Upland rice yield as affected by Brachiaria coverage management

Produtividade do arroz de terras altas em função do manejo da cobertura de Brachiaria

Adriano S. Nascente Luís F. Stone Cleber M. Guimarães About the authors

Abstracts

An important point in no-tillage system is the time between cover crop glyphosate desiccation and rice sowing. This study aimed to verify the effect of Brachiaria ruziziensis management time before rice sowing on rice yield and its components. The experiment was conducted under greenhouse conditions and consisted of four types of B. ruziziensis management: with Brachiaria and with herbicide (WBWH), without Brachiaria shoots and with herbicide (NBWH), without Brachiaria shoots and without herbicide (NBNH), and with Brachiaria and without herbicide (WBNH), at four times: 30, 20, 10, and 0 days, preceding the rice sowing. The amount of B. ruziziensis dry matter increased as the management was done closer to the rice sowing date. The WBWH and WBNH managements (this one causes the lowest rice grain yield) must be done 30 days before rice sowing; while NBWH management must be done ten or more days before rice sowing. On the other hand, NBNH management (this one favors the best rice grain yield) can be done until rice sowing day. Despite some reduction in rice yield caused by the B. ruziziensis management, when it was done at the proper time the rice grain yield was similar to the control (without Brachiaria sowing and without herbicide application).

Oryza sativa ; no-tillage system; glyphosate; cover crop


No sistema de plantio direto é importante o tempo entre a dessecação da cobertura com glifosato e a semeadura do arroz. Este estudo objetivou verificar o efeito da época de manejo da Brachiaria ruziziensis antes da semeadura do arroz na produtividade do arroz e seus componentes de produção. O experimento foi conduzido em casa de vegetação, com quatro tipos de manejo da B. ruziziensis: com Brachiaria e com herbicida (CBCH), sem a parte aérea da Brachiaria e com herbicida (SBCH), com Brachiaria e sem herbicida (CBSH) e sem a parte aérea da Brachiaria e sem herbicida (SBSH), em quatro épocas: 30, 20, 10 e 0 dias anteriores à semeadura do arroz. A matéria seca de B. ruziziensis aumentou à medida que o manejo foi realizado próximo à semeadura do arroz. Os manejos CBCH e CBSH (este proporcionou a menor produtividade de arroz) devem ser feitos 30 dias antes da semeadura do arroz; já o manejo SBCH deve ser feito dez ou mais dias antes da semeadura. O manejo SBSH, que proporcionou a maior produtividade de arroz, pode ser feito até o dia da semeadura do arroz. Apesar de alguma redução na produtividade causada pelo manejo da B. ruziziensis, quando ele foi feito no momento adequado a produtividade do arroz foi semelhante ao controle (sem semeadura da Brachiaria e sem herbicida).

