Dry season soil conditions and soil nitrogen availability to wet season wetland rice

A pot experiment with Maahas clay soil covered three consecutive crops. After uniform growth of the first crop, the soils were subjected to different moisture conditions during the dry season. Prolonged drying before wet season flooded rice stimulated increased release of mineral nitrogen but moistening of the dry soil for a dryland crop or by occasional rain during the dry season reduced nitrogen use from the soil in the next wet season. One cycle of alternate wet and dry soil preparation for 20 days before transplanting rice improved soil nitrogen availability and plant uptake of fertilizer nitrogen.

The initial growth of rice was retarded after flooding the previously moist dryland or dried soil, but not in the continuously flooded soils.

Losses of applied nitrogen were small in continuously flooded soils and were greater in the previously moist dryland and dry treatments. Uptake of soil nitrogen, however, was much higher in the air-dried soil treatment and in the dry with alternate wet and dry preparation treatments. Total nitrogen uptake (soil+fertilizer) was also greater in those dry treatments. Uptake of soil nitrogen in the wet-season crop was roughly proportional to the amounts of ammonia measured just before transplanting.

The proportion of the uptake of immobilized fertilizer nitrogen to available soil nitrogen was constant among treatments. Release of immobilized fertilizer nitrogen was also greatly enhanced by soil drying. For 1976 wet-season crop, the availability of fertilizer nitrogen immobilized in the 1975 wet season was three times higher than that of native soil nitrogen.     

Effect of Lime and Flooding on Phosphorus Availability and Rice Growth on Two Acidic Lowland Soils

Abstract

Loss of soil‐water saturation may impair growth of rainfed lowland rice by restricting nutrient uptake, including the uptake of added phosphorus (P). For acidic soils, reappearance of soluble aluminum (Al) following loss of soil‐water saturation may also restrict P uptake. The aim of this study was to determine whether liming, flooding, and P additions could ameliorate the effects of loss of soil‐water saturation on P uptake and growth of rice. In the first pot experiment, two acid lowland soils from Cambodia [Kandic Plinthaqult (black clay soil) and Plinthustalf (sandy soil)] were treated with P (45 mg P kg^?1 soil) either before or after flooding for 4 weeks to investigate the effect of flooding on effectiveness of P fertilizer for rice growth. After 4 weeks, soils were air dried and crushed and then wet to field capacity and upland rice was grown in them for an additional 6 weeks. Addition of P fertilizer before rather than after flooding depressed the growth of the subsequently planted upland rice. During flooding, there was an increase in both acetate‐extractable Fe and the phosphate sorption capacity of soils, and a close relationship between them (r²=0.96–0.98). When P was added before flooding, Olsen and Bray 1‐extractable P, shoot dry matter, and shoot P concentrations were depressed, indicating that flooding decreased availability of fertilizer P. A second pot experiment was conducted with three levels of lime as CaCO₃ [to establish pH (CaCl₂) in the oxidized soils at 4, 5, and 6] and four levels of P (0, 13, 26, and 52 mg P kg^?1 soil) added to the same two acid lowland rice soils under flooded and nonflooded conditions. Under continuously flooded conditions, pH increased to over 5.6 regardless of lime treatment, and there was no response of rice dry matter to liming after 6 weeks' growth, but the addition of P increased rice dry matter substantially in both soils. In nonflooded soils, when P was not applied, shoot dry matter was depressed by up to one‐half of that in plants grown under continuously flooded conditions. Under the nonflooded conditions, rice dry matter and leaf P increased with the addition of P, but less so than in flooded soils. Leaf P concentrations and shoot dry matter responded strongly to the addition of lime. The increase in shoot dry matter of rice with lime and P application in nonflooded soil was associated with a significant decline in soluble Al in the soil and an increase in plant P uptake. The current experiments show that the loss of soil‐water saturation may be associated with the inhibition of P absorption by excess soluble Al. By contrast, flooding decreased exchangeable Al to levels below the threshold for toxicity in rice. In addition, the decreased P availability with loss of soil‐water saturation may have been associated with a greater phosphate sorption capacity of the soils during flooding and after reoxidation due to occlusion of P within ferric oxyhydroxides formed.     

