Long-Term Studies on Agronomic Effectiveness of African and Indian Phosphate Rocks in Relation to Productivity of Maize and Wheat Crops in Mountain Acid Soils of Western Himalayas (India)

摘要

The mountain acid soils of the Western Himalayas, in India, occupy about 0.1 million ha that are characterized by features such as marginality, inaccessibility and fragility where cereals, pulses, oilseeds, vegetables, and fruit crops are grown for the nutritional security of small and marginal farmers. And yet the productivity of the crops is poor; for example, wheat at 1.5 tonnes/ha, rice 1.2 tonnes/ha, and maize 2 tonnes/ha. Among the soil fertility constraints responsible for low productivity ofcrops, the dominant ones are: phosphorus (P) deficiency, its poor availability to crops coupled with low P use efficiency and high P fixation. Consequently, to overcome some of these problems; many African phosphate rocks (PRs) with high content of citrate-soluble P are entering the Indian market under liberalization program because Indian PRs have less citrate-soluble P than the African ones. In this background, the African PRs could prove economically better compared with Indian PRs, if they demonstrate agronomic effectiveness and improvement in soil properties. Long-term field experiments were, therefore, conducted to study the comparative agronomic effectiveness of African and Indian PRs in relation to productivity of maize and wheat crops in mountain acid soils of the Western Himalayas (India) with effect from 1994 to 1999. Phosphorus at 500 kg P_2O_5/ha was applied once at the start of the trial to 10 crops (5 maize and 5 wheat) in the form of three African PRs [Tebessa, Youssofia, and Gafsa (30% P_2O_5)] and one Indian PR, Mussoorie PR (18% P_2O5). Single superphosphate (SSP) was applied each season for each crop of maize and wheat at 50 kg P_2O_5/ha for 5 years. The results suggested that a one-time application of P for 5 years at 500 kg/ha as Tebessa, Gafsa, and Youssofia has had a significant effect in improving the average productivity of maize giving an average yield of 4.63,4.78, and 4.64 tonnes/ha, which was 49.8%, 54.7%, and 50.2% greater than control. The three PRs did not differ significantly among themselves. However, the hidian Mussoorie PR recorded a comparatively lower yield of 4.22 tonnes/ha than did the African PRs though significantly greater than the control (36.6%). If the African PRs along with Indian Mussoorie PR are compared with direct application of P as SSP, the performance of SSP in terms of grain yield and P uptake was significantly better than all the PRs. As for the wheat crop, it was found that the average grain productivities, on a one-time application of African PRs at 500 kg P_2O_5/ha applied as Tebessa, Gafsa, Youssofia, and also hidian PR were 54.1%, 39.8%, 50.8%, and 39.8% greater than the control and that the trend of P uptake was also of similar nature. The attainment of average grain productivity of wheat following application of P each season for 5 years at 50 kg P_2O_5/ha as SSP was maximum (61.4%), and the same was true for P uptake by wheat. The relative performances of the phosphorus sources on the productivity of crops were: Maize: SSP > Gafsa= Youssofia = Tebessa > Mussoorie Wheat: SSP > Tebessa = Youssofia > Gafsa = Mussoorie Further, there was an immense improvement in soil quality in terms of amelioration of soil characteristics that are often associated with the availability of P from PRs such as soil pH, organic C, exchangeable Ca, Al, acidity, effective CEC, pH, buffer capacity, extractable Al and P fixing capacity. The monetary benefits accrued were of greater magnitude in respect of African PRs compared with SSP.