Oryza sativa ; sistema de plantio direto; glifosato; cultura de cobertura


Introduction

In no-tillage system (NTS) straw on the soil surface is an essential requirement before the deployment of crops (Dabney et al., 2001Dabney, S. M.; Delgado, J. A.; Reeves, D. W. Use of winter cover crops to improve soil and water quality. Communications in Soil Science and Plant Analysis, v.7, p.1221-1250, 2001. http://dx.doi.org/10.1081/CSS-100104110
http://dx.doi.org/10.1081/CSS-100104110...
; Yahuza, 2011Yahuza, I. Review of some methods of calculating intercrop efficiencies with particular reference to the estimates of intercrop benefits in wheat/faba bean system. International Journal of Biosciences, v.1, p.18-30, 2011. ; Nascente et al., 2013aNascente, A. S.; Crusciol, C. A. C.; Cobucci, T. The no-tillage system and cover crops – Alternatives to increase upland rice yield. European Journal of Agronomy, v.45, p.124-131, 2013a. http://dx.doi.org/10.1016/j.eja.2012.09.004
http://dx.doi.org/10.1016/j.eja.2012.09....
). Once the amounts of biomass produced by cash crops are not enough for an adequate ground cover, it is necessary to introduce cover crops to produce the required volume of biomass in the off-season (Crusciol et al., 2012Crusciol, C. A. C.; Mateus, G. P.; Nascente, A. S.; Martins, P. O.; Borghi, E.; Pariz, C. M. An innovative crop-forage intercrop system: Early cycle soybean cultivars and palisadegrass. Agronomy Journal, v.104, p.1085-1095, 2012. http://dx.doi.org/10.2134/agronj2012.0002
http://dx.doi.org/10.2134/agronj2012.000...
; Nascente et al., 2013cNascente, A. S.; Crusciol, C. A. C.; Stone, L. F.; Cobucci, T. Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops. Planta Daninha, v.31, p.147-155, 2013c. http://dx.doi.org/10.1590/S0100-83582013000100016
http://dx.doi.org/10.1590/S0100-83582013...
). Then, soil will remain covered as long as possible until the following summer crop (Nascente et al., 2012bNascente, A. S.; Guimarães, C. M.; Cobucci, T.; Crusciol, C. A. C. Brachiaria ruziziensis and herbicide on the yield of upland rice. Planta Daninha, v.30, p.729-736, 2012b. http://dx.doi.org/10.1590/S0100-83582012000400006
http://dx.doi.org/10.1590/S0100-83582012...
). Forage species such as Brachiaria genus is being used as a cover crop because it produces large amounts of biomass and persists longer on the soil surface, especially in times of shortage of rain (Valle & Pagliarini, 2009Valle, C. B.; Pagliarini, M. S. Biology, citogenetics, and breeding of Brachiaria. In: Singh, R. J. Genetic resources, chromossome engineering and crop managements, v.5. Boca Raton: CRC Press, 2009. p.103-152. http://dx.doi.org/10.1201/9781420047400.ch5
http://dx.doi.org/10.1201/9781420047400....
; Crusciol et al., 2013Crusciol, C. A. C.; Nascente, A. S.; Mateus, G. P.; Borghi, E.; Leles, E. P.; Santos, N. C. B. Effect of intercropping on yields of corn with different relative maturities and palisadegrass. Agronomy Journal, v.105, p.599-606, 2013. http://dx.doi.org/10.2134/agronj2012.0426
http://dx.doi.org/10.2134/agronj2012.042...
; Freitas et al., 2013Freitas, R. J.; Nascente, A. S.; Santos, F. L. S. Corn plant population intercropped with Urochloa ruziziensis. Pesquisa Agropecuária Tropical, v.43, p.79-87, 2013. http://dx.doi.org/10.1590/S1983-40632013000100011
http://dx.doi.org/10.1590/S1983-40632013...
).

An important point to be considered is the time between desiccation of the cover crops and main crop sowing (Nascente & Crusciol, 2012Nascente, A. S.; Crusciol, C. A. C. Cover crops and herbicide timing management on soybean yield under no-tillage system. Pesquisa Agropecuária Brasileira, v.47, p.187-192, 2012. http://dx.doi.org/10.1590/S0100-204X2012000200006
http://dx.doi.org/10.1590/S0100-204X2012...
). Herbicide application on cover crops close to cash crop sowing has caused difficulties in sowing operations and in the early crop development, reducing crop grain yield (Grisso et al., 2009Grisso, R. B.; Holshouser, D.; Pitman, R. Planter/drill considerations for conservation tillage systems. Petersburg: Virginia Cooperative Extension Publication 2009, p.442-457. http://pubs.ext.vt.edu/442/442-457/442-457.html.
http://pubs.ext.vt.edu/442/442-457/442-4...
; Nascente et al., 2013bNascente, A. S.; Crusciol, C. A. C.; Cobucci, T.; Velini, E. D. Cover crop termination timing on rice crop production in a no-till system. Crop Science, v.53, p.2659-2669, 2013b. http://dx.doi.org/10.2135/cropsci2013.01.0047
http://dx.doi.org/10.2135/cropsci2013.01...
). It may happen because the systemic characteristic of glyphosate, the principal herbicide used in chemical management of cover crops, which take some days to dry completely the crops (Franz, 1985Franz, J. E. Discovery, development and chemistry of glyphosate. In: Grossbard, E.; Atkinson, D. The herbicide glyphosate. London: Butterworths, 1985. p. 3-17. ). Therefore, at the cash crop sowing day cover crops are not completely dry and with high amount of biomass it can cause difficulties to cut their leaves by the discs of the planter (Grisso et al., 2002Grisso, R. B.; Holshouser, D.; Pitman, R. Equipment considerations for no-till soybean seeding. Petersburg: Virginia Cooperative Extension Publication 2002, p.442-456. http://pubs.ext.vt.edu/442-456/442-456.html.
http://pubs.ext.vt.edu/442-456/442-456.h...
; Nascente et al., 2013cNascente, A. S.; Crusciol, C. A. C.; Stone, L. F.; Cobucci, T. Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops. Planta Daninha, v.31, p.147-155, 2013c. http://dx.doi.org/10.1590/S0100-83582013000100016
http://dx.doi.org/10.1590/S0100-83582013...
). In addition, other factors such as an initial shading in the crops, possible translocation of herbicide from target plants (cover crops) to non-target plants (cash crops), increasing demand for nitrogen by decomposing microorganisms, allelopathic effects and other aspects still must be studied, understood and avoided (Weston, 1990Weston, L. A. Cover crop and herbicide influence on row crop seedling establishment in no-tillage culture. Weed Science, v.38, p.166-171, 1990. ; Miyazawa et al., 2002Miyazawa, M.; Pavan, M. A.; Franchini, J. C. Evaluation of plant residues on the mobility of surface applied lime. Brazilian Archives of Biology and Technology, v.45, p.251-256, 2002. http://dx.doi.org/10.1590/S1516-89132002000300001
http://dx.doi.org/10.1590/S1516-89132002...
; Barbosa et al., 2008Barbosa, E. G.; Pivello, V. R.; Meirelles, S. T. Allelopathic evidence in Brachiaria decumbens and its potential to invade the Brazilian cerrados. Brazilian Archives of Biology and Technology, v.51, p.625-631, 2008. http://dx.doi.org/10.1590/S1516-89132008000400021
http://dx.doi.org/10.1590/S1516-89132008...
; Nascente et al., 2012aNascente, A. S.; Crusciol, C. A. C.; Cobucci, T. Ammonium and nitrate in soil and upland rice yield as affected by cover crops and their desiccation time. Pesquisa Agropecuária Brasileira, v.47, p.1699-1706, 2012a. http://dx.doi.org/10.1590/S0100-204X2012001200004
http://dx.doi.org/10.1590/S0100-204X2012...
).

