The no-tillage system and cover crops—Alternatives to increase upland rice yields

Europ. J. Agronomy 45 (2013) 124–131

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The no-tillage system and cover crops—Alternatives to increase upland rice yields Adriano Stephan Nascente a,∗ , Carlos Alexandre Costa Crusciol b , Tarcísio Cobucci a a b

Brazilian Agricultural Research Corporation (EMBRAPA), Rice and Beans Research Center, Santo Antonio de Goiás, Goiás, Brazil São Paulo State University (UNESP), College of Agricultural Sciences, Department of Crop Science, Lageado, Experimental Farm, Botucatu, São Paulo, Brazil

a r t i c l e

i n f o

Article history: Received 28 May 2012 Received in revised form 13 September 2012 Accepted 18 September 2012 Keywords: Sustainable agriculture Cover crops Soil management Crop–livestock integration

a b s t r a c t Upland rice (Oryza sativa L.) cultivation has been increasing in importance in Asia while water availability for irrigation has been decreasing because of rapid growth in industry and urban centers. Therefore, the development of technologies that increase upland rice yields under aerobic conditions, thereby saving water, would be an effective strategy to avoid a decrease in global rice grain production. The use of the no-tillage system (NTS) and cover crops that maintain soil moisture would prove advantageous in the move toward sustainable agriculture. However, upland rice develops better in plowed soil, and it has been reported that this crop does not perform well under the NTS. Therefore, the aim of this study was to investigate the effect of cover crops on upland rice grain yield and yield components sowed in a NTS. A field experiment was conducted during two growing seasons (2008–2009 and 2009–2010), and treatments consisted of growing rice under five cover crops in a NTS and two control treatments under the conventional tillage system (plowing once and disking twice). Treatments were carried out in a randomized block design with three replications. Our findings are as follows: On average, Brachiaria brizantha (12.32 Mg ha−1 ), Brachiaria ruziziensis (11.08 Mg ha−1 ) and Panicum maximum (11.62 Mg ha−1 ) had outstanding biomass production; however, these grasses provided the worst upland rice yields (2.30, 2.04, and 2.67 Mg ha−1 , respectively) and are not recommended as cover crops before upland rice. Millet and fallow exhibited the fastest straw degradation (half-lives of 52 and 54 days, respectively), and millet exhibited the fastest nitrogen release (N half-life of 28 days). The use of a NTS was promising when millet was used as a cover crop; this allowed the highest upland rice yield (3.94 Mg ha−1 ) and did not statistically differ from plowed fallow (3.52 Mg ha−1 ). © 2012 Elsevier B.V. All rights reserved.

1. Introduction Rice is included in the diet of half of the world’s population (CGIAR, 2006; Africa Rice Center, 2009; Kumar and Ladha, 2011). Most of this cereal is grown on irrigated land (Farooq et al., 2009; Prasad, 2011). However, available water resources have been reduced due to the competing demands of industry and population, and consequently, alternatives are sought that allow greater efficiency of water use (Feng et al., 2007; Qu et al., 2008). Some alternatives include growing rice under aerobic conditions (both irrigated and not irrigated), the use of cover crops and better conservation of soil moisture (Bouman and Tuong, 2001; Tao et al., 2006). Atlin et al. (2002) reported that in Northeast China, where lowland irrigated rice production is no longer possible due to water shortages, upland rice cultivars occupy approximately 120,000 ha. Tuong and Bouman (2003) have predicted that by 2025, approximately 15–20 million ha of lowland irrigated rice will suffer from

Abbreviations: NTS, no-tillage system; CTS, conventional tillage system. ∗ Corresponding author. E-mail address: [email protected] (A.S. Nascente). 1161-0301/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.eja.2012.09.004

some degree of water scarcity. Bouman et al. (2007) adds that farmers are already growing upland rice on approximately 80,000 ha in Northern China. Upland rice is cultivated in Asia, Africa and the Americas (CGIAR, 2006). In these places, rice is normally associated with poor farmers, who use low-level technology and have problems with drought, one of the major upland production constraints, resulting in low upland rice yields (Crusciol et al., 2006; CGIAR, 2006; Erenstein and Laxmi, 2008; Heinemann et al., 2011; Kumar and Ladha, 2011; Oonyu, 2011; Prasad, 2011). According to Kumar and Ladha (2011), the major challenge in rice production is to produce this grain using less water, labor, and chemicals, thereby ensuring long-term sustainability. These authors added that agronomic management and technological innovation are needed to address rice production and to avoid imbalances between long-term supply and demand. In this sense, the no-tillage system (NTS) has demonstrated impressive growth worldwide and is used in almost 117 million ha in Latin America (58 million ha), the USA and Canada (40 million ha), and Australia (17 million ha) (FAO, 2012). Kumar and Ladha (2011) reported that the direct seeding of rice can provide several benefits to farmers and the environment compared with

