Lowland Paddy Rice Research Articles

Diversity and Population of Weed Propagule in Two Rice Cropping Systems

Weeds can reduce rice yields by 20-89%, mainly due to competition for nutrients, water, sunlight, and growing space. Weeds that grow in rice fields come from propagules previously in the soil. Seedlings are formed from the previous season, so the cultivation system greatly affects them. This study aims to determine the diversity and population of weed propagules in upland rice and lowland rice. This research was conducted by survey method in Semanu District, Gunungkidul Regency, Special Region of Yogyakarta, by taking soil samples from three plots of upland rice and lowland rice paddy. Soil sampling was conducted four times before tillage, 3, 6, and 9 weeks after planting. The results showed that the diversity of weed propagules in upland rice was higher than in lowland rice fields with more weed propagule species. Annual terrestrial weed propagules dominate in upland rice, while in lowland rice fields, it is dominated by annual aquatic weed propagules. The diversity index of weed propagules in upland rice and rice paddy is included in the medium criteria. The number of species and individual propagule weeds in upland rice is more than in the upland rice fields. The results of this study can be used as a basis for proper weed management so that it does not disturb and harm rice plants.

PRODUKTIVITAS USAHATANI PADI SAWAH LEBAK DENGAN PEMBIAYAAN USAHATANI SISTEM TUNAI DAN YARNEN DI KECAMATAN SANGA DESA KABUPATEN MUSI BANYASIN

This study aims to find out how much farming productivity is in lowland paddy fields with cash and yarnen systems, the difference in productivity between farmers who buy production facilities with cash and yarnen systems and to find out how much income the farmers who buy production inputs with cash and yarnen systems earn. Simple random sampling methode is used in this study. The results of this study indicate that the productivity level of lowland paddy rice farming with the yarnen system is higher then cash system, where the average productivity of the yarnen system is 5,106 Kg/ha while the cash system is 4,583 Kg/ha. There is a significant difference between them. The average income of farmers with a cash system is Rp. 16,755,810 while the average income of farmers with the yarnen system is Rp. 13,130,817.

The assessment of rill irrigation and perforated pipes for Lowland paddy rice under the system of rice intensification (SRI)

The assessment of rill irrigation and perforated pipes for Lowland paddy rice under the system of rice intensification (SRI)

Acaulospora as the Dominant Arbuscular Mycorrhizal Fungi in Organic Lowland Rice Paddies Improves Phosphorus Availability in Soils

Flooding in rainfed lowlands greatly impairs the mutualistic relationship between indigenous arbuscular mycorrhizal fungi (AMF) and rice. In flooded soils, root colonization by AMF is arrested, but some AMF genera, defined as the core AMF, remain present. However, the core AMF in rainfed lowlands and their symbiotic roles remain unknown. Here, we showed that Acaulospora fungi were the core AMF in rice seedling roots of the Sangyod Muang Phatthalung (SMP) landrace rice variety grown in non-flooded and flooded paddy soils. Subsequently, indigenous Acaulospora spores were propagated by trap cultures using maize as the host plants. Therefore, to clarify the roles of cultured Acaulospora spores in a symbiotic partnership, the model japonica rice variety Nipponbare was grown in sterile soil inoculated with Acaulospora spores, and recolonized with a native microbial filtrate from the organic rice paddy soil. Our data demonstrated that the inoculation of Acaulospora spores in well-drained soil under a nutrient-sufficient condition for six weeks enabled 70 percent of the rice roots to be colonized by the fungi, leading to higher phosphate (Pi) accumulation in the mycorrhizal roots. Unexpectedly, the growth of rice seedlings was significantly suppressed by inoculation while photosynthetic parameters such as fractions of incoming light energy and relative chlorophyll content were unaltered. In the soil, the Acaulospora fungi increased soil phosphorus (P) availability by enhancing the secretion of acid phosphatase in the mycorrhizal roots. The findings of this work elucidate the symbiotic roles of the dominant Acaulospora fungi from lowland rice paddies.

