Evaluation of alternative tillage and crop establishment methods in a rice–wheat rotation in North Western IGP

The rice–wheat rotation covering 13.5 million ha in the Indo-Gangetic Plains is vital for food security. Its sustainability is at risk as the current production practices are inadequate resulting in high cost of cultivation and inefficient use of inputs (i.e. water, labor and energy). In a field study, we evaluated resource conserving and cost-saving alternative tillage and crop establishment options with an aim to improve system productivity and efficiency. Treatments included transplanting and direct-seeding of rice after reduced and no-tillage, followed by wheat after no-tillage. Conventional-tilled (puddled) transplanted rice followed by conventional-tilled wheat was included as a current practice. Rice yields of transplanted rice were similar irrespective of tillage/puddling. However, both dry and wet direct-seeded rice yielded 0.45–0.61 Mg ha⁻¹ lower than puddled transplanted rice. Wheat yield after no-tillage was either higher or equivalent to conventional practice. Wheat provided more economic return (US $35 ha⁻¹) than rice. No-till wheat was 6% more profitable than the conventional practice (T1). Rice transplanting with or without puddling had similar water application but dry direct-seeded rice had 10–12% lower and wet direct-seeded rice 20–24% higher. Machine labor without tillage was lower by maximum of 51 and 43% in rice and wheat, respectively. Similarly, human labor was also 9–16% lower in no-till rice compared to other practices. Two years results consistently showed $35 more net income when rice was transplanted without puddling than that of conventional practice. Direct-seeded/un-tilled rice had variable response in 2 years; US $16 more in year 1 and similar in year 2 to the puddled transplanted rice. Direct-seeded or transplanted rice after no-tillage can be more efficient and profitable alternatives to current practice (puddled transplanted rice), however, require further refinement in areas of cultivar development for no-till direct-seeding condition, nutrient, water and weed management to harness maximal potential.     

Spatial variation of infiltration rate and compactness in paddy fields

Percolation loss of water in rice fields is a major cause of low water use efficiency. Variation of infiltration rate and soil compactness in four paddy fields (with clay, silty clay, clay loam, and loam textures) was investigated in northern Iran. In each field, in longitudinal and transverse directions, points located 0.5, 2.5, 6.5, 12.5, … m from the bunds were selected and water infiltration rate and resistance to penetration of a pocket penetrometer were measured. The results showed that in clay soil, average final infiltration rate (f _c) in longitudinal direction, transverse direction, and center of the field was 0.216, 0.136, and 0.08 cm day⁻¹, respectively. The f _c for loamy soil was 2.77, 2.32, and 0.409 cm day⁻¹, respectively. Similar differences were observed in the other two soil textures. In general, effect of direction of the field for measuring infiltration rate was not statistically significant. Loam and clay loam soils, with resistance to penetration of 0.37 and 0.33 kg cm⁻², were not significantly different. But, clay and silty clay soils with resistance to penetration of 0.25 and 0.14 kg cm⁻² were significantly different (P < 0.05). Resistance to penetration of the penetrometer was not affected significantly (P < 0.05) by direction of measuring this parameter in the field. The conclusion is that if measured soil physical properties in a paddy field are going to be representative of the whole field, they should be measured at different locations, especially near the bunds. Another strategy for obtaining a representative infiltration rate or compactness for a paddy field is uniform puddling of the field.     

