SYNCHRONY OF NITROGEN RELEASE WITH CROP DEMAND IN GLIRICIDIA – MAIZE ALLEY CROPPING IN HUMID TROPICAL SOIL

Abstract

This study was carried out to synchronize the timing of Nitrogen release from decomposing Gliricidia sepium prunings with Maize crop demand in an alley cropping system so as to optimize the N-use efficiency of the high quality litter. Agroforestry demonstration plot of the Department of Forestry and Wood Technology, Federal University of Technology, Akure, was used for the study. The experiment was laid out in Completely Randomized Design (CRD) with four treatments, each with three replicates. The treatments consisted of prunings application at 2, 4 and 6 Weeks after planting and control plot without prunings application. Three contiguous rows of 7-year old Gliricidia alley with escapement of 0.25m (25cm) were cleared of existing weeds and each row was demarcated into four plots of 4m x 4m with a buffer of 1m between plots. Maize seeds (Zea mays, L 3-month var.) were sown at three seeds per hole at 30cm x 100cm (within and between rows) during the raining season. The seedlings were thinned to one per hole a week after germination. Pruning regime and litter application at 2, 4 and 6 weeks after seed sowing were carried out except for control plots (without litter application). One hundred grammes of fresh prunings were used to mulched the plots evenly for decomposition and subsequent mineralization of N from the decomposing litter. At each pruning regime and litter application, soil sample were taken under the decomposing litter at (0-10cm) at three days interval for a period of 15 days. At each sampling time, decomposing litter samples were collected at 3-day interval for a period of 15 days (2 weeks). Also at each pruning regime one maize plant per replicate per treatment was harvested and analysed for N storage in the leaf, stem and root. The dry weights of the plant parts were also obtained at 1st, 2nd and 3rd pruning regimes. Plant height, collar diameter and numbers of leaves were measured and counted respectively at each sampling time during the growth phase of maize plant in each of the treatment plot. The collected soils litter and plant samples were analysed for N contents. Significantly higher N content in the soil under decomposing Gliricidia litter was found at 3 days of decomposition (4.21%) than the content at 6 days (3.34%), 9 days (2.68%), 12 days (2.62%) and 15 days (1.75%). It was also found in the study that at 4WAP, the N content in the shoot (1.69%) and root (1.21%) were significantly higher for 1st pruning regime than those of 2nd, 3rd regime and the control which do not differ significantly in their N content for both the shoot and the root components. At 6WAP, the N content in the stem component part (2.87%) was significantly higher for 2nd pruning regime than those of control (1.54%), 3rd (1.80%) and 1st (1.91%) regime which were not significantly different (p>0.05). In the root component part, N content was significantly higher for 2nd pruning regime (1.72%) and the 1st pruning regime (1.21%) than those of control (0.98%) and 3rd pruning regime (0.95%) which were not significantly different (p>0.05). Irrespective of the fact that both 1st and 2nd pruning regimes benefited from Gliricidia pruning application, the nitrogen contents in the leaf, stem and root were significantly higher for the 2nd pruning regime treatment than those of 1st, 3rd pruning regime control and treatment. The treatment plots that were mulched with Gliricidia at 3rd pruning regime did not show any significant increase in N content in the Maize component parts at this growth stage. The results of this study show that the N demand by Maize is by far higher at early growth stage (2-4 weeks after planting) than at later growth stage (6-8 weeks after planting). It is also evident from the result of this study that timing of the transfer of prunings N to maize crop occurred mainly during the early growth phase of the crop and in particular with high quality litter like Gliricidia sepium.