Cattle biogas effluent application with multiple drainage mitigates methane and nitrous oxide emissions from a lowland rice paddy in the Mekong Delta, Vietnam

Household biogas production from livestock manure is popular in Vietnam. Effluent from the biogas production can be effectively used as organic fertilizer for rice cultivation. However, there is concern about enhanced methane (CH4) emission from the flooded soil under reductive conditions because the effluent contains labile organic carbon, the substrate for microbial CH4 production. We therefore combined multiple drainage with “cattle biogas effluent” (BE) application to mitigate CH4 emission by ameliorating the reductive soil conditions while obtaining grain yields comparable to the conventional practice, a combination of synthetic fertilizers (SY) application and continuous flooding (CF). We performed a 1-year experiment on a lowland (0 m a.s.l.) paddy field in the Mekong Delta, Vietnam, under a triple cropping system. We examined the effects of fertilizer type (SY and BE) and water management (CF, alternate wetting and drying [AWD], and midseason drainage followed by intermittent irrigation [MiDi]) on rice growth and yield and on CH4 and nitrous oxide (N2O) emissions. For AWD, a surface water level of −15 cm was used as the threshold for re-irrigation after natural drainage, whereas MiDi used a fixed irrigation schedule with one-time forced drainage during the midseason drainage period. Surface water level did not drop sufficiently in either AWD or MiDi due to the lowland conditions, and both practices caused similar seasonal changes in water level except for the forced drainage in MiDi. A significant (P = 0.05) interaction between fertilizer type and water management on grain yield was found only in dry season (winter–spring) with the highest yield level. Despite the poorly drained conditions, CH4 emission was significantly reduced by AWD and MiDi (by 27–30%), and both practices offset the significant CH4 emission enhancement by BE application. N2O emission was significantly reduced by BE application, whereas it was not affected by water management because flooded conditions were maintained during every nitrogen fertilizer application. Our results indicate that the combination of BE application and multiple drainage can mitigate CH4 and N2O emissions from a lowland rice paddy in the Mekong Delta without yield loss.

Is the energy balance in a tropical lowland rice paddy perfectly closed?

A two-year (2015 and 2016) field experiment was carried out to study the surface energy budget and energy balance closure (EBC) in a tropical lowland rice paddy in Cuttack, India. Maintenance of a standing water layer in lowland irrigated rice ecosystem makes it unique and this strongly influences the surface energy balance which may alter the surface runoff, ground water storage, water cycle, surface energy budget, and possibly microclimate of the region. To study this, an experiment was conducted using eddy covariance system to measure the surface energy balance components during two cropping seasons (dry season, DS and wet season, WS) and two consecutive fallow periods (dry fallow, DF and wet fallow, WF). The rice was grown in puddled wet lands in DS and WS and the ground was left fallow (DF and WF) during the rest of the year. Results displayed that daily average latent heat flux at surface (LE) and at canopy height (LEc) dominated over sensible heat flux at surface (H) and canopy height (Hc), respectively due to the presence of water source coming from the standing water in the rice field. The EBC was evaluated by ordinary least square (OLS), energy balance ratio (EBR) and residual heat flux (RHF). In OLS, the slope ranged 0.38-0.89 (2015) and 0.28-0.99 (2016) during the study period. Average RHF was 10.3-12.0% higher in WS as compared to DS. It was concluded that the EBC estimated using RHF is the most suitable way to calculate closure for lowland rice paddy since it can distinguish different seasons distinctively, followed by OLS. Much variation was not observed in EBR after inclusion of storage terms (water, soil, photosynthesis, canopy) to the classical EBR.