Study on the improvement of fertilizer dressing and soil management in the rice field

Major part of nitrogen and phosphorus in the harvested rice plants was proved to be derived from soil nutrients by our field tracer experiments using 15-N and 32-P, even under heavy dressing of ammonium sulfate and superphosphate of over 75 kg per hectare in terms of N and P₂O₅ respectively. It fits quite nicely to Japanese farmer's common understanding, that the upland crops grow on the basis of fertilizer, and paddy rice on soil fertility. The Japanese rice soils, particularly under waterlogged conditions in summer, liberate rich nutrients from the organic matter, and the fertility of soils presents continuous supply of nitrogen and phosphorus throughout the rice Plant life.     

Influence of water regime on growth,yield, and nitrogen uptake of rice

Abstract

Greenhouse and field experiments were conducted to study the effects of water regime on growth of rice. The greenhouse experiment investigated the effects of two water regimes‐continuous flooding and flooding with soil drying between crops for 2 to 3 weeks on the growth of rice during six cropping (for six week each) on seven soils varying widely in total N contents (0.07 to 0.35%). The results averaged for the 7 soils indicated that the drymatter production or N uptake of rice was not affected by the water regimes during the six croppings.

The field experiment conducted during the dry season for two consecutive years (1976 and 1977) on a near neutral clay soil studied the effects of three water regimes (continuous flooding alternate flooding and soil drying every 2 weeks, and continuous flooding with 2 weeks mid season soil drying after 6 weeks of transplanting) and three levels of fertilizer N (0, 100 and 200 kg N/ha as urea) on grain yield and N uptake of rice. The results confirmed the absence of any significant reduction in grain yield or N uptake as a result of any of the soil drying treatments during the growing season on the unfertilized plots carrying a rice crop. On the plots fertilized with 100 or 200 kg N/na, alternate flooding and drying resulted in a significant depression in both grain yield and N uptake. Soil analysis supported heavy losses of N in the fertilized plots that underwent alternate flooding and soil drying apparently by nitrification and denitrification reactions.

The results of this study suggest that alternate flooding and drying of soils in the presence of established rice plants itiay not cause a significant loss of nitrogen in unfertilized plots although in plots fertilized with high rates of N the losses may be large as indicated by the performance of rice crop.     

Comparison of soil properties between continuously cultivated and adjacent uncultivated soils in rice-based systems

To assess cultivation-induced changes followed during the Green Revolution on continuous rice–rice and rice–wheat cropping, fence-line comparisons between cultivated and adjacent noncultivated soils were made to (a) quantify changes in selected soil chemical and biological properties at two moisture conditions, (b) determine the N, P, and K uptake of rice and wheat as affected by changes in soil properties, and (c) determine the relationship between N, P, and K uptake and soil properties. Two parallel experiments were conducted: laboratory incubation and a greenhouse experiment with soils collected from seven rice–wheat and two rice–rice soils. As an average, NH₄OAc-extractable K, water soluble organic carbon, and hot water soluble organic carbon were all lower by 48%, total carbon by 35%, total nitrogen by 33%, and microbial biomass carbon by 38% in the cultivated soils, whereas no significant change was observed in the enzyme activities. Changes were mostly associated with the existing fertilizer practices and moisture status of the soil during cultivation. In general, fertilizers were not sufficient to replenish crop removal. Soil type also influenced cultivation changes especially soil carbon parameters. Lighter soil texture had higher decomposable organic C and total C declined than heavy soils. Soils with higher declined in both decomposable organic C and total C had higher reduction in functional diversity of culturable microorganisms. The declining C pools caused lower N uptake and there was a clear association between organic matter parameters and N uptake. Olsen P was correlated with P uptake and extractable K with K uptake. As expected, crop biomass correlated with N, P, and K uptake of plants. Comparison of cultivated and its corresponding uncultivated soil provides possibility to determine management effect on soil status.     

Fate and interaction with native soil N of ammonium N applied to wetland rice (Oryza sativa L.) grown under saline and non-saline conditions

Summary The effect of salts on the balance of fertilizer N applied as ¹⁵N-labelled ammonium sulphate and its interaction with native soil N was studied in a pot experiment using rice (Oryza sativa L.) as a test crop. The rice crop used 26%–40% of the applied N, the level of applied N and salts showing no significant bearing on the uptake of fertilizer N. Losses of fertilizer N ranged between 54% and 68% and only 5%–8% of the N was immobilized in soil organic matter. Neither the salts nor the rate of N application had any significant effect on fertilizer N immobilization. The effective use of fertilizer N (fertilizer N in grain/fertilizer N in whole plant) was, however, better in the non-saline soil. The uptake of unlabelled N (N mineralized from soil organic matter and that originating from biological N₂ fixation in thes rhizosphere) was inhibited in the presence of the salts. However, in fertilized soil, the uptake of unlabelled N was significantly enhanced, leading to increased A values [(1-% Ndff/% Ndff)x N fertilizer applied, where Ndff is N derived from fertilizer], an index of interaction with the added N. This added N interaction increased with increasing levels of added N. Since the extra unlabelled N taken up by fertilized plants was greater than the fertilizer N immobilized, and the root biomass increased with increasing levels of added N, a greater part of the added N interaction was considered to be real, any contribution by an apparent N interaction (pool substitution or isotopic displacement) to the total calculated N interaction being fairly small. Under saline conditions, for the same level of fertilizer N addition, the added N interaction was lower, and this was attributed to a lower level of microbial activity, including mineralization of native soil N, rootdriven immobilization of applied N, and N₂ fixation.     

