Technical adaptations for mechanized SRI production to achieve water saving and increased profitability in Punjab, Pakistan

Even in a country with a large population and rapid population growth, there can be labor shortages in the agricultural sector, because of outmigration of the able-bodied work force. The System of Rice Intensification (SRI) is not necessarily more labor-intensive once the methods have been learned, but the initial labor requirements can be a barrier to adoption, and farmers with large land areas cannot find the labor needed to use these more productive methods. Recognizing this problem, a set of agricultural implements have been designed for mechanizing the operations of SRI, with a view to reducing water requirements as well as labor requirements because the current conditions for agricultural production in the Punjab region of Pakistan include water scarcity and poor water quality as well as labor shortages. This article reports on the process of mechanizing SRI production in Punjab, which has been quite successful so far. Average yield is considerably increased with a 70% reduction in water requirements and a similar reduction in labor needs. The machinery and methods have been further adapted to other crops, being grown on permanent-raised beds, so that SRI with organic fertilization is combined with Conservation Agriculture. This combination is referred to as “paradoxical agriculture” because it enables farmers to achieve higher outputs with reduced inputs.     

Aflatoxins and ochratoxin A contamination in rice,corn and corn products from Punjab,Pakistan

In present study, a total of 275 retail cereal samples including rice, corn and corn products was analyzed for the presence of aflatoxins and ochratoxin A (OTA) using HPLC equipped with a fluorescence detector. The data has shown that 38 out of 68 samples of rice, 37/105 of corn and 43/102 samples of corn products have been found contaminated with AFs, average level of AFB₁ and total AFs, 8.23 and 19.54, 7.90 and 12.08, and 5.47 and 7.85 μg/kg, respectively. Furthermore, 34, 28 and 26 numbers of rice, corn and corn product samples were found to be contaminated with OTA with an average level of 12.94, 5.29 and 3.69 μg/kg, respectively. The samples of rice, corn and corn products found above the permissible European Union (EU) limit for AFB₁ and total AFs were 18, 13 and 14 and 28, 14 and 20%, respectively; however, the samples of rice, corn and corn products above the EU limit were 40, 14 and 15%, respectively.     

Aflatoxins and ochratoxin A contamination in rice,corn and corn products from Punjab,Pakistan

In present study, a total of 275 retail cereal samples including rice, corn and corn products was analyzed for the presence of aflatoxins and ochratoxin A (OTA) using HPLC equipped with a fluorescence detector. The data has shown that 38 out of 68 samples of rice, 37/105 of corn and 43/102 samples of corn products have been found contaminated with AFs, average level of AFB₁ and total AFs, 8.23 and 19.54, 7.90 and 12.08, and 5.47 and 7.85 μg/kg, respectively. Furthermore, 34, 28 and 26 numbers of rice, corn and corn product samples were found to be contaminated with OTA with an average level of 12.94, 5.29 and 3.69 μg/kg, respectively. The samples of rice, corn and corn products found above the permissible European Union (EU) limit for AFB₁ and total AFs were 18, 13 and 14 and 28, 14 and 20%, respectively; however, the samples of rice, corn and corn products above the EU limit were 40, 14 and 15%, respectively.     

Comparison of N uptake and internal use efficiency in two tobacco varieties

To explain the observation in field experiments that tobacco variety CB-1 was more nitrogen(N)-efficient than K326, the influence of two N levels on growth, N uptake and N flow within plants of the two tobacco varieties was studied. Xylem sap from the upper and lower leaves of both tobacco varieties cultured in quartz sand was collected by application of pressure to the root system. CB-1 took up more N with smaller roots at both high(HN, 10 mmol L-1) and low(LN, 1 mmol L-1) N levels, and built up more new tissues in upper leaves especially at LN level,than K326. Both varieties showed luxury N uptake, and CB-1 accumulated significantly less NO-3in new tissues than K326, when grown at the HN level. At both N levels, the amount of xylem-transported N and phloem-cycled N from shoot to root in K326 was greater than those in CB-1, indicating higher N use efficiency in CB-1 shoots than in K326 shoots. The major nitrogenous compound in the xylem sap was NO-3irrespective of N level and variety. Low N supply did not cause more NO-3reduction in the root. The results indicated that the N-efficient tobacco variety CB-1 was more efficient in both N uptake by smaller roots and N utilization in shoots, especially when grown at the LN level.     