Despite of the importance of the subject, there are very few studies on this subject in upland rice (Nascente et al., 2013dNascente, A. S.; Li, Y. C.; Crusciol, C. A. C. Cover crops and no-till effects on physical fractions of soil organic matter. Soil and Tillage Research, v.130, p.52-57, 2013d. http://dx.doi.org/10.1016/j.still.2013.02.008
http://dx.doi.org/10.1016/j.still.2013.0...
). Identification of the correct interval between cover crops desiccation and rice sowing could be important to increase its grain yield adjust at NTS. This measure may provide greater availability of nutrients, greater presence of straw on the soil surface and less possible release of allelopathic substances to the soil (Weston, 1990Weston, L. A. Cover crop and herbicide influence on row crop seedling establishment in no-tillage culture. Weed Science, v.38, p.166-171, 1990. ; Barbosa et al., 2008Barbosa, E. G.; Pivello, V. R.; Meirelles, S. T. Allelopathic evidence in Brachiaria decumbens and its potential to invade the Brazilian cerrados. Brazilian Archives of Biology and Technology, v.51, p.625-631, 2008. http://dx.doi.org/10.1590/S1516-89132008000400021
http://dx.doi.org/10.1590/S1516-89132008...
, Zaidan & Carreira, 2008Zaidan, L. B. P.; Carreira, R. C. Seed germination in Cerrado species. Brazilian Journal of Plant Physiology, v.20, p.167-181, 2008. http://dx.doi.org/10.1590/S1677-04202008000300002
http://dx.doi.org/10.1590/S1677-04202008...
; Weih et al., 2008Weih, A. U. M. E.; Didon, A. A. C.; Rönnberg-Wästljung, B. C.; Björkman, M. Integrated agricultural research and crop breeding: Allelopathic weed control in cereals and long-term productivity in perennial biomass crops. Agricultural Systems, v.97, p.99-107, 2008. http://dx.doi.org/10.1016/j.agsy.2008.02.009
http://dx.doi.org/10.1016/j.agsy.2008.02...
; Nascente et al., 2013dNascente, A. S.; Li, Y. C.; Crusciol, C. A. C. Cover crops and no-till effects on physical fractions of soil organic matter. Soil and Tillage Research, v.130, p.52-57, 2013d. http://dx.doi.org/10.1016/j.still.2013.02.008
http://dx.doi.org/10.1016/j.still.2013.0...
).

In this context, a test was performed under controlled conditions to verify the effect of Brachiaria ruziziensis management, with or without herbicide, in different times preceding upland rice sowing in the grain yield and its components.

Material and Methods

The study was performed in Santo Antônio de Goiás, GO, Brazil (16° 27' latitude, 49º 17' longitude and 823 m altitude) under greenhouse conditions between January and August of 2010. The experimental units consisted of PVC columns with 0.25 m in diameter and 1.0 m tall (0.25 m3), filled with soil (35% sand, 12% silt and 53% clay), classified as a Rhodic Ferralsol, from the layer 0-20 cm deep, previously sieved through 5 mm mesh. Chemical analysis showed pH in H2O = 5.0, Al+3, H+ + Al+3, Ca+2 and Mg+2 was 0.2, 5.00, 0.45 and 0.14 cmol c kg-1, respectively, P = 9.2 mg kg-1, K = 19 mg kg-1, and soil organic matter = 16 g kg-1. P and K were extracted by Mehlich 1 extracting solution (0.05M HC1 in 0.0125M H2SO4). In the extracted solution, phosphorus was determined colorimetrically and K by flame photometry. Calcium, Mg and Al were extracted with 1M KC1. Aluminum was determined by titration with NaOH and Ca and Mg by titration with EDTA from the extracted solution and pH was determined in water using pHmeter.