Inhibition of nitrogen mineralization in young humic fractions by anaerobic decomposition of rice crop residues

Field observations indicate a long‐term decrease in crop uptake of N derived from soil organic matter under continuous production of irrigated lowland rice (Oryza sativa L.). Decreased availability has been associated with an accumulation of phenolic lignin residues in soil organic matter, which can chemically bind N. To evaluate the hypothesis that the decrease in N availability results primarily from anaerobic decomposition of incorporated crop residues, ¹⁵N‐labelled fertilizer was applied three times during one growing season in a field study that compared anaerobic decomposition with aerobic decomposition for annual rotations of rice (Oryza sativa L.)–rice and rice–maize (Zea mays L.). Contents of ¹⁵N and total N during the growing season were measured in humic fractions and total soil organic matter. Results indicated an inhibition of N mineralization for the rice–rice rotation with anaerobic decomposition of crop residues, both for ¹⁵N that was immobilized after application and for total N. The inhibition was strongest for ¹⁵N that was applied at planting. It became more evident as the season progressed and reached significant levels during mid‐season stages of plant growth when crop demand for N peaks. These results were clearest for a young, phenolic‐rich humic fraction that was active in ¹⁵N immobilization and remineralization. Comparable but less significant trends were evident for a more recalcitrant humic fraction and for soil organic matter. Trends in crop‐N uptake associated the combination of rice–rice rotation and anaerobic decomposition with inhibited uptake of soil organic N but uninhibited uptake of fertilizer N. Increased aeration of rice soils through aerobic decomposition of crop residues or crop rotation is a promising management technique for improving soil N supply in lowland rice cropping.     

土地利用方式对田间植物残体中C、N矿化的影响

Four kinds of plant materials(astragalus,azolla,rice straw and water hyacinth) were allowed to decom-pose for 10 years in two soils with different mineralogical characteristics in fields under upland and submerged conditions.Greater amounts of C and N from azolla were retained in soils throughout the 10-year experi-mental period compared to those from the other plant materials.The residual C of all the plant materials in the two soils under upland conditions mineralized at rates corresponding to half-lives between 4.4-6.6 years,while the corresponding figures for those under submerge conditions were between 6.5-13.1 years,Minera-liztion of residual organic N followed the same pattern as residual C.Compared to residual C,however,the mineralization rates of residual organic N in most cases were significantly lower and the percentages of added N retained in soils were higher.More N from plant materials was retained in the yellow-brown soil than in the red soil,but no consistent differences in the amounts of C from plant materials and in the mineraliztion rates of both residual C and residual organic N between the wto soils could be folund.     

北方地区滨海盐渍土型稻田土壤供氮能力的研究

采用短期淹水密闭淋洗培养法(恒温30℃),研究北方地区滨海盐渍土型旱地土壤(种植苜蓿草)开垦种植水稻5年和30年稻田土壤供氮能力。结果表明:(1)3种土壤初始矿质氮主要分布在0~20 cm土层,且土壤初始矿质氮含量的高低顺序为旱地土壤>30年稻田土壤>5年稻田土壤;5年稻田土壤与旱地土壤之间初始矿质氮含量差异达5%显著水平。(2)相同土层,土壤矿化氮量高低顺序为30年稻田土壤>旱地土壤>5年稻田土壤;任意2种土壤之间矿化氮量差异均达1%显著水平。(3)相同土层,土壤供氮能力大小为30年稻田土壤>旱地土壤>5年稻田土壤;其中,在0~20 cm和40~60 cm土层,任意2种土壤之间供氮能力差异均达1%显著水平,在20~40 cm土层,30年稻田土壤与旱地土壤、5年稻田土壤之间供氮能力差异均达1%显著水平,而旱地土壤与5年稻田土壤之间供氮能力则无明显差异。这表明滨海盐渍土型旱地土壤开垦种植水稻后,不仅影响了土壤有机质(氮)含量,而且也影响了土壤有机氮品质,种植水稻5年使土壤供氮能力显著下降,而种植30年使土壤供氮能力显著上升。     

