The leaf water potential, gas-exchange parameters and chlorophyll fluorescence were evaluated in five common oil palm (Elaeis guineensis Jacq.) tenera hybrids 913X1988, 1425X2277, 748X1988, 7418X1988, and 690X1988 under water deficit with an aim to identify hybrids which can cope up better under such conditions and understand possible differences among hybrids in relation to the physiological mechanisms triggered by water deficit. Our findings indicate oil palm hybrids 913X1988, 1425X2277, and 7418X1988 maintained higher leaf water potentials than the other hybrids. Hybrids 7418X1988 and 1425X2277 recorded lower stomatal conductance after water deficit, which resulted in higher intrinsic water-use efficiency. The excess light energy produced due to decreased photosynthesis in 7418X1988 and 690X1988 hybrids under water deficit was dissipated as heat by higher nonphotochemical quenching. The maximum efficiency of photosystem II was not affected, even after withholding water for 24 days, suggesting an increased efficiency of photoprotection mechanisms in all these oil palm hybrids.
The gas-exchange characteristics, leaf water potential and chlorophyll (Chl) a fluorescence of oil palm (Elaeis guineensis Jacq.) seedlings subjected to water stress and recovery were investigated in a greenhouse experiment. At 24 days after imposition of stress, leaf water potential in water-stressed seedlings was doubled compared to that of control and there was a drastic decline in gas-exchange parameters viz. photosynthesis, transpiration, and stomatal conductance. Water stress did not irreversibly affect gas-exchange parameters and quantum efficiency of photosystem II, as seedlings exhibited total recovery of photosynthetic apparatus by 12 th day of rehydration. These findings indicate that oil palm exhibits physiological plasticity to water stress during the seedling stage.
Net photosynthetic rate (P N ), transpiration rate (E), and stomatal conductance (g s ) in an adult oil palm (Elaeis guineensis) canopy were highest in the 9 th leaf and progressively declined with leaf age. Larger leaf area (LA) and leaf dry mass (LDM) were recorded in middle leaves. P N showed a significant positive correlation with g s and a negative relationship with leaf mass per area (ALM). The oil palm leaf remains photosynthetically active for a longer time in the canopy which contributes significantly to larger dry matter production in general and greater fresh fruit bunch yields in particular.
A field experiment was conducted during the rabi seasons of 2012-13 and 2013-14 to study the influence of sowing window, nutrient dose and foliar spray on yield and nutrient uptake of pigeonpea on sandy loam soil which was low in available nitrogen, medium in available phosphorus and available potassium. The experiment was conducted in a split-split plot design, consisting of three sowing windows in main plots, three nutrient doses in sub-plots and two foliar sprays in sub-sub plots. Crop sown during II FN of September produced significantly higher seed and stalk yield, nutrient content and uptake. Application of 30-60-20 kg N, P2O5 and K2O ha-1 improved seed yield, stalk yield, nutrient content and uptake of redgram. Higher seed yield, stalk yield and nutrient uptake by the crop was recorded with foliar application of NAA (25 ppm) and DAP (2 per cent) applied at 60 and 80 DAS. Interaction between sowing window and nutrient doses, sowing window and foliar sprays were significant in influencing yield of pigeonpea.
A field experiment was conducted on sandy clay loam soils of Tirupati Campus of ANGR Agricultural University, Andhra Pradesh to optimise the sowing time and nutrient needs of rabi pigeonpea [Cajanus cajan (L.) Millsp.] for its sustained productivity and profitability. Three sowing times: II FN of September, I FN of October and II FN of October; three nutrient levels (N-P2O5-K2O kg ha-1): 10-40-0, 20-50-10 and 30-60-20 and two foliar treatments: NAA (25 ppm) and DAP (2%) at 60 DAS, 60 and 80 DAS were tested on LRG 41 pigeonpea cultivar in split-split plot design, replicated thrice. Earliest sown pigeonpea (II FN September) resulted in significantly higher seed yield (1700 kg ha-1) and net returns ( 32239) due to improvement in yield attributes like pod bearing branches plant-1, number of pods branch-1, number of seeds pod-1 and test weight. Highest nutrient level (30-60-20 NPK ha-1) produced significantly higher seed yield (1589 kg ha-1) and net returns (28448) due to improvement in yield attributes. Foliar application of NAA (25 ppm) and DAP (2%) applied at 60 and 80 DAS recorded significantly highest seed yield (1434 kg ha-1) and net returns (24111) due to its positive effect on pigeonpea yield attributes. Benefit:cost ratio was significantly high (2.71) due to earliest sowing, highest level of nutrient supply (2.46) and foliar application of NAA (25 ppm) and DAP (2%) applied at 60 and 80 DAS (2.26). Early sowings resulted in significantly higher seed yields at higher levels of nutrient supply. Foliar application of DAP (2%) at 60 and 80 DAS recorded significantly higher pigeonpea yield with early sowings. Early sown pigeonpea resulted in significantly higher seed yield at all levels of nutrient supply and foliar applications. Rabi redgram gave optimum yield and economic returns sown during II FN of September with 30-60-20 kg N, P2O5 and K2O ha-1 along with foliar spray of NAA (25 ppm) and DAP (2 per cent) twice at 60 and 80 DAS.
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