以河西绿洲灌区春小麦调亏灌溉2年的平均产量、水分利用效率、供水效率和2年后的土壤养分综合指标4个单项参评因子为参数建立单因子评判矩阵,对干旱环境下春小麦调亏灌溉制度进行了综合评价。结果表明,调亏灌溉处理的综合评价指标以HFF处理最高,其次为MFM处理,而以LLL处理最低,但所有调亏灌溉处理综合评价指标均显著高于高水分处理FFF。因此,无论是从作物生产力、水资源利用效率还是水资源和土壤养分的可持续利用方面来说,HFF处理调亏灌溉模式均因其最高的作物生产力和水分利用效率、较高的供水效率(为最大值的96.3%)及较高的土壤养分综合指标(为最大值的97.7%)而具有最高的综合评价指标,成为试区推荐的春小麦全生育期最优调亏灌溉模式,即春小麦孕穗和抽穗期及灌浆—生理成熟期均高水分处理(65%~70%田持)而拔节期重度水分调亏(45%~50%田持),其灌溉定额为440 mm左右(包括晚秋季储水灌100 mm)。     

不同水分条件下旱稻磷效应及水分生产率

研究了4种灌溉水平的旱稻磷素效应和水分生产率,结果表明：水分胁迫并未降低旱稻根系含磷量,而且在严重水分胁迫下有所增加,但根系磷素累积量在营养生长阶段-30 kPa水分胁迫处理显著低于-10 kPa处理,中后期随水分胁迫程度加深而降低.在营养和生殖生长阶段旱稻茎含磷量和磷素累积量随水分胁迫程度加深而降低.分蘖期-10 kPa处理叶片含磷量最高,分蘖期、幼穗分化期和乳熟期-10 kPa处理叶片磷素累积量最大.穗含磷量以-10 kPa处理最高.与其他处理相比,-30 kPa处理产量虽然稍低,但可以提高水分生产率和磷素效率.     

Remote sensing of biotic and abiotic stress for irrigation management of cotton

The applicability of commercially available remote sensing instrumentation was evaluated for site-specific management of abiotic and biotic stress on cotton (Gossypium hirsutum L.) grown under a center pivot low energy precision application (LEPA) irrigation system. This study was conducted in a field where three irrigation regimes (100%, 75%, and 50% ET_c) were imposed on areas of Phymatotrichum (root rot) with the specific objectives to (1) examine commercial remote sensing instrumentation for locating areas showing biotic and abiotic stress symptomology in a cotton field, (2) compare data obtained from commercial aerial infrared photography to that collected by infrared transducers (IRTs) mounted on a center pivot, (3) evaluate canopy temperature changes between irrigation regimes and their relationship to lint yield with IRTs and/or IR photography, and (4) explore the use of deficit irrigation and the use of crop coefficients for irrigation scheduling. Pivot-mounted IRTs and an IR camera were able to differentiate water stress among irrigation regimes. The IR camera distinguished between biotic (root rot) and abiotic (drought) stress with the assistance of groundtruthing. The 50% ET_c regime had significantly higher canopy temperatures than the other two regimes, which was reflected in significantly lower lint yields when compared to the 75% and 100% ET_c regimes. Deficit irrigation down to 75% ET_c had no impact on lint yield, indicating that water savings were possible without reducing yield.     