Yield, grain quality and water use efficiency of rice under non-flooded mulching cultivation

Plastic film or straw mulching cultivation under non-flooded condition has been considered as a new water-saving technique in rice production. This study aimed to investigate the yield performance in terms of quality and quantity and water use efficiency (WUE) under such practices. A field experiment across 3 years was conducted with two high-yielding rice cultivars, Zhendao 88 (a japonica cultivar) and Shanyou 63 (an indica hybrid cultivar) and four cultivation treatments imposed from transplanting to maturity: traditional flooding as control (TF), non-flooded plastic film mulching (PM), non-flooded wheat straw mulching (SM), and non-flooded no mulching (NM). Compared with those under the TF, root oxidation activity, photosynthetic rate, and activities of key enzymes in sucrose-to-starch conversion in grains during the grain filling period were significantly increased under the SM, whereas they were significantly reduced under the PM and NM treatments. Grain yield showed some reduction under all the non-flooded cultivations but differed largely among the treatments. The reduction in yield was 7.3–17.5% under the PM, 2.8–6.3% under the SM, and 39–49% under the NM. The difference in grain yield was not significant between TF and SM treatments. WUE for irrigation was increased by 314–367% under the PM, 307–321% under the SM, and 98–138% under the NM. Under the same treatment especially under non-flooded conditions, the indica hybrid cultivar showed a higher grain yield and higher WUE than the japonica cultivar. The SM significantly improved milling, appearance, and cooking qualities, whereas the PM or the NM decreased these qualities. We conclude that both PM and SM could significantly increase WUE, while the SM could also maintain a high grain yield and improve quality of rice. The SM would be a better practice than the PM in areas where water is scarce while temperature is favorable to rice growth, such as in Southeast China.     

Highly client-oriented breeding,using local preferences and selection,produces widely adapted rice varieties

When explicit measures are taken to account for the needs of clients (farmers and consumers) it results in highly client-oriented breeding. This involves the participation of farmers to specify the design of desirable varieties and, once they are produced, their testing without delay with the target clients in the target environments. The term highly client-oriented breeding (COB) explains the purpose of farmer involvement – the deliberate achievement of a high degree of client orientation – rather than simply explaining the process of farmers participating in plant breeding (participatory plant breeding). Client-oriented breeding is sometimes based on the preferences of relatively few farmers in a small area, so a possible drawback is that it will produce varieties that are too locally adapted. We describe the testing of varieties in the High Barind Tract (HBT) of Bangladesh from a COB programme carried out in Chitwan district, Nepal. The two best lines, Judi 582 and Judi 567, yielded 19–50% more during the T. Aman season and 106% more during the Aus season than check varieties in the HBT. Research to determine farmers’ preferences and adoption consistently showed these varieties were preferred over all available alternatives. The new varieties were broadly adapted as they were superior in all the three rice-growing seasons over varying levels of inputs. This broad adaptation could be explained by the breeding method: the generations were advanced in two contrasting seasons and each generation was grown on a different farmer's field under different management and planting dates. Because the segregating generations were grown under moderate and fluctuating levels of nitrogen, it is to be expected that genotypes with good nitrogen use efficiency will be selected that can also respond to added nitrogen. Overall, the cost-effectiveness of COB was high as it produced widely adapted genotypes from a small breeding programme, and knowledge of farmers’ preferences increased the efficiency of targeting new germplasm.     

