Subsequent Rice Crop Research Articles

Coupling of reduced inorganic fertilizer with plant-based organic fertilizer as a promising fertilizer management strategy for colored rice in tropical regions

Colored rice is a type of high-quality, high-added-value rice that has attracted increasing attention in recent years. The use of large amounts of inorganic nitrogen fertilizer in rice fields results in low fertilizer use efficiency and high environmental pollution. Organic fertilizer is a promising way to improve soil quality and sustain high yields. However, most studies focus on the effect of animal-based organic fertilizers. The effects of different ratios of plant-based organic fertilizer and inorganic fertilizer on the grain yield and quality of colored rice have rarely been reported. Therefore, a two-year field experiment was conducted in 2020 and 2021 to study the effects of replacing inorganic N fertilizers with plant-based organic fertilizers on the yield, nitrogen use efficiency (NUE), and anthocyanin content of two colored rice varieties in a tropical region in China. The experimental treatments included no nitrogen fertilization (T1), 100% inorganic nitrogen fertilizer (T2), 30% inorganic nitrogen fertilizer substitution with plant-based organic fertilizer (T3), 60% inorganic nitrogen fertilizer substitution with plant-based organic fertilizer (T4), and 100% plant-based organic fertilizer (T5). The total nitrogen provided to all the treatments except T1 was the same at 120 kg ha–1. Our results showed that the T3 treatment enhanced the grain yield and anthocyanin content of colored rice by increasing nitrogen use efficiency compared with T2. On average, grain yields were increased by 9 and 8%, while the anthocyanin content increased by 16 and 10% in the two colored rice varieties under T3 across the two years, respectively, as compared with T2. Further study of the residual effect of partial substitution of inorganic fertilizers showed that the substitution of inorganic fertilizer with plant-based organic fertilizer improved the soil physio-chemical properties, and thus increased the rice grain yield, in the subsequent seasons. The highest grain yield of the subsequent rice crop was observed under the T5 treatment. Our results suggested that the application of plant-based organic fertilizers can sustain the production of colored rice with high anthocyanin content in tropical regions, which is beneficial in reconciling the relationship between rice production and environmental protection.

A rice–chicory rotation pattern ensures safe grain production and phytoremediation of cadmium-contaminated paddy fields: A four-year field experiment in southern China

Cadmium (Cd) contamination in paddy systems is a serious problem, and a strategy must be devised that ensures safe grain production and rapid remediation of soil Cd contamination. To investigate the remediation potential of crop rotation and its effect on Cd accumulation in rice, a four-year (seven-season) rice–chicory rotation field trial was conducted on a moderately acidic Cd-contaminated paddy soil. Rice was planted in summers, followed by straw removal, and chicory, a Cd-enrichment plant, was planted during winter fallows. Rotation effects were compared with those with rice only (control). Rice yields between the rotation and control were not significantly different, whereas Cd concentrations in rice tissues decreased in the rotation. Cd concentration in brown rice of the low-Cd variety decreased to less than 0.2 mg/kg (national food safety standard) from the third season onward, whereas in the high-Cd variety, it decreased from 0.43 mg/kg in the first season to 0.24 mg/kg in the fourth season. The highest Cd concentration in chicory aboveground parts was 24.47 mg/kg, with an enrichment factor of 27.81. Chicory had high regenerative capacity and was repeatedly harvested for biomass in multiple mowings, with average aboveground biomass over 2000 kg/ha in a single mowing. Theoretical phytoextraction efficiency (TPE) of one rice season with straw removal was 0.84%–2.44%, whereas the highest TPE of one chicory season reached 8.07%. The seven seasons of rice–chicory rotation extracted up to 407 g/ha Cd from soil with a TPE exceeding 20%. Therefore, rice–chicory rotation and straw removal can effectively reduce Cd accumulation in subsequent rice crops, without interrupting production and simultaneously rapidly remediating Cd-contaminated soil. Thus, the production potential of light to moderately Cd-contaminated paddy fields can be realized with crop rotation.