稻麦轮作区秸秆还田对水稻土结构的影响

为探明稻麦轮作区秸秆还田对水稻土结构的影响,依托常熟农业生态试验站25 a的长期定位试验,研究秸秆还田对水稻土容重、团聚体分布及稳定性、团聚体有机碳分布和孔隙大小分布的影响。试验设不施肥(CK)、单施化肥(NPK)、化肥和半量秸秆还田(NPKS1)、化肥和全量秸秆还田(NPKS2)等处理。采集各小区耕层水稻土,通过湿筛的方法测定团聚体分布及稳定性,通过X射线CT扫描和图像处理得到孔隙结构信息。结果显示,与CK相比,单施化肥(NPK)能显著提高土壤有机碳含量、降低土壤容重,对团聚体分布及稳定性、大孔隙度(大于0.032 mm)、孔隙大小分布没有显著影响。与NPK处理相比,秸秆还田(NPKS1、NPKS2)分别使土壤容重降低14.0%和19.4%,有机碳含量提高10.0%和23.1%,但是对团聚体分布及稳定性影响不显著;化肥和半量秸秆还田(NPKS1)对大孔隙度和孔隙大小分布没有显著影响,化肥和全量秸秆还田(NPKS2)的大孔隙度(大于0.032 mm)提高了110.6%,各当量孔径范围的孔隙度也明显提高(大于1.5 mm除外)。结果表明,经过25 a的秸秆还田,稻麦轮作区全量秸秆还田能够降低土壤容重,增加土壤有机碳含量和各级团聚体中有机碳含量,增大土壤总孔隙度和大孔隙度,改善水稻土的物理结构;而半量秸秆还田没有显著改善水稻土的孔隙结构。     

Water productivity of contrasting rice genotypes grown under water-saving conditions in the tropics and investigation of morphological traits for adaptation

Alternate wetting and drying (AWD) irrigation in lowland rice has been successfully implemented in farmers’ fields to reduce water input, and thereby increasing water productivity. Reported effects on grain yield were, however, contradictory: yield was reduced, maintained, or even increased when compared with continuously flooded (CF) conditions. This study was conducted in heavy clay soil to investigate yield variation among a range of genotypes grown under AWD and to determine some aboveground traits related to crop adaptation. The effect of AWD on grain yield, with a critical threshold of soil water potential for irrigation fixed at −30 kPa, varied among the 10 genotypes evaluated. Two adapted genotypes were identified with similar grain yield under CF and AWD in both experimental seasons. The grain yield of the aerobic-adapted cultivar included in the study was also maintained under AWD, however, its yield was comparatively low. The reduction in grain yield of the non-adapted genotypes ranged from 9 to 13% in the 2006 dry season and from 6 to 17% in the 2008 dry season. None of the yield components could explain by itself the variability in genotype response: in adapted genotypes, grain yield was maintained because of compensation from or maintenance of yield components, whereas, in non-adapted genotypes, grain yield reduction was not due to the decrease of one component only. Modified biomass partitioning appeared as a main driver for adaptation to AWD: adapted genotypes were characterized by larger sink size at flowering, and weaker stems and less unfilled grain number at maturity, suggesting an increase in the sink strength of the filling spikelets. The aboveground traits identified here will be of great help to further increase water productivity under the AWD strategies set up previously by IRRI water scientists.     

Urban agriculture, using sustainable practices that involve the reuse of wastewater and solid waste

This study proposes a safe method for the disinfection of wastewater destined for reuse in urban agriculture. It also discusses the year-round production of fresh vegetables in confined urban spaces, using sustainable practices that involve the recycling and reuse of waste while at the same time saving water. To address the aforementioned problems, this study aimed to determine the efficiency of applying organoponic techniques to urban crops, using selected organic compounds and recyclable solid waste products, plus home-made organic fertilizers and treated wastewater. The results obtained demonstrate that in addition to disinfecting the wastewater, ozone contributes oxygen and nutrients to the soil, thereby reducing the need for chemical fertilizers. Ozone also reduces the risk of infection by eliminating highly pathogenic micro-organisms, and increases the rate of plant growth such as: radishes (Raphanus sativus L.), tomatoes (Lycopersicum esculentum), spearmint (Mentha piperita), camomile (Matricaria recutita), Romaine lettuce (Lactuca sativa) and Chinese cabbage (Brassica rapa). Great benefits can therefore be derived from employing these urban agriculture techniques because, in addition to putting to good use waste products that are generated by the ton, these techniques also produce quality food plants that are 100% organic.     