Evaluation of potato seed tubers from different sources in the Punjab plain of Pakistan

Inability to produce large quantities of high quality, relatively diseasefree potato seed is a major constraint to providing economic support to a highly important and rapidly expanding potato production industry in Pakistan. Studies were undertaken for 5 years to evaluate productivity of seed of cultivars Red Bad, Ajax, Atica, Patrones, Montana, Cosima, Desiree, and Cardinal grown at five environmentally diverse locations in Pakistan versus seed of the same cultivars imported from Europe. The productivity trials were conducted during the autumn and spring seasons at the Ayub Agricultural Research Institute, Faisalabad (Punjab Plains). The results from the 5-year test period indicate that seed of each of the cultivars produced in the high hills (Baluchistan, Northwest Frontier Province) and during autumn (September to December) in the Punjab Plains, the latter cold stored until the following September, are equally as productive as seed imported from Europe.     

Nitrogen use efficiency in selected rice (Oryza sativa L.) genotypes under different water regimes and nitrogen levels

Water and nutrient availability are two major constraints in most rice-based rainfed shallow lowland systems of Asia. Both stresses interact and contribute to the low productivity and widespread poverty in this environment. The objective of this study was to improve the understanding of interaction between the two factors and to identify varietal characteristics beneficial for productivity in a water- and nutrient-limited rice environment. For this purpose, we screened 19 rice genotypes adapted to different rice environments under two water and two nutrient treatments during the wet season of 2004 and 2005 in southern Luzon, Philippines. Across all genotypes tested and in comparison with the irrigated control, rainfed conditions reduced grain yield of the treatment without N application by 69% in 2004 and by 59% in 2005. The mean nitrogen fertilizer response was highest in the dryer season of 2004 and the rainfed treatment, indicating that water stress had no effect on fertilizer response. Nitrogen application reduced the relative yield loss to 49% of the irrigated treatment in 2004 and to 52% of the irrigated treatment in 2005. Internal efficiency of N (IEN) and recovery efficiency of applied N (REN) were significantly different between genotypes, but were not affected by water availability (REN) or by water and nutrient availability (IEN). In contrast, grain yield and total N uptake were affected by cultivar, N and water availability. Therefore, germplasm for rainfed environments should be screened under conditions of limited and good nitrogen and water supplies. The four best cultivars, CT6510-24-1-2, IR55423-01, IR72, and IR57514-PMI5-B-1-2, performed well across all treatments and both years. Except for IR72, they were all characterized by medium height, medium duration, high early vigor, and a moderate level of drought tolerance. This combination of characteristics seems to enable the optimal use of limited water and nutrient resources occurring in many shallow rainfed lowlands. We also concluded that moderate drought stress does not necessarily affect the response to moderate N rates, provided that drought does not induce high spikelet sterility and that fertilizer N is properly managed.     

Developing green super rice varieties with high nutrient use efficiency by phenotypic selection under varied nutrient conditions

The development of green super rice varieties with improved nutrient use efficiency(NuUE)is a vital target area to increase yield and make it more stable under rainfed conditions.In the present study, we followed an early backcross(BC) breeding approach by using a highyielding and widely adapted Xian variety, Weed Tolerant Rice 1(WTR-1), as a recipient and a Geng variety, Hao-An-Nong(HAN), as a donor.Starting from the BC1F2 generation, the BC population went through one generation of selection under irrigated, low-input, and rainfed conditions, followed by four consecutive generations of screening and selection for high grain yield(GY) under six different nutrient conditions(NPK, 75 N,-N,-P,-NP, and-NPK), leading to the development of 230 BC1F6 introgression lines(ILs).These 230 ILs were evaluated under the same six nutrient conditions for 13 agro-morphological and grain yield component traits in comparison to four checks and parents.Significant trait variations were observed between the treatments and ILs.Positive correlations were identified for GY with biomass, panicle length, flag-leaf area, flag-leaf width, filled grain number per panicle,1000-grain weight, and tiller number under-N,-P,-NP, and-NPK conditions.Out of 230 ILs,12 were identified as promising under two or more nutrient deficiency conditions.The results demonstrated an efficient inter-subspecific BC breeding procedure with a first round of selection under rainfed-drought conditions, followed by four generations of progeny testing for yield performance under six nutrient conditions.The promising ILs can be useful resources for molecular genetic dissection and understanding the physiological mechanisms of NuUE.     