Effects of crop establishment techniques on weeds and rice yield

Field and pot studies were conducted to evaluate the effects of seven rice establishment techniques {puddling transplanting (PT), no tillage transplanting (NTT), puddling drum wet seeding (PDWS), no tillage drum wet seeding (NTDWS), conventional tillage dry drilling (CTDD), furrow irrigated raised beds system dry drilling (FIRBSDD), and no-tillage dry-drilling (NTDD)} and water submergence stress on weeds and rice yield. The highest yield and least weed abundance were in the PT treatment. The direct seeded rice (DSR), both dry and wet exhibited severe weed infestation, and compared to transplanting showed reduced yield both in the presence and absence of weeds. The yield losses due to weeds in the DSR treatments ranged from 91.4 to 99.0%, compared to 16.0 and 42.0% in the transplanting treatments (PT and NTT). Weeds, including Cyperus rotundus L., Dactyloctenium aegyptium (L.) Willd., Digera arvensis Forsk., Phyllanthus niruri L., and Trianthema portulacastrum L. which were found in the un-puddled DSR treatments were absent in the puddled plots, particularly the PT treatments. In pot studies, continuous water-submergence (2.5 cm) for 20 days reduced the emergence of C. rotundus, D. aegyptium, T. portulacastrum, and Echinochloa crus-galli (L.) Beauv. by 99.4, 100, 100, and 24.4%, respectively, compared to alternate wetting–drying. In farmer's field studies, when compared to the PT treatments, the DSR treatments exhibited lower yields (15.8%) with coarse varieties (HKR-47 & IR-64), but fine cultivars (Sharbati & PB-1) exhibited similar yields under both systems. In view of the shortage of labour for manual transplanting, there is a need to develop suitable cultivars for aerobic system conditions (unpuddled DSR and NT machine-transplanting).     

Spatial variability of soil saturated hydraulic conductivity in paddy field in accordance to subsurface percolation

Insufficient puddling with inappropriate implements or imprecise time/intensity may alter saturated water flow in paddy soil spatially or temporary due to change in aggregate size distribution, dry bulk density, saturated hydraulic conductivity, and percolation rate of the soil. In this study, spatial variability of saturated hydraulic conductivity (K _s), a key parameter of the saturated water flow, in Fuchu Honmachi paddy plot (100 m × 28 m) was characterized based on dielectric or ADR dry bulk density (ρ_b-ADR) with help of non-similar media concept (NSMC) and geostatistics model to meet its correlation to subsurface percolation. A 100 cc core and an ADR data were sampled from each sub-plot (7 m × 7.5 m), and then were used for measuring and predicting ρ_b and K _s. The predicted data agreed with the measured ones, in which they fitted well the x = y line with RMSE of 0.029 cm³ cm⁻³ (R ² = 0.68), 0.027 g cm⁻³ (R ² = 0.71) (ρ_b), and 0.098 cm d⁻¹ (R ² = 0.45) for θ, ρ_b, and K _s, respectively. The predicted ρ_b and K _s had similar trend in spatial variability to the measured ones particularly within the distance of 46.3–51.9 m and 26.2–27.9 m, respectively. The spatial variability of the predicted K _s coincided to that of the subsurface percolation rate, in which they had similar distance of dependence. The results indicated that the presenting method can be reasonably accepted.     

The implications of land preparation, crop establishment method and weed management on rice yield variation in the rice-wheat system in the Indo-Gangetic plains

The implications of adopting alternative seeding methods for rice and wheat establishment were examined at three geographically separate sites in the rice-wheat system of the Indo-Gangetic plains, across northern India. Rice yields in cultivated plots, established by either wet or dry seeding methods, were evaluated in comparison to yields from zero-tillage plots and under conventional transplanting methods. In the same trials, the effects of crop establishment methods in wheat were assessed both on wheat yields and rice yields. Rice crop establishment methods markedly influenced the emerging weed flora and attainable yields were measured in relation to intensity of weed management. Over four years, average rice grain yields in the absence of weed competition were greatest (6.56 t ha⁻¹) under wet seeding (sowing pre-germinated rice seed on puddled soil), and similar to those from transplanted rice (6.17 t ha⁻¹) into puddled soil, and dry seeded rice after dry soil tillage (6.15 t ha⁻¹). Lowest yields were observed from dry seeded rice sown without tillage (5.44 t ha⁻¹). Rice yield losses due to uncontrolled weed growth were least in transplanted rice (12%) but otherwise large (c. 85%) where rice had been sown to dry cultivated fields or to puddled soil, rising to 98% in dry seeded rice sown without soil tillage. Weed competition reduced multiple rice yield components, and weed biomass in wet seeded rice was six-fold greater that in rice transplanted into puddled soil and twice as much again in dry seeded rice sown either after dry tillage or without tillage. Wheat grain yields were significantly higher from crops sown into tilled soil (3.89 t ha⁻¹) than those sown without tillage (3.51 t ha⁻¹), and also were elevated (5% on average) where the soil had been dry cultivated in preparation for the previous rice crops rather than puddled. The method of wheat cultivation did not influence rice yield. Soil infiltration rates in the wheat season were least where the land had been puddled for rice (1.52 mm h⁻¹), and greater where the soil had been dry-tilled (2.63 mm h⁻¹) and greatest after zero-tillage (3.54 mm h⁻¹).These studies demonstrated at research managed sites across a wide geographic area, and on farmers’ fields, that yields of dry seeded rice sown after dry cultivation of soil were broadly comparable with those of transplanted rice, providing weed competition was absent. These results support the proposition that direct seeding of rice could provide an alternative to the conventional practice of transplanting, and help address rising costs and threats to sustainability in the rice-wheat rotation. Further, analysis of patterns of long-term rainfall data indicated that farmers reliant on monsoon rainfall could prepare fields for dry direct seeded rice some 30 days before they could prepare fields for either transplanting or seeding with pre-germinated seed. Dry, direct seeding of rice contributes a valuable component of an adaptive strategy to address monsoonal variability that also may advance the time of wheat establishment and yield. Whilst the results illustrate the robustness, feasibility and significant potential of direct seeded rice, they also highlight the critical nature of effective weed control in successful implementation of direct seeding systems for rice.     