Synthetic and organic mulching and nitrogen effect on winter wheat (Triticum aestivum L.) in a semi-arid environment

Field experiments were conducted in 2002-2003 and 2003-2004 to evaluate the relative performance of synthetic (black polyethylene) and organic (paddy husk and straw) mulches on soil and plant water status vis-a-vis N uptake in wheat in a semi-arid environment of India. Scope of better utilization of soil moisture was documented through all the mulches, especially during initial crop growth stages, when the moisture content was 1-3% higher in mulches. Soil temperature was more moderate under organic mulches. Paddy husk recorded significantly higher plant biomass, while the effect of mulching in enhancing root growth was clearly documented. Organic mulches produced more roots (25 and 40% higher root weight and root length densities compared to no-mulch) in sub-surface (>0.15 m) layers, probably due to greater retention of soil moisture in deeper layers and relatively narrow range of soil temperature changes under these systems. Incremental N dose significantly improved all the plant parameters in both mulch and no-mulch treatments. Grain yield was 13-21% higher under mulch and so with increasing N levels. Nitrogen uptake was higher in organic mulches and also with higher N doses, while polyethylene mulch showed mixed trend. Mulches were effective in reducing 3-11% crop water use and improved its efficiency by 25%. Grain yield and biomass were well-correlated with leaf area index (r = 0.87 and 0.91, respectively) and water use was better correlated with root length than its weight. Results indicated substantial improvement in water and N use efficiency and crop growth in wheat under surface mulching, and the organic mulches, especially rice husk performed better than synthetic mulches.     

Tillage and irrigation effects on crop yields and soil properties under the rice-wheat system in the Indian Himalayas

Conservation tillage systems generally improve soil organic C (SOC), plant available water capacity (PAWC), aggregation and soil water transmission. A field experiment was conducted for 4 years (2001-2002 to 2004-2005) to study tillage (conventional tillage (CT) and zero tillage (ZT)) systems. The selected irrigation treatments were at four levels (I₁: pre-sowing (PS), I₂: PS + active tillering (AT)/crown root initiation (CRI), I₃: PS + AT/CRI + panicle initiation (PI)/flowering (FL), and I₄: PS + AT/CRI + PI/FL + grain filling (GF)), applied at the critical growth stages on rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Their effects on direct seeded rice productivity and soil properties (SOC and selected physical properties) after rice and wheat harvest were investigated. Soil organic C contents after rice and wheat harvest in the 0-15 cm soil depth were higher under ZT than under CT. Soil organic C increased significantly with I₂ over I₁ for both crops and with I₄ over I₂ for the wheat crop. The PAWC was significantly higher with ZT than CT. Zero tilled and frequently irrigated plots showed enhanced infiltration characteristics (infiltration rate, cumulative infiltration and sorptivity) and saturated hydraulic conductivity. Both direct seeded rice and wheat yields were not significantly different in the plots under ZT and CT. There was a significant increase in both rice and wheat yields in the plots under I₂ over I₁. However, water use efficiency between irrigation treatments was not significantly different. Hence, under direct seeded rice-wheat system in a sandy clay loam soil of the sub-temperate Indian Himalayas, farmers may adopt ZT with two irrigations in each crop for optimum resource conservation.     

A comparison between low-cost drip irrigation,conventional drip irrigation,and hand watering in Nepal