The Study of Soil Physical Properties of the Rice-dominated Cropping Area of Tangi Choudwar

Wetland rice agriculture includes puddling practices, which facilitate transplanting and weed control easier and lowers water and nutrient loss through percolation. However, in addition to these benefits, the puddling alters the soil's physical properties, which is harmful to subsequent rice crops.100 gridded soil sample was collected from 24 panchayats of Tangi Choudwar. In this study, soil physical properties like texture, water holding capacity (WHC), and bulk density (BD) were measured in twenty-four panchayats in Tangi Choudwar, Odisha. It was recorded that BD varied from 1.32 to 1.63 Mg/m3 and the WHC of soil varied from 36.70 to 64.70%. The proportion of sand, silt, and clay varied from 35 to 84%, 6 to 34%, and 12 to 38%, respectively. From the correlation study, WHC showed a positive correlation with clay content and a negative correlation with sand content, whereas BD showed negative correlation with the clay content (r=-0.261, P=0.01) and positive with sand content (r=0.167, P=0.05). The findings of this study may provide guidance for effective cultivation management techniques and assist in enhancing crop productivity and soil quality.

Metal doped nitrogenous hydroxyapatite nanohybrids slowly release nitrogen to crops and mitigate ammonia volatilization: An impact assessment

To supply adequate food, the ongoing and unrestrained administration of nitrogen fertilizer to agricultural fields is polluting the climate and living organisms. On the other hand, the agriculture sector urgently needs a technological upgrade to effectively confront hunger and poverty. Here, we report a rapid synthesis of zinc and magnesium-doped hydroxyapatite-urea nanohybrids for slow release and delivery of nitrogen to wheat and rice crops. Nanohybrids slowly release nitrogen for up to six weeks compared to the burst release of nitrogen from urea, and their use substantially reduces, by at least 3.8 times, ammonia emissions into the environment compared with that of urea fertilizer. A half‑nitrogen dose applied as multi-nutrient complexed nanohybrids maintained crop growth, yield, and nutritional compositions in wheat and subsequent rice crops. Nanohybrids enhanced the wheat crop yield and nitrogen uptake by 22.13% and 58.30%, respectively. The synthesized nitrogen nanohybrids remained in the soil for two continuous crop cycles, reduced ammonia volatilization, and achieved nitrogen delivery to the crops. Additionally, soil dehydrogenase activity (534.55% above control) and urease activities (81.82% above control) suggest that nanohybrids exhibited no adverse impact on soil microorganisms. Our comprehensive study demonstrates the advantages of ‘doping’ as a method for tailoring hydroxyapatite nanoparticles properties for extended agricultural and environmental applications. The use of nanohybrids substantially reduced greenhouse gas emissions and enabled the reduction, by half, of nitrogen inputs into the agricultural fields. This study, therefore, reports a novel nano-enabled platform of engineered hydroxyapatite-urea nanohybrids as a nitrogen fertilizer for efficient nitrogen delivery that results in improved crop growth while minimizing environmental pollution.

Short phases of tropical forage legumes increase production of subsequent cereal crops in the seasonally dry tropics of eastern Indonesia