Effect of tillage intensity on population densities of Heterodera glycines in intensive soybean production systems

The effects of tillage on Heterodera glycines, the most important yield-reducing pathogen of soybean in the U.S., were examined in a long-term tillage and crop sequence study initiated in 1975 on a mollisol at Purdue University. Population densities of H. glycines were monitored under corn–soybean rotation and soybean monoculture in 2003 and 2004. Tillage treatments included: (A) fall moldboard plow + spring secondary tillage; (B) fall chisel plow + spring secondary tillage; (C) ridge tillage; and (D) no-tillage. In both years in the rotational plots, final population densities of H. glycines were proportional to tillage intensity. Under both soybean and corn rotation crops, highest population densities were observed with plowing + secondary tillage and lowest population densities were detected under no-tillage. In 2004, population densities in monoculture soybean soil declined with depth intervals in layers of 0–10, 10–20, and 20–30-cm depth under no-till, but not in plowed plots. Multiple regression analysis determined that the stratification of nematode population densities was strongly correlated to penetrometer resistance and potassium concentration of the soil. Tillage seemed to affect population densities of H. glycines by modification of the soil physical parameters in corn–soybean rotation plots. Reducing tillage intensity was beneficial in reducing population densities of H. glycines in rotational soils. Thus, the choice of tillage system can reduce the risk for damage by this widely distributed pathogen.     

Water balance and rice growth responses to direct seeding,deep tillage,and landscape placement: Findings from a valley terrace in Nepal

For maximizing water retention and attaining high yields, transplanting into puddled soil (TPR) is often considered the optimal method of rice (Orzya sativa L.) establishment. Alternative management techniques like direct seeding (DSR) and deep tillage have been proposed as mechanisms to improve soil physical properties for subsequent dry-season crops, but the risks to rice are uncertain. In this full factorial study on a valley terrace in Nepal, the influence of tillage (shallow—T₁, deep chisel—T₂, deep chisel + moldboard plough—T₃) and establishment practice (TPR, DSR) on the field water balance and rice performance were evaluated in two adjacent landscape settings (terrace edge “upland”, central terrace “lowland”). Although deep tillage had only modest influences on seepage and percolation (SP) rates in both years (Y₁, Y₂), landscape placement and establishment practice had significant implications for the water balance (e.g. Y₂ SP cm day⁻¹: TPR-lowland = 1.6, DSR-lowland = 2.3, TPR-upland = 4.1, DSR-upland = 6.1). During low rainfall periods, however, soil water potential and drought vulnerability were governed solely by landscape placement. Despite water balance differences, there was little evidence that rice rooting behavior was substantially modified by landscape or establishment method. Weed biomass was higher in DSR, but was uncorrelated with water balance and productivity trends. In Y₁, lower SP rates and more days with continuous flooding were positively associated with rice productivity. DSR yields were significantly lower than TPR in both landscape positions, with the lowland outperforming the upland (Y₁ mt ha⁻¹: TPR-lowland = 6.4, DSR-lowland = 5.2, TPR-upland = 5.7, DSR-upland = 4.7). To determine if N dynamics were contributing to productivity differences, fertilizer nitrogen was increased from 120 to 150 kg N ha⁻¹ in Y₂. Results suggest that DSR performance is comparable – and landscape less important – if nitrogen is non-limiting (Y₂ mt ha⁻¹: TPR-lowland = 6.9, DSR-lowland = 6.5, TPR-upland = 7.0, DSR-upland = 6.5); no aspect of the field water balance was associated with yield variability in Y₂. For direct seeding in N-deficient farming systems, landscape criteria may prove useful for minimizing production risks by identifying field areas with lower SP rates.     

