PhD

Hybrid napier, an inter-specific cross between bajra and napier, is a popular
fodder grass because of its high yield potential and quality. Three field trials were
conducted during 2013–2015 with the objectives of assessing shade tolerance of
selected hybrid napier cultivars, finding out optimum nitrogen levels and harvesting
frequency, and studying the influence of different cutting heights on regrowth and
mortality of major cultivars under rainfed condition.
The performance of six cultivars of hybrid napier(CO-3, CO-4, Suguna,
IGFRI-3, DHN-6 and PTH) at three different shade levels (0 per cent, 25 per cent and
50 per cent) were studied under rainfed condition. Increasing shade levels had a
facilitating effect on plant height, leaf length, leaf width, leaf area index, leaf area
ratio, leaf weight ratio, leaf- stem ratio, chlorophyll content and PAR interception,
whereas, number of tillers, number of leaves, specific leaf weight, and fodder yield
were reduced under shade. ‘Suguna’ had the highest fodder yield followed by ‘CO-3’
and ‘CO-4’. Shade also affected the nutritive value and quality of leaves and stems.
Oxalate content in plants increased with increasing shade and ‘IGFRI-3’ had the
highest content.
The effect of nitrogen levels (0, 100, 200, 300, and 400 kg/ha) and three
cutting intervals (30, 45, and 60 days) were tested on hybrid napier cultivar ‘CO-3’.
Cutting frequency and nitrogen affected plant growth, yield, and yield attributes.
Delayed harvesting reduced fodder quality. Crude protein, crude fat, Ca, Mg, oxalate,
and nitrate contents increased with increasing nitrogen levels while total ash, K and P
contents remained unaffected. The nitrogen use efficiency (NUE) decreased with
increasing cutting intervals and nitrogen doses. The highest NUE was recorded at 45
days cutting interval and with 200 kg/ha N. Soil organic carbon content increased
after the experiment but available N, P, and K declined.
The experiment to study the effect of different cutting heights (5, 10, 15, and
20 cm) on regrowth and mortality of major cultivars (CO-3. CO-4, Suguna, DHN-6
and PTH) revealed that cutting height management affected yield attributing factors
such as tiller and leaf production and fodder yield. The fodder yield increased with
increasing cutting height. Hybrid napier showed maximum regrowth rate when
harvested at 20 cm height and showed a declining trend when harvested at lower
cutting heights. The cultivars ‘CO-3’, ‘CO-4’ and ‘Suguna’ had comparable regrowth
rate.
The results from the present investigation have implications for Kerala
where land and water are scarce resources for fodder production. As ‘Suguna’ and
‘CO-3’ performed better than other cultivars under shade, these two can be grown
where the intercrops receive at least 50 per cent of the incoming solar radiation.
Applying 200 kg/ha nitrogen and cutting at 20 cm height at 45-60 days interval seem
to be satisfactory for hybrid napier under rainfed condition.