Co-application of poultry-litter biochar with Azolla has synergistic effects on CH4 and N2O emissions from rice paddy soils

Poultry-litter biochar and Azolla as green manure amendments are reported to enhance paddy soil fertility and rice yields. However, whether their co-application in lowland rice paddies has synergistic effects and whether those benefits are accompanied by greenhouse gas (GHG) emissions remains unknown. The objective of this study was to determine the effects of poultry-litter biochar (hereafter: biochar) and its co-application with Azolla as green manure (hereafter: Azolla), on the simultaneous methane (CH4) and nitrous oxide (N2O) emissions from a lowland paddy soil planted with rice during a single rice growing season in Tsuruoka, Yamagata, Japan. Biochar and Azolla amendments were applied once before rice was transplanted at a density of 20 t ha−1 and 133.9 kg N ha−1, respectively. Compared with NPK, NPK + biochar, and Azolla only treatments, Azolla and biochar co-application (i.e., Azolla + biochar) significantly increased CH4 emissions by 33%–197.6% in the early stages of rice growth (before 63 days after transplanting, DAT), but did not significantly influence CH4 emissions at both late rice growth stages (after 63 DAT,) and whole rice growth period (112 DAT). Conversely, Azolla + biochar significantly reduced N2O emissions by 83.0%–97.1% before 63 DAT, and by 76.4%–95.9% during the whole rice growth period at 112 DAT, with a significantly high interaction between biochar and fertilizer amendments. There were no significant N2O emission differences among all treatments after 63 DAT. Additionally, Azolla + biochar significantly increased rice grain yield by 27.3%–75.0%, and consequently, decreased both yield-equivalent CH4 emissions by 24.7%–25.0% and N2O emissions by 81.8%–97.7%. Our findings suggest that the co-application of poultry-litter biochar and Azolla as green manure offers a novel approach to increase rice yield while reducing the emissions of non-carbon dioxide greenhouse gases.

Accumulation of copper and cadmium in soil-rice systems in terrace and lowland paddies of the Red River basin, Vietnam: the possible regulatory role of silicon.

Rice production in floodplain deltas is currently vulnerable to climate change and contamination from anthropogenic activities. The relocation of rice production to upland regions could be an option for increasing the sustainability of rice production. Our study evaluated the spatial patterning of heavy metals, i.e., copper (Cu) and cadmium (Cd), in rice along a topogradient from terrace to lowland areas in the Red River basin. The dataset obtained from the analysis of 61 farm sites throughout the whole basin indicated a large discrepancy in the Cu and Cd contents in rice grains from terrace and lowland paddies. While Cu and Cd were not found in most of the rice grain samples from the terrace paddies, the median Cu and Cd contents of the lowland paddy rice were 1.895 and 0.033mgkg-1, respectively. Assessing the relationship of Cu and Cd in the soil-rice system to soil properties revealed possible correlations between soil available silicon (Si) and the Cu and Cd contents in rice grain. The enrichment of Si in rice plants likely reduces the translocation of Cu and Cd from soil to grain. Therefore, management of the Si supply, particularly in lowland paddies, should be highlighted as a way to reduce dietary intake of Cu and Cd.

Water-saving and drought-resistance rice: from the concept to practice and theory

The resource and environmental challenges faced by rice production call for resource-saving and environment-friendly rice varieties. Water-saving and drought-resistance rice (WDR) is a new type of cultivated rice combining both high yield potential and acceptable grain quality as a current lowland paddy rice, as well as water-saving and drought resistance as a traditional upland rice. The lowland and upland rice are two ecotypes adapted to contrasting soil water status, originating mainly because of their differentiated drought resistance. Upland rice, domesticated in a water–limited environment and experiencing a bidirectional selection process, has better drought resistance and especially better drought avoidance. Though the potential tradeoff between drought resistance and productivity is very common in rice, the bidirectional selection could overcome this tradeoff and accumulate recombination genotypes. It is very important to choose elite parents on the basis of studies on the great genetic diversity of rice yield and drought resistance among the rice germplasm resources and adapt the bidirectional selection strategies to especially integrate drought avoidance, drought tolerance, high water use efficiency, and productivity in WDR breeding. The breeding history and genomic studies indicated that lowland paddy rice and upland rice hybridization breeding with suitable selection in different environments is an effective approach to improving complex traits such as yield potential and drought resistance. Meanwhile, molecular technology shows higher efficiency on value-added breeding such as transferring and pyramiding pest- and disease-resistant genes, which helps WDR obtain other green characters. Twenty-two WDR varieties were registered and distributed to farmers in recent years and could be planted in both irrigated and rainfed ecosystems, thus showing promising application prospects. The major crop management technology of WDR in lowland paddy fields with water-saving cultivation and in rainfed fields by dry seeding with aerobic cultivation were also discussed in this article.

