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CROP ECOLOGY, MANAGEMENT & QUALITY

High-Yielding Rice Cultivars Perform Best Even at Reduced Nitrogen Fertilizer Rate

Division of Upland Farming, Tohoku National Agricultural Research Center, National Agricultural Research Organization, Aza harajuku-minami 50, Arai, Fukushima 960-2156, Japan

^* Corresponding author (hasegawa{at}affrc.go.jp)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
A production system consisting of high-yielding cereal crop cultivars, together with high inputs of fertilizers, chemicals, and irrigation has increased yields in developed and developing countries during the past decades. This has led many to believe that high-yielding cereal cultivars may not be used in alternative cropping systems in which external inputs and adverse environmental effects are minimized. The objective of this study was to test the hypothesis that high-yielding temperate rice (Oryza sativa L.) cultivars do not perform well under a reduced N fertilizer rate. A field experiment was conducted from 1992 through 1994 at Hokuriku National Agricultural Experiment Station, Japan, on soil classified as clayey montmorillonitic, mesic Typic Endoaquepts. Thirteen rice cultivars released between 1893 and 1995 and one breeding line were grown at conventional (120 kg ha^-1) and reduced (40 kg ha^-1) N fertilizer rates, with a sufficient supply of other nutrients and water. Insects, diseases, and weeds were controlled by agrochemicals. In spite of contrasting weather from 1992 through 1994, there were highly positive correlations in grain yield of the rice cultivars between conventional and reduced N rates. At the reduced N rate, high-yielding cultivars Akichikara, Fukuhibiki, Habataki, Hokuriku 153, and Xin Ging Ai 1 consistently surpassed others not only in grain yield (P < 0.01), but also in aboveground dry matter (DM), harvest index (HI), N utilization efficiency (NUE), and sink capacity (P < 0.01) with two exceptions. There are significant advantages to the use of high-yielding rice cultivars at reduced N fertilizer rates, giving such cultivars potential benefits in alternative cropping systems for temperate regions.

Abbreviations: DM, aboveground dry matter • HI, harvest index • NUE, N utilization efficiency • TGW, 1000-grain weight

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
THE PRODUCTION SYSTEM of the three major cereal crops, rice, wheat (Triticum spp.), and maize (Zea mays L.), consisting of high-yielding cultivars and high inputs of fertilizers, agrochemicals, and irrigation, contributed to great yield increases in developed and developing countries during the past decades (Evans, 1993; Conway, 1997). Adverse effects of high input agriculture have been recognized, however. Nitrate and agrochemicals discharged from agriculture cause surface water pollution (National Research Council, 1989). Agriculture accounts for 15% of emissions of global warming effect gases from anthropogenic sources. Especially, N₂O emissions resulting from agricultural activities are responsible for 92% of anthropogenic N₂O production, which is in part due to high rates of N fertilizers (Duxbury et al., 1993).

Thus, the need for alternative agricultural practices mitigating these adverse effects is urgent practices (National Research Council, 1989). Nitrogen fertilizer is one of the most important inputs in the production package. Fertilizers account for almost half of the energy used in world agriculture, and the manufacture of N fertilizer is about 10 times more energy-intensive than that of P and potash fertilizers (Evans, 1993). For rice, reduced N rates can diminish the occurrence of blast disease [Pyricularia grisea (Cooke) Sacc.; Kozaka, 1965] and of several insect pests such as planthoppers (Laodelphax striatellus Fallén and Sogatella furcifera Horváth; Litsinger, 1994), and can reduce the use of the fungicides and insecticides. Because fossil fuels are currently energy sources for manufacturing N fertilizers and agrochemicals, the more efficient use of those inputs will save fossil fuels and result in decreased CO₂ emissions. In addition, reduced N rates can contribute to reducing N₂O emissions from agricultural soils.