半湿润区秸秆还田及耕作技术对土壤水分、玉米光合特性及产量的影响

研究土壤水分、玉米光合特性及产量对秸秆不同还田耕作技术的响应,为半湿润区水分、光能高效利用及玉米增产栽培模式提供理论依据。2018和2019年,采用秸秆还田和土壤耕作相结合的方法,设置秸秆离田旋耕起垄（CK）、秸秆深翻还田（SP）、免耕秸秆覆盖还田（SC）、秸秆覆盖深松（SS）4个处理。研究结果表明,2018和2019年各生育时期土壤含水率、叶面积指数、叶片的P_n、G_s、C_i和T_r,SS处理均显著高于CK处理。与CK相比,SS、SP、SC处理2018和2019年的玉米产量分别增加13.88%和14.82%、7.59%和9.12%、7.42%和8.5%。秸秆条带覆盖深松技术适合作为半湿润区水分、光能高效利用和玉米增产的一种优化栽培技术进行推广应用。     

Root growth,soil water content and yield of barley under different tillage systems on two soils in semiarid conditions

An experiment was conducted on two soils in a semiarid area in the Spain’s Ebro valley. Soil A was a Fluventic Xerochrept of 120 cm depth and Soil B was a Lithic Xeric Torriorthent of 30 cm depth. Three tillage systems were compared in Soil A: subsoiler tillage, minimum tillage and no-tillage, and two (minimum tillage and no-tillage) in Soil B. The experiment was repeated for 5 years on Soil A and 3 years on Soil B. Root length density, volumetric water content and dry matter were measured at important developmental stages. Yield was determined at harvest. In Soil A, root length density and volumetric water content were significantly greater for no-tillage than for subsoiler or minimum tillage (up to 1.4 cm cm⁻³ and 5%, respectively), mainly in the upper part of the soil profile. At lower depths, differences as great as 0.8 cm cm⁻³ and 6% were also found. Mean yield (4 years) was similar between no-tillage (3608 kg ha⁻¹) and minimum tillage (3508 kg ha⁻¹), and significantly smaller for subsoiler tillage (3371 kg ha⁻¹). In Soil B, no differences were observed between tillage systems for volumetric water content. Significant interactions between tillage and year were found for root length density, dry matter and yield. Mean yield (3 years) was not significantly different for minimum tillage (1806 kg ha⁻¹) and no-tillage (1867 kg ha⁻¹). The results in Soil A showed that surface conditions are of major importance in the water content of the soil and determined the differences among tillage systems. No-tillage favoured greater and deeper water accumulation in the soil profile and greater root growth. This makes this system potentially better for years of low rainfall. In Soil B no tillage system proved to be better because of the low water-holding capacity of this soil (56 mm).     