Combined effects of straw and water management on CH4 emissions from rice fields

Water and organic amendments are the two most important factors that control methane (CH4) emissions from rice fields, the combined effect of which on CH4 emissions has been rarely studied. Thus, a field experiment in a split-plot design was conducted to investigate the combined effect of straw and water management on CH4 emissions. Main plots had water treatments: continuous flooding (CF), flooding – midseason drying – flooding (FDF), and flooding for transplanting – rainfed (RF); and subplots had straw treatments: straw incorporated into soil (SI), straw mulching (SM), and without straw. Results showed that the presence of water layer led to substantial increase in CH4 emissions which were enhanced by straw application. Cumulative CH4 emissions were influenced by water, straw, and their interactions significantly (P < 0.05). The cumulative CH4 emissions were 505.3, 241.2, and 56.5 kg ha−1 for CF, FDF, and RF, respectively. By contrast, SI under CF, FDF, and RF increased CH4 emissions by 265.4, 271.4, and 175.6 kg ha−1, respectively. And SM under CF, FDF, and RF increased CH4 emissions by 213.3, 112.8, and 14.6 kg ha−1, respectively. The results indicated that SM resulted in less CH4 emissions compared with SI, especially in plots frequently with absence of water layer. Besides, SM had a potential to increase rice yield in rice paddies that had a lack of water. Therefore, in-season straw application should be avoided in lowland rice paddies, and straw mulching is practical in rice paddies lack of water.

Improving Efficiency and TFP of Lowland Paddy Rice Farmers in Kwara State of Nigeria

Purpose: The pressure on land for agricultural purposes is on the rise and sustainable agriculture remains the panacea for herdsmen attack on arable crop farmers in the study area. The present research empirically measured and identified the factors that influenced efficiency and Total Factor Productivity (TFP) of lowland paddy rice farmers in Kwara State of Nigeria.Research Methodology: The study made use of cross-sectional data collected from 200 active farmers during the 2016 cropping season via Multi-stage sampling technique. Instrument used to elicit information from the active farmers was structured questionnaire complemented with interview schedule and the collected data were analyzed using descriptive and inferential statistics.Findings: The results proved that majority of the farmers were not smart farmers which is responsible for negative TFP in most of the Decision making units (DMUs) as evident from poor robust increase in output index. However, the study inferred that there remained more untapped potentials in paddy rice production in the studied area.Limitations: The scope of the research is limited to lowland rice farmers in Kwara State of Nigeria.Originality/Value: Therefore, it was recommended that Government and non-governmental organisations should formulate supportive policies targeting sustainability of rice production viz. proper allocation of farm resources and also welfare improvement of the resource poor farmers for cultivating rice crops in the studied area.