In temperate systems, it is well known that forage legumes can improve both nitrogen (N) supply and yields of subsequent cereal crops. While this is assumed to be true in tropical systems, it is less well tested, particularly in smallholder settings where forage is often cut and removed from the field. This paper confirms the potential of short phases of tropical forage legumes to provide N to subsequent crops in seasonally dry tropical farming systems. Across five experiments, maize and rice grain yields increased by up to 80 % after 4−8 month rotations of forage legumes, but the benefits were smaller when legume growth was reduced, biomass was removed for forage, or the yield potential of cereal crops was lower. We found that the additional N cycling from legumes can last for at least 2 years, although the benefit diminishes with time. When all legume material was retained as mulch, the estimated additional N provided to subsequent no-till maize crops was the equivalent of 9−15 kg urea-N per tonne of above-ground legume biomass produced but fell to 1.5−3 kg urea-N/t if forage was removed. After shoot removal, more legume N cycled to a subsequent rice crop (equivalent of 11–13 kg urea-N/t of legume biomass) than to a no-till maize crop, presumably because more below-ground material mineralised. Of the legumes tested, Clitoria ternatea grew best across a variety of environments and use patterns and provided the largest yield benefits to subsequent crops. This research demonstrates the potential to integrate short phases of tropical herbaceous forage legumes into smallholder crop-livestock systems in the seasonally dry tropics, and, in doing so, improve or maintain staple grain crop production and household food self-sufficiency.

Influence of soybean management decisions on the subsequent rice crop's response to nitrogen

AbstractLittle is known about the effects of soybean [Glycine max (L.) Merr.] management practices on the success of the subsequent rice (Oryza sativa L.) crop. A study was initiated to determine how rice was affected by the preceding soybean crop's maturity group (MG) and planting date when grown in rotation on silt loam and clay soils. Optimum and late soybean planting dates and MGs (3.5, 4.7, 5.4, and 5.6) were followed by a rice crop. The results differed by soil texture, with the planting date and MG selection of the previous soybean crop more influential to the rice crop produced on a silt loam soil than a clay soil. Rice grown on a clay soil produced a higher grain yield when following a 5.4 MG soybean, whereas the planting date of a previous soybean crop influenced the soil‐N credits measured at rice emergence. On a silt loam soil, the interaction of both planting date and MG of the previous soybean crop influenced the maximal grain yield achieved by the rice crop. When soybean is planted during an optimum planting date, soybean MG has little effect on the successive rice crop. However, when the soybean crop is planted late, a determinate MG should be selected to achieve the highest rice crop total N uptake, maximal grain yield, and reduce the rate of fertilizer‐N needed to achieve 95% relative grain yield. Management techniques should be considered when implementing a soybean–rice rotation to maximize rice grain yield and overall farm profitability.

Upland rice yield enhanced by early nitrogen fertilization on previous palisade grass

High grain yields of upland rice (Oryza sativa L.) can be achieved in no-tillage systems. However, managing nitrogen (N) fertilization for rice in succession to forage grasses is a challenge because forage residues change N cycling and increase microbial immobilization of N, thereby reducing N availability to the subsequent cash crop. In the present study, two field experiments were conducted to determine if applying all or part of the N fertilizer on preceding palisade grass (Urochloa brizantha) and ruzigrass (Urochloa ruziziensis) or their desiccated residues immediately before rice seeding can supply N to the subsequent rice crop. Forage biomass yield (8–16 Mg ha− 1), N accumulation, and N supply to the subsequent upland rice were highest when all of the N fertilizer was applied on forage grasses at 50, 40 or 35 days before rice seeding (DBS), as opposed to the conventional split application at rice seeding and at tillering. On average, the grain yield of upland rice was 54% higher in succession to palisade grass compared with ruzigrass. The grain yield of rice was higher when N was applied to palisade grass at 35 DBS and ruzigrass at 50 DBS, reaching 5.0 Mg ha− 1 and 3.7 Mg ha− 1, respectively. However, applying N to ruzigrass was less effective for increasing upland rice yields since the yields did not differ from the treatments with the conventional split application. Adjusting the time of N application to forage grasses to increase the grain yields of subsequent upland rice is a sustainable alternative that can promote the economic viability of upland rice production.

