Groundnut growth and yield response to fertilizer application
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Groundnut is an important food, feed and cash crop in Eastern Africa but in Kenya it has a yield gap of 2.5 t ha-l and this is attributed to low soil fertility, diseases, poor seed quality and poor husbandry practices. Soil exhaustion being ranked as the major groundnut production constraint in Sub Saharan Africa and particularly in Western Kenya it was necessary to evaluate the response of growing high yielding and disease tolerant (groundnut rosette virus disease) varieties with the use of various fertilizer types and rates. This would ensure increased productivity for the smallholder farmers who predominantly produce the crop at a profitable production regime. On-station experiments (fertilizer types and rates) were conducted in two sites, which included Kenya' Agricultural Research Institute (KARl) site at Alupe in Busia district and Ministry of Agriculture's Agricultural Training Centre (ATC) site at Siaya district during the long rain (March - July 2007). The on-farm data collection was done through a survey conducted on the farmer's fields at Siaya and Busia districts. The objectives of fertilizer types experiment were (i) to determine the effect of basal application of nitrogen and phosphorous (20 kg ha') from different fertilizer types on improved groundnut varieties growth and yield (ii) to evaluate varietal yield performance across two major groundnut regions in Western Kenya and (iii) to evaluate the effect of fertilizer types on groundnut rosette viral disease. The fertilizer types treatments included calcium ammonium nitrate (CAN), di-ammoniurn phosphate (DAP), single super phosphate (SSP), triple super phosphate (TSP), Mavuno, Farmyard Manure and a control (without fertilizer). The objectives of fertilizer rates experiment were (i) to evaluate the response of improved groundnut growth and yield to varying Mavuno fertilizer rates, (ii) evaluate varietal performance across two major groundnut growing regions and (iii) evaluate the effect of Mavuno fertilizer rates on groundnut rosette virus disease. The fertilizer used was Mavuno selected on the basis of having all the recommended nutrients for groundnut growth and since it is locally blend at Athi-River Mining Company likely to be available to farmers at the time of planting. The Mavuno fertilizer rate experiment had five treatments levels which were 0 kg ha', 25 kg ha-l , 50 kg ha-l , 100 kg ha-l , and 200 kg ha-'. The improved groundnut varieties included two Spanish types (small seeded lCG 12991 and medium seeded lCGV SM 99568) and Virginia type (large seeded lCGV SM 90704). The experimental design was a randomized complete block design laid out as a split plot with three replications, varieties was the main plot and fertilizer types / rates was the sub plots. Data collected included days to emergence, days to flowering, and days to maturity; plant height at maturity, number of leaves per plant at flowering, number of branches per plant at maturity, dry matter per plant at flowering, leaf area index per plant at flowering, number of nodules per plant at flowering, groundnut rosette virus disease incidence, number of pods per plant at maturity, number of pops at maturity, one hundred seed weight and kernel yield. An on-farm survey was carried out in September 2007 at Siaya District (Yala Division) and Busia District (Matayos Division) with an objective of evaluating the extent of fertilizer use on ground nut farmers' fields and its effect on groundnut yield. The survey targeted two categories of farmers i.e. contracted farmers by Leldet Seed Company and non-contracted farmers. Ninety contracted farmers were interviewed and out of these only thirty one had mature groundnuts in their field for data collection while fifty non contracted farmers were interviewed with only forty seven farmers having mature groundnuts for data collection. The on-farm data collection was achieved by use of a structured questionnaire and by collecting plant samples from the groundnut fields. The crop sampling was done by randomly uprooting 100 plants from mature groundnut fields and the various parameters recorded i.e. spacing, pod fresh mass, number of plants per every three meters in three quadrants to acquire germination.percentage, no of pops and rosette incidence scoring. The pod samples were then sun dried for 10 days to achieve 10% moisture content and they were shelled to record the kernel weight (translated to yield per ha) and 100 seed mass. All the data obtained from the on-station experiments was subjected to analysis of variance (ANOV A) using Genstat statistical package and means separated using Least Significant Difference (LSD) at 5% probability level. The on station experiments results indicated that fertilizer types, site and varieties significantly affected groundnut growth and yield while the fertilizer rates, site and variety significantly affected groundnut growth but had no effect on the yield. Site and variety significantly influenced days to flowering and maturity with Alupe resulting in early flowering and maturity in comparison to Siaya. In terms of plant growth and yield Siaya performed better in comparison to Alupe. SSP, TSP, FYM and Mavuno fertilizer treatments resulted in the tallest plant height, highest number of branches, highest number of leaves, highest number of nodules, highest leaf area index, highest hundred seed mass and the highest yield in comparison to the control treatment,. At Alupe 100 kg halresulted in the highest plant growth while at Siaya 25 kg ha-I , 50 kg ha-I and 200 kg ha-I fertilizer rates effects were comparable and they resulted in the highest plant growth and yield. ICGV SM 90704 had the lowest disease incidence, highest plant growth and the best yield followed closely by ICG 12991 and lowest was observed from ICGV SM 99568 for all the treatments and sites. The results should be adopted with a caution that the experiment was conducted in only one season and a repeat of the same in other seasons may result to different observations. The survey results showed that most farmers preferred using fertilizer on cash crops or other food crops i.e. maize since the return on fertilizer cost from groundnut was low. Groundnut yield from farmers was very low i.e. an average of 700 kg ha-I as compared to Kenya's adopted yield of 3 t ha-l reasons being that farmers have poor access to improved seed, highly priced inputs and poor market structure. It was observed that ICGV SM 90704 was a superior variety compared to other varieties that farmers grew because it resulted in the highest kernel yield as compared to other varieties and it had the lowest rosette incidence.