RESPONSE OF LABLAB (Lablab purpureus L. Sweet) TO PHOSPHORUS APPLICATION AND CUTTING TREATMENTS

RESPONSE OF LABLAB (Lablab purpureus L. Sweet) TO PHOSPHORUS APPLICATION AND CUTTING TREATMENTS

Abstract:

Field trials were conducted during the 2006, 2007 and 2008 cropping seasons at the Institute for Agricultural Research (IAR) Experimental Farm, Samaru in the northern Guinea savanna zone of Nigeria, to study the response of lablab (Lablab purpureus (L.)Sweet) to phosphorus application rate, cutting height and cutting age with regards to growth, herbage yield, seed yield and herbage quality. The treatments were composed of factorial combinations of four levels of phosphorus fertilizer (0, 12, 24 and 36 kg P ha-1) and two cutting heights (10 and 20cm) in the main plot and four cutting ages (6, 12, 18 weeks and maturity) in the sub-plot of a split-plot experimental design with three replications. The application rate of 12 kg P ha-1 increased lablab sward height, 100-seed weight and ground cover score by up to 4% while 24 kg P ha-1 increased leaf area index (10%), leaf area per plant (18%), number of root nodules (42%) and nodule dry weight (50%) above the control. Cutting lablab to a 20cm stubble height produced significantly higher sward, ground cover score, pod length and 100-seed weight, whereas a 10cm cutting height produced significantly higher calcium and phosphorus concentrations in the dry herbage. The highest sward height, cumulative fresh, dry and initial herbage yields of lablab were obtained at the 18-week cutting age. Cutting lablab at 6 weeks did not decrease seed yield, relative to cutting at maturity. The highest crude protein and crude fibre concentrations of lablab herbage were obtained at the 12-week and maturity cutting ages respectively, and both parameters were enhanced by cutting age. Lablab ether extract concentration decreased while Ca: P ratio increased as cutting age increased but cutting age did not increase the value of either of the two parameters. Combination of phosphorus application rate of 36 kg P ha-1 and 20cm cutting height produced the highest sward. The highest number of root nodules was obtained when lablab was supplied with 24 kg P ha-1 and cut to a height of 10cm, while the heaviest 100-seed was produced by a combination of 12 kg P ha-1 application rate and a 20cm cutting height. In addition, a phosphorus application rate of 12 kg P ha-1 produced the highest ether extract, ash, number of primary branches, and proximate dry matter concentration in lablab herbage when cutting was done at 6, 12 and 18WAS, and at maturity respectively. However, the highest phosphorus concentration of lablab herbage was produced when no P was applied (0 kg P ha-1) at a cutting height of 10cm. Crude protein concentration of lablab herbage was highest at the application rate of 0 kg P ha-1 combined with a cutting age of 6 weeks while crude fibre was highest when lablab plants received no phosphorus application and was cut at maturity. The highest cumulative dry herbage yield obtained at 18 weeks was 62 and 117% higher than those obtained at maturity and the 6-week cutting age respectively, irrespective of the cutting height. A positive and significant correlation was observed between cumulative dry herbage yield and stand count, sward height, ground cover score, number of root nodules and nodule dry weight of lablab. The path coefficient analysis showed that nodule dry weight, sward height and stand count had positive direct contributions. However, nodule dry weight was the highest individual contributor to the cumulative dry herbage yield of lablab even though the residual contribution was 76.7%. The polynomial response analysis did not produce a best fitting curve for cumulative dry herbage yield of lablab in this study. It is suggested that lablab be fed pre-rather than post-harvest maturity to reduce dry matter(about 67%) and crude protein(about 35%) wastages and also to develop lablab as a ley (temporary) pasture crop in the farming systems of the northern Guinea savanna in order to enhance its contribution to the livestock industry.

RESPONSE OF LABLAB (Lablab purpureus L. Sweet) TO PHOSPHORUS APPLICATION AND CUTTING TREATMENTS

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