水稻不同品种(组合)谷粒分离力研究

水稻谷粒分离力指将稻谷谷粒从穗上拉下时所需的拉力,该指标是影响水稻脱粒性能的主要因素。分离力太小,稻谷在收获作业过程中,特别是机械收获时,极易丢粒。造成较大的落粒损失。分离力太大,则造成脱粒困难。在收获过程中产生较大的脱不净损失,本试验的目的在于研究水稻不同品种(组合)的谷粒分离力的一些特点,为减少稻谷收获过程中的损失提供参考依据。     

Physiological responses of argentine peanut varieties to water stress.: Light interception, radiation use efficiency and partitioning of assimilates

In Argentina, peanut production is concentrated in areas where unpredictable and intermittent periods of water deficit occur almost every year especially, during the pod growth period. Florman INTA is the most popular variety among peanut producers, but it is highly sensitive to drought. Manfredi 393 INTA was released as a drought-tolerant variety. Differences between these varieties in radiation interception and crop mass accumulation relative to light levels, as well as in allocation of assimilate to economic yield under water deficit, have not been previously studied.

An experiment was set with two different regimes of water supply. Half of the crop was irrigated (IRR) from sowing to maturity, while the other half received no water between 47 and 113 days after sowing. The fraction of PAR intercepted, (f), leaf area, pod and vegetative above-ground biomass and leaf carbon dioxide exchange rate (CER) were measured periodically during the water deficit period. The leaf area index, degree of leaf folding, canopy extinction coefficient, radiation use efficiency (RUE), partitioning factor, (p), and harvest index (HI) were calculated from the measurements.

Under water stress, f was reduced in both varieties with respect to their controls, and the reduction was proportionally higher in Florman INTA as a consequence of a higher leaf area reduction and degree of leaf folding. However, f remained higher in Florman INTA than in Manfredi 393 INTA due to the enhanced capacity of the former to generate leaf area under non-limiting water supply.

RUE values were higher in Manfredi 393 INTA than in Florman INTA, both under irrigation as well as under severe water deficit, where they were obtained using a two-parameter exponential model. The reason for the higher RUE values in Manfredi 393 INTA was its ability to maintain a higher leaf CER.

Partitioning to pods under irrigation was greater in Manfredi 393 INTA than in Florman INTA, as a result of a longer pod filling period and higher p. Towards the end of podfill, there was a rapid increase of p in Florman INTA, but too late to improve its HI. Under water stress, the time course of p for both varieties was lower than in the IRR treatments and consequently, HI at harvest was reduced. Low HI values could be attributed to some extent to the mechanical impedance of the upper soil layer, caused by water deficit. Mechanical impedance alters the relation among p and HI values obtained under irrigation and water stress. However, even if it is accounted for, cultivars with high HI under IRR conditions usually have high HI under water deficit.     

Variation in vitamin E level and aflatoxins contamination in different rice varieties

In the present study, a total of 380 samples of 5 rice varieties were investigated for the presence of aflatoxins (AFs) and tocopherols (Vitamin E) using HPLC, equipped with a fluorescence detector. The data revealed that super basmati rice has the highest mean level of total AFs (12.45 μg/kg) followed by KS-282 (11.2 μg/kg), basmati PK-385 (9.8 μg/kg), Irri-6 (9.7 μg/kg) and the lowest mean level was found in Irri-9 (8.9 μg/kg). Furthermore, the results have shown that the variety with lowest level of AFs has the highest level of tocopherol content; i.e. Irri-9 (53.2 mg/100 g), basmati PK-385 (45.9 mg/100 g), Irri-6 (45.3 mg/100 g), KS-282 (40.4 mg/100 g) and super basmati rice (40.2 mg/100 g). The data has shown correlation (r = −0.62, p < 0.05) between vitamin E content and AFs concentration in different rice varieties. The results are interesting and need further study to investigate the mechanistic background of vitamin E content and its effect on aflatoxins contamination.     