Status of Dhaincha Incorporated Soil After Rice Harvest in (Boro) Rice–Dhaincha–Rice (T. Aman) Cropping Pattern

AbstractAn experiment was conducted at Field Laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, to find out the effect ofdhainchaincorporation on subsequent rice crop yield and postharvest soil nutrient status. The experiment was laid out in a randomized complete block design having three replications. Ninedhainchaaccessions were used as experimental materials along with a control (withoutdhainchaplant). Seeds ofdhainchaaccessions were sown in experimental plot @ 60 kg ha−1. Sixty days olddhainchaplants were mixed up with soil. Soil samples were collected twice, before sowing ofdhainchaseeds and after rice crop harvest. Forty five days old healthy rice seedlings were transplanted in the well prepareddhainchaincorporated plots at the spacing of 15 cm x 25 cm (plant-plant x row-row). The pH and nutrient status were improved indhainchaincorporated soil over the control. The highest grain yield (5.81 t ha−1) was obtained fromdhainchaAcc. 33 incorporated plot followed by Acc. 25 (5.73 t ha−1) and the lowest in control (4.35 t ha−1). Due to the incorporation ofdhainchabiomass in soil, the rice grain yield increased 7.82% to 33.56% over the control. Among thedhainchaaccessions, number 33 showed the best performance in terms of influencing grain yield. A precise conclusion to be built up through collection of large number of germplasms from Bangladesh is needed.

Phosphorus fertilizing potential of bagasse ash and rice husk ash in wheat–rice system on alkaline loamy sand soil

SUMMARYBagasse and rice husk are two important agro-industrial by-products that are used as fuel in the sugar and rice mill industries, thus producing large quantities of bagasse ash (BA; 0·05 of bagasse) and rice husk ash (0·20 of rice husk) as waste material. Applying BA and rice husk ash (RHA) to agricultural land improves yield, nutrient uptake and chemical fertility of soil, particularly with special reference to available phosphorus (P) and potassium (K). The present field experiment was conducted for 3 years to evaluate the P fertilizer value of these agro-industrial waste materials in a wheat–rice system (WRS). The experiment was laid out in a split-plot design with RHA and BA applied at 10 t/ha and including a no-amendment control as the main plot treatments and three levels of fertilizer P (0, 13 and 26 kg P/ha; designated P0, P13and P26, respectively) as sub-plot treatments to wheat in WRS. Application of fertilizer P increased the wheat grain yield up to P26in the un-amended control treatment. However, a significant response of wheat to fertilizer P was also observed up to P13in the presence of BA and RHA, thereby saving 50% of fertilizer P. Both RHA and BA increased wheat productivity by 12 and 16%, respectively, over the un-amended control. The subsequent rice crop also produced 14% higher paddy yield when the two ashes were applied along with P13to the previous wheat crop. The increases in grain yield were accompanied by significant increases in the uptake of P and K, and P content (Olsen P) in the soil. The application of recommended P (P26) in un-amended plots resulted in a negative P balance of 9·3 kg P/ha/year. On the other hand, the application of BA alone and RHA along with P13resulted in neutral/slightly positive P balance. A strong linear relationship (R2= 0·98) was observed between P balance and Olsen-P build up in the soil. It may be concluded that application of BA and RHA has the potential to increase system productivity and reduce the cost of inputs in terms of reduced application of fertilizer P to wheat and rice.

Improvement of the value of green manure via mixed hairy vetch and barley cultivation in temperate paddy soil