A.S. Nascente et al. / Europ. J. Agronomy 45 (2013) 124–131

the conventional practice of puddling and transplanting. These authors added that this system has great potential in South Asia as an alternative method of producing rice with less water consumption. Supporting this idea, new upland rice cultivars with improved lodging resistance, harvest index, and input responsiveness have been developed in breeding programs in China, Brazil, and the Philippines (Atlin et al., 2002). In addition, Barbosa Filho and Yamada (2002), Saito et al. (2005), Crusciol et al. (2011) and Oonyu (2011) reported that it is possible to achieve yields of 4000–5000 kg ha−1 of upland rice under adequate hydric conditions. However, upland rice crop is not doing well under the NTS (Olofintoye and Mabbayad, 1980; Kluthcouski et al., 2000; Crusciol et al., 2010a; Nascente et al., 2011b; Pacheco et al., 2011; Nascente et al., 2012). This could occur because rice has a very sensitive root system that is unable to grow in compacted soil (Kluthcouski et al., 2000). Under the NTS, soil bulk density can increase due to the use of machines during sowing, cultivation and crop harvest without tillage, thereby decreasing upland rice shoot growth (Guimarães and Moreira, 2001). Another reason for the poor performance of upland rice under the NTS could be the lack of nitrogen available during early rice development under the NTS. This could happen because when there is high amount of straw on the soil surface with high C N relation, it can cause reduction of the nitrogen in the soil. Bacteria and fungi consume inorganic molecules like nitrogen and incorporate them into their cells. Therefore, it does not move easily through the soil and is unavailable to plants (Fageria et al., 2011). Nascente et al. (2011a) reported that rice growing in the NTS achieved grain yields similar to that under plowing, when was applied at 45 kg ha−1 of nitrogen one day before rice planting in addition to the use of nitrogen at planting. On the other hand, when this nutrient was applied only as a topdressing (at 45 days after rice planting, the tillering stage) in addition to the use of nitrogen at planting, the rice yield under NTS was lowest and differed from the conventional tillage system (CTS, plowing once and disking twice). Upland rice in Brazil and Africa achieves highest yields under CTSs (Olofintoye, 1989; Pacheco et al., 2011). Tillage generally improves soil conditions for plant growth, especially under circumstances where the soil presents zones of high strength and compaction (Kluthcouski et al., 2000). Olofintoye and Mabbayad (1980) reported that higher upland rice yields were obtained under the CTS due to higher seedling establishment. Olofintoye (1989) added that upland rice plant height and tillering at early growth stages were lower in no-till than in conventional and minimum tillage plots. Nascente et al. (2011a), comparing eight upland rice cultivars under the NTS and CTS, observed higher yields in the CTS for seven cultivars. Only one cultivar gave similar yields in both tillage systems. Therefore, it is very common in Brazil to plow degraded pastures containing Brachiaria brizantha and afterward, to introduce upland rice for two growing seasons before returning the land once more to pasture (Kluthcouski et al., 2000). Brazilian agriculture uses a land area of approximately 50 million ha; NTSs are used on almost 25 million ha of this, and the area is increasing (Nascente and Crusciol, 2012). In these areas, the main cash crops are corn, soybean, and cotton, and farmers are unwilling to till the soil to introduce upland rice to this system. Therefore, it is important to develop technologies that achieve high rice grain yields under NTSs that are similar to those obtained under the CTS, and in this way, to develop sustainable agriculture, improve food production and use less water (Farooq et al., 2009). Under the NTS, covering the soil with straw before cash crop deployment is an essential requirement (Dabney et al., 2001; Sulc and Tracy, 2007; Allen et al., 2007; Russele et al., 2007; Aranda et al., 2011; Crusciol et al., 2012; Nascente and Crusciol, 2012). Nascente et al., 2012 Because cash crops do not yield sufficient straw to cover the soil throughout the year, forage species are increasingly being

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grown as cover crops in Brazil (Crusciol et al., 2012; Nascente and Crusciol, 2012). Millet is an attractive option because of its rapid nutrient release, especially nitrogen (Crusciol et al., 2010b). In addition, Pacheco et al. (2011) reported good upland rice development under millet in a NTS. Additionally, grasses of the genus Brachiaria and Panicum, which are already being used under NTSs as cover crops for corn and soybean (Nascente and Crusciol, 2012), could be an effective alternative to upland rice. These perennial forage species originate from Africa and have vigorous and deep root systems and high drought tolerance (Valle and Pagliarini, 2009). In addition, these forage crops produce approximately 20 t ha−1 of dry matter per year and can improve soil physical characteristics (Kluthcouski et al., 2000; Valle and Pagliarini, 2009; Crusciol et al., 2010b, 2012; Calonego et al., 2011; Castro et al., 2011; Pacheco et al., 2011; Nascente and Crusciol, 2012). However, little information is available regarding the behavior of upland rice cultivars under various cover crops in NTSs. Given this fact, and starting from the hypothesis that some cover crop species can create appropriate conditions for upland rice development under the NTS, the aim of this study was to investigate the effect of cover crops on upland rice yield and its components in the no-tillage system.