The impact of on-farm water saving irrigation techniques on rice productivity and profitability in Zhanghe Irrigation System,Hubei, China

To optimize the use of limited water resources, surface irrigation systems in parts of China have introduced a new water saving irrigation method for rice termed alternate wetting and drying (AWD). The basic feature of this method is to irrigate so that the soil alternates between periods of standing water and damp or dry soil conditions from 30 days after crop establishment up to harvesting. However, many Chinese rice farmers still practice the continuous irrigation method with late- season drying of the soil.A comparative assessment of these two methods of on-farm water management for rice was conducted at two sites within the Zhanghe Irrigation System (ZIS) in Hubei province of China for the 1999 and 2000 rice crops. The objective was to evaluate the impact of AWD on crop management practices and the profitability of rice production. In conjunction with irrigation district officials, two sites within ZIS were selected for study, one where AWD was supposed to be widely practiced (Tuanlin, TL) and one where it had not been introduced (Lengshui, LS). It was found that farmers at both sites do not practice a pure form of either AWD or continuous flooding. However, farmers in TL did tend to let the soil dry more frequently than their counterparts in LS.Because most farmers practice neither pure AWD nor pure continuous flooding, an AWD score was developed that measures the frequency with which farmers allow their soil to dry. This AWD score was not significantly correlated with yield after controlling for site and year effects and input use. AWD scores were also not correlated with input use. We conclude that AWD saves water at the farm level without adversely affecting yields or farm profitability.     

行向对不同穗型水稻品种的影响

以直立穗型和弯曲穗型两种类型水稻为材料,研究了不同行向对水稻分蘖数、维管束和穗部性状的影响。试验结果表明:行向对群体分蘖数的影响较小,分蘖数主要由品种决定;不同行向处理对不同穗型水稻的维管束影响较小,但对穗部性状有一定的影响。     

Yield potential and water use efficiency of aerobic rice (Oryza sativa L.) in Japan

Intensive rice farming in aerobic soil, referred to herein as aerobic rice, can greatly reduce the water input compared to that of flooded rice cultivation. The objective of this study was to compare the potential productivity of aerobic rice and flooded rice using high-yielding varieties at two locations in Japan in two successive years. In aerobic fields, the total amount of water supplied (irrigation plus rainfall) was 800–1300 mm. The soil water potential at 20-cm depth averaged between −15 and −30 kPa each growing season, but frequently reached −60 kPa. The average yield under aerobic conditions was similar to or even higher than that achieved with flooded conditions (7.9 t ha⁻¹ in 2007 and 9.4 t ha⁻¹ in 2008 for aerobic versus 8.2 t ha⁻¹ for flooded). The average water productivity under aerobic conditions was 0.8–1.0 kg grain m⁻³ water, slightly higher than common values in the literature. The super-high-yielding cultivar Takanari achieved yields greater than 10 t ha⁻¹ with no yield penalty under aerobic conditions in 3 out of 4 experiments. The favorable agronomic characteristic of Takanari was its ample sink capacity (grain number × grain weight). In conclusion, high-productivity rice cultivation in aerobic soil is a promising technology for water conservation. With continued breeding, future aerobic rice varieties will possess large numbers of spikelets and sufficient adaptation to aerobic conditions such that they will consistently achieve yields comparable to the potential yield of flooded rice.     

Nutrient uptake and water use efficiency as affected by modified rice cultivation methods with reduced irrigation