Characterization of land surface energy fluxes in a tropical lowland rice paddy

A field experiment was conducted in 2015 to study the land surface energy fluxes from tropical lowland rice paddy in eastern India with an objective to determine the mass, momentum, and energy exchange rates between rice paddies and the atmosphere. All the land surface energy fluxes were measured by eddy covariance (EC) system (make Campbell Scientific) in dry season (DS, 1–125 Julian days), dry fallow (DF, 126–181 Julian days), wet season (WS, 182–324 Julian days), and wet fallow (WF, 325–365 Julian days). The rice was cultivated in dry season (January–May) and wet season (July–November) in low wet lands and the ground is kept fallow during the remainder of the year. Results showed that albedo varied from 0.09 to 0.24 and showed positive value from morning 6:00 h until evening 18:00 h. Mean soil temperature (Tg) was highest in DF, while the skin temperature (Ts) was highest in WS. Average Bowen ratio (B) ranged from 0.21 to 0.64 and large variation in B was observed during the fallow periods as compared to the cropping seasons. The magnitude of aerodynamic, canopy, and climatological resistances increased with the progress of cropping season and their magnitudes decreased during the end of both cropping seasons and found minimum during the fallow periods. At a constant vapor pressure deficit (VPD) at 0.16, 0.18, 0.15, and 0.43 kPa, latent heat flux (LE) initially increased, but later it tended to level off with an increase in VPD. The actual evapotranspiration (ETa) during both the cropping seasons was higher than the fallow period. This study can be used as a source of default values for many land surface energy fluxes which are required in various meteorological or air-quality models for rice paddies. A larger imbalance of energy was observed during the wet season as the energy is stored and perhaps advected in the fresh water.

Estimating nitrogen and phosphorus losses from lowland paddy rice fields during cropping seasons and its application for life cycle assessment

Estimating nitrogen and phosphorus losses into water bodies is crucial for evaluating the environmental impacts of rice cultivation. In this study, published data (N = 80) were used to estimate the total nitrogen (TN) and total phosphorus (TP) that could be lost through leaching and runoff during cropping seasons, taking into account factors that influence these losses. According to second-order Akaike's Information Criterion (AICc, one of the model selection methods), a model with soil temperature, TN input, inflow water, the incorporation of rice straw residue, puddling, and the use of slow-release fertilizer (P < 0.05) was chosen to estimate TN losses. A model with soil temperature, no application of phosphate fertilizer, medium- and coarse-textured soils (P < 0.05) and inflow water was chosen to estimate TP losses. The root mean square error was reduced by 34.5% for TN and by 21.8% for TP when these models were used compared to when the average proportions of outflowing nutrients were used (e.g., 17.0% for TN and 7.3% for TP in this study). The multiple regression model, taking into account site-specific conditions, was proven to be a readily available method to obtain knowledge of nutrient loading. Once process-based models are readily available, they will improve the estimates of eutrophication potential in life cycle assessments. Further improvement of the method is required, especially for the winter fallow period.

Burkholderia pseudomallei in a lowland rice paddy: seasonal changes and influence of soil depth and physico-chemical properties

Melioidosis, a severe infection with the environmental bacterium Burkholderia pseudomallei, is being recognised increasingly frequently. What determines its uneven distribution within endemic areas is poorly understood. We cultured soil from a rice field in Laos for B. pseudomallei at different depths on 4 occasions over a 13-month period. We also measured physical and chemical parameters in order to identify associated characteristics. Overall, 195 of 653 samples (29.7%) yielded B. pseudomallei. A higher prevalence of B. pseudomallei was found at soil depths greater than the 30 cm currently recommended for B. pseudomallei environmental sampling. B. pseudomallei was associated with a high soil water content and low total nitrogen, carbon and organic matter content. Our results suggested that a sampling grid of 25 five metre square quadrats (i.e. 25 × 25 m) should be sufficient to detect B. pseudomallei at a given location if samples are taken at a soil depth of at least 60 cm. However, culture of B. pseudomallei in environmental samples is difficult and liable to variation. Future studies should both rely on molecular approaches and address the micro-heterogeneity of soil when investigating physico-chemical associations with the presence of B. pseudomallei.