2. Materials and methods 2.1. Site descriptions A field experiment was conducted in a Cerrado region in Santo Antônio de Goiás county in the State of Goiás, Brazil (16◦ 27’ latitude, 49◦ 17’ longitude and 823 m local elevation). The regional climate is tropical savanna and is classed as Aw according to the Köppen classification. There are two well-defined seasons: normally dry from May to September and rainy from October to April; the long-term (1962–2012) annual mean rainfall is 1500 mm. The long-term annual mean temperature is 22.7 ◦ C, and the long-term temperature average of the coldest month (July) is 14.2 ◦ C and the warmest (September) is 31.7 ◦ C. During the experimental period, rainfall and temperature were measured (Fig. 1). The soil was an Oxisol in gently undulating topography. The textural values were clay 540 g kg−1 , silt 110 g kg−1 and sand 350 g kg−1 . To characterize the soil, 48 samples were collected at depths of 0–0.05 m, 0.05–0.10 m and 0.10–0.20 m for chemical analysis before installation of the experiment (Table 1). P and K were extracted using the Mehlich 1 extracting solution (0.05 M HC1 in 0.0125 M H2 SO4 ). The phosphorus content of the extracted solution was determined colorimetrically, and K was determined using flame photometry. Ca, Mg, and Al were extracted with 1 M KC1. Aluminum was determined by titration with NaOH, and Ca and Mg were determined by titration with EDTA from the extracted solution. Micronutrients were determined in a portion of the phosphorus extract using atomic absorption spectrophotometry (Table 1). The experimental area had been under a no-tillage system for six years (from 2001–2002 to 2006–2007) and had been cultivated in rotations, with corn and soybean in the rainy season and fallow in the dry season. Therefore, the area was cultivated in 2001–2002 with corn, 2002–2003 with soybeans, 2003–2004 with corn, 2004–2005 with soybeans, 2005–2006 with corn, and 2006–2007 with soybeans. The study continued for three years. In the first year (November 2007), cover crops were sown. In the second year (November 2008), upland rice was sown under these cover crops. In March 2009 after rice harvesting, all cover crops were sown again. In the third year (November 2009), upland rice was re-sown under cover crops.

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Fig. 1. Temperature and rainfall during the trials at Santo Antônio de Goiás, Goiás state, Brazil.

Table 1 Soil chemical properties at the experimental area before deployment of the experiment at Santo Antônio de Goiás, Goiás state, Brazil. Depth

pH

cm

water

0–5 5–10 10–20

6.6 6.2 5.9

a

Ca

Mg

Al

P

K

Cu

−1

cmolc kg 2.5 1.9 1.6

1.0 0.7 0.5

Zn

Fe

Mn

−1

g kg−1

mg kg 0.0 0.0 0.1

12.1 14.3 11.2

194.4 107.7 69.5

1.6 1.6 1.7

SOMa

3.9 3.6 3.5

29.4 30.2 29.5

20.8 18.8 17.7

21.1 20.1 19.3

Soil organic matter.

2.2. Experimental design and treatments The experimental design was a randomized block with three replications, and each plot measured 6.0 m × 10 m. The treatments consisted of the following cover crops: 1–Fallow [spontaneous vegetation, predominantly Bidens pilosa L., Commelina benghalensis L., Conyza bonariensis (L.) Cronquist and Cenchrus echinatus L.], 2–Panicum maximum Jacq., 3–Brachiaria ruziziensis R. Germ. And C.M. Evrard, 4–B. brizantha (Hochst. Ex A. Rich.) Stapf.–cultivar Marandu, and 5–millet [Pennisetum glaucum (L.) R. Br.–cultivar BN2]. In addition, two control treatments were included to conduct the conventional tillage system (CTS); these were 6–B. brizantha and 7–fallow incorporated 30 days before sowing the crop. These plowing treatments were used only to compare whether the NTS would provide similar yields to those obtained under a CTS. 2.3. Crop management In November of 2007 and March of 2009, tropical perennial forages, and millet in March 2008 and March 2009, were sown in 0.20 m rows using a mechanical planter set to distribute seeds aiming a population of 40 plants m−2 (Kluthcouski et al., 2000). Rice was sown in November of 2008 and November of 2009. Thus, the cultivar of upland rice, BRS Sertaneja, was spaced at 0.35 m, aiming a population of 180 plants m−2 ; the plants were fertilized using 20 kg ha−1 of N as urea, 120 kg ha−1 of P2 O5 as triple super phosphate and 60 kg ha−1 of K2 O as potassium chloride with a Model 13 Personalle drill (Semeato). In addition, 45 kg of N ha−1 as urea was applied on the soil surface one day after emergence (DAE) of upland rice, and a further 45 kg N ha−1 as urea was applied at the beginning of tillering. Crop management was performed according to rice needs (EMBRAPA ARROZ e FEIJÃO, 2003). The cover crop was desiccated by applying the herbicide glyphosate at 1.8 kg ha−1 acid equivalent twice, 30 days before and immediately before upland rice sowing. To control weeds, Paraquat was applied (0.3 kg ha−1 a.e.) two days after rice planting, and the sodium salt of bentazon, Basagran (0.72 kg ha−1 a.e.), was applied