A field experiment was conducted in 2005 to investigate the effects of modified rice cultivation methods on: water use efficiency, the uptake of nutrients (N, P and K) by plants, and their distribution within plants and their internal use efficiency. The treatments were modified methods of irrigation, transplanting, weeding, and nutrient management, comparing the System of Rice Intensification (SRI) with standard rice-growing methods including traditional flooding (TF). Results showed that the uptake of N, P, and K by rice plants during their growth stages was greater with SRI management compared to TF, except during the tillering stage. At maturity stage, SRI plants had taken up more nutrients in their different major organs (leaves, stems, and sheaths; panicle axis; and seeds), and they translocated greater amount of nutrients to the grain. Under SRI, the ratio of N, P, and K in seed grain to total plant N, P, and K was 4.97, 2.00, and 3.01% higher, respectively, than with TF. Moreover, under SRI management, internal use efficiency of the three macronutrients (N, P, and K) was increased by 21.89, 19.34, and 16.96%, respectively, compared to rice plants under TF management. These measurements calibrate the crop’s physiological response to differences in cultural practices, including the maintenance of aerobic versus anaerobic environment in the root zones. With SRI, irrigation water applications were reduced by 25.6% compared to TF. Also, total water use efficiency and irrigation water use efficiency was increased with SRI by 54.2 and 90.0%, respectively. Thus, SRI offered significantly greater water saving while at the same time producing more grain yield, in these trials 11.5% more compared to TF.     

Genotypic variation in nitrogen use efficiency in medium- and long-duration rice

A field experiment was conducted in the dry season at Los Baños, Philippines, to assess the differences in grain yield and N utilization of 10 medium-duration (119±4 days after seeding [DAS]) genotypes and 10 long-duration (130±4 DAS) ones with varying acquisition and usage of soil and fertilizer N. Significant differences among genotypes were observed in grain yield and N uptake, efficiency and partitioning parameters (physiological N use efficiency [PNUE], agronomic N use efficiency [ANUE], apparent recovery [AR], partial factor productivity of applied N [PFP_N], N productivity index [NPI], and N harvest index [NHI]). The N-efficient genotypes that produced high grain yield at both low and high levels of N were IR54790-B-B-38, BG380-2, BG90-2 (medium-duration), and IR3932-182-2-3-3-2, IR54853-B-B-318, and IR29723-88-2-3-3 (long-duration). Inefficient genotypes that produced low yields at low N levels but responded well to N application were IR58125-B-B-42, IR49457-33-1-2-2-2, and BG34-8 (medium-duration), and IR8192-200-3-3-1-1, IR21848-65-3-2-2, and PR106 (long-duration). IR20 (medium) and Palawan (long-duration) were N-inferior genotypes giving low yields at both low and high N levels. Increase in grain yield was highly correlated with N uptake (r²=0.75**). The grain yield-N uptake relationship for individual genotypes indicated significant differences in slope and in the yield obtained with soil N (GY₀). Differences in GY₀ were due to genotypic variation in N uptake and efficiency of use. NHI was related to both N uptake and use efficiency. NPI, which integrated both GY₀ and PNUE, provided a better ranking of genotypes. The performance of efficient and inefficient genotypes over a range of soil and fertilizer N supply was consistent over three seasons of trials.     

Radiation use efficiency,N accumulation and biomass production of high-yielding rice in aerobic culture

The concept of aerobic culture is to save water resource while maintaining high productivity in irrigated rice ecosystem. This study compared nitrogen (N) accumulation and radiation use efficiency (RUE) in the biomass production of rice crops in aerobic and flooded cultures. The total water input was 800–1300 mm and 1500–3500 mm in aerobic culture and flooded culture, respectively, and four high-yielding rice cultivars were grown with a high rate of N application (180 kg N ha⁻¹) at two sites (Tokyo and Osaka) in Japan in 2007 and 2008. The aboveground biomass and N accumulation at maturity were significantly higher in aerobic culture (17.2–18.5 t ha⁻¹ and 194–233  kg N ha⁻¹, respectively) than in flooded culture (14.7–15.8 t ha⁻¹ and 142–173 kg N ha⁻¹) except in Tokyo in 2007, where the surface soil moisture content frequently declined. The crop maintained higher N uptake in aerobic culture than in flooded culture, because in aerobic culture there was a higher N accumulation rate in the reproductive stage. RUE in aerobic culture was comparable to, or higher than, that in flooded culture (1.27–1.50 g MJ⁻¹ vs. 1.20–1.37 g MJ⁻¹), except in Tokyo in 2007 (1.30 g MJ⁻¹ vs. 1.37 g MJ⁻¹). These results suggest that higher biomass production in aerobic culture was attributable to greater N accumulation, leading to higher N concentration (N%) than in flooded culture. Cultivar differences in response to water regimes were thought to reflect differences in mainly (1) early vigor and RUE under temporary declines in soil moisture in aerobic culture and (2) the ability to maintain high N% in flooded culture.     