Access to irrigation water is a critical element in meeting the food demands of a rapidly increasing population in the Middle Mountains of Nepal. The recent introduction of low-cost drip irrigation (LCDI) to Nepal represents an affordable means of expanding irrigation into rainfed areas, thereby increasing land productivity. This study presents a comparison of the effects on soil volumetric water content and cauliflower yield of three irrigation methods (LCDI, conventional drip irrigation (CDI), and hand watering) operated under three different irrigation regimes in the Jhikhu Khola Watershed, Nepal. Irrigation regime R₁ supplied only half of the estimated crop water requirement, characterized by small volumes applied on alternate days. The other two irrigation regimes (regimes R₂ and R₃), supplied the full estimated crop water requirement, however differed in application timing. Small volumes were applied frequently (daily) under regime R₂, whereas in regime R₃, greater water volumes were applied less frequently (alternate days for the majority of experiment). Although differences in the soil volumetric water content (SVWC) were present between the irrigation methods, differences were not consistent between the three irrigation regimes. Regardless of irrigation regime, cumulative cauliflower yields were lowest under conventional drip irrigation. In contrast, there were significant differences in cauliflower yield between LCDI and hand watering between irrigation regimes. Irrigation regime R₁ resulted in lower SVWC and lower cumulative yields than regimes R₂ and R₃, however, water-use efficiency was greater under regime R₁ than under regimes R₂ and R₃. These results suggest that LCDI and hand watering are both viable options to increase food production in water scarce, small-scale farming in Nepal, however, long-term economic and labour benefits are greater under LCDI.     

Root growth, water potential, and yield of irrigated rice

Root length density (Lv), leaf water potential (Ψ leaf) and yield of rice were studied in 1983 and 1984 on a Phool bagh clay loam (Typic Haplaquoll) and on a Beni silty clay loam (Aquic Hapludoll) in the Tarai region of Uttar Pradesh under naturally fluctuating shallow (0.07–0.92 m) and medium-depth (0.13–1.26 m) water table conditions with six water regimes ranging from continuous submergence under 0.05 m ± 0.02 m (Ic) to completely rainfed (Io). In irrigation treatments, Ic1, Ic3, Ic5, and Ic7, 0.07 m irrigation was applied on days 1, 3, 5, and 7 respectively, after the disappearance of ponded water. Maximum rooting depth (0.55 m in the shallow and 0.65 m in the medium-depth water table) was attained at the dough stage (125 days after transplanting) and was more strongly influenced by fluctuations in water table depth than by the water regime. For wet regimes (Ic1–Ic5), roots were concentrated at and above the water table interface and had greater horizontal development, whereas in dry regimes, (Ic7 and Io) they were concentrated in lower horizons and had a more vertical distribution. Like Lv, Ψ leaf was not significantly affected by water regime up to 90–95 days after rice transplanting but was significantly affected thereafter, except for Lv beneath 0.2 m–0.25 m. Grain yields with irrigation treatments Ic1 and Ic3 under shallow and Ic1 under medium-depth water table conditions were not significantly different from those under continuous submergence, but there was a (nonsignificant) trend to lower yield with less water. However, differences among the wet regimes (Ic, Ic1, and Ic3) were small (141–490 kg ha^–1) under shallow and 413–727 kg ha^–1 under medium-depth water table conditions. The results demonstrate that optimum yield (5500–6000 kg ha^–1) could be obtained under Tarai conditions by adopting an intermittent irrigation schedule of 3–5 days after the disappearance of ponded water under shallow, and of 1–3 days under medium-depth water table conditions, in place of continuous submergence. Received: 26 February 1996     

有机肥与化肥配施对茶叶生长和土壤养分的影响

设置醋糟有机肥和化肥不同配比的5个处理:100%有机肥、70%有机肥+30%化肥、50%有机肥+50%化肥、30%有机肥+70%化肥以及100%化肥,并以不施肥为对照(CK),研究不同肥料配比对春茶生长、产量、品质及茶园土壤养分含量的影响。结果表明,不同施肥处理都有促进春茶产量、品质和土壤养分含量的作用,但处理之间差异较大。增产作用以70%有机肥+30%化肥的处理最显著,比对照平均增产276.91%,30%有机肥+70%化肥的处理次之,50%有机肥+50%化肥的处理居中;茶叶的新梢长、叶面积、芽密度、百芽质量等生长指标,以及茶多酚、氨基酸、咖啡碱、水浸出物等品质指标都以70%有机肥+30%化肥的处理为最高。茶园土壤中有机质、碱解氮、速效磷和速效钾含量均随有机肥在肥料中所占比例的增加而增加,即以100%有机肥的处理最高,70%有机肥+30%化肥的处理次之,但两者差异不显著。综合分析表明,70%有机肥+30%化肥的配施是值得在茶园推广应用的优化方案。     