Metagenomic assessment of methane production-oxidation and nitrogen metabolism of long term manured systems in lowland rice paddy

Biochemical pathways of methanogenesis and methanotrophy coupled with carbon (C)-nitrogen (N) metabolism were studied in long term (13years) manured systems in lowland rice paddy through metagenomics approach. Manured systems included in this study were, control (exclusion of application of any manure), farm yard manure (FYM, @5Mgha−1yr−1) and green manuring (GM with Sesbania aculeata). Metagenomic sequence data revealed the dominance of C decomposing bacterial communities' like Proteobacteria, Planctomycetes, Actinobacteria, Firmicutes, Acidobacteria, in manure amended soils as compared to control. Diversities for assimilatory and dissimilatory N-fixing microorganisms at phylum level were found higher under GM as compared to rest. Two genera responsible for methanogenesis, viz. Methanolobus and Methanotorris were absent in manured systems as compared to control. The acetoclastic and serine pathway was found as the predominant pathway for methanogenesis and methanotrophy, respectively, in tropical lowland rice paddy. Abundance reads of enzymes were in the range of 254–445 in the acetoclastic methanogenesis pathway. On the other hand, these were varied from 165 to 216 in serine pathway of methanotrophy. Lowland paddy soil exhibited higher functional and structural diversities in manured systems as compared to unamended control in respect to labile C pools and CH4 production. Methane (CH4) emission was 31% higher in FYM system than GM. However, nitrous oxide (N2O) emission was found 25% higher in GM as compared to FYM. As a whole, bacterial diversities were higher under FYM system in tropical lowland rice paddy as compared to GM and unamended systems.

Synthetic Aperture Radar (SAR)-based paddy rice monitoring system: Development and application in key rice producing areas in Tropical Asia

Reliable and regular rice information is essential part of many countries’ national accounting process but the existing system may not be sufficient to meet the information demand in the context of food security and policy. Synthetic Aperture Radar (SAR) imagery is highly suitable for detecting lowland paddy rice, especially in tropical region where pervasive cloud cover in the rainy seasons limits the use of optical imagery. This study uses multi-temporal X-band and C-band SAR imagery, automated image processing, rule-based classification and field observations to classify rice in multiple locations across Tropical Asia and assimilate the information into ORYZA Crop Growth Simulation model (CGSM) to generate high resolution yield maps. The resulting cultivated rice area maps had classification accuracies above 85% and yield estimates were within 81-93% agreement against district level reported yields. The study sites capture much of the diversity in water management, crop establishment and rice maturity durations and the study demonstrates the feasibility of rice detection, yield monitoring, and damage assessment in case of climate disaster at national and supra-national scales using multi-temporal SAR imagery combined with CGSM and automated methods.

Utilizing rainfall and alternate wetting and drying irrigation for high water productivity in irrigated lowland paddy rice in southern Taiwan

Taiwan’s average annual rainfall is high compared to other countries around the world; however, it is considered a country with great demand for water resources. Rainfall along with alternate wetting and drying irrigation is proposed to minimize water demand and maximize water productivity for lowland paddy rice cultivation in southern Taiwan. A field experiment was conducted to determine the most suitable ponded water depth for enhancing water saving in paddy rice irrigation. Different ponded water depths treatments (T2 cm, T3 cm, T4 cm and T5 cm) were applied weekly from transplanting to early heading using a complete randomized block design with four replications. The highest rainwater productivity (2.07 kg/m3) was achieved in T5 cm and the lowest in T2 cm (1.62 kg/m3). The highest total water productivity, (0.75 kg/m3) and irrigation water productivity (1.40 kg/m3) was achieved in T2 cm. The total amount of water saved in T4 cm, T3 cm and T2 cm was 20, 40, and 60%, respectively. Weekly application of T4 cm ponded water depth from transplanting to heading produced the lowest yield reduction (1.57%) and grain production loss (0.06 kg) having no significant impact on yield loss compared to T5 cm. Thus, we assert that the weekly application of T4 cm along with rainfall produced the best results for reducing lowland paddy rice irrigation water use and matching the required crop water.