Effect of Soil Moisture Content and Phosphorus Application on Phosphorus Nutrition of Rice Cultivated in Different Water Regime Systems

Abstract

Pot experiments were conducted in a glasshouse to investigate the effect of soil water content and phosphorus (P) supply on biomass, P uptake by rice cultivated in soils with different water regimes and soil available P. Results showed that P application rates had greater effect on P nutrition of rice than soil moisture content. Yield of rice grain was significantly decreased when soil moisture content was kept at 60% of water holding capacity (WHC) while the yields of rice grain were not significantly different when soil moistures were remained at 80% of WHC and waterlogged. This meant that it was possible for paddy rice variety to be cultivated in aerobic soil under the condition of sufficient P supply. The highest biomass of rice and highest P uptake by rice were found in the treatment with 0.0300 g P kg^?1 of P application rate and with 80% of WHC. Soil available P content decreased with the decrease of both the soil moisture content and the P applied. Rice crop exhausted soil P to a great extent leading to very low available soil P content when the rice crop was harvested, especially in the soil receiving no or small amounts of P fertilizer. All the results obtained in this experiment could provide the theoretic base for water and P management of paddy rice variety cultivated in aerobic soil in the southern hilly areas of China.     

Dynamics of 15N-labeled ammonium sulfate in various inorganic and organic soil fractions of wetland rice soils

Summary The dynamics of basally applied ¹⁵N-labeled ammonium sulfate in inorganic and organic soil fractions of five wetland rice soils of the Philippines was studied in a greenhouse experiment. Soil and plant samples were collected and analyzed for ¹⁵N at various growth stages. Exchangeable NH₄ ⁺ depletion continued after 40 days after transplanting (DAT) and corresponded with increased nitrogen uptake by rice plants. Part of the applied fertilizer was fixed by 2:1 clay minerals, especially in Maligaya silty clay loam, which contained beidellite as the dominant clay mineral. After the initial fixation, nonexchangeable ¹⁵N was released from 20 DAT in Maligaya silty clay loam, but fixation delayed fertilizer N uptake from the soil. Part of the applied N was immobilized into the organic fraction. In Guadalupe clay and Maligaya silty clay loam, immobilization increased with time while the three other soils showed significant release of fertilizer N from the organic fraction during crop growth. Most of the immobilized fertilizer N was recovered in the nondistillable acid soluble (alpha-amino acid + hydrolyzable unknown-N) fraction at crop maturity. Between 61% and 66% of applied N was recovered from the plant in four soils while 52% of fertilizer N was recovered from the plant in Maligaya silty loam. Only 20% – 30% of the total N uptake at maturity was derived from fertilizer N. Nmin (mineral N) content of the soil before transplanting significantly correlated with N uptake. Twenty-two to 34% of applied N was unaccounted for possibly due to denitrification and ammonia volatilization.     

Influences of starch and Zn-EDTA on Zn-desorption and rice ( Oryza sativa L.) nutrition under different moisture regimes

Desorption of Zn from sorbed Zn in soils is controlled by different moisture regimes in rice fields and thus control the Zn availability to rice. A laboratory experiment was conducted at different moisture regimes viz. flooded-dried, alternate wetting and drying and preflooding condition in two Inceptisols and two Alfisols of West Bengal, India, with (50?g kg^???1) and without starch as control to investigate the desorption of adsorbed Zn from Zn-EDTA (0.0, 0.1, and 0.2?mg Zn g^???1 soil). Percent desorption of Zn was found significantly higher on alternate wetting and drying condition in Alfisols. Starch applications enhanced desorption under flooded-dried and alternate wetting and drying, but decreased it under preflooding conditions. The variations in Zn desorption among soils and moisture treatments are the result of changes in soil pH, Fe-oxides, bonding energy constants, and free energies for Zn adsorption. After desorption experiment a pot trial was conducted with rice (cv. IET-4094) under alternate wetting and drying moisture conditions. The results show that the dry matter yield and 1000 grain weight of rice are appreciably higher when alternate flooding and drying moisture condition was maintained. This finding was in close agreement with the Zn desorption studies under the alternate flooding and drying moisture regimes.     