Potential impacts of water harvesting and ecological sanitation on crop yield, evaporation and river flow regimes in the Thukela River basin, South Africa

In this study we explore the potential impacts of two strategies, namely in situ water harvesting (in situ WH) and fertilisation with stored human urine (Ecosan), to increase the water and nutrient availability in rain-fed smallholder agriculture in South Africa's Thukela River basin (29,000 km²). We use the soil and water assessment tool (SWAT) to simulate potential impacts on smallholder maize yields, river flow regimes, plant transpiration, and soil and canopy evaporation during 1997-2006. Based on the results, the impacts on maize yields are likely to be small with in situ WH (median change: 0%) but significant with Ecosan (median increase: 30%). The primary causes for these effects are high nitrogen stress on crop growth, and low or untimed soil moisture enhancement with in situ WH. However, the impacts vary significantly in time and space, occasionally resulting in yield increases of up to 40% with in situ WH. Soil fertility improvements primarily increase yield magnitudes, whereas soil moisture enhancements reduce spatial yield variability. Ecosan significantly improves the productivity of the evaporative fluxes by increasing transpiration (median: 2.8%, 4.7 mm season⁻¹) and reducing soil and canopy evaporation (median: −1.7%, −4.5 mm season⁻¹). In situ WH does not generally affect the river flow regimes. Occasionally, significant regime changes occur due to enhanced lateral and shallow aquifer return flows. This leads to higher risks of flooding in some areas, but also to enhanced low flows, which help sustain aquatic ecosystems in the basin.     

Assessment of drip and flood irrigation on water and fertilizer use efficiencies for sugarbeets

Mismanagement of nitrogenous fertilizers has caused serious nitrate (NO₃) contamination in many flood-irrigated regions of the western US. Low-volume irrigation practices, such as drip irrigation, can offer an alternative approach for controlling NO₃ leaching and agricultural water use. The objectives of this study were to compare NO₃ movement through soils under flood and drip irrigation practices for sugarbeet production, and to evaluate the agronomic feasibility of implementing drip irrigation. A field experiment was conducted during the sugarbeet (Beta vulgaris L.) growing seasons of 1996 and 1997 in southeastern Wyoming, where NO₃ contamination is a continued concern and sugarbeet is a major cash crop. Three drip irrigation regimes, corresponding to 20, 35, and 50% water depletion of field capacity (designated as D1, D2, and D3, respectively), were compared against flood irrigation. The irrigation plots were treated with 112, 168, and 224 kg N ha⁻¹ (designated as F₀, F₁, and F₂, respectively). Sugarbeet (SB) yields and sugar contents under drip irrigation were higher (3–28%) than those with flood irrigation; yields and sugar contents for the drip systems were in the order of D1>D2>D3. For all of the irrigation applications, there was an increasing trend in yields with increasing fertilizer rates. Drip regime resulted in greater residual soil NO₃ (RSN) for both 1996 and 1997 seasons as compared to flood practices. Values of RSN in both years followed the trend: F₂>F₁>F₀. Soil NO₃ in all three drip regimes was higher (1.6–2.4 times) than that with flood irrigation. In the overall root zone, NO₃ concentrations between D1 and D2 were comparable, whereas both of those levels were lower than D3. Greater NO₃ concentrations with D3 were observed at all depths. The amount of applied irrigation water with the drip system was lower than that for flood irrigation. Agronomic water use efficiency (WUE) and fertilizer use efficiency (FUE) for drip irrigation were always higher than those for flood irrigation. In 1996, WUE and FUE maintained an order of D1>D2>D3. There was a decreasing pattern in FUE values with increasing fertilizer rates. The overall results indicated that SB production could be sustained with lower water and fertilizer use by using drip irrigation. The p-values (≤0.05), based on both F-test (p_f) and two-tailed student’s t-test (p_t), suggested a significant difference between the yield means obtained under drip and flood irrigation practices. As compared to the flood irrigation, the least p-values were obtained with D1 followed by D2 and D3, respectively, thus, confirming that D1 was the most effective treatment. The p-values for SB yields under comparative fertilizer treatments and same drip application showed no significant difference between the means, thus, suggesting the feasibility of using lower fertilizer rate while sustaining the targeted yield under drip irrigation. The comparative estimation of water losses by drainage between flood and drip irrigation suggested that the later practice reduced the quantity of water leaching beyond the root zone. Among the three drip treatments, the lowest drainage amount was observed with D1 as a result of its higher irrigation frequency and smaller quantity of water input during each application.     

