trabalho completo

52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
Effect of height residue and cutting frequency on morphological and gravimetrical characteristics of Piatãgrass roots¹
Herlon Meneguelli Alhadas², Domingos Sávio Queiroz³, Gustavo da Silveira 4, Dilermando Miranda da Fonseca5,
Ana Clara Baião Menezes6
(1)
Research Funded by FAPEMIG and CNPq
Zootechnics Student/UFV, Scientific Initiation, FAPEMIG/EPAMIG, [email protected];
(3)
EPAMIG Researcher, FAPEMIG Fellow, INCT Animal Science Member, [email protected];
(4)
Doctoral student, UFV, [email protected]
(5)
Professor department Zootecnia/UFV, [email protected]
(6)
Master Degree Zootecnia/UFV, [email protected]
(2)
Abstract: The importance of root system is much known, but just few studies are found in the literature about it,
and studies about morphological characteristics of root system are very rare. This work was developed to evaluate
the influence of residue’s height and cutting frequencies on gravimetrical and morphological characteristics of
Piatã-grass roots (Brachiaria brizantha). It was conducted an experiment in a greenhouse testing three residue’s
heights (10, 15 and 20 cm) and three cutting frequencies (14, 28 and 56 days), arranged in a factorial randomized
blocks with five repetitions. At the end of the evaluation, the roots were extracted, washed and weighted,
withdrawing a sample to determinate the morphological characteristics of roots in a scanner coupled to WinRhizo
Pro 2007a software, to obtain the total root length, length of fine roots, length intermediate roots, length of thick
roots, total volume, volume of fine roots, volume of intermediate roots, volume of thick roots and the average
diameter of roots. The cutting frequency has a greater influence on the weight and root length compared to the
height residue. The reduction of the interval between cuts reduces the length and weight of root system.
Keywords: Brachiaria brizantha, roots morphology, roots scanner
Influência da altura de resíduo e da frequência de corte nas características morfológicas e gravimétricas das raízes
de Capim-Piatã
Resumo: Embora se reconheça a importância do sistema radicular, poucos trabalhos são encontrados na literatura a
seu respeito, sendo ainda mais raros aqueles que descrevem suas características morfológicas. O objetivo deste
trabalho foi avaliar a influência da altura de resíduo e da frequência de corte nas características gravimétricas e
morfológicas das raízes do capim-piatã (Brachiaria brizantha). Foi feito um experimento em casa de vegetação
para testar três alturas de resíduo (10, 15 e 20 cm) e três frequências de corte (14, 28 e 56 dias), arranjado num
esquema fatorial em blocos casualizados com cinco repetições. Ao final do período de avaliação, as raízes foram
extraídas, lavadas e pesadas, retirando-se uma subamostra para leitura das características morfológicas num scanner
de raízes acoplado ao software WinRHIZO Pro 2007a, para obtenção do comprimento total de raízes, comprimento
de raízes finas, comprimento de raízes intermediárias, comprimento de raízes grossas, volume total, volume de
raízes finas, volume de raízes intermediárias, volume de raízes grossas e diâmetro médio de raízes. A frequência de
corte apresenta maior influência sobre o peso e o comprimento radicular quando comparada à altura de resíduo,
sendo que quanto menor o intervalo entre uma desfolha e outra, mais leve e mais curto se torna o sistema radicular.
Palavras–chave: Brachiaria brizantha, morfologia de raiz, scanner de raiz
Introduction
Brachiaria brizantha cv. Piatã is a tropical grass released by Embrapa in 2007 as an alternative to
Brachiaria brizantha cv Marandu, because it is more tolerant to flooding. As a new cultivar, it needs more studies,
particularly in relation to management. Frequently the recommendations are based almost exclusively on evaluation
of canopy parameters, leaving aside the growth kinetics and senescence of root system. Few studies are found in the
literature describing these effects when subjected to some kind of management. Most studies evaluate only the root
mass, because there is a great difficulty to evaluate morphological characteristics such as length, diameter, among
others. However, the gravimetric measuring not only correlates well with absorptive capacity, since it is known that
different classes of roots, according the diameter (fine, intermediate, and thick), have different capabilities in
nutrients absorption. Fine roots, which are also the most superficial, have a higher absorptive activity when
compared with thick roots, that have a great importance in deepening the roots and water absorption. This pattern
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52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
was described by Fitter (1999) and certified by Fransen et al., (1998), who did not find relation between the ability
to acquire nutrients (N or P) and the root growth of five grass. Therefore, in addition to assess mass and root length,
it is important to know the contribution of each root class. One of the most striking grazing factors is the constant
removal of the leaf blade by animals. Therefore, it is important the quantification of how the intensity and
frequency of shoot removal affects the response of root system. The objective of this study was to evaluate the
effect of residual height and frequency of cutting on root growth of Piatã grass.