Long-term fertilizer management in NERICA cultivated upland affects on soil bio-chemical properties

ABSTRACT

This study aims to characterize soil chemical properties and microbial biomass, greenhouse gas production, and organic matter dynamics in upland rice field as affected by the long-term fertilizer managements in Uganda. Soil total C (TC) and N (TN) contents were in the relatively smaller range under different fertilizer treatments, even after 20 crop seasons. However, available phosphate contents showed positive correlation with average yield of upland rice. Incubation experiments were conducted under aerobic or under flooding conditions to measure CO₂, methane, and nitrous oxide productions. After the incubation, soil samples were extracted to quantify nitrification rate for aerobic condition and ammonification rate for flooding condition. Soil microbial biomass carbon (MBC) and nitrogen were measured. Stable isotope ratio of ¹³C and ¹⁵N were also determined for the soil samples. CO₂ production potential under aerobic condition was higher than the flooding condition. The qCO₂ (CO₂/MBC) in the treatment applied with compost tended to be higher than the other treatments. Positive correlation between nitrous oxide production and nitrification was found. The delta ¹³C values of the soil samples indicated that the effect of C4 plants before rice cultivation still remained, while the contribution of biological N₂ fixation was little according to delta ¹⁵N values. These results indicate that soil microbial biomass in upland rice field of the long-term fertilizer experiment in Uganda was characterized with higher qCO₂. Greenhouse gas production was affected by fertilizer management, while soil organic C before the long-term experiment still remained in the experiment.     

Organic Matter and Mineralizable Nitrogen Relationships in Wetland Rice Soils

Abstract

Soil nitrogen (N) supply plays a dominant role in the N nutrition of wetland rice. Organic matter has been proposed as an index of soil N availability to wetland rice. This is based on the finding that mineralizable N produced under waterlogged conditions is related to soil organic carbon (C) and total N. The relationship between organic matter and mineralizable N is a prerequisite for determining the N requirement of wetland rice. However, no critical analysis of recent literature on organic matter–mineralizable N relationships has been made. This article evaluates current literature on the relationships of mineralizable N or ammonium N production with soil organic C in wetland rice soils. A number of studies with diverse wetland rice soils demonstrate a close relationship of N mineralized (ammonium‐N) under anaerobic conditions with organic C or total N. However, a few recent studies made on sites under long‐term intensive wetland rice cropping showed that strong positive relationships of mineralizable N with organic C or total N do not hold. Clearly, both quantity and quality of organic matter affect N mineralization in wetland rice soils. Future research is needed to clarify the role of quality of organic matter, especially its chemistry, as modified by the chemical environment of submerged soils, on the mineralization of organic N in wetland rice soils.     

Degradation of PCP in soils

In laboratory experiments, the degradation of PCP in soil with regard to the relationship to soil properties was studied under upland and flooded conditions using gas-chromatographic techniques. The degradation products and their behavior were elucidated by using 10 diCferent soils collected from rice fields and adjacent upland fields and one sample of a subsoil from the forest. The results are as follows:

1) The degradation of PCP in soils was faster under flooded conditions than upland conditions.

2) The degradation under flooded conditiont was more rapid in soils collected from rice fields than in those from adjacent upland fields, Tbe reverse was true under upland conditions.

3) The degradation rate was highly correlated with the organic matter content of the soil. Almost 100% of the PCP remained in the subsoil sample even after 50 days of incubation. The rate was slightly correlated with the clay mineral composition, free iron content, phosphate absorption coefficient and C.E.C., but hardly at all with texture, clay content, degree of base saturation, soil pH and available phosphorus content.

4) As the degradation products of PCP, 3 tetrachlorophenols, 4 or 5 trichlorophenols and PCP methyl ether were detected, PCP methyl elher and 2, 3, 4, 5-tetrachlorophenol were the major products, but the amount of the latter varied greatly during the course of incubation.     

Diffusion of ammonium and nitrate ions in flooded soil and nitrogen use efficiency of an irrigated rice system

Abstract

A laboratory study was used to simulate the pattern of diffusion of ammonium and nitrate ions in flooded soil. Ammonium, deep incorporated in a submerged irrigation system, diffused upward from the anaerobic to the aerobic layer where biochemical oxidation nitrified it to NO₂ and NO₃. These oxidized N species diffused downward from the aerobic layer to the anaerobic layer where most or at least partly, was lost as gaseous end products. Three crops of rice were grown in a glasshouse experiment to estimate N use efficiency under various combinations of irrigation and N management practices. Overall N use efficiency averaged 45%. Under continuous flooding, almost two thirds of the applied fertilizer N (647% use efficiency) was recovered by the rice crop. Under alternate flooding and drying, the response was very poor, with only about one fourth (26% use efficiency) of the applied fertilizer N being recovered by the crop. This demonstrated importance of the proper combination of irrigation and fertilizer management in paddy soils to maximize N utilization.     

