N.V. SARALA*, N. SABITHA, M. SUBBA RAO, M. HEMANTH KUMAR, B. VAJANTHA AND V. GIRIDHAR
Agricultural Research Station Perumallapalle 517 505, Chittoor (Dt.), A.P.
Field trials were conducted at Agricultural Research Station, Perumallapalle, during 2012-13 and 2013-14 to evaluate the response of promising early maturing sugarcane varieties to different levels of nitrogen. Six early maturing varieties, viz., 2003V46, 2006T3, 2006T36, 2006T19, 2006T23 and 2006T8 were tested at five nitrogen levels, i.e. 0, 75, 100, 125 and 150 per cent of recommended dose of nitrogen (RDN: 224 kg ha-1). Application of nitrogen at 125 per cent RDN produced significantly greater number of millable canes, stalk yield and sucrose per cent. However, the effect of nitrogen levels on juice sucrose per cent was not significant. Hence, application of nitrogen at 280 kg ha-1 (125% RDN) is the most economical and viable nitrogen level for the plant cane in sandy loam soils of Southern agro climatic zone of Andhra Pradesh. Among the six early varieties, 2006T36 followed by 2006T19 responded well to the applied nitrogen and recorded higher cane yield.
Sugarcane early varieties, Nitrogen levels, Cane yield, Juice quality
Sugarcane is an important commercial crop in Andhra Pradesh. Most of the soils in the Southern agro climatic zone of Andhra Pradesh, where sugarcane is grown low in available nitrogen. This was coupled with long term monocropping and more number of ratoons. The nitrogen fertilizer is costly and its indiscriminate management such as inappropriate rate, time and method may lead to poor crop performance and yield besides, it may results in loss of nitrogen due to leaching, denitrification and ammonium volatilization with serious environmental pollution. Nitrogen has been considered as the most limiting nutrient in sugarcane farming. Different sugarcane varieties have different yield potentials and other specific attributes (Stevenson et al. 1992). The new varieties developed have improved cane and sugar yields, resistance to pests and diseases, good milling qualities and adaptability to local growing conditions. These varieties are expected to yield as per the potential when cultivated in the recommended agro ecological zones with appropriate agronomic practices. Variation in the varietal response to nitrogen was reported by Rama Krishna Rao et al. (1989) and Srinivas et al.(2003). One of the causes of declining sugarcane yield is speculated to be declining soil fertility as a result of depletion of the essential plant nutrients, viz. N, P and K (Bell et al., 2001; Gerside and Bell, 2003) with low rates of replenishment. These macronutrients play a major role in sugarcane physiology, growth and development Malavolta, 1994 and Rice et al., 2002). Nitrogen is essential for photosynthesis, sugar production and growth. This study was undertaken to determine the optimum nitrogen fertilizer rate for increased and sustained cane yields for promising sugarcane varieties
The field experiments were conducted at Agricultural Research Station, Perumallapalle, Andhra Pradesh, during 2012-13 and 2013-14. The soil of the experimental field is sandy loam in texture, neutral in pH, normal in EC, low in available nitrogen (190 kg ha-1) medium in available phosphorus (14 kg ha-1) and high in available potassium (279 kg ha-1). The experiment was designed in a split plot with three replications. Six promising early maturity varieties, viz. 2003V46, 2006T3, 2006T36, 2006T19, 2006T23 and 2006T8 were included in the study
with five levels of nitrogen viz. 0, 75, 100, 125 and 150 recommended dose of nitrogen (RDN: 224 kg ha-1). Nitrogen was applied in the form of urea in two equal splits at 45 and 90 days after planting. Phosphorus and potassium were applied @ 112 kg ha-1 in the form of Single Super Phosphate and Muriate of Potash, respectively as basal. Furrows were made at a spacing of 80 cm and three budded setts @ 40,000 ha-1 were planted in the first fortnight of January. Atrazine 2 @ kg a.i ha-1 was sprayed as pre-emergence herbicide on the 3rd day after planting of setts. Irrigations were provided as and when necessary. All other agronomic practices like hand weeding, earthing up, trash twist propping etc. were carried out according to the recommendations. Yield attributing parameters like number of millable canes, cane length, cane diameter were recorded at the time of harvest. Cane yield was recorded after stripping of the leaves and detopping. Juice quality parameters viz. Brix, Sucrose per cent were recorded at harvest by following standard procedures (Spencer and Meade, 1963). Brix was recorded by using hydrometer and sucrose was estimated by pol per cent with polarimeter.
Results pertaining to yield attributes, yield and juice quality parameters are presented and discussed below.
Among the varieties, 2006T36 produced the highest NMC followed by 2006T19 due to higher conversion efficiency of tillers into millable canes. A variation in varieties for their response to nitrogen was also reported by Srinivas et al. (2003), Shukla (2007). The number of millable canes is a major constituent of cane yield. Tillering which provides the plant with the optimum number of stalks needed for a good yield is known to be affected by the availability of various nutrients. The highest number of millable canes at harvest was recorded with 125% RDN i.e. 280 kg N ha-1.
The results are in accordance with Naga Madhuri et al.
(2011) for promising early maturing sugarcane varieties.
The highest cane yield was recorded by the variety 2006T36 followed by 2006T19. Highest shoot population coupled with efficient conversion of tillers into millable canes at harvest in these varieties could have contributed to higher cane yield. Same results have been reported by Srinivas et al. (2003). Cane yield was significantly enhanced with increasing levels of nitrogen application from 75 per cent to 150 per cent of RDN (Table 1). Application of nitrogen @ 150% RDN (336 kg N ha-1) resulted in highest cane yield which was on par with 125% RDN and both were significantly higher than 100% and 75% RDN.
For sugarcane, the quality of the crop is assessed by the sugar produced per tonne of cane, Nitrogen has the greatest influence on cane growth, ripening and juice quality (Hussain et al 1990). The quality parameter which include sucrose % is not affected by increasing nitrogen application. This could be due to the early application of nitrogen (90 days after planting). Thus the detrimental effect of higher nitrogen on juice quality was minimized before the maturity age of the cane (Gana et al., 2007). Higher quantity of nitrogen fertilizer generally results in luxurious growth and increases percentage of reducing sugars. But as the crop ages and matures, it is expected that nitrogen content will be reduced and there is an increasing conversion of the reducing sugars to sucrose (Hussain et al., 1990).
The study revealed that among the varieties, 2006 T36 followed by 2006T19 responded well to the applied nitrogen and recorded the higher cane yield. Application of nitrogen @ 125% RDN i.e 280 kg N ha-1 is optimum for obtaining higher cane yield in sandy loam soils of Southern agro climatic zone of Andhra Pradesh
Plant height is also a major parameter of growth and yield. Although length, thickness and shape of the internodes are varietal characteristics, the rate of elongation and length of internodes are influenced by the nutrient availability. Varieties did not differ among them with regard to cane length and diameter. The lengthier canes were recorded when nitrogen is applied @ 150% RDN.