Pedo-transfer function for saturated hydraulic conductivity of lowland paddy soils

In paddy field, soil saturated hydraulic conductivity (K _s) plays as an important component in the calculation of irrigation requirement of the water balance equation and also for irrigation efficiency. Several laboratory and field methods can be used to determine K _s. Laboratory and field determinations are usually time consuming, expensive and labour intensive. Pedo-transfer functions (PTF) serve to translate the basic information found in the soil survey into a form useful for broader applications through empirical regression of functional relationships, such as simulation modelling. Since PTFs have not been applied to paddy soils in the study area, a lot of field measurements will require high labour input to determine K _s hence high cost. This study attempts to seek a simplified method for determining K _s values based on common existing soil properties through PTF technique. Soil samples (n = 408 samples) were collected randomly depending on the soil series within the 2,300 ha Sawah Sempadan rice cultivation area. Both field work and laboratory work were carried out. The samples were then analysed for the following properties: dry bulk density (D _b), soil particle percentage (Sand-S, Silt-Si and Clay-C), organic matter (OM) and geometric mean diameter (GMD). The measured K _s values were obtained by using the falling head method. The parameters were then used as inputs for developing a K _s model by regression analysis using Statistical Analysis System (SAS) package. Stepwise regression analysis was applied to determine the best fit model based on R ² and significant level. The results of the study showed that there is a high spatial variability of the saturated hydraulic conductivity in the paddy area. The best regression model for estimating K _s was based on C, D _b, OM and GMD with the dependent variable (K _s) in a form of natural logarithm. The model inputs introduced by stepwise regression are commonly available therefore, this model is useful to replace the conventional method.     

不同耕作和种植方式对稻田杂草及水稻产量的影响

采用田间试验,研究了7种不同水稻耕作和种植方式[水田翻耕移栽(puddling transplanting,PT)、免耕移栽(no tillage transplanting,NTT)、水田翻耕滚筒湿播(puddling drum wet seeding,PDWS)、免耕滚筒湿播(no tillage drum wet seeding,NTDWS)、传统耕作旱穴播(conventional tillage dry drilling,CTDD)、沟垄灌溉旱穴播(furrow irrigated raised beds system dry drilling,FIRBSDD)和免耕旱穴播(no-tillage dry-drilling,NTDD)对稻田杂草和水稻产量的影响。结果表明,PT处理下水稻产量最高,杂草干物质量最低;与移栽相比,直播(direct seeded rice,DSR),包括旱直播和湿直播,杂草生长能力最强,且不管有无杂草均降低了水稻产量;直播处理因杂草使水稻减产91.4%~99.0%,而PT和NTT处理分别减产16.0%和42.0%;香附子、龙爪茅、长穗苋、珠子草和假海马齿等杂草种类在DSR处理中大量出现,但在PT处理中未出现。大田示范试验结果表明,普通水稻品种(HKR-47和IR-64)在DSR处理较PT处理减产达15.8%,但优质水稻品种(Sharbati和PB-1)在两处理间无明显差异。当前劳动力紧缺,人工插秧需要大量劳力,因此亟需开发好氧栽培(如免耕直播和机插)模式下的适宜水稻品种及其相关配套农业机械及技术。     

耕作措施与不同秸秆还田方式对黑土物理指标及固定态铵的影响

通过两年田间定位试验,探究深翻与旋耕处理及其不同秸秆还田条件下农田黑土耕层(0～20 cm)土壤容重、三相比和固定态铵的影响。结果表明,深翻能改善因长期旋耕造成的土壤紧实状况,显著降低20～40 cm土壤容重;秸秆还田方式对土壤容重、三相比有显著影响,影响效果由大到小依次为秸秆还田秸秆还田配施有机肥秸秆不还田处理;耕层土壤固定态铵对两种耕作处理无明显响应,对不同秸秆还田方式则具有显著响应,其中秸秆还田配施有机肥能有效增加固定态铵,秸秆还田次之;不同秸秆还田方式耕层土壤固定态铵含量与固相比呈显著负相关(R2=0.538)。深翻结合秸秆还田配施有机肥能较好地改善农田黑土土壤容重、三相比、提高固定态铵含量,可在该区域适当推广。     

Root Growth and Water Extraction Response of Doubled-Haploid Rice Lines to Drought and Rewatering during the Vegetative Stage