Irrigation, tillage and mulching effects on soybean yield and water productivity in relation to soil texture

Depleting groundwater resources in Indian Punjab call for diversifying from rice to crops with low evapo-transpiration needs and adopting water-saving technologies. Soybean offers a diversification option in coarse- to medium-textured soils. However, its productivity in these soils is constrained by high soil mechanical resistance and high soil temperature during early part of the growing season. These constraints can be alleviated through irrigation, deep tillage and straw mulching. This 3-years field study examines the individual and combined effects of irrigation, deep tillage, and straw mulching regimes on soybean yield and water productivity (WP) in relation to soil texture. Combinations of two irrigation regimes viz., full irrigation (I_f), and partial irrigation (I_p) in the main plot; two tillage regimes viz., conventional-till (CT)-soil stirring to 0.10 m depth, and deep tillage (DT)-chiseling down to 0.35 m depth followed by CT in the subplot; and two mulch rates viz., 0 (M₀) and 6 t ha⁻¹ (M) in the sub-subplot on two soils differing in available water capacity were evaluated.Seed yield was greater in the sandy loam than in the loamy sand reflecting the effects of available water capacity. Irrigation effects were greater on loamy sand (40%) than on sandy loam (5%) soil. Deep tillage benefits were also more on loamy sand (14%) compared to sandy loam (5%) soil. Yield gains with mulching were comparable on the two soils (19%). An evaluation of interaction effects showed that mulching response was slightly more in I_p (20%) than in I_f regimes (17%) in the sandy loam; while in the loamy sand, mulching gains were comparable (18-19%) in both irrigation regimes. Benefits of deep tillage in the loamy sand soil were more in I_p (20%) than in I_f regimes (17%). Deep tillage and straw mulching enhanced WP (ratio of seed yield/water use) from 1.39 to 1.97 kg ha⁻¹ mm⁻¹ in I_p regime, and from 1.87 to 2.33 kg ha⁻¹ mm⁻¹ in I_f regime in the loamy sand soil. These effects on WP were less in the sandy loam soil with greater available water capacity. Yield and WP gains are ascribed to deeper and denser rooting due to moderation of soil temperature and water conservation with straw mulching and tillage-induced reduction in soil mechanical resistance. Root mass in CTM₀, CTM, DTM₀ and DTM was 2.79, 5.88, 5.34 and 5.58 mg cm⁻² at pod-filling in the loamy sand soil. Comparable yield responses to deep tillage or mulching in the loamy sand soil suggest that either of the options, depending on their cost and availability considerations, can be employed for improving soybean yield and water productivity.     