Legume hairy vetch and non-legume barley mixtures are broadly cultivated to improve the value of cover crops in mono-rice paddies. Nevertheless, the effects of mixing conditions of the two cover crops on biomass and nutrient productivities and on the yield characteristics of subsequent rice crops have not been well studied. To evaluate the effects of mix-seeding legume and non-legume cover crops on the value of green manure in paddy soil, barley and hairy vetch were sown at the rice harvesting stage as pure crops at the recommended rates (180kgha−1 of barley, B100; 90kgha−1 of hairy vetch, V100), and as mixtures, in which the two cover crops were mix-seeded with varying seed ratios according to the replacement principle. The mixed seeding of the two crops significantly increased the cover crop biomass and nutrient productivities compared with the single barley and hairy vetch cultivation. Biomass productivity linearly increased with increasing barley seeding level, but it was not affected by the hairy vetch seeding rate. The total N content of the barley biomass clearly increased as the proportion of the total biomass accounted for by hairy vetch was increased, and this significantly improved the value of the green manure of cover crop biomass. In contrast, the total N content of the hairy vetch biomass was not affected by changes in the barley proportion. Biomass produced in the pure barley seeding could not produce the nutrients required by the recommended chemical fertilization level (N–P2O5–K2O=90–45–57kgha−1) for rice, but the biomass increase caused by mixed seeding of the two cover crops resulted in enough nutrients to satisfy the recommended fertilization level. The highest biomass and nutrient yields were observed for the mixed seeding of barley and hairy vetch at 25 and 75% (B75V25) of their respective recommended seeding rates. This increased nutrient input stimulated the rice plant growth and significantly improved the rice yields. The highest yields were achieved with the B75V25 treatment. In conclusion, mixed seeding of legume hairy vetch and non-legume barley could be a very useful agronomic practice for increasing the cover crop biomass and its nutrient productivity and to improve the productivity of subsequent rice crops in temperate rice paddies.

Wheat Residue Management Options Affect Crop Productivity, Weed Growth, and Soil Properties in Direct‐Seeded Fine Aromatic Rice

Wheat residue management can influence soil health, weed growth, and productivity of subsequent rice crop. A field study was conducted to appraise the influence of different wheat residue management options viz., surface mulching of wheat residue (SMWR), wheat residue soil incorporation, wheat residue burning, zero tillage (ZT), and surface seeding on weed growth, soil physico‐chemical properties, and productivity of fine aromatic rice crop. Traditional transplanted rice (TPR) was maintained as control. The response of rice yield and its components including the number of productive tillers, grains per panicle and 1000‐grain weight differed significantly under the influence of various residue management options. SMWR recorded the highest grain yield (3.86 t ha−1) after TPR (4.18 t ha−1). Furthermore, the leaf area index and crop growth rate were also higher in SMWR and TPR compared with other treatments. Residue management options had a significant effect on weed population and dry biomass. A minimum weed density was observed in TPR (33–39 plants m−2) followed by SMWR (78–93 plants m−2). Available phosphorus in the experimental soil of TPR and SMWR treatments was increased by 74 and 45% compared to its initial value. Moreover, other soil attributes like organic matter, available potassium, and soil nitrogen were also improved by the application of wheat residue. Conclusively, SMWR was the best treatment for direct‐seeded rice among the residues management options in terms of final yield, weed burden, and improvement of soil health, although nitrogen and organic matter was higher under ZT.

Effect of <i>Stylosanthes guianensis</i> and Upland Rice Intercropping Ssystem to Rice Productivity

Upland rice grown with legume crop is thought to help in the nitrogen economy of the rice field, improve soil organic matter content through litter fall, and contributes to the control of weeds. Therefore, the objective of this study is to optimize establishment, survival of Stylosanthes plants and to achieve Stylosanthes biomass accumulation during fallow period for subsequent rice crop season, while minimizing competition with rice crop during Stylosanthes establishment. Stylosanthes was broadcasted and seeded in line four weeks after rice sowing at rate of 4 gm-2. The effect of Stylosanthes establishment on tiller number, plant height, biomass, panicle length, spikelet fertility, 1000 seed weight and rice grain yield was evaluated. Number of plants, plant height, canopy width and biomass of Stylosanthes also were measured. No competition effect on rice- Stylosanthes intercropping treatment was observed when compared with rice monoculture. Number of Stylosanthes plants and its biomass was about 3 times greater when Stylosanthes was line-sown than broadcasted into the rice stand. Similarly, stylosanthes plants were taller and its canopy was wider when line-sown than when broadcasted. Further it needs to evaluate the effect of relay-seeding Staylosanthes residuals either as short–term or long-term fallow crops in improving rice productivity.