Decomposition of rice residue in tropical soils

Nitrogen mineralization and immobilization of rice residue in Maahas clay soil under lowland and upland conditions were investigated by using ¹⁵N-labelled rice straw. The mineralization of residue-nitrogen was taking place even though the net mineralization was depressed by incorporation of rice residue.

There were some significant differences in the pattern of nitrogen transformation between lowland and upland soil conditions. The nitrogen transformation measured by mineralization of soil nitrogen and rice-residue nitrogen and the nitrogen immobilization into rice residue were more active under lowland conditions than under upland conditions, during the earlier period of residue decomposition.     

Residual Effect of Phosphorus Fertilizer in a Low‐Humic Andosol with Low Extractable Phosphorus

Abstract

Phosphorus (P) fertilization is quite important for crop production grown on Andosols. Fertilizer P‐use efficiency was 17% in a long‐term wheat experiment on a low‐humic Andosol. Residual effects of P fertilization were investigated using field soils in pot experiments. Topsoil was collected from the plots with or without annual P fertilizer at the rate of 65 kg‐P ha^?1 for 23 years (nitrogen phosphorous potassium (NPK) soil and nitrogen potassium (NK) soil, respectively). There was no significant difference in dry matter of wheat and P uptake between NPK and NK soils. However, dry matter of rice and P uptake were higher in NPK soil than in NK soil. Inorganic aluminum P (Al‐P_i) and iron P (Fe‐P_i) increased in NPK soil. Increase in Al‐P_i and Fe‐P_i during 23 years contributed little to P uptake by wheat, and repeated P fertilization is indispensable to obtain acceptable grain yield.     

Response of flooded rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) to nitrogen application at two root-zone temperature regimes in a pot experiment

In a greenhouse experiment, the response of three cultivars of rice to N application was studied at two root-zone moisture regimes. The response was measured in terms of dry matter yield, uptake of N from applied fertilizer and soil organic matter, loss of fertilizer N, and interaction of applied N with the native soil N. Nitrogen was applied as ¹⁵N-labelled ammonium sulphate and two temperature regimes in the root-zone were established by digging one set of pots into the soil, while keeping the other set on the surface. This setup created and maintained a temperature difference of 5–7°C in the rhizosphere, temperature being lower in the buried pots throughout the growth period. The rice cultivars included a coarse-grain and high-yielding cultivar (IR-6) and two aromatic fine-grain cultivars (Bas-198 and Bas-Pak). IR-6 showed a negative response to higher root-zone temperature with resultant reduced efficiency of soil N and fertilizer N. The other two cultivars were relatively insensitive. The effect of temperature was more pronounced for N yield than dry matter accumulation. Loss of applied N occurred in all cases, but it was more pronounced in IR-6 at the higher temperature regime. Application of labelled fertilizer N led to an increase in the uptake of unlabelled N due to a real "added nitrogen interaction" which was attributed mainly to an increase in root biomass.     

干湿交替灌溉与施氮耦合对水稻根际环境的影响

为了探讨不同水氮耦合对水稻根际土壤环境及根系分泌有机酸总量的影响,以新稻20号为材料,进行盆栽试验,设置浅水层、轻度(-20 k Pa)和重度干湿交替灌溉(-40 k Pa)3种灌溉方式及不施氮肥,中氮(normal nitrogen,MN,240 kg/hm~2)和高氮(high nitrogen,HN,360 kg/hm~2)3种氮肥水平9个处理。结果表明:轻度干湿交替灌溉及中氮增加了土壤酶活性,提高土壤中微生物数量,根系分泌有机酸总量显著提高(P0.05);重度干湿交替灌溉及重施氮肥则降低土壤酶活性及微生物的数量,显著(P0.05)减少根系分泌有机酸的总量;相关分析表明:根际土壤酶活性及微生物数量与不同生育期根系分泌有机酸总量呈显著(P0.05)或极显著(P0.01)的正相关关系。土壤酶活性、微生物数量及有机酸总量的供氮效应为正效应,轻度干湿交替灌溉供水效应及耦合效应均为正效应,而重度干湿交替灌溉的控水及耦合效应则为负效应。研究可为通过水氮耦合调控水稻良好的根际环境提供依据。