Orthic Ferralsols of the moist Mid-Altitude Central Plateau of Madagascar are characterized among other things by low pH, low exchangeable bases especially Ca, and high deficiency in P and N. Low and declining fertility from soil nutrient mining without replenishment are responsible for the poor production levels of smallholder farms with limited cash access. Local rock phosphate named Barren hyperphosphate or simply Barren Phosphate (HB) can be an alternative to imported phosphate fertilizers, whose purchase price is not affordable by resource-poor peasants for alleviating soil Ca and P depletion. An experiment consisting of three trials was conducted at Ankazobe site (18°99'S, 47°07'E) located at 100 km north of Antananarivo, over two consecutive cropping seasons to investigate the effect of local rock phosphate fertilizer on maize grain yields. The experiment was laid out in RCBD with 4 replications. In the first trial, HB fertilizer was evaluated (direct and residual effects) in comparison with two imported P-fertilizers : Reno Hyperphosphate (HR) and NPK at the rate of 300 kg ha-l, for two seasons (1997/1998-1998/1999). In the second trial, the direct and residual effects of cattle manure at the rates of 5 and 10 t ha-1 supplemented with HB at the rate of 150 and 300 kg ha-1 were evaluated over the same seasons. In the third trial, four application methods (two broadcasting and two station placement) were investigated over the next two campaigns (1999/2000 -2000/2001 ). Results showed that during the first season (direct effect evaluation) there was no significant grain yield difference between the two rock phosphates (HB and HR) without N/NK supplement and the unfertilized control: HB and HR supplied alone were equivalent and had no direct effect in the first year of application. Supplementing rock phosphate fertilizers with top-dressed NK (45: 60) doubled the yield (6.4 t ha.1 with NK against 3.6 t ha-1 without) : effectiveness of P-fertilizers was enhanced by the presence of NK-fertilizer. There was no significant grain yield difference between HB (300 kg ha-l) + NK (35: 45) applied at planting time and the compound P-fertilizer NPK (300 kg ha-1). Results of the second trial showed that HB was inefficient in the first year without manure: there was effectively no significant yield difference between HB (150 kg ha-l) without cattle manure and the unfertilized check. The best yield (7.0 t ha.1 was obtained from combination of the highest rates of manure (10 t ha-l) and HB (300 kg ha-1). Results of rock phosphate fertilizers residual effect investigation during the second season showed that there was no significant yield difference (i) between HB alone, HR alone and unfertilized control, that is rock phosphate fertilizers without supplement had no residual effect in the second year, (ii) between the two rock phosphates with or without top-dressed N/NK. Concerning the 'Manure x HB' trial, there was no significant yield difference between HB without manure for 2 years and unfertilized check: there was virtually no residual effect of HB alone in the second year. Results of the third trial highlighted the superiority of station (hole) placement over the other methods. To sum up, the four seasons' experimentation showed that (i) during the first two years rock phosphate fertilizers applied alone have no effect, (ii) to get adequate maize grain yield it is necessary to supplement rock phosphates with urea or with FYM, (iii) station placement of phosphate fertilizers is recommended.

English

0410|AGRIS 0401|AL-Maize Program

Juan Carlos Mendieta

CIMMYT Publications Collection