Influence of Rapeseed Cake on Heavy Metal Uptake by a Subsequent Rice Crop After Phytoextraction Using Sedum plumbizincicola

A glasshouse pot experiment was conducted to study the effects of phytoextraction by Sedum plumbizincicola and application of rapeseed cake (RSC) on heavy metal accumulation by a subsequent rice (Oryza sativa L.) crop in a contaminated paddy soil collected from east China. After phytoextraction by S. plumbizincicola the soil and brown rice Cd concentrations effectively declined. After phytoextraction, RSC application reduced brown rice Cd concentrations in the subsequent rice crop to 0.23–0.28 mg kg−1, almost down to the standard limit (0.2 mg kg−1). After phytoextraction and then application of RSC, the soil solution pH, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations increased during early stages of rice growth resulting directly and indirectly in lowering the bioavailability of the heavy metals. Thus the grain yield of the subsequent rice crop increased and the heavy metals in the brown rice declined significantly. In this contaminated acid soil, growing the hyperaccumulator S. plumbizincicola and rice in rotation together with RSC application may therefore be regarded as a viable strategy for safe grain production and bioremediation.

Methane and nitrous oxide emissions from flooded rice fields as affected by water and straw management between rice crops

Rice fields in the tropics can vary in water regime before production of rice on flooded soil, but relatively little is known about the effects of soil water regime and crop residue management between rice crops (i.e., fallow period) on methane (CH4) and nitrous oxide (N2O) emissions during a subsequent rice crop. We measured CH4 and N2O emissions during two cropping seasons in the Philippines from field plots exposed to contrasting treatments during the fallow before land preparation for rice cultivation. The fallow treatments were continuous soil flooding (flooded), soil drying with exclusion of rainfall (dry), soil drying with dry tillage (dry+tillage), and a control with soil drying and wetting from rainfall (dry and wet). All plots were subdivided into removal of all aboveground rice residues from the previous crop (without residue) and retention of standing biomass after harvest of the previous rice crop (with residue). Emitted gas was collected weekly using chambers. Fallow treatments greatly influenced greenhouse gas (GHG) emissions during rice growth. Methane emissions and global warming potential (GWP) in both cropping seasons were highest following the flooded fallow, intermediate following the dry and wet fallow, and lowest following dry and dry+tillage fallows. The GWP was higher with than without residue across all fallow treatments. Nitrous oxide emissions were small during the season, and CH4 emissions contributed more than 90% of the cumulative GWP during the rice crop regardless of fallow and residue management. Soil drying between rice crops in the tropics can reduce CH4 emissions and GWP during the subsequent rice crop.

Wet cultivation in lowland rice causing excess water problems for the subsequent non-rice crops in the Mekong region

Crop diversification is advocated for improvement of income of lowland rice farmers in the Mekong region, including Laos, Cambodia and Thailand. One common problem of adding non-rice crops after wetland rice is excess water caused by reduced drainage associated with the hard pan that is commonly created to store water in the paddy for the rice crop. This paper firstly describes the water balance in the lowland fields particularly on how deep percolation is decreased by the hard pan, and the effect of wet cultivation on soil compaction and water availability in the subsequent crops such as mungbean. Experimental work in Cambodia shows how non-rice crops such as mungbean and peanut often fail completely or partially due to excess water. The common experience is complete failure of the early wet season non-rice crop when rain started earlier and the lowland paddy is saturated with water, but also non-rice crops often do not grow well due to shallow root systems confined to the top soil above the hard pan. Destructing the hard pan may help non-rice crops, but the process is expensive and may have an adverse effect on subsequent rice crops. Experimental work has also demonstrated that where irrigation water is available, irrigation is often not effective as it causes soil saturation in the top soil. Ways to minimize the excess water problem are discussed.