Abstract

Doubled haploid lines (DHLs) of rice (Oryza sativa L.) were used to examine responses to drought and rewatering in controlled rainfed lowland conditions, in order to determine whether confounding by unrelated traits would be less than has been reported previously for contrasting cultivars that differ in genetic background. IR62266 and four DHLs derived from the cross between IR62266 and CT9993 (DHL-32, -51, -54 and -79) were grown in pot experiments in the greenhouse during the 2000 dry and wet seasons at IRRI, Los Baños, Philippines. There were two water regimes (well-watered and drought). Estimated water extraction obtained by time domain reflectometry (TDR) was similar to cumulative transpiration estimated from pot weighing for each genotype. Genotypic variation was observed in root traits and water extraction, with extraction slower in DHL-32 and faster in DHL-79, especially in deeper soil layers. An upper bound relationship between water extraction from a soil layer and root length density (RLD) in that layer was readily apparent over DHLs and soil depths, suggesting a critical value of RLD for water extraction of 0.30 cm cm^?3 in these conditions. Because soils in the field would not be as homogenous as the puddled soils used in these greenhouse experiments, this critical RLD for water extraction from a soil layer is a reference for ideal conditions, and requires careful validation in the field. Use of DHLs permitted comparisons with reduced confounding by genetic background, with consequent improvements in precision.     

Comparison of conventional puddling and dry tillage in rice–wheat system

In many parts of Asia, rice is transplanted in puddled fields and after the harvest of this crop wheat is grown. This traditional method of growing rice may have deleterious effect on the growth of the subsequent crop in a rice–wheat cropping system. Wheat crop was planted in the same plots following a rice crop to evaluate the residual effects of various tillage treatments suitable for rice on the growth of the subsequent crop. Rice cultivar Super-basmati was grown in summer and wheat cultivar Auqab-2000 in autumn after rice. Four treatments were used to grow rice viz. transplanting in continuously flooded conditions (TRF), transplanting with intermittent flooding and drying (TRI), direct seeded using dry seeds (DSR) and direct seeded using primed seeds (DSP). Traditional puddling tillage system was followed in TRF and TRI, while for DSR and DSP, dry tillage system was followed. For convenience, the abbreviations of the rice treatments were used to indicate the same plots during the wheat crop. For the rice crop, tiller number, fertile tillers, kernel and straw yield, and harvest index were significantly better with transplanted treatments (TRI and TRF) than the direct seeded treatments. TRI also gave a yield advantage of 5% over TRF. For wheat, crop following direct seeded rice was better than transplanting. This study suggests that intermittent irrigation in the traditional puddling tillage system and DSP dry tillage system are the promising alternatives that may be opted.     

Dynamics of dissolved ions in the soil of abandoned terraced paddy fields in Sado Island, Japan

We investigated the soil and soil water chemistry in abandoned terraced paddy fields (reed stand) and a thicket of deciduous broad-leaved trees (thicket stand) on the same slope in Sado Island, Japan. The soils gathered from these plots were incubated under different water conditions to examine the dynamics of dissolved ions. The organic carbon pool in the soil in the reed stand at the lower slope position was greater than the thicket stand at the middle slope position. The high concentration of base cations and an almost neutral pH of the soil water at the reed stand corresponded with the high exchangeable cation concentrations and base saturation in the soil. These results reflect the mineral-rich groundwater percolating down the slope, which may be produced by chemical weathering. An in situ sulfate reduction in the reed stand at deeper soil horizons was identified. The different water conditions in the incubated soils affected the soil pH(H₂O), transformation of Fe, and dominant anions (NO₃ ⁻, HCO₃ ⁻, and SO₄ ²⁻). These biogeochemical processes were more conspicuous in the reed stand at the lower slope position where the concentrations of organic matter and base cations were high. When the abandoned terraced paddy field is developed for the conservation of the Japanese crested ibis (Nipponia nippon) habitat in Sado Island, the reductive subsoil at the lower slope position should be kept waterlogged to limit sulfuric acid generation.     