The experiment was conducted in four (managements) x four (times of Brachiaria drying/cutting) factorial + one control treatment (no-planting Brachiaria and no-herbicide application) in a completely randomized design with three replications, totaling 51 experimental units. Four types of Brachiaria management were established: with Brachiaria and with herbicide (WBWH), without Brachiaria shoots and with herbicide (NBWH), without Brachiaria shoots and without herbicide (NBNH), and with Brachiaria and without herbicide (WBNH).

The periods of drying/removal of the Brachiaria shoots were at 30, 20, 10 and 0 days before rice sowing.

In each column ten seeds of B. ruziziensis were sown. Fertilizer application consisted of 5 g per column with triple superphosphate (equivalent to 69.87 kg of P ha-1), one day before forage sowing. At 60 days after germination, when Brachiaria plants had approximately three to four tillers, proceeded to the beginning of the forage management (30 days before rice sowing).

In NBWH management, 48 h after herbicide application a cutting was made at ground level with removal all shoots of B. ruziziensis. In NBNH management, at the same time, despite of not applying herbicide removal of the forage shoots was done and the sprout was removed weekly. In WBNH management, at the time of herbicide application in the other treatments, Brachiaria shoots were cut and put on the soil surface, removing sprouts weekly too.

The application of glyphosate (1.8 kg ha-1 acid equivalent) was done using a vacuum pump, stationary, with constant pressure of 207 kPa, equipped with a fan type tip (TeeJet XR 110.02) positioned 0.5 m from the target surface, applying the equivalent of 200 L ha-1 of spray.

In each column ten seeds of upland rice cultivar BRS Sertaneja were sown at a depth of 2 cm. Fertilization at sowing was 5 g per column equivalent to 20 kg ha-1 of N as urea, 52 kg ha-1 of P as triple superphosphate and 49.8 kg ha-1of K as potassium chloride and 45 days after germination, 2.5 g per column of ammonium sulfate (equivalent to 40 kg ha-1 of N) was applied. At 5 days after germination thinning was done and three rice plants per column were left.

The amount of shoot dry matter produced by Brachiaria was assessed in each season of forage management (30, 20, 10 and 0 days before rice sowing). Brachiaria shoots were collected and packed in paper bags and dried in an oven with air circulation at 60 ºC until constant weight. In addition the relative growth rate (RGR, g g-1 d-1) of the grass was calculated, following the method proposed by Reader et al. (1994), using the formula:

where:

M1 and M2 - weight of Brachiaria shoots dry matter (g) at times t1 and t2

t1 and t2 - time of sampling plants (30 and 0 d prior to rice sowing)

To evaluate rice yield all rice plants in each experimental plot were collected, grains were corrected to 13% moisture and then weighed. For yield components, the number of panicles per pot, spikelets per panicle, number of filled spikelets and 1000 grain weight were evaluated.

Data were subjected to variance analysis in a factorial design and means were compared by t test at p < 0.05. Regression analysis was carried out for the growth rate of Brachiaria and for rice grain yield and its components with the time of Brachiaria management, for each type of management. Comparison of treatments with control treatment was also performed by analysis of variance, and the means of the treatments were compared to control treatment by Dunnett's test at p < 0.05. All tests were performed using statistical program Statistical Analysis System (SAS, 1999SAS Institute. Procedure guide for personal computers. Version 5. Cary: SAS Institute, 1999. 552p.).

Results and Discussion

The amount of Brachiaria ruziziensis dry matter increased as the management was done closer to the rice sowing day, with a significant linear regression (Figure 1). Regarding yield components, they all had lowest values when the forage management was done closer to the rice sowing day (Figures 2A to 2D), although it was not significant for number of panicles. There were interactions between types and times of Brachiaria management for number of spikelets per pot (Figure 2A). Number of viable spikelets and 1000 grain weight were not affected by Brachiariamanagement but only by the management time (Figures 2B and 2C).