Management of Volunteer Corn Seedlings in Dry-Seeded Rice

The demand for corn is increasing in Asia for feed and biofuel. It is grown in the rice-corn cropping system. During harvest of corn, however, seeds drop on the soil surface and become problems as volunteer corn seedlings in the subsequent dry-seeded rice crop, in which the suppressive effect of standing water is absent. A study was conducted in screenhouse and field conditions to evaluate the effect of rice herbicides on the management of volunteer corn seedlings. In the screenhouse experiment, bispyribac-sodium at 0.030 and 0.045 kg·ai·ha-1 provided complete control of corn seedlings. Fenoxaprop + ethoxysulfuron and penoxsulam + cyhalofop did not provide effective control of corn seedlings. In the field, the sole application of bispyribac and sequential application of oxadiazon and bispyribac suppressed corn biomass by 60%-82% and 89%-91%, respectively, as compared with the nontreated control. The results of this study demonstrate that, in the absence of other management strategies, volunteer corn seedlings in dry-seeded rice systems can be managed by using bispyribac-sodium.

Managing Rice Residues and Fertilization to Improve Nutrient Use and Productivity of Irrigated Lowland Rice

Two field experiments were conducted in two sites with different soil properties to determine the appropriate management of rice residues coupled with cultural practices, including land preparation and fertilization to improve the nitrogen use efficiency and productivity of irrigated lowland rice. The study showed that in general, mowing of rice stubbles and either plowing or rotavating the soil did not affect the plant nutrient uptake (PNU), grain and straw yields, and yield components. In 2010 dry season, the highest PNU, yield, and return on investment (ROI) were obtained from the Minus-one Element Technique (MOET)-based fertilization compared to Nutrient Manager (NM)-based. In contrast, NM-based treatments had higher agronomic (AEN) and physiological efficiency of fertilizer nitrogen (PEN) due to higher level of N applied using the MOET compared to NM-based fertilization. In 2010 wet season, the incorporation of rice straw alone increased the uptake of P and K, similar to the crop supplied with additional inorganic fertilizer. Inorganic fertilizer treatments with or without additional chicken manure (CM) had higher grain and straw yields, yield components specifically number of tillers and panicles compared to CM and control treatments. The AEN of NSIC Rc212 was highest in plots with RIF, while CM produced the highest PEN due to higher percentage utilization or absorption of N in treatment with the least amount of N applied. Supplemental inorganic fertilizers in addition to rice residues and CM are indispensable to increase the rice yield. Incorporation of 4-5 t ha-1 rice straw for one cropping season of rice is not sufficient to significantly increase the N uptake and yield of the subsequent rice crop. The 2 month- fallow period after incorporation of straw and stubbles prior to transplanting did not affect rice yields suggesting that this length of time was sufficient to decompose the incorporated rice residues. The application of organic materials like rice straw and chicken manure was also instrumental in attaining adequate level of ROI. Therefore, continuous recycling and incorporation of rice straw in the soil during fallow period is not detrimental to the subsequent rice crop and contributes to the soil nutrient reserves which may lead to the improvement of yield and income in the long run.

Land application of rice husk ash, bagasse ash and coal fly ash: Effects on crop productivity and nutrient uptake in rice–wheat system on an alkaline loamy sand

Large quantities of rice husk ash (RHA), bagasse ash (BA) and coal fly ash (FA) are available in many Asian countries as waste materials, which create a serious disposal problem. Recycling of these ashes on agricultural land can help to improve physical and chemical fertility of soil. The present field experiment was conducted for three and half years to explore the possibilities to utilize these waste materials as soil amendments to improve productivity of rice–wheat system (RWS). The treatments consisted of application of RHA and BA at 10Mgha−1 to either wheat or to rice or to both wheat and rice and 20Mgha−1 to rice alone. The rates used for FA were 15 and 30Mgha−1. Addition of RHA and BA significantly increased the grain yield of wheat and rice but FA caused small increases in crop yields. Direct application of RHA and BA to wheat was significantly superior than their application to rice in the RWS. Direct application of RHA and BA to wheat resulted in 25 and 24% increase in mean grain yield of wheat and 10 and 11% increase in subsequent rice crop, respectively. However, direct application to rice resulted in 8 and 11% yield increase in rice and 10 and 14% increase in subsequent wheat for RHA and BA, respectively. Application of RHA and BA at 20Mgha−1 to rice resulted in lower RWS productivity than that applied at 10Mgha−1 to wheat. There was no significant effect of these ashes on heavy metal contents in grain and straw of the 7th crop of wheat. Application of three types of ashes generally resulted in positive P balance in RWS, however, K balance remained negative. These results suggest that RHA and BA can be recycled successfully in rice–wheat system to improve its productivity with no adverse effect on soil health.