Genetic improvements need to be made in crops that will be used in alternative agriculture, in which external inputs and adverse environmental effects should be minimized, but most of the genetic improvements have been conducted in high input conditions. De Datta and Malabuyoc (1976) observed high-yielding tropical rice cultivars outyielded traditional ones not only at high N fertilizer rates (120 to 150 kg N ha^-1) but at a reduced N fertilizer rate (30 kg N ha^-1). With wheat, Austin et al. (1980) found high-yielding cultivars performed better than traditional ones in both fertile and less fertile soils. New maize hybrid cultivars also outperformed old ones even at reduced N rates (Castleberry et al., 1984; Duvick, 1984). Ortiz-Monasterio et al. (1997) also found that newly released wheat cultivars surpassed ones previously released in grain yield even at the zero N fertilizer rate. In spite of these studies, because there are more strong opinions than strong data (Evans, 1993, p. 334), the idea persists that high-yielding cereal cultivars may not be used in alternative cropping systems. Actually, there are few comparable studies for temperate rice. Thus, the objective of this study was to test the hypothesis that high-yielding temperate rice cultivars do not perform well under a reduced N fertilizer rate, and to analyze underlying agronomic implications, while insects, diseases, and weeds are well controlled and other nutrients and water are sufficiently applied.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments were conducted during 1992 to 1994 at Hokuriku National Agricultural Experiment Station (latitude 37°06' N and elevation 11 m), Jouetsu, Niigata, Japan, on a Typic Endoaquepts soil. The experimental field had been used as a rice paddy before this experiment started. The field was kept fallow after the rice growing season. Because there were plenty of rain and snow during the late fall and winter, the soil was kept moist. Because of low temperature during that period, little N was mineralized. The pH, total C, total N, Bray 2 P, exchangeable K, Ca, and Mg of the soil were 5.7, 21 g kg^-1, 2.1 g kg^-1, 67 mg kg^-1, 179 mg kg^-1, 3533 mg kg^-1 and 539 mg kg^-1, respectively. No organic matter was applied to the soil during the experiments.

Thirteen rice cultivars released between 1893 and 1995 and one breeding line were grown at conventional (120 kg ha^-1) and reduced (40 kg ha^-1) N fertilizer rates in 1993 and 1994. An experiment was performed in 1992 to compare grain yield of 10 cultivars, excluding ‘Kamenoo’, Hokuriku 153, ‘Mizuhatamochi’, and ‘Sekiminori’. Akichikara, Fukuhibiki, Habataki, and Hokuriku 153 were bred as high-yielding cultivars under high N inputs at Hokuriku and Tohoku National Agricultural Experiment Stations. Xin Ging Ai 1 was introduced from China as a high-yielding cultivar. Hokuriku 153 had the highest 1000-grain weight (TGW; 27 g), whereas Habataki had the most spikelets per panicle (>150) with less panicle density and small TGW. Akichikara, Fukuhibiki, and Xin Ging Ai 1 were intermediate between the two cultivars in terms of yield components. Cultivars Kamenoo and Rikuu 132 were bred when the use of chemical N fertilizers was rare. When cultivars Honenwase, Sekiminori, Koshihikari, and Sasanishiki were developed, N fertilizer rates were much less than today. They have high palatability, but are susceptible to lodging at high N rates. Cultivars Kinuhikari and Dontokoi are resistant to lodging while retaining high palatability. An upland cultivar, Mizuhatamochi, was included assuming that an upland rice cultivar with a larger root system would perform better at the reduced N rate than others (Table 1).

View this table: [in this window] [in a new window]   Table 1. Fourteen rice cultivars grown at conventional (120 kg N ha-1) and reduced (40 kg N ha-1) N fertilizer rates to compare yield performance on a typic endoaquepts soil in Jouetsu, Japan, during 1992 to 1994. The rice paddy was fully irrigated. Cultivars received 70 kg ha-1 of P2O5 and K2O. Fungicides, insecticides, and herbicides were applied many times not only to maximize the yield potential but also to eliminate even small pest damage.

Plots were laid out on group-balanced blocks in split-plot design (Gomez and Gomez, 1984), with N fertilizer rate as main plot and maturity group (early and medium) as subplot. A 0.3-m barrier, impervious to water, was inserted in the soil between subplots to prevent fertilizer contamination between treatments through the soil or flood water. The plot size for each cultivar was 10.5 m² (5 by 2.1 m).

Seedlings that were 28 to 30 d old were transplanted to 22.2 hills m^-2 using three plants per hill and were grown in a fully irrigated paddy. A relatively high rate (70 kg ha^-1) of P₂O₅ and K₂O was applied before the transplanting, and fungicides, insecticides, and herbicides were applied numerous times throughout the seasons not only to maximize the yield potential but also to eliminate even small pest damage.