Simulation of salt and water movement and estimation of water productivity of rice crop irrigated with saline water

The HYDRUS-ID model was experimentally tested for water balance and salt build up in soil under rice crop irrigated with different salinity water (ECiw) of 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ in micro-lysimeters filled with sandy loam soil. Differences of means between measured (M) and HYDRUS-1D predicted (P) values of bottom flux (Q _o) and leachate EC as tested by paired t test were not found significant at P = 0.05 and a close agreement between RMSE values showed the applicability of the HYDRUS-1D to simulate percolation and salt concentration in the micro-lysimeters under rice crop. Potential ET values of rice as obtained from CROPWAT matched well with model predicted and measured one at all ECiw treatments. The model predicted root water uptake varied from 66.1 to 652.7 mm and the maximum daily salt concentration in the root zone was 0.46, 2.3, 4.5, 6.7, 8.4 and 10.2 me cm⁻³ in 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ ECiw treatments, respectively. The grain production per unit evapotranspiration ( \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} ) value of 2.56 in ECiw of 0.4 dS m⁻¹ treatment declined to 1.31 with ECiw of 2 dS m⁻¹. The \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} reduced to one-fifth when percolation was included in the productivity determination. Similarly, the water productivity in respect of total dry matter production (TDM) was also reduced in different treatments. Therefore, the model predicted values of water balance can be effectively utilized to calculate the water productivity of rice crop.     

Long-term effect of tillage systems on soil microbiological,chemical and physical parameters and the incidence of charcoal rot by Macrophomina phaseolina (Tassi) Goid in soybean

A 20-year field experiment was employed with the aim of evaluating the effect of tillage systems on biological, chemical and physical aspects of the soil, and to establish whether there was a correlation of these parameters with the incidence of charcoal rot (Macrophomina phaseolina) of soybean and crop yield. The tillage systems evaluated were direct seeding (DS), DS + scarifier (DS + S), minimum tillage (MT) and conventional tillage (CT). DS presented higher values than CT in culturable total fungi (26.33 × 10⁵ vs. 2.33 × 10⁵ CFU g⁻¹ dry soil), total bacteria (182 × 10⁷ vs. 64 × 10⁷ CFU g⁻¹ dry soil), microbial respiration (0.77 mg CO₂ g⁻¹ week⁻¹ vs. 0.45 mg CO₂ g⁻¹ week⁻¹) and fluorescein diacetate (FDA) hydrolysis (4.17 ug fluorescein g⁻¹ h⁻¹ vs. 1.70 ug fluorescein g⁻¹ h⁻¹ in CT. Fungal and bacterial community fingerprints, by terminal restriction fragment length polymorphism (T-RFLP) analysis, of Intergenic spacer regions of rRNA and 16S rRNA genes, respectively, were influenced by the tillage system. Also FAME (fatty acid methyl ester) profiles showed that microbial community structure in DS and CT was clearly different. DS samples contained significantly higher total microbial biomass than the other tillage treatments, but there were no significant differences in fungal biomass or any consistent trend with respect to stress index. Our results showed that microbial communities were more abundant and active in DS than in CT in response to high nutrient content in soil. Indeed, DS systems presented higher soil OM, total N, K and Ca than CT. Electrical conductivity and aggregate stability (AS) were also improved by DS. Soybean grown in high-quality soil was not affected by charcoal rot, however, under CT, disease incidence in soybean was 54%. These differences were correlated to the higher microbial abundance and activity under DS, the biological component being a key factor determining soil capacity to suppress the soilborne pathogen.     

Micro paddy lysimeter for monitoring solute transport in paddy environment

The micro paddy lysimeter (MPL) was developed and evaluated for its performance to simulate solute transport in paddy environment under laboratory conditions. MPLs were constructed using soil collected from Field Museum Honmachi of Tokyo University of Agriculture and Technology, Japan. For the physical characteristics of the hardpan layer, parameters such as thickness, and soil aggregate size, affecting the percolation rate were studied. For the plow layer, two types of plow soils, sieved and un-sieved soils were compared. The sieved soil plow layer was produced by mixing air-dried soils of different aggregate sizes of D > 9.50, 9.50 ≥ D > 4.75, 4.75 ≥ D > 2.0 mm and D ≤ 2.0 mm at 47.1, 19.5, 20.6, and 12.8%, respectively. The un-sieved plow layer soil was directly used after collecting from the field. Inert tracer was applied to ponding water with controlled boundary conditions to evaluate the reproducibility of the soil hydraulic characteristics. HYDRUS-1D was used to evaluate the movement of bromide tracer in the MPL. The proposed conditions of the MPL were that the hardpan layer can be made from soil aggregates smaller than 0.425 mm with 2 cm thickness and that the plow layer can be prepared with sieved or un-sieved soils. With these conditions, the obtained results proved that MPLs can be a useful tool to simulate solute transport in paddy environment.     