Changing local land systems: Implications of a Chinese rubber plantation in Nambak District, Lao PDR

This paper investigates the direct and cascading land system consequences of a Chinese company's land acquisition for rubber cultivation in northern Laos. Transnational land acquisitions are increasingly acknowledged as an important driver of direct land use conversion with implications for local land‐based livelihoods. The paper presents an empirical case study of the village of Na Nhang Neua in Nambak District, Luang Prabang Province, using a mixed methods approach to investigate the positive and negative implications for household agricultural strategies, income generation and food security. Combining the conceptual lenses of land systems and livelihood approaches, this paper demonstrates how the land use system has changed substantially because of the establishment of the rubber plantation by the company, notably in the linkages between livestock rearing, upland shifting cultivation and lowland paddy rice cultivation. The changes go beyond the immediate competition for land caused by the rubber plantation: a penalty scheme introduced by the rubber company for damage to rubber trees caused by browsing animals has led the villagers to abandon livestock rearing, causing a cascade of negative effects on the entire land use system, especially on soil fertility, rice yields and food production.

Within field spatial variation in methane emissions from lowland rice in Myanmar.

An assessment of within field spatial variations in grain yield and methane (CH4) emission was conducted in lowland rice fields of Myanmar. Two successive rice fields (1st field and 2nd field) were divided into fertilized and non-fertilized parts and CH4 measurements were conducted at the inlet, middle and outlet positions of each field. The results showed that CH4 emissions at non-fertilized parts were higher than those at fertilized part in both rice fields. The average CH4 emissions ranged from 8.7 to 26.6 mg m-2 h-1 in all positions in both rice fields. The spatial variation in CH4 emission among the positions was high in both rice fields with the highest emissions in the outlet of the 1st field and the inlet of the 2nd field. The CH4 emissions at these two positions showed 2 - 2.5 times higher than those at other positions in both rice fields. Stepwise regression analysis indicates that soil total carbon content is the primary factor for CH4 emission. The average CH4 emissions during rice growing season were 13.5 mg m-2 h-1 for the 1st field and 15.7 mg m-2 h-1 for the 2nd field. Spearman rank order correlation analysis showed that CH4 emission was significantly and positively correlated with soil temperature, surface water depth and negatively correlated with soil redox potential. The result indicated that high within field spatial variation in CH4 emissions required different site specific management practices to mitigate CH4 emissions in lowland paddy rice soil.

Evaluation of N environmental risks on Andosols from an intensive dairy farming watershed using DNDC

Manure nitrogen (N) in the livestock sector has become a key driver of environmental change. The denitrification–decomposition (DNDC) model was used to evaluate N pollution strengths on Andosols with intensive dairy manure application in Upper Naka River Watershed, Japan. The calibrated model was capable of predicting Andosol N flows because the simulated soil mineral N content, soil nitrogen oxide (N2O) fluxes, denitrification rate, and crop N uptake matched the patterns and magnitudes of the field observations from a wide range of soil textures, as well as manure management and cropping systems. The simulations showed that current intensive manure application systems caused low crop N use efficiency and a large amount of NO3−-N leaching and N2O emission. The crop N use efficiency was 27%–42% and 37%–55% of input N for uplands and paddy rice, respectively. The uplands showed much more serious N environmental pollution risks with N leaching 123–362kgNha−1yr−1 and N2O emissions 6.53–11.8kgNha−1yr−1 than that in the lowland paddy rice with N leaching 17.4–103kgNha−1yr−1 and N2O emissions 0.59–2.77kgNha−1yr−1. Forage rice/barley crop systems have high N cleaning capability due to the greater crop N uptake which reached to 304kgNha−1yr−1. High precipitation stimulated more NO3−-N leaching. Sandy soil also showed higher N leaching and was unsuitable for paddy rice. Slurry application stimulated more N2O emission than compost manure. To mitigate the current high N pollution, the critical N application rate was recommended to be approximately 380, 470, 640, and 390kgNha−1yr−1 for loam sand planted with maize/grass, loam soil with maize/grass, forage rice/barley, and rice/fallow with winter manure application, respectively.