Figure 1
Shoot dry mass accumulation by Brachiaria ruziziensis plants, considering days before rice sowing

** significant at p < 0.01

Figure 2
Number of spikelets per pot (A); Viable spikelets, % (B); 1000-grain mass (C); Rice grain (D) yield as a function of the day which was done Brachiaria ruziziensis management in relation to rice sowing

*Significant by p < 0.05; **Significant by p < 0.01, and ns – No significant

There was interaction between types and times of Brachiaria management in upland rice grain yield (Figure 2D). The lowest yields were observed when Brachiaria straw management was done on the rice sowing day. Treatments with Brachiaria cutting and maintenance of the shoots on the soil surface was the worst for rice yield. On the other hand, the highest grain yields were observed when grass shoots were removed and there was no application of herbicide. In the absence of Brachiaria shoots, the herbicide application also reduced the rice yield.

It was found by statistical analysis that there was high correlation between amount of dry matter produced by Brachiaria on the management day and rice yield, with value -0.57 (Table 1). The same happened to all yield components in relation to the grass biomass, with exception of 1000 grain weight. On the other hand, WBNH management at 30 days before rice sowing was satisfactory and rice grain yield did not differ from the control treatment (Table 2).

Table 1
Pearson correlation coefficient and p value among rice yield components, rice yield and Brachiaria dry matter at the management day during 2010 growing season
Table 2
Evaluation of the rice yield and its components under different treatments in greenhouse conditions in comparison to the control treatment during 2010 growing season

Regarding Brachiaria biomass accumulation, through the results it was observed that management with-grass and no-herbicide at sowing rice day, had the presence of 45 g of straw dry matter on the soil surface and it could hindered emergence of rice seedlings. This amount of straw on the soil surface is equivalent to 2.3 t of dry matter ha-1 and it is sufficient to cover about 40% of the soil (Miyazawa et al., 2002Miyazawa, M.; Pavan, M. A.; Franchini, J. C. Evaluation of plant residues on the mobility of surface applied lime. Brazilian Archives of Biology and Technology, v.45, p.251-256, 2002. http://dx.doi.org/10.1590/S1516-89132002000300001
http://dx.doi.org/10.1590/S1516-89132002...
; Mauli et al., 2011Mauli, M. M.; Nóbrega, L. H. P.; Rosa, D. M.; Lima, G. P.; Ralish, R. Variation on the amount of winter cover crops residues on weeds incidence and soil seed bank during an agricultural year. Brazilian Archives of Biology and Technology, v.54, p.683-690, 2011. http://dx.doi.org/10.1590/S1516-89132011000400006
http://dx.doi.org/10.1590/S1516-89132011...
). It is noteworthy that this value is even lower, considering that Brachiaria species have potential to produce 20 t ha-1 of dry matter (Fischer et al., 2001Fischer, A. J.; Ramirez, H. V.; Gibson, K. D.; Pinheiro, B. D. S. Competitiveness of semidwarf upland rice cultivars against palisadegrass (Brachiaria brizantha) and signalgrass (B. decumbens). Agronomy Journal, v.93, p.967-73, 2001. http://dx.doi.org/10.2134/agronj2001.935967x
http://dx.doi.org/10.2134/agronj2001.935...
; Crusciol et al., 2012Crusciol, C. A. C.; Mateus, G. P.; Nascente, A. S.; Martins, P. O.; Borghi, E.; Pariz, C. M. An innovative crop-forage intercrop system: Early cycle soybean cultivars and palisadegrass. Agronomy Journal, v.104, p.1085-1095, 2012. http://dx.doi.org/10.2134/agronj2012.0002
http://dx.doi.org/10.2134/agronj2012.000...
; Nascente et al., 2013aNascente, A. S.; Crusciol, C. A. C.; Cobucci, T. The no-tillage system and cover crops – Alternatives to increase upland rice yield. European Journal of Agronomy, v.45, p.124-131, 2013a. http://dx.doi.org/10.1016/j.eja.2012.09.004
http://dx.doi.org/10.1016/j.eja.2012.09....
).

This small accumulation of Brachiaria biomass can be explained due to its slow initial growth (Valle & Pagliarini, 2009Valle, C. B.; Pagliarini, M. S. Biology, citogenetics, and breeding of Brachiaria. In: Singh, R. J. Genetic resources, chromossome engineering and crop managements, v.5. Boca Raton: CRC Press, 2009. p.103-152. http://dx.doi.org/10.1201/9781420047400.ch5
http://dx.doi.org/10.1201/9781420047400....
; Crusciol et al., 2012Crusciol, C. A. C.; Mateus, G. P.; Nascente, A. S.; Martins, P. O.; Borghi, E.; Pariz, C. M. An innovative crop-forage intercrop system: Early cycle soybean cultivars and palisadegrass. Agronomy Journal, v.104, p.1085-1095, 2012. http://dx.doi.org/10.2134/agronj2012.0002
http://dx.doi.org/10.2134/agronj2012.000...
), that was observed by the relative growth rate (increase in grams of dry biomass per unit of material present in the observation period) which was 0.043 g g-1 (Figure 1). Similar values were obtained by Valle & Pagliarini (2009)Valle, C. B.; Pagliarini, M. S. Biology, citogenetics, and breeding of Brachiaria. In: Singh, R. J. Genetic resources, chromossome engineering and crop managements, v.5. Boca Raton: CRC Press, 2009. p.103-152. http://dx.doi.org/10.1201/9781420047400.ch5
http://dx.doi.org/10.1201/9781420047400....
, 0.050 g g-1 at 60 days after grass germination, same time of onset Brachiaria management in our study. However, even this amount of Brachiaria dry matter on the soil surface was not beneficial for rice plants, once plots with lower levels of Brachiaria biomass (management carried out in a period larger in relation to rice sowing day) allowed higher rice yield (Figure 2D). On the other hand, as higher the amount of accumulated Brachiaria dry matter as lower was the rice yields in all types of Brachiaria management.