Influence of rice varieties,nitrogen management and planting methods on methane emission and water productivity

A field experiment was conducted during rainy seasons of 2009 and 2010 at New Delhi, India to study the influence of varieties and integrated nitrogen management (INM) on methane (CH₄) emission and water productivity under flooded transplanted (FT) and aerobic rice (AR) cultivation. The treatments included two rice (‘PB 1’ and ‘PB 1121’) varieties and eight INM practices including N control, recommended dose of N through urea, different combinations of urea with farmyard manure (FYM), green manure (GM), biofertilizer (BF) and vermicompost (VC). The results showed 91.6–92.5 % lower cumulative CH₄ emission in AR compared to FT rice. In aerobic conditions, highest cumulative CH₄ emission (6.9–7.0 kg ha^?1) was recorded with the application of 100 % N by organic sources (FYM+GM+BF+VC). Global warming potential (GWP) was significantly lower in aerobic rice (105.0–107.5 kg CO₂ ha^?1) compared to FT rice (1242.5–1447.5 kg CO₂ ha^?1). Significantly higher amount of water was used in FT rice than aerobic rice by both the rice varieties, and a water saving between 59.5 and 63 % were recorded. Under aerobic conditions, both rice varieties had a water productivity of 8.50–14.69 kg ha^?1, whereas in FT rice, it was 3.81–6.00 kg ha^?1. In FT rice, a quantity of 1529.2–1725.2 mm water and in aerobic rice 929.2–1225.2 mm water was used to produce one kg rice. Thus, there was a saving of 28.4–39.6 % total water in both the rice varieties under AR cultivation.     

Performance of polymer-coated urea in transplanted rice: effect of mixing ratio and water input on nitrogen use efficiency

Polymer-coated urea (PCU) is an important alternative to uncoated urea for improving nitrogen (N) use efficiency (NUE). Only a few studies discuss their utility for lowland rice systems. A 2-year field study was conducted to examine if nitrogen loading is reduced in lowland rice ecosystem by using mixture of PCU and uncoated urea without sacrificing yield. Five treatments involving two mixtures of PCU with 50 and 70% coated urea each at 70 and 50% of recommended dose (80 kg N ha⁻¹) and one with uncoated urea at 100% recommended dose were laid out in a completely randomized design. Selected plant growth parameters and plant available N contents (NH₄–N plus NO₃–N) in soil solution and ponded water were measured over a period of 65 days after transplanting. Results showed no significant difference for vegetative and yield parameters among different treatments suggesting that treatments receiving lower doses of nitrogen exhibited higher NUE. Analysis of partial factor of productivity (PFP) for N suggested that the total N dose may be reduced by 50% using mixtures of coated and uncoated urea. Similarly, statistically similar PFP values for treatments receiving the same amount of total N for both years and for both total N dose suggested that the proportion of coated urea may also be reduced to as low as 50% without sacrificing yield. Correlation analysis on nitrogen contents in ponded water and soil solutions and the analysis of water productivity and PFP showed that soil water regime could also significantly influence the nitrogen status in soil even when PCU are applied. In turn, both the water regime and N contents in soil ultimately influences grain yield. Although the constant release of N from coated fertilizer ensures adequate N supply for plant uptake, it may not completely avoid N deficit condition especially during heavy rainfall. Analysis of the developed production function suggested that 55–65% polymer coating and about 100 cm total water input may be ideal for achieving maximum yield. The production function was developed for PCU treatments using data observed in treatments receiving 70% recommended N dose. The range of water input in these treatments was 86.5–174.0 cm.