Effect of water management on dry seeded and puddled transplanted rice: Part 2: Water balance and water productivity

Labour and water scarcity in north west India are driving researchers and farmers to find alternative management strategies that will increase water productivity and reduce labour requirement while maintaining or increasing land productivity. A field experiment was done in Punjab, India, in 2008 and 2009 to compare water balance components and water productivity of dry seeded rice (DSR) and puddled transplanted rice (PTR). There were four irrigation schedules based on soil water tension (SWT) ranging from saturation (daily irrigation) to alternate wetting drying (AWD) with irrigation thresholds of 20, 40 and 70 kPa at 18–20 cm soil depth. There were large and significant declines in irrigation water input with AWD compared to daily irrigation in both establishment methods. The irrigation water savings were mainly due to reduced deep drainage, seepage and runoff, and to reduced ET in DSR. Within each irrigation treatment, deep drainage was much higher in DSR than in PTR, and more so in the second year (i.e. after 2 years without puddling). The irrigation input to daily irrigated DSR was similar to or higher than to daily irrigated PTR. However, within each AWD treatment, the irrigation input to DSR was less than to PTR, due to reduced seepage and runoff, mainly because all PTR treatments were continuously flooded for 2 weeks after transplanting. There was 30–50% irrigation water saving in DSR-20 kPa compared with PTR-20 kPa due to reduced seepage and runoff, which more than compensated for the increased deep drainage in DSR. Yields of PTR and DSR with daily irrigation and a 20 kPa irrigation threshold were similar each year. Thus irrigation and input water productivities (WP_I and WP_I+R) were highest with the 20 kPa irrigation threshold, and WP_I of DSR-20 kPa was 30–50% higher than of PTR-20 kPa. There was a consistent trend for declining ET with decreasing frequency of irrigation, but there was no effect of establishment method on ET apart from higher ET in DSR than PTR with daily irrigation. Water productivity with respect to ET (WP_ET) was highest with a 20 kPa irrigation threshold, with similar values for DSR and PTR. An irrigation threshold of 20 kPa was the optimum in terms of maximising grain yield, WP_I and WP_I+R for both PTR and DSR. Dry seeded rice with the 20 kPa threshold outperformed PTR-20 kPa in terms of WP_I through maintaining yield while reducing irrigation input by 30–50%.     

Effect of initial water content on saturated hydraulic conductivity in desalinization with slaking and drying

Soil slaking is an environment-friendly technique that is gaining importance in restoring saline soils. The objective of this article is to evaluate the effect of initial water content (IWC) on saturated hydraulic conductivity (K _s) in desalinization with slaking and drying. Accordingly, a slaking test was carried out during February, 2009 for evaluating the effects of slaking and drying on K _s, sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) under various IWC. We prepared natural and air-dried soils of paddy field in Kojima Bay Polder, Japan to give different pre-drying, air-dried, and not dried (natural). The air-dried soils were resaturated. Each soil was well mixed, then dried to different initial moisture contents (60, 50, 40, 30, 20, and 10% by weight). The specimens were immersed into water in the pot for 24 h. The K _s was measured, and cations in slaked and unslaked soils were analyzed. The K _s was high under the water content below 30% in both the natural and the air-dried soils. But the effects were more pronounced in the natural soil. The air-dried soil showed far smaller K _s than the natural soil. In outer solution, the highest SAR was noted at 30% in the natural and 30 and 20% in the air-dried soils. Significant decrease in ESP of the soils (slaked + unslaked) was also observed at the same water content. Lower water content was more effective in decreasing the soil ESP after desalinization from saline soil. The natural soil showed lower ESP and higher porosity, which was considered as a reason for higher K _s of natural soil than that of air-dried soils. The results indicated that lower water content (10–30%) had no hazardous effect on K _s by slaking and drying of soil.