Fischer et al. (1995)Fischer, A. J.; Chatel, M.; Ramirez, H.; Lozano, J.; Guimarães, E. Components of early competition between upland rice (Oryza sativaL.) and Brachiaria brizantha (Hochst. ex A.Rich) Stapf. International Journal of Pest Management, v.41, p.100-103, 1995. http://dx.doi.org/10.1080/09670879509371931
http://dx.doi.org/10.1080/09670879509371...
, Crusciol et al. (2012)Crusciol, C. A. C.; Mateus, G. P.; Nascente, A. S.; Martins, P. O.; Borghi, E.; Pariz, C. M. An innovative crop-forage intercrop system: Early cycle soybean cultivars and palisadegrass. Agronomy Journal, v.104, p.1085-1095, 2012. http://dx.doi.org/10.2134/agronj2012.0002
http://dx.doi.org/10.2134/agronj2012.000...
and Nascente et al. (2013a)Nascente, A. S.; Crusciol, C. A. C.; Cobucci, T. The no-tillage system and cover crops – Alternatives to increase upland rice yield. European Journal of Agronomy, v.45, p.124-131, 2013a. http://dx.doi.org/10.1016/j.eja.2012.09.004
http://dx.doi.org/10.1016/j.eja.2012.09....
add that species of Brachiaria spp. produce large amount of biomass, which if not properly managed, can undermine emergence and establishment of rice plants. Corroborating this information, there was negative correlation between amount of Brachiaria dry matter with rice grain yield and all yield components, with exception of 1000 grain weight.

Treatment with-Brachiaria which keeps the shoots on the soil surface simulating mowing, was the most detrimental to the rice yield. According to Nascente et al. (2013c)Nascente, A. S.; Crusciol, C. A. C.; Stone, L. F.; Cobucci, T. Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops. Planta Daninha, v.31, p.147-155, 2013c. http://dx.doi.org/10.1590/S0100-83582013000100016
http://dx.doi.org/10.1590/S0100-83582013...
, mowing does not kill the plants and the grass keeps competing with the cash crop, with constant sprout, which can significant reduce grain yield. The application of herbicide in WBWH management minimized this effect. According to Dabney et al. (2001)Dabney, S. M.; Delgado, J. A.; Reeves, D. W. Use of winter cover crops to improve soil and water quality. Communications in Soil Science and Plant Analysis, v.7, p.1221-1250, 2001. http://dx.doi.org/10.1081/CSS-100104110
http://dx.doi.org/10.1081/CSS-100104110...
and Nascente et al. (2013cNascente, A. S.; Crusciol, C. A. C.; Stone, L. F.; Cobucci, T. Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops. Planta Daninha, v.31, p.147-155, 2013c. http://dx.doi.org/10.1590/S0100-83582013000100016
http://dx.doi.org/10.1590/S0100-83582013...
,d)Nascente, A. S.; Li, Y. C.; Crusciol, C. A. C. Cover crops and no-till effects on physical fractions of soil organic matter. Soil and Tillage Research, v.130, p.52-57, 2013d. http://dx.doi.org/10.1016/j.still.2013.02.008
http://dx.doi.org/10.1016/j.still.2013.0...
benefits of managing cover crops with herbicide or mowing before main crop sowing are: reducing competition for water in the early crop development, promotes decomposition of cover crop residues or weeds, which can provide nutrients to the crops, improves uniformity of sowing; reduce possible allelopathic effects of cover crops or weeds, and provides increased in crops yield. According to Nascente et al. (2013b)Nascente, A. S.; Crusciol, C. A. C.; Cobucci, T.; Velini, E. D. Cover crop termination timing on rice crop production in a no-till system. Crop Science, v.53, p.2659-2669, 2013b. http://dx.doi.org/10.2135/cropsci2013.01.0047
http://dx.doi.org/10.2135/cropsci2013.01...
the time to apply herbicide will depend of the cover crop specie, for example for millet (Pennisetum glaucum) this time is around 10-14 days before sowing and for Brachiaria species this time is around 30 days before rice sowing.