Plant samples were manually harvested at maturity from 45 hills for yield measurement and from 15 hills for determination of yield components and DM. Grain yield was determined using brown rice at 150 g kg^-1 moisture content. Harvest index was determined using dry grain weight (0 g kg^-1) divided by DM. Samples for yield component determination were manually threshed after counting panicle number, and then the spikelets obtained were dipped in water. Spikelets which sunk in the water were judged as filled grain. Sink capacity is the product of the number of spikelets per unit area multiplied by an average brown rice kernel weight (Venkateswarlu and Visperas, 1987) at 150 g kg^-1 moisture content. Total culm length is the length of the longest culm of a hill from the soil surface to the top of the panicle. Lodging degree is classified into six classes (0 = none to 5 = greatest). Plant samples for total N analysis were separated into panicle and leaf and stem to ground after oven drying at 80°C for a few days (Mizuno, 1990). Total N concentrations of plant samples were analyzed using the indophenol colorimetric method (Ohyama, 1990) following Kjeldahl digestion. Nitrogen utilization efficiency is the product of grain yield divided by N uptake (Moll et al., 1982).

Analysis of variance was conducted using the General Linear Model procedure (SAS Institute, 1989). For 1993 and 1994, the statistical significance of year (Y), block (B), N, maturity group (G), cultivar (C), and their interactions was tested using a split-plot model, Yield = Y x B x N x G x G(C). The statistical test in 1992 was performed using a Yield = B x N x G x G(C) split-plot model (Table 2). Further analyses of variance and CONTRAST procedures on yield, DM, HI, yield components, and NUE at a reduced N rate were conducted by year with a split-plot model, such as Yield = B x G x G(C) (Table 3), because the Y x C interaction was highly significant. When the error, C(B x G), was significant, the significance between cultivar groups was manually calculated based on Okuno and Haga (1969) using SAS outputs, because SAS does not allow for comparing cultivars in different maturity groups in the CONTRAST statement. When the error was insignificant, a randomized complete block model, Yield = B x C, was used to conduct the CONTRAST statement to compare the differences between cultivar groups.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

Yield of High-Yielding Cultivars
The analysis of variance for the 1993 and 1994 seasons demonstrated that Y, N, G, and C effects were highly significant for grain yield. In addition, the Y x N, Y x C, and N x C interactions were highly significant. By contrast, only N and C effects were significant in 1992.

In the 1993 growing season, cultivars responded only a little to N fertilizer because of very insufficient solar radiation during the final 45 d, whereas cultivars showed a positive N response in 1992 and 1994 due to favorable weather (Fig. 1). Response to the addition of N is defined as the yield increase from 40 to 120 kg N ha^-1 rates. The responses averaged 0.36 Mg ha^-1 for high-yielding cultivars (Akichikara, Fukuhibiki, Habataki, Hokuriku 153, and Xin Ging Ai 1) and -0.23 Mg ha^-1 for others in 1993, compared with 1.51 Mg ha^-1 and 0.90 Mg ha^-1 in 1994. In 1992, the responses of four high-yielding cultivars (without Hokuriku 153) were 1.30 Mg ha^-1 and 0.69 Mg ha^-1, respectively. In spite of the harsh weather of 1993, high-yielding cultivars outyielded other cultivars not only in the conventional N rate (by 1.44 Mg ha^-1, P < 0.01) but also in the low N rate (by 0.81 Mg ha^-1, P < 0.01). In 1994, high-yielding cultivars surpassed others by 1.59 Mg ha^-1 (P < 0.01) at the conventional N rate and by 1.11 Mg ha^-1 (P < 0.01) at the reduced N rate, while by 0.92 Mg ha^-1 (P < 0.01) and by 0.31 Mg ha^-1 (P < 0.05) in 1992. As a consequence, there were positive significant correlations for grain yield of 14 rice cultivars between conventional and reduced N rates in 1993 (r² = 0.724, P < 0.001) and in 1994 (r² = 0.557, P < 0.01), and for 10 cultivars (r² = 0.439, P < 0.01) in 1992 (Fig. 1).

View larger version (17K): [in this window] [in a new window]   Fig. 1. Comparison of grain yields of 14 rice cultivars grown with reduced (40 kg ha-1) and conventional (120 kg ha-1) N fertilizer rates on a typic endoaquepts soil for three years in Jouetsu, Japan. r2 = 0.439 (P < 0.01) in 1992, r2 = 0.724 (P < 0.001) in 1993, and r2 = 0.557 (P < 0.01) in 1994. Numbers identify cultivars (see Table 1).