Root growth, water potential and yield of irrigated wheat

Root length density (LV), mid-day leaf water potential (Ψ _leaf) and yield of wheat were studied in 1983 – 1984 and 1984 – 1985 on a Phoolbagh clay loam (Typic Haplaquoll) and on a Beni silty clay loam (Aquic Hapludoll) in the Tarai region of Uttar Pradesh under naturally fluctuating shallow (0.4 – 0.9 m, SWT) and medium-depth (0.8 – 1.3 m, MWT) water table conditions with six water regimes: rainfed (I₀); irrigation at cown root initiation (I₁); at crown root initiation and milk (I₂); at crown root initiation, maximum tillering and milk (I₃); at crown root initiation, maximum tillering, flowering and milk (I₄); and at crown root initiation, maximum tillering, flowering, milk and dough (I₅). Maximum rooting depth (0.8 m under SWT and 1.05 m under MWT conditions) was attained at the dough stage (115 days after sowing, DAS) and was more strongly influenced by fluctuations in water table depth than by the water regime. For wet regimes (I₂– I₅), roots were concentrated at and above the water table interface and had greater horizontal development, whereas in dry regimens (I₀ and I₁), due to deficient moisture conditions in the upper soil layer (0.45 m) they invaded lower horizons and had a greater vertical distribution Ψ _leaf was not significantly affected by water regime (I₁– I₅) up to 94 DAS during a wet year (1983 – 1984) and up to 74 DAS during a dry year (1984 – 1985), but was significantly affected thereafter. Grain yields with water regimens I₁– I₅ during a wet year and for the I₂– I₅ treatments during a dry year at either water table depth were not significantly different, but there was a (non-significant) trend to lower yield with increasing soil water deficit. Under SWT in I₂, the average grain yield wsa 5130 kg ha^–1 and under the I₃ regime, 5200 kg ha^–1. Likewise, under MWT in I₃, it was 5188 kg ha^–1 and under the I₄ regime, 5218 kg ha^–1. The results indicate that application of irrigation of more than 120 and 180 mm under SWT and MWT conditions, respectively, did not raise yield. Irrigation given as per schedule I₂ under SWT and I₃ under MWT conditions in the Tarai situation, appears to be more effective than a very wet regime (I₅). Received: 9 December 1997     

Linking hydro-meteorological factors to the assessment of nutrient loadings to streams from large-plotted paddy rice fields

Excessive nutrient loadings from rice paddy fields has been a great concern in Korea as rice paddy area spans over 1,153,000 ha, which covers approximately 60% of the total agricultural land area in Korea. The principal tasks of this study included undertaking work to better identifying the scope of the nutrient loadings from paddy fields to assess their adverse effects. Hydro-meteorological factors, rainfall and surface discharge, were considered as the major driving forces of nutrients into the water. A Generalized Regression Neural Network (GRNN) model was applied and its capability evaluated to predict the nutrient loading into the neighboring water. The 15 ha paddy fields surrounded by drainage and irrigation channels were chosen as a study area. Field data, such as rainfall, quantities of irrigation and discharge water, and nutrient contents (total nitrogen (T-N) and total phosphorus (T-P)) from two different water sources, were obtained throughout the study period. Simulation results showed that surface discharge had a positive correlation with rainfall (R = 0.84). In addition, the resulting predictions for nutrient concentrations corresponding to surface discharge were varied (R = 0.72 and 0.40 in total nitrogen and total phosphorus, respectively). This study found that both natural and artificial variations of nutrient contents in irrigation streams were significantly influenced the model results of nutrient predictions. Therefore, the nutrient loadings into the neighboring water can be accurately described with a more comprehensive and sufficient representation of both environmental inputs and hydrological processes.     

气候变化对水稻生长影响的模拟分析

运用大气环流模式(HadCM3)和统计降尺度模型(SDSM)模拟了漳河地区不同排放情景下(A2、B2)的未来气候变化规律,结合ORYZA2000模型分析了不同气候情景模式下水稻生长的差异,从水稻生产的角度探讨了不同水肥耦合调控方式对各种情景的适用性。结果表明,SDSM对温度、降雨、日照都有较好的模拟效果。在A2情景下,水稻产量减少,灌溉定额和氮肥吸收率增加;在B2情景下,水稻产量较高,水分和氮肥利用率较高,水稻生长状态较好;增加CO2质量分数可以提高产量,同时减少了不同水肥管理模式下产量的差异。间歇灌溉和3次追肥的水肥耦合调控方式对各种气候情景的适用性最好。