08-08-2012, 11:59 AM
IMPACT OF DIFFERENT NITROGEN LEVELS ON COTTON GROWTH, YIELD AND N-UPTAKE PLANTED IN LEGUME ROTATION
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Abstract
A series of experiments were conducted at Sindh Agriculture University, Tandojam. The
experiment was laid out in Randomized Complete Block Design (RCBD) with factorial
arrangement consisting four replications and repeated in the 2nd year. The treatments consisted crop
two sequences [(C1= Cotton (before legume) and C2= Cotton (after legume)] and varying fertility
levels (F1=150-50, F2=100-50 and F3=150-50 NP Kg ha-1). The berseem was cultivated as
leguminous crop in the sequence. The crop sequences revealed that the cotton crop sown after
legume produced tall plants (99.41 cm), higher production of monopodia plant-1 (2.68), sympodia
plant-1 (14.10), more bolls plant-1 (24.83), heavier seed index (6.83 g), maximum GOT (34.47%),
better staple length (28.83mm), higher oil content (22.87%), superior seed cotton yield (2428 kg ha-
1) and N-uptake increased upto 91.17 kg ha-1. The incorporation of NP fertilizer significantly
affected crop parameters. Among the tested fertilizers, 150-50 NP kg ha-1 recorded maximum plant
height (102.63 cm), monopodia plant-1 (2.61), sympodia plant-1 (13.70), bolls plant-1 (26.40), seed
index (6.83g), GOT (34.57%), staple length (28.65mm), oil content (23.10%), seed cotton yield
(2538.25 kg ha-1) and N-uptake (113.43 kg ha-1). It is concluded that nitrogen and phosphorus
fertilizers are essential nutrients, but for maintenance of soil fertility and enhancement of crop
productivity the inclusion of leguminous crop at least once in a two year cropping sequence is
necessary, because leguminous crops enrich soil fertility by fixing environmental nitrogen in their
root nodules, which in turn supply residual food nutrients to the succeeding crop. Thus,
(i) continuous cropping in the sequence of wheat-cotton be avoided, (ii) the higher yields of cotton and
wheat could be achieved in the farming system which includes legumes in crop rotation,
(iii) the application of 150-50 NP kg ha-1 is sufficient for satisfactory yield and qualitative characters of
cotton and
(iv) the use of in-organic nitrogenous fertilizers could be minimized by succession of
legume crop in the crop sequence.
Introduction
The crop rotation improve or maintain soil fertility, reduce erosion, reduce the risk of
weather damage, reduce reliance on agricultural chemicals and increase net profits
(Liebman & Davis, 2000; Bauman et al., 2000). The planned rotation sequence may be of
a two or three years or longer period which exhibit the beneficial effects like: improved
soil physical, chemical and biological quality; improved energy conservation and
timeliness of land preparation; and better water conservation (Cooper, 1999; Rochester et
al., 2001; Hulugalle & Daniells, 2005). The research reports indicate that the 3-year
cotton-corn soybean rotation with a legume and with 134 kg N ha-1 year-1 had higher
amounts of soil organic matter, soil microbial biomass C and crop yield, but cotton grown
every year without a legume or N fertilizer had a lower amount of soil organic matter,
soil microbial biomass C and N and cotton seed yield than all other rotations (Entry et al.,
Results and Discussion
Soil analysis: The chemical analysis of the soil before experiment showed that soil was
sandy clay loam in texture, calcareous in nature (CaCO3 11.20%), alkaline in reaction (pH
8.19), non-saline (EC 0.21 dSm-1), low in organic matter (0.82%) and nitrogen (0.047%),
medium in available phosphorus (6.17ppm) and high in potassium (127.50 ppm).
Plant height (cm): Fertilizer levels significantly increased plant height. Subsequent
increase in N levels from 50 to 150 kg ha-1 resulted in proportionate increase in the plant
height. The taller plants were recorded in the treatments where 150 kg N ha-1 was
applied. It is well known fact that nitrogen application boosts crop growth and
development. The increased plant height is the result of flamboyant and vigorous plant
growth. The crop sequences also highly significantly affected plant height. Maximum
plant height was recorded in the crop sequence where preceding crop was a legume. This
may also be due to provision of additional residual fertility left over by bacterial activity
of the preceding crop. These results are in agreement with those of Rochester et al.,
(2001) that plant height in cotton is related to nitrogen application.
Monopodial and sympodial branches plant-1: A gradual increase in monopodial and
sympodial branches with the subsequent increases in the nitrogen application rates was
noted. Maximum number of monopodial branches was observed in experimental units
where 150 kg N ha-1 was applied. Nitrogen played its part in the exuberant vegetative
growth of the plants. Monopodial and sympodial branches are also vegetative branches
and showed better response to the increased nitrogen levels. As for as the results for the
effect of crop sequences on branches are concerned, higher number of branches were
counted in the crop sequence where preceding crop was a leguminous crop. The residual
fertility caused vigorous growth of cotton crop with increased branches plant-1. Thus, the
maximum number of branches was produced in the crop year where the preceding crop
was legume.
Bolls plant-1: Maximum bolls plant-1 were produced by the higher nitrogen application.
The reason for increased number of bolls plant-1 with increased N fertilizer levels may be
due to the active role of N in the growth and development of cotton plant. Sufficient
amount of N when applied is utilized by the plants in photosynthesis process and the
resultant photosynthates are diverted to different parts of the plant where they are needed
as sink. Suitable amounts of photosynthates when provided at boll formation stage result
into proliferation of bolls. Crop sequences also highly significantly affected the number
of bolls plant-1. Maximum boll number was recorded in the crop sequence in which
preceding crop was a leguminous crop. This can be due to the additional supply of
residual fertility deposited in the soil by the symbiotic bacterial activity by the preceding
leguminous crop. Similar results were reported by Ram Parkash & Mangal Prasad (2000)
that boll production was significantly higher with the application of adequate nitrogen
and when crop is grown in the field left by legume crop.
Conclusions
It is concluded that nitrogen fertilizer is essential nutrients which enhance growth,
yield and N-uptake of the cotton crop. The application of 150-50 NP kg ha-1 found
sufficient dose for satisfactory yield and qualitative characters. The continuous cropping
in the sequence of wheat-cotton will be avoided. It is suggested that for maintenance of
soil fertility and enhancement of crop productivity the inclusion of leguminous crop at
least once in a two year cropping sequence is necessary.