Performance of two winter cover crops and their impacts on soil properties and two subsequent rice crops in Dongting Lake Plain, Hunan, China

Winter cover cropping is a common practice in paddy soils in southern China. This two year study (2008–2010) was undertaken to determine dry matter productivity and N uptake of two winter cover crops: ryegrass (Lolium multiflorum Lam.) and Chinese milkvetch (Astragalus sinicus L.) and their effects on soil properties as well as two subsequent rice (Oryza sativa L.) crops in Dongting Lake Plain in Hunan, China. Cover crops were broadcast sown in October, approximately 10d before the harvest of late rice. Ryegrass was first cut in March and finally harvested in April coincident with the plough of milkvetch. Two consecutive rice crops were grown following the cover crops without application of chemical N. Averaged over two years, ryegrass produced more aboveground dry matter and accumulated higher amounts of N than milkvetch (4.7Mgha−1 vs. 2.4Mgha−1, 128kgha−1 vs. 71kgha−1). Compared to CK (bare fallow without weed), both ryegrass (RG) and milkvetch (CMV) treated plots had lower soil bulk density at 0–15cm and 15–30cm depths. At the harvest of cover crops, CMV increased soil NH4+-N concentration at 0–10cm, 10–20cm and 20–30cm depths. In contrast, RG decreased soil NH4+-N and NO3−-N concentrations in the three depths. Averaged over four sampling dates in the double rice seasons in 2010, soil microbial biomass C was slightly different between RG (257mgkg−1) and CMV (249mgkg−1), and these were significantly higher than CK (218mgkg−1). Soil microbial biomass N was highest for CMV (15.4mgkg−1), followed by RG (11.3mgkg−1) and CK (6.1mgkg−1). Grain yield and total N yield of early rice were 0.6Mgha−1 and 11kgha−1 higher for CMV, respectively, and 1.0Mgha−1 and 20kgha−1 lower for RG as compared with CK averaged over years. Grain yield and total N yield of late rice were not significantly affected by cover crops.

Can rodent outbreaks be driven by major climatic events? Evidence from cyclone Nargis in the Ayeyawady Delta, Myanmar

Massive rodent population outbreaks occurred in the Ayeyarwady Delta, Myanmar, in July 2009, 15 months after cyclone Nargis. Satellite imagery with high temporal frequency was used to identify the area and planting time of rice at a landscape scale of > 80 000 ha, and household surveys of farmers were conducted to validate the mapping and to quantify losses. Farmers did not have problems with rodents in 2007-2008; rodents were the principal problem in the 2009 summer and monsoon rice crops. The landscape scale modeling indicated that high rodent densities in 2009 were associated with extended or delayed cropping and harvesting time because of asynchronous planting, and with an increase in the amount of abandoned agricultural land after cyclone Nargis. Asynchronous planting following cyclone Nargis provided abundant high-quality food for an extended period, which in turn led to a lengthened breeding season of rodents. The outbreak of populations 15 months after cyclone Nargis is consistent with the time it would take rodent populations to build from a low base after a major flooding event. To prevent rodent outbreaks effectively, synchronous planting, use of rice varieties with a similar maturation date and good field sanitation are important actions for subsequent rice crops after a major weather event.