The NBNH management, when grass straw was removed from the soil surface, allowed the greatest rice yield in comparison to all kinds of Brachiariamanagement. On the other hand, the WBNH management, when shoot straw was on the soil surface, caused greater reductions in rice yield and its components in management carried out on the days 20, 10, and 0 prior to sowing of rice. These results allow us to infer that shoots straw of Brachiaria has detrimental effect on rice plants. When we used the management that took out Brachiaria shoots the effects on rice yield and its components were smaller. According to Weston (1990)Weston, L. A. Cover crop and herbicide influence on row crop seedling establishment in no-tillage culture. Weed Science, v.38, p.166-171, 1990. , Barbosa et al. (2008)Barbosa, E. G.; Pivello, V. R.; Meirelles, S. T. Allelopathic evidence in Brachiaria decumbens and its potential to invade the Brazilian cerrados. Brazilian Archives of Biology and Technology, v.51, p.625-631, 2008. http://dx.doi.org/10.1590/S1516-89132008000400021
http://dx.doi.org/10.1590/S1516-89132008...
, Zaidan & Carreira, (2008)Zaidan, L. B. P.; Carreira, R. C. Seed germination in Cerrado species. Brazilian Journal of Plant Physiology, v.20, p.167-181, 2008. http://dx.doi.org/10.1590/S1677-04202008000300002
http://dx.doi.org/10.1590/S1677-04202008...
and Weih et al. (2008)Weih, A. U. M. E.; Didon, A. A. C.; Rönnberg-Wästljung, B. C.; Björkman, M. Integrated agricultural research and crop breeding: Allelopathic weed control in cereals and long-term productivity in perennial biomass crops. Agricultural Systems, v.97, p.99-107, 2008. http://dx.doi.org/10.1016/j.agsy.2008.02.009
http://dx.doi.org/10.1016/j.agsy.2008.02...
although there are many advantages for the presence of mulch on the soil over fallow, some types of coverage may have inhibitory effects on crops seedling emergence and these effects can be physical, allelopathic or biological (reduction of soil microbial population).

In the WBWH management the highest yields were obtained at treatments which management were done 30 days before rice sowing and were not different from the control treatment. In these treatments, herbicide reduced Brachiaria effect and had better rice yield and its components in comparison to treatments with only Brachiaria (no herbicide). According to Nascente & Crusciol (2012)Nascente, A. S.; Crusciol, C. A. C. Cover crops and herbicide timing management on soybean yield under no-tillage system. Pesquisa Agropecuária Brasileira, v.47, p.187-192, 2012. http://dx.doi.org/10.1590/S0100-204X2012000200006
http://dx.doi.org/10.1590/S0100-204X2012...
and Nascente et al. (2013c)Nascente, A. S.; Crusciol, C. A. C.; Stone, L. F.; Cobucci, T. Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops. Planta Daninha, v.31, p.147-155, 2013c. http://dx.doi.org/10.1590/S0100-83582013000100016
http://dx.doi.org/10.1590/S0100-83582013...
it is important to wait two or three weeks between the cover crop desiccation and annual crop sowing to avoid possible translocation of the herbicide from target (cover crop) to no-target plants (rice), possible release of allelopathic substances from the cover crop and shade in the seedling. Waiting a while before cash crop sowing could allow plants to have a rapid and vigorous initial development. For rice it seems that this period must be greater, about 30 days before rice sowing. Nascente et al. (2012a)Nascente, A. S.; Crusciol, C. A. C.; Cobucci, T. Ammonium and nitrate in soil and upland rice yield as affected by cover crops and their desiccation time. Pesquisa Agropecuária Brasileira, v.47, p.1699-1706, 2012a. http://dx.doi.org/10.1590/S0100-204X2012001200004
http://dx.doi.org/10.1590/S0100-204X2012...
under field conditions reported that Brachiaria ruziziensis desiccated 30 days before rice sowing allow the highest grain yield. Matallo et al. (2009) add that due to systemic nature of glyphosate its effect on plants is slow and coverage takes a few days to die completely. When using the system to apply this herbicide on cover crops close to sowing day, these plants are not yet completely dried and may impair the operations of sowing, and the initial crop development (Grisso et al., 2002Grisso, R. B.; Holshouser, D.; Pitman, R. Equipment considerations for no-till soybean seeding. Petersburg: Virginia Cooperative Extension Publication 2002, p.442-456. http://pubs.ext.vt.edu/442-456/442-456.html.
http://pubs.ext.vt.edu/442-456/442-456.h...
; 2009Grisso, R. B.; Holshouser, D.; Pitman, R. Planter/drill considerations for conservation tillage systems. Petersburg: Virginia Cooperative Extension Publication 2009, p.442-457. http://pubs.ext.vt.edu/442/442-457/442-457.html.
http://pubs.ext.vt.edu/442/442-457/442-4...
; Nascente et al., 2012bNascente, A. S.; Guimarães, C. M.; Cobucci, T.; Crusciol, C. A. C. Brachiaria ruziziensis and herbicide on the yield of upland rice. Planta Daninha, v.30, p.729-736, 2012b. http://dx.doi.org/10.1590/S0100-83582012000400006
http://dx.doi.org/10.1590/S0100-83582012...
; 2013cNascente, A. S.; Crusciol, C. A. C.; Stone, L. F.; Cobucci, T. Upland rice yield as affected by previous summer crop rotation (soybean or upland rice) and glyphosate management on cover crops. Planta Daninha, v.31, p.147-155, 2013c. http://dx.doi.org/10.1590/S0100-83582013000100016
http://dx.doi.org/10.1590/S0100-83582013...
).