Material e Methods
The experiment was conducted in a greenhouse in the Federal University of Viçosa, located in Viçosa-MG,
during the period from January to May of 2014. Was studied the combination of three residue heights (10, 20 and
30 cm) and three cutting frequencies (14, 28 and 56 days) which reported nine treatments, arranged in a randomized
block design, with 5 repetitions, totaling 45 pots. The experimental units were constituted of PVC pots of 6 dm³
volume, which were filled with a mixture of 20% soil, 40% commercial substrate and 40% river sand. This mixture
received the equivalent fertilization 86, 300 and 170 mg/dm³ of N, P2O5 and K2O, respectively, using NPK 04-1408 formulated. There were sowed ten Piatã grass seeds per pot. After 28 days of sowing the thin out was done,
leaving three plants per pot. Forty days after sowing, a nitrogenous fertilization of 240 mg/dm as urea was held.
After 51 days after sowing the plants were cut into the residues heights to start the cutoff frequency. On this date
was made another nitrogen fertilization of 240 mg/dm as urea. From this date, plants subjected to 56 days of
frequency grew freely until the evaluation, the 28 days were cut one time and the 14 days were cut three times
(Figure 1). The roots were then rinsed with water over a 1 mm sieve, so that nothing was lost. After washing, all the
roots were weighed and a subsample was withdrawn to evaluate morphological characteristics. These were
measured by using the WinRhizo root-scanning (WinRhizo 2007a Pro) software to obtain the values of full length
of roots, length of thin roots (RF d <0.25 mm), length of intermediate roots (RI; 0.25 <d <1.5 mm), length of thick
roots (RP d> 1.5 mm), total volume, volume of fine roots, volume of intermediate roots, volume of thick roots and
average diameter of roots. During the experimental period the pots were watered twice a day to avoid water stress.
Data were subjected to analysis of variance and average test with 5% significance using the SAEG software.
15/01/14
Sowing
28°
40°
Thin out
N
fertilization
51°
65°
First cut and Cut with 14
days
N fertiliz.
Figure 1 – Timeline of activities developed in the experiment.
79°
93°
107°
Cut with 14
and 28
days
Cut with 14
days
Evaluation
Results and Discussion
The following parameters: total root weight, length of intermediate roots, length of thick roots and total
length; do not presented effect of residue's height, being significant for cutting frequencies (Table 1). There was a
significant interaction between cutting frequency and residue's height to length of fine root (LFR) (Table 2). The
total root weight was highly influenced by cutting frequency, it results in a significant response to rise on regrowth
period (Table 1). This was expected, since frequent cutting promotes mobilization of reserves from the root to the
formation of new leaves and at the same time reduces the photosynthesis by the elimination of active leaves,
resulting in a greater impact on roots accumulation. The new aspect of this work is how roots classes respond to the
shoot cutting. Fine roots represented on average 83.32% of the total root length, compared to 13.89% of
intermediate roots and 2.79% of thick roots, demonstrating its important absorptive contribution. All classes
reduced root length in response to the increase of cutting frequency (Table 1). There was no difference on thick
roots length for frequencies of 56 and 28 days, suggesting that this class of roots are less sensitive and presented
minor variations. However, at a frequency of 14 days, more severe, effects achieved even this root class. On the
other hand, intermediate and fine roots responded quickly to the stress caused by cutting and even on the frequency
of 28 days of interval showed reduction in length in relation to frequency of 56 days. This result set up an alert
about the harvest intervals practiced on current management recommendations and their effects on the root system
of forage grass. Andrade & Assis (2010) recommend the use of grazing with rotational allotment adopting the
interval of 22 to 28 days of rest and residue’s height of 15 to 20 cm to Piatã grass pastures during the rainy season