View larger version (25K): [in this window] [in a new window]   Fig. 2. Relationships between grain yields and aboveground dry matter (r2 = 0.456** in 1993 and r2 = 0.610*** in 1994), sink capacity (r2 = 0.560** in 1993 and r2 = 0.910*** in 1994) and N uptake (r2 = 0.239 in 1993 and r2 = 0.204 in 1994). Fourteen rice cultivars were grown at the reduced N fertilizer rate (40 kg ha-1) on a Typic Endoaquepts soil for 2 yr in Jouetsu, Japan. **, *** Significant at the 0.01 and 0.001 probability levels, respectively. Numbers identify cultivars (see Table 1).

View larger version (18K): [in this window] [in a new window]   Fig. 3. Relationship between sink capacity and N utilization efficiency of 14 rice cultivars at the reduced N fertilizer rate (40 kg ha-1) on a typic endoaquepts soil for 2 yr in Jouetsu, Japan. r2 = 0.476 (P < 0.01) in 1993 and r2 = 0.800 (P < 0.001) in 1994. Numbers identify cultivars (see Table 1).

View larger version (29K): [in this window] [in a new window]   Fig. 4. Relationships between N utilization efficiency and panicle N concentration (r2 = 0.531** in 1993 and r2 = 0.315* in 1994) and leaf and stem N concentration (r2 = 0.261 in 1993 and r2 = 0.860*** in 1994). Fourteen rice cultivars were grown at the reduced N fertilizer rate (40 kg ha-1) on a typic endoaquepts soil for 2 yr in Jouetsu, Japan. *, **, *** Significant at the 0.05, 0.01, and 0.001 probability levels, respectively. Numbers identify cultivars (see Table 1).

Under fully irrigated conditions, however, paddy soil is much more fertile than upland soil. Paddy soil is waterlogged during most of the growing season and waterlogging prevents oxidation of soil organic matter. Additionally, in Japan, 1500 mm of irrigation water is applied. A lot of nutrients are supplied through irrigation. Consequently, average yield of continuous paddy rice without N fertilizers across 44 sites in Japan was 3.66 Mg ha^-1 (Toriyama, 2002), compared with only 1.65 Mg ha^-1 in unfertilized continuous wheat in the Rothamsted Experiment Station (Dyke et al., 1982). The average yield reduction in continuous wheat across 19 yr at the 48 kg N ha^-1 rate relative to the 144 kg N ha^-1 rate was 34% (Dyke et al., 1982), whereas the yield reduction at the 40 kg N ha^-1 rate of this experiment was at maximum 29% even with the favorable weather of 1994. Thus, yield reduction up to 30% at reduced N rates seems quite normal in fully-irrigated rice.

Maturity Group
The average yield difference between medium- and short- maturity cultivars across the 2 yr and N rates was 0.94 Mg ha^-1. This was comparable with the differences between high-yielding and other cultivars (0.72 Mg ha^-1 in 1993 and 0.82 Mg ha^-1 in 1994). Additionally, three of five high-yielding cultivars used were medium-maturity cultivars. Thus, it seems appropriate to select medium-maturity high-yielding cultivars for N-reduced input systems. On the other hand, the yield of Fukuhibiki (early-maturity high-yielding) was not significantly different from other medium-maturity high-yielding cultivars (Habataki, Hokuriku 153, and Xin Ging Ai). This indicates that Fukuhibiki is an example of a cultivar with high yield potential similar to later maturity cultivars (e.g., Habataki) under low N input.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
These findings indicate that, in spite of harsh rice growing season weather in 1993, hot weather in 1994, and intermediate weather in 1992, the advantages of high-yielding temperate rice cultivars were consistent even when one of important external inputs, N fertilizer, was substantially reduced (up to one third). The yields of high-yielding cultivars Akichikara, Fukuhibiki, Habataki, Hokuriku 153, and Xin Ging Ai 1 always surpassed those of the other nine cultivars used. Further, high-yielding cultivars significantly surpassed the other cultivars in DM, HI, sink capacity, and NUE. Consequently, high-yielding rice cultivars have the potential for alternative cropping systems. These finding are directly opposite to the idea that high-yielding cereal cultivars would perform well only in the presence of sufficient amounts of N fertilizers. Although the inputs of P, K, and agrochemicals were high in this experiment, those inputs can be changed for alternative management practices (National Research Council, 1989). The spread of high-yielding cultivars and the resulting disappearances of indigenous crop races are often blamed for narrowing the genetic diversity of crops, which may result in the occurrence and spread of new insect biotypes or disease races. Genetic improvements for alternative agriculture must be performed to overcome this drawback.

Received for publication February 8, 2002.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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