What are the gaps in nutrient management for lowland rice production? How much can proper nutrient management contribute to productivity? Dr. Pompe Sta. Cruz, a professor at the UPLB Crop Science Cluster, delivered his paper which centered on these two questions during the Agriculture and Development Seminar Series at SEARCA on June 28, 2011.
Although nutrient management has been studied for a long time and adopted all over the country, current production data from the Bureau of Agricultural Statistics show that there is only low to medium (average of 3.68 t/ha) productivity in Philippine lowland rice areas.
Dr. Sta. Cruz emphasized that without applying fertilizers, lowland rice production can sustain 2 to 3 t/ha, yield under good crop management (except the nutrient management component). In fact, in IRRI study of five extensive rice growing areas in south and southeast Asia, an average yield of 2.61 t/ha was produced without fertilizer application, utilizing only the available nutrient in the soil. When the recommended practices for nutrient management were compared with Filipino farmers’ actual current practices, it was observed that farmers apply less than half of the recommended amount of nitrogen (115 kg/ha) to achieve yields of 5-6 t/ha. The same is true for the other two main nutrients with farmers applying 12 kg/ha instead of 27 kg/ha of phosphorous (P2O5) and 8.3 kg/ha instead of the recommended 57.5 kg/ha of potassium (K2O). Thus, the need to increase fertilizer application at the farmer level was reiterated. If farmers applied 81.8 kg of nitrogen, 11 kg of phosphorous and 29.1 kg of potassium per hectare, their yield can increase up to 1 ton above the average yield of 3.68 t/ha.
Dr. Sta. Cruz also pointed out that the timing of most fertilizer applications neglect the stage at which grain filling is maximum so that there is lower yield due to unfilled grains. To improve yield-determining components, especially for medium- to late-maturing varieties, appropriate timing of fertilizer application should target the pre-post