on Acre. Obviously, a work developed on pots with uniform cut by an instrument, needs to be viewed carefully, but
it also shows the necessity to develop studies focused in the classes of root system and its effects on management
practices, especially because the contribution of intermediate and fine roots is higher than the contribution of thick
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52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
roots. So, the total length tended to follow the sensitivity model to the cutting frequency to intermediate and fine
roots, which is higher for 56 days and equal to 14 and 28 days. The variables: volume of fine roots (mean = 8.54
cm³/pot), volume of thick roots (mean = 67.45 cm³/pot), total volume (mean = 136.07 cm³/pot) and average
diameter (average = 0.37 mm) were not influenced by treatments. The volume of intermediate roots was affected by
residue’s height, being statistically superior to the height of 10 cm (64.43 cm³/pot), and equal to the heights of 15
and 20 cm (52.49 and 52.38 cm³/pot respectively). The roots length showed clear the effect of cutting frequencies,
but the volume did not show sensibility to the treatments. What is the meaning of these effects on the capacity of
recovery of the forage plant? It is an unexplored area and needs more studies to elucidate it.
Table 1- Influence of cutting frequency on total root weight, length of fine roots, length of intermediate roots,
length of thick roots and total length
Cutting frequency (days)
Variables
14
28
56
Total radicular weight (g/pot)
197,04 c
256,22 b
307,03 a
Length of fine roots (m/pot)
83,91 b
100,88 b
121,94 a
Length of intermediate roots (m/pot)
13,98 b
16,52 b
20,16 a
Length of thick roots (m/pot)
2,43 b
3,63 a
4,51 a
Total lenght (m/pot)
100,32 b
121,08 b
146,61 a
Same letters in the line do not differ by SNK test at 5% significance level.
The LFR increased with the reduction in the frequency of cuts, but the effects of residual height only were
showed in the 56-day frequency. Allowing a greater period of regrowth, the LFR was favored by more intense cut
at 10 cm height. It is speculated that on this time, the plant was able to mobilize the reserves for expansion of new
leaves and, from there, returns its normal photosynthetic activity, allowing the fine roots that have come to
senescence, could be replaced by new roots, higher than the most highest residues. On the frequencies of 14 and 28
days, there was no effect of residue heights on the LFR. Looking only for LFR, if applies a more lenient grazing,
the root system may be benefited by a high grazing intensity. On the other hand, frequently harvests were not
beneficiated from higher residues, expressed by the absence of significant differences between residues of 10 and
20 cm at frequencies of 14 and 28 days of cut of aerial part.
Table 2 - Length of fine roots (m/pot) according to the cut frequencies and the residue’s heights
Cutting frequencie (days)
Residue height (cm)
Mean
14
28
56
10
79,79 Ab
90,50 Ab
149,85 Aa
106,71A
15
83,04 Aa
106,93 Aa
111,44 Ba
100,47A
20
88,89 Aa
105,22 Aa
104,53 Ba
99,55A
Mean
83,91b
100,88b
121,94a
Same capital letters at the column and lowercase letters at the line do not differ by SNK test at 5% significance
level.
Conclusions
Cutting frequency has a greater effect on the weight and root length compared to residue's height. The
shortest the interval between one and another cut, lighter and shorter becomes the radicular system. These effects
manifest itself differently depending on the roots’ thickness.
References
FITTER, A. H. Roots as dynamics systems: the developmental ecology of roots and root systems. In: PRESS,
M.C.; SCJOLES, J. D.; BARKER, M. G. (Ed.) Physiological plant ecology. Cap. 6, p. 115-131, 1999.
FRANSEN, B.; de KROON, H.; BERNSDE, F. Root morphological plasticity and nutrient acquisition by perennial
grass species from habitats of different availability. Oecologia, v. 115, p. 351-358, 1998.
ANDRADE, C. M. S.; & ASSIS, G. M. L. Brachiaria brizantha cv. Piatã: Gramínea Recomendada para Solos
Bem-drenados do Acre, junho 2010. Rio branco. 8p
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