In NBWH management (herbicide application and removal of grass shoots two days after), to check the effect of the herbicide without Brachiaria shoots, management carried out 10 or more days before rice sowing had similar rice yields and not differ from control treatment. Without Brachiaria shoots glyphosate effect was fewer than in the management with only Brachiaria or with Brachiaria and herbicide. Again, it could see that something in the Brachiaria shoots are causing damage in rice and should be more understood.

Summarizing the results allow inferring that management of cover crops before rice sowing has significant effect on the grain yield and its components and therefore should be done at the correct time. In this sense, despite of some Brachiariamanagements are harmful to rice yield and its components, it cannot eliminate the use of cover crops in a crop rotation management on rice crops, once cover crops in rotation with rice are very important to NTS and have many interesting features like nutrients cycling, protection against erosion, weed control and increase soil organic matter (Dabney et al., 2001Dabney, S. M.; Delgado, J. A.; Reeves, D. W. Use of winter cover crops to improve soil and water quality. Communications in Soil Science and Plant Analysis, v.7, p.1221-1250, 2001. http://dx.doi.org/10.1081/CSS-100104110
http://dx.doi.org/10.1081/CSS-100104110...
; Filizadeh et al., 2007Filizadeh, Y.; Rezazadeh, A.; Younessi, Z. Effects of crop rotation and tillage depth on weed competition and yield of rice in the paddy fields of Northern Iran. Journal of Agricultural Science and Technology, v.9, p.99-105, 2007.; Yahuza, 2011Yahuza, I. Review of some methods of calculating intercrop efficiencies with particular reference to the estimates of intercrop benefits in wheat/faba bean system. International Journal of Biosciences, v.1, p.18-30, 2011. ; Crusciol et al., 2012Crusciol, C. A. C.; Mateus, G. P.; Nascente, A. S.; Martins, P. O.; Borghi, E.; Pariz, C. M. An innovative crop-forage intercrop system: Early cycle soybean cultivars and palisadegrass. Agronomy Journal, v.104, p.1085-1095, 2012. http://dx.doi.org/10.2134/agronj2012.0002
http://dx.doi.org/10.2134/agronj2012.000...
; Nascente et al., 2013dNascente, A. S.; Li, Y. C.; Crusciol, C. A. C. Cover crops and no-till effects on physical fractions of soil organic matter. Soil and Tillage Research, v.130, p.52-57, 2013d. http://dx.doi.org/10.1016/j.still.2013.02.008
http://dx.doi.org/10.1016/j.still.2013.0...
). When Brachiaria management was done at the correct time it allowed satisfactory results and it was enough to have rice yield similar to the control treatment. Therefore, farmers can chose all kind of management, but must pay attention to correct time to avoid damage in rice yield.

Conclusions

1. Management of B.ruziziensis with herbicide and without removing the straw must be done 30 days before rice sowing.

2. Chemical control of B. ruziziensis with removal of straw must be done ten or more days before rice sowing.

3. Management where B. ruziziensis straw is removed from the soil surface and without herbicide application is the best for rice yield and can be done until on the day of rice sowing.

4. Management that remained Brachiaria straw on the soil surface without herbicide application cause lowest rice yield and must be done 30 days before the rice sowing.

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Publication Dates

  • Publication in this collection
    Jan 2015

History

  • Received
    24 Nov 2013
  • Accepted
    15 Aug 2014
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