14 days after rice emergence. For these applications, a boom sprayer was used with a spray volume of 200 l ha−1 . 2.4. Cover crop dry matter, degradation and nitrogen release Cover crops were sampled on the day of rice sowing and at 7, 14, 21, 28 and 35 days after this. Each time, samples were collected from a 1.0 m × 1.0 m randomly selected area in each plot. The collected plant materials were placed in paper bags, dried in a forced ventilation oven at 65 ◦ C and weighed. The data for the first day was used to evaluate the amount of cover crop present on the soil surface on the upland rice sowing day. The levels of nitrogen in the coverage straws were determined via dry combustion (Dumas method) using an elemental analyzer (CHNS/O 2400 Series II from PerkinElmer). To evaluate cover crop degradation and nitrogen release, we used an exponential mathematical model (Thomas and Asakawa, 1993) according to the following formula: y = y0 .exp(−kt) ,

(1)

where y is the amount of cover or nutrient still present at time t, y0 is the amount of potentially decomposable residue or nutrient, and k is the constant of decomposition of the residue or nutrient. Using the value of k, the half-lives (t1/2 life) of the cover crop, straw and nitrogen were calculated using the formula proposed by Paul and Clark (1989): t1/2 life =

0.693 k

(2)

Therefore, there are two ks, one for biomass and one for nitrogen. 2.5. Upland rice harvesting Manual harvest was conducted when approximately 90% of panicles contained grains of typical mature coloration. The panicles were dried in the sun for 1–2 days and later submitted to mechanical threshing using a research plot thresher. The

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evaluations performed were as follows: number of panicles per square meter (obtained by counting the number of panicles in 2.0 m of plants in two central rows from the usable area of each plot), total number of spikelets per panicle (obtained by counting the number of spikelets in 20 panicles from the useable area), spikelet fertility (calculated as the number of grain-bearing spikelets/total number of spikelets per panicle × 100), weight of 1000-grains (evaluated by random collection and weighing of 4 samples of 1000 grains from each plot (130 g kg−1 wet basis), and grain yield (unhulled grain weight collected from three central rows of 5 m in each plot, eliminating 2.5 m on each side of the plots from the usable areas, correcting their moisture content to 130 g kg−1 (wet basis) and converting to Mg ha−1 ). 2.6. Statistical analysis All data were analyzed using the statistical software package SAS (SAS, 1999). Cropping system (five cover crops + two control crops, seven treatments in total) and year were considered fixed effects. Two error terms were considered in the analysis of the data, one associated with the cropping system and the other associated with the year and the interaction (cropping system × year). Mean separations were conducted using the Tukey test. Effects were considered statistically significant at P ≤ 0.05. 3. Results The precipitation from November to March during the 2008–2009 season was 1026.7 mm (Fig. 1). In 2009–2010, the precipitation was 1028.4 mm. Cover crops produced different amounts of dry matter (Table 2). In general, cover crops grew better during the 2008–2009 season (10.28 Mg ha−1 ) than in 2009–2010 (8.75 Mg ha−1 ). Millet produced the lowest amount of dry matter and differed from all other cover crops in both years (6.07 Mg ha−1 , 2008 and 4.22 Mg ha−1 , 2009). On average, P. maximum (11.62 Mg ha−1 ), B. ruziziensis (11.08 Mg ha−1 ) and B. brizantha (12.32 Mg ha−1 ) produced the greatest amount of biomass and differed from fallow (7.42 Mg ha−1 ) and millet (5.14 Mg ha−1 ). Millet (52 days) and fallow (54 days) straw degraded faster and had the lowest half-lives; the comparable values for the other crops were P. maximum (74 days), B. ruziziensis (75 days) and B. brizantha (76 days) (Table 3). In addition, millet stood out due to its rapid N release and had the lowest N half-life, 28 days (Table 3). On the other hand, B. brizantha, B. ruziziensis, and P. maximum had higher straw half-lives and might persist longer on the soil surface. Regarding upland rice yield components, under fallow had the highest number of panicles per square meter (115) and differed from B. ruziziensis (77), B. brizantha (70) and B. brizantha plowed

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Table 2 Cover crop dry matter accumulation during two growing seasons (2008–2009 and 2009–2010), the average, and ANOVA significance at Santo Antônio de Goiás, Goiás State, Brazil. Cover crops

08–09

09–10

Average

Mg ha−1 Fallow Panicum maximum Brachiaria ruziziensis Brachiaria brizantha Millet Average

8.02 12.60 11.36 13.37 6.07 10.28 A

Cover crop (C) Year (Y) C×Y

6.82 10.63 10.81 11.28 4.22 8.75 B ANOVA (F probability) <0.001 0.043 0.317

7.42 ba 11.62 a 11.08 a 12.32 a 5.14 c 9.52

a Indicates that values within the same column followed by the same letter, lowercase vertically or uppercase horizontally, do not differ using the Tukey test at the 5% level.

