Response of Ethiopian field pea (Pisum sativum L.) cultivars to phosophorus fertilization of Nitosols

[摘要] Field pea (Pisum sativum L.) is the third most important grain legume in Ethiopia where itsproductivity is constrained by several biotic, abiotic and socioeconomic factors. The crop isgrown mainly on a wide range of soil types throughout the highlands (1800 to 3200 m.a.s.l.) inwell drained soils like Nitosols that developed from volcanic rocks. Nowadays the blanketrecommendation of diammonium phosphate (DAP) at 100 kg ha to this low input crop isquestioned by the farmers and development workers. Hence, experiments have been conductedwith the major objective of quantifying the response of Ethiopian field pea cultivars tophosphorus fertilization of Nito soIs under both glasshouse and field conditions.Glasshouse experiments: Topsoil from Ilala and Cheffa were used. Experiments were laid out in asplit plot design with three phosphorus fertility levels (Extractable phosphorus: low = 5, medium= 15 and high = 30 mg kg-I) as the main plot treatments and factorial combinations of two peacultivars (TIala soils: Holetta and G22763-2C; and Cheffa soils: Tegegnech and Cheffa local) andsix phosphorus application rates (0, 7.5, 15, 30, 60 and 120 mg P kg) as the sub-plot treatmentsin a randomized complete block design with four replications. The phosphorus fertility levelstogether with the phosphorus application rates had positive influences on the growth anddevelopment of the pea crop as manifested in the biomass yield of the different cultivars. Criticalphosphorus levels were estabilished by relating relative biomass yield to extractable soilphosphorus. In the case of the Bray 2 extractions, the critical phosphorus levels for TIala soilswere 14 and 15 mg P kg for cvs. G22763-2C and Holetta respectively, for Cheffa soils 17 and20 mg P kg for cvs. Cheffa local and Tegegnech respectively. However, in the case of Olsenextractions the critical phosphorus levels for TIala soils were 17 and 27 mg P kg for cvs. Holettaand G22763-2C respectively, and for Cheffa soils 20 and 22 mg P kg for cvs. Cheffa local andTegegnech respectivelyField experiments: Two sets of experiments were conducted, viz. the first set at Holetta (1996 to1999) and Bekoji (1996 to 1998) and the second set in 2001 at TIalaand Cheffa. For the first setof experiments a factorial combination of five phosphorus rates (0, 10, 20, 40 and 60 kg P ha)and three pea cultivars (Holetta site: Tegegnech, G22763-2C, Holetta local; and Bekoji siteTegegnech, G22763-2C and Cheffa local) were laid out in a randomized complete block designwith four replications. On the other hand, for the second set of trials a split plot design was usedwith three phosphorus fertility levels (Extractable phosphorus: low = 5, medium = 15 and high =30 mg kg) as the main plot treatments and the factorial combinations of five phosphorusapplication rates (0, 10, 20, 40 and 80 kg ha) and two pea cultivars (llala site: G22763-2C andHoletta; and Cheffa site: Tegegnech and Cheffa local) as the sub-plot treatments which werereplicated four times. At the Holetta and llala sites, grain yield response of the pea crop tophosphorus a.pplication was poor regardless of the phosphorus application rates or the cultivars .As a result, low marginal rate of returns (MRRs) were computed which implicated thatphosphorus fertilization is not economically viable. On the contrary, at the Bekoji and Cheffasites, the grain yield response of the pea crop to the application of phosphorus was good withsignificant differences between phosphorus fertility levels and cultivars. The interaction ofphosphorus application rate and cultivars was significant (p < 0.05). A MRR of 100% wasobtained at an application of21 kg P ha-I for cv. Tegegnech, 10 kg P ha for cv. G22763-2C and5 kg P ha-I for cv. Cheffa local. The 100% MRR computed implicated that phosphorusfertilization to all cultivars at the low phosphorus fertility level was economically viable with thecurrent prices of grain and fertilizer in the zone.Unfortunately, no critical soil phosphorus levels could be estabilished under field conditions. Thecritical soil phosphorus levels that were established under glasshouse conditions should thereforestill be validated in the field. However, the fact that the pea crop did respond to phosphorusapplication mainly at the low phosphorus fertility levels in the field confirms already to someextent their validity. In general, the improved pea cultivars responded better to phosphorusfertilization than the local cultivar. A thorough investigation on phosphorus use efficiency of peagenotypes to' identify low phosphorus requiring ones should be considered to benefit resourcepoor farmers. The aspect of soil pH modifications through liming, and the use of non-nitrogenousphosphorus fertilizer sources for field peas are recommended.

[发布机构] University of the Free State