(81) (Table 4 ). under B. brizantha (194), millet (198) and fallow plowed (190) had the highest number of spikelets per panicle and differed from the other treatments. Under millet (80%) had the highest spikelet fertility and differed from fallow (70%), B. ruziziensis (72%) and B. brizantha (74%) (Table 5). Fallow plowed (78%), P. maximum (78%) and B. brizantha plowed (77%) also had high spikelet fertility and did not differ from millet. All treatments yielded similar weights of 1000-grains and were not statistically different in this respect. Upland rice yields were higher under the cover crops of millet (3.94 Mg ha−1 ) and fallow (3.43 Mg ha−1 ) in the NTS and under fallow plowing (3.52 Mg ha−1 ) in the CTS (Table 6). However, the cover crops B. brizantha (2.30 Mg ha−1 ), P. maximum (2.67 Mg ha−1 ) and B. ruziziensis (2.04 Mg ha−1 ) under the NTS and B. brizantha under plowing (2.55 Mg ha−1 ) in the CTS provided the worst rice yields. 4. Discussion According to Bouman et al. (2007), well-distributed rainfall between 400 and 600 mm during the upland rice-growing season is sufficient to achieve high grain yields. In this sense, precipitation during the two growing seasons was adequate to allow the proper development of the rice plants (Fig. 1). A higher amount of cover crop dry matter was observed in the first year than in the second year (Table 2). This probably occurred because during the first season, cover crops were sown at the beginning of the rainy season (November 2007) and had more time (12 months) to develop until the following season (November 2008). In the second season, in contrast, the sowing of cover crops occurred in March 2009, after rice harvesting, and therefore, the

Table 3 Half-life (t1/2 ) of straw and nitrogen release during two growing seasons (2008–2009 and 2009–2010) and ANOVA significance at Santo Antônio de Goiás, Goiás State, Brazil. Cover crops

Fallow Panicum maximum Brachiaria ruziziensis Brachiaria brizantha Millet Year (Y) Cover crop (C) C×Y a

Straw

Nitrogen

08–09

09–10

Average

t1/2 (days) 55 76 76 78 54

53 72 74 74 50

54 ba 74 a 75 a 76 a 52 b

0.1198 <0.001 0.8632

08–09

61 52 67 54 31 ANOVA (F probability)

09–10

Average

55 48 59 52 25

58 ab 50 b 63 a 53 b 28 c

0.075 <0.001 0.2291

Indicates that values within the same column followed by the same lowercase letter vertically do not differ using the Tukey test at the 5% level.

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Table 4 The number of panicles per square meter and the number of spikelets per panicle of upland rice cultivars as affected by cover crop under the no-tillage and conventional tillage systems during two growing seasons (2008–2009 and 2009–2010) and ANOVA significance at Santo Antônio de Goiás, Goiás State, Brazil. Panicle m−2

Cover crops 08–09

Spikelets panicle−1

09–10

Average

119 98 75 72 113 105 79

115 aa 92 ab 77 b 70 b 105 ab 101 ab 81 b

08–09

09–10

Average

172 177 166 196 206 196 176

170 b 171 b 162 b 194 a 198 a 190 a 169 b

◦

Fallow Panicum maximum Brachiaria ruziziensis Brachiaria brizantha Millet Fallow plowed B. brizantha plowed

n 110 86 80 68 97 96 83

Year Cover crop Year × Cover crop a

167 165 158 192 190 184 162 ANOVA (F probability)

0.217 0.032 0.289

0.428 <0.001 0.634

Indicates that values within the same column followed by the same lowercase letter do not differ using the Tukey test at the 5% level.

Table 5 Spikelet fertility and the weight of 1000-grains (W1000) of upland rice cultivars as affected by cover crop under the no-tillage and conventional tillage systems during two growing season (2008–2009 and 2009–2010) and ANOVA significance at Santo Antônio de Goiás, Goiás State, Brazil. Cover crops

Fallow Panicum maximum Brachiaria ruziziensis Brachiaria brizantha Millet Fallow plowed B. brizantha plowed

Spikelet fertility 09–10

Average

% 68 77 72 73 83 76 77

72 78 72 75 78 80 76

70 ca 78 ab 72 bc 74 bc 80 a 78 ab 77 ab

Year Cover crop Year × Cover crop a

W1000

08–09

08–09

Grams 28 24 23 24 27 25 25 ANOVA (F probability)

0.613 0.039 0.248

09–10

Average

24 22 24 24 22 23 24

26 a+ 23 a 24 a 24 a 25 a 24 a 24 a

0.587 0.172 0.661

Indicates that values within the same column followed by the same lowercase letter do not differ using the Tukey test at the 5% level.

Table 6 The grain yield of upland rice cultivars as affected by cover crop under the notillage and conventional tillage systems during two growing seasons (2008–2009 and 2009–2010) and ANOVA significance at Santo Antônio de Goiás, Goiás State, Brazil. Cover crops

Grain yield 08–09

09–10

Average

−1

Fallow Panicum maximum Brachiaria ruziziensis Brachiaria brizantha Millet Fallow plowed B. brizantha plowed Year Cover crop Year × Cover crop

Mg ha 3.40 2.59 1.91 2.25 3.62 3.27 2.49

3.46 2.76 2.18 2.36 4.26 3.77 2.62 ANOVA (F probability) 0.198 <0.001 0.231

3.43 aa 2.67 b 2.04 c 2.30 bc 3.94 a 3.52 a 2.55 bc

a Indicates that values within the same column followed by the same lowercase letter do not differ using the Tukey test at the 5% level.

cover crops had less time (8 months) to develop (November 2009). Fallow and millet produced the least amount of dry matter, probably because these plants are not perennials. After they finish their life cycle, these plants spread their seeds to the soil. When rain begins (September), these plants grow from the seeds remaining in the soil and do not have sufficient time (only two months) to accumulate dry matter (November) (Pacheco et al., 2011). The other

grasses produced high amounts of straw because these cover crops are perennials and had root systems already; after the first rains, the presence of these roots favored the absorption of water and nutrients and the resumption of shoot growth (Portes et al., 2000; Pacheco et al., 2011). Therefore, these cover crops accumulated dry matter after the rain season began (September), even after six months without rain, which is characteristic of these places (Cerrado or African Savannas). In this context, Timossi et al. (2007), Pacheco et al. (2011), Nascente and Crusciol (2012) and Nascente et al., 2012 obtained large quantities of straw from Panicum and Brachiaria. This characteristic is very important for protecting the soil against erosion and is useful to the NTS. Furthermore, heavy amounts of straw accumulation from cover crops could lead to more nutrients cycling (Crusciol et al., 2010b; Nascente et al., 2011a; Pacheco et al., 2011; Nascente et al., 2012). This is important, particularly in poor soils such as those in Cerrado regions or African Savannas (Africa Rice Center, 2009; Oliveira Junior et al., 2011; Oonyu, 2011). A similar half-life for millet straw degradation was obtained by Ferreira et al. (2010), i.e., 49 days. This value indicates that millet exhibits rapid mineralization and can release nutrients quickly to the soil, thereby benefiting the following crop (Ferreira et al., 2010; Pacheco et al., 2011). Crusciol et al. (2010b) and Pacheco et al. (2011) also reported fast release of N from millet as a cover crop. On the other hand, B. brizantha, B. ruziziensis, and P. maximum exhibited outstandingly long half-lives and may persist longer on

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the soil surface. Timossi et al. (2007), Crusciol et al. (2010b), Pacheco et al. (2011) and Nascente and Crusciol (2012) reported that these grasses could remain covering the soil longer due to their perennial characteristic and high proportion of C in relation to N. Allen et al. (2005), Russele et al. (2007) and Sulc and Tracy (2007) reported that multiple agronomic and environmental benefits can be realized when land is covered throughout the year, with annual cropping of rotations that include the introduction of perennial forage and the integration of livestock. The highest average upland rice yields under cover crops were millet (3.94 Mg ha−1 ) and fallow (3.43 Mg ha−1 ) in the NTS and under fallow plowed (3.52 Mg ha−1 ) in the CTS (Table 6). The grain yield of rice is determined by four components: (1) number of panicles m−2 , (2) number of spikelets panicle−1 , (3) spikelet fertility and (4) the weight of 1000 grains (Yoshida, 1981). The superiority of millet observed in the present study was due to a larger number of panicles m−2 (105), spikelets panicle−1 (198) and spikelet fertility (80%) (Table 5). The fallow plowed trial also had a high number of panicles m−2 (101), spikelets panicle−1 (190) and spikelet fertility (78%). The fallow NTS trial exhibited a higher number of panicles m−2 (115) and differed from B. ruziziensis, B. brizantha and B. brizantha (plowed). The finding that the highest grain yield and yield components in upland rice occurred under millet may be due to the rapid release of N from millet straw (Table 3). According to Yoshida (1981) and Fageria et al. (2011), nitrogen is one of the most important nutrient in increasing yield and yield component of rice. Crusciol et al. (2011) and Pacheco et al. (2011) also observed better upland rice yields when millet was used as a cover crop. These authors state that this may have occurred because millet was already in an advanced state of decomposition when upland rice was sown, which favored nutrient cycling to the following crop. In this context, Nascente et al. (2011b) and Moura Neto et al. (2002) reported that under the NTS, it is important to increase N fertilization at the planting date, as was done in this experiment (45 kg ha−1 of N), one day after rice planting. The high upland rice yield under fallow may also have occurred because of fast N release (Table 3) and due to the proper management of weeds, which favored the full development of the rice plants. Rice plants have slow initial growth and great sensitivity to competition with other plants (Olofintoye and Mabbayad, 1980; Fischer et al., 1995, 2001; Olofintoye, 1989; Nascente et al., 2011a; Prasad, 2011). However, using continuous fallowing in the NTS in rotation with cash crops could increase the number of weeds in agricultural areas (Mateus et al., 2004; Borghi et al., 2008; Castro et al., 2011). Additionally, fallowing incorporated into the NTS allowed good rice yield and confirmed the results reported by Kluthcouski et al. (2000), Nascente et al. (2011a) and Pacheco et al. (2011), which can be attributed to a low resistance for root development. Tilling once generally improves soil conditions for plant growth, especially under circumstances where the soil presents zones of high strength and compaction (Kluthcouski et al., 2000). On the other hand, under the cover crops B. brizantha, P. maximum and B. ruziziensis, the NTS resulted in the lowest rice yields (2.30, 2.67 and 2.04 Mg ha−1 , respectively). These grasses are difficult to control, and if not properly managed, can cause decreases in crop yield (Fischer et al., 1995, 2001; Constantin et al., 2009; Monquero et al., 2010 and Pacheco et al., 2011; Nascente et al., 2012). These grasses exhibit slow initial development but then grow rapidly (Valle and Pagliarini, 2009). Rice does not have a strong ability to compete with any plants, especially these aggressive grasses (Olofintoye and Mabbayad, 1980; Fischer et al., 1995, 2001; Olofintoye, 1989). Supporting this statement, Fischer et al. (2001) and Prasad (2011) reported that plant competition is one of the most yield-limiting constraints in aerobic rice production and could reduce rice yield by 50%. Fischer et al., 1995, 2001 added that

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efforts are needed to develop highly competitive rice cultivars. In this sense, we had to apply herbicide 30 days before, immediately before and two days after rice sowing and again at 14 days after rice emergence to avoid yield losses. However, this could increase production cost. These grasses may also exhibit an allelopathic effect that hampers the development of aerobically grown rice plants. Souza Filho et al. (1997), Martins et al. (2006) and Souza et al. (2006) reported allelopathic effects that were caused by species of Brachiaria in rice. The authors reported that these species could reduce crop seed germination and plant development, resulting in low crop yields. Therefore, based on the data obtained, B. brizantha, B. ruziziensis, and P. maximum do not appear to be the ideal cover crop for upland rice despite the fact that they are very important to the NTS because of their heavy production of biomass. However, when considering an agricultural system, we could infer that it is important to introduce millet as a cover crop before upland rice. After upland rice harvesting (March), perennial forage such as P. maximum, B. brizantha or B. ruziziensi could be introduced. This would provide a great amount of cover crop biomass at the beginning of the following rainy season (Table 2) that could be used to cultivate another cash crop (in November). Allen et al. (2005) observed higher cotton yields under forage species than under monoculture. Kluthcouski et al. (2000) obtained higher corn, soybean and common bean yields using straws of P. maximum and B. brizantha. Crusciol et al. (2010b) also obtained better yields of soybean, white oat (Avena sativa L.), and corn under Brachiaria straw. Nascente and Crusciol (2012) obtained the highest soybean yields under B. brizantha, B. ruziziensis, P. maximum, and millet under the NTS, and this result differed from a fallow plowed trial. Based on these results, it is possible to obtain high upland rice yields under the NTS if the correct cover crop is chosen. This information could increase upland rice cultivation in the Americas, Africa and Asia, thereby allowing farmers to increase their revenue and contributing to sustainable agriculture. The NTS could suppress weeds, protect against erosion, increase soil organic matter, conserve soil moisture and favor an increase in crop yields (Crusciol et al., 2012). Besides, in places such as Asia, an alternative to produce rice under aerobic condition must be found because water for rice irrigation is becoming increasingly scarce (Kumar and Ladha, 2011). The production of upland rice under the NTS requires less water consumption and labor than lowland rice systems and could be highly mechanized, thereby ensuring long-term sustainability (Farooq et al., 2009). To support this system, new upland rice cultivars with improved lodging resistance, harvest index, and input responsiveness have been developed by breeding programs in China, Brazil and the Philippines (Atlin et al., 2002).

5. Conclusion On average, B. brizantha (12.32 Mg ha−1 ), B. ruziziensis (11.08 Mg ha−1 ) and P. maximum (11.62 Mg ha−1 ) had the statistically highest biomass production; however, these grasses also exhibited the statistically smallest upland rice yield (2.30, 2.04, and 2.67 Mg ha−1 , respectively) and are not recommended as cover crops before upland rice. Millet and fallow straw degraded most rapidly (half-lives of 52 and 54 days, respectively), and millet exhibited the most rapid nitrogen release (N half-life, 28 days). Based on these results, the use of NTS showed promise when using millet as a cover crop, which allowed the statistically highest upland rice yield (3.94 Mg ha−1 ), although this did not differ from fallow plowing (3.52 Mg ha−1 ). The use of millet as a cover crop is an important option to produce rice under aerobic conditions, thereby conserving water and possibly helping to change the existing management regime of this crop, including

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the low use of technology, its being an activity of poor farmers and consequently, providing low yields; instead, a new regime could prevail, including the use of NTS, the input of technologies, sustainable agriculture, a high revenue per area and an increase in upland rice yield. In addition, when cover crops are planted after cash crop harvesting in March, a large amount of dry matter was observed at the outset of the following season (November) from B. brizantha, B. ruziziensis and P. maximum. Therefore, there was sufficient time to grow cash crops and afterward, to introduce perennial forage as a cover crop that could be used as straw for the NTS or as animal grazing. Acknowledgments To EMBRAPA (Brazilian Agricultural Research Corporation), for supporting this research and for providing Ph.D. scholarship to the first author, and to CNPq (National Council of Scientific and Technological Development), for an award for excellence in research of the second author. References Africa Rice Center (WARDA), 2009. The Growing NERICA Boom in Uganda. WARDA Publications, Cotonou, Benin. Allen, V.G., Baker, M.T., Segarra, E., Brown, C.P., 2007. Integrated irrigated crop–livestock system in dry climates. Agronomy Journal 99, 346–360. Allen, V.G., Brown, C.P., Kellison, R., Segarra, E., Wheeler, T., Dotray, P.A., Conkwright, J.C., Green, C.J., Acosta-Martinez, V., 2005. Integrating cotton and beef production to reduce water withdrawal from the Ogallala aquifer in the southern High Plains. Agronomy Journal 97, 556–567. ˜ Aranda, V., Ayora-Canada, M.J., Dominguez-Vidal, A., Martín-García, J.M., Calero, J., Delgado, R., Verdejo, T., González-Vila, F.J., 2011. Effect of soil type and management (organic vs. conventional) on soil organic matter quality in olive groves in a semi-arid environment in Sierra Mágina Natural Park (S Spain). Geoderma 164, 54–63. Atlin, G.N., Laza, M., Amante, M, Lafitte, H.R., 2002. Agronomic performance of tropical aerobic, irrigated, and traditional upland rice varieties in three hydrological environments at IRRI. (accessed 31.05.12). Barbosa Filho, M.P., Yamada, T., 2002. Upland rice production in Brazil. Better Crops 16, 43–46. Borghi, E., Costa, N.V., Crusciol, C.A.C., Mateus, G.P., 2008. Influence of the spatial distribution of maize and Brachiaria brizantha intercropping on the weed population under no-tillage. Planta Daninha 26, 559–568. Bouman, B.A.M., Feng, L.P., Tuong, T.P., Lu, G.A., Wang, H.Q., 2007. Exploring options to grow rice using less water in northern China using a modeling approach II: quantifying yield, water balance components, and water productivity. Agricultural Water Management 88, 23–33. Bouman, B.A.M., Tuong, T.P., 2001. Field water management to save water and increase its productivity in irrigated lowland rice. Agricultural Water Management 49, 11–30. Calonego, J.C., Borghi, E., Crusciol, C.A.C., 2011. Least limiting water range and soil compactation as related to intercropped maize and brachiaria. Revista Brasileira de Ciência do Solo 35, 2183–2190. Castro, G.S.A., Calonego, J.C., Crusciol, C.A.C., 2011a. Soil physical properties in crop rotation systems as affected by liming materials. Pesquisa Agropecuária Brasileira 46, 1690–1698. Castro, G.S.A., Crusciol, C.A.C., Negrisoli, E., Perim, L., 2011b. Weed incidence in grain production systems. Planta Daninha 29, 1001–1010. CGIAR Science Council, 2006. IRRI’s upland rice research follow-up review to the 6th IRRI EPMR. Rome, Italy, Science Council Secretariat. Constantin, J., Oliveira Júnior, R.S., Inoue, M.H., Cavalieri, S.D., Arantes, J.G.Z., 2009. Burndown systems on growth and grain yield in soybeans in Paraná State, Brazil. Bragantia 68, 125–135. Crusciol, C.A.C., Soratto, R.P., Arf, O., Mateus, G.P., 2006. Yield of upland rice cultivars in rainfed and sprinkler-irrigated systems in the Cerrado region of Brazil. Australian Journal of Experimental Agriculture 46, 1515–1520. Crusciol, C.A.C., Costa, A.M., Borghi, E., Castro, G.S.A., Fernandes, D.M., 2010a. Fertilizer distribution mechanisms and side dress nitrogen fertilization in upland rice under no-tillage system. Scientia Agricola 67, 562–569. Crusciol, C.A.C., Soratto, R.P., Borghi, E., Matheus, G.P., 2010b. Benefits of integrating crops and tropical pastures as production systems. Better Crops 94, 14–16. Crusciol, C.A.C., Garcia, R.A., Castro, G.S.A., Rosolem, C.A., 2011. Nitrate role in basic cation leaching under no-till. Revista Brasileira de Ciência do Solo 35, 1975–1984. Crusciol, C.A.C., Mateus, G.P., Nascente, A.S., Martins, P.O., Borghi, E., Pariz, C.M., 2012. An innovative crop-forage intercrop system: early cycle soybean cultivars and palisadegrass. Agronomy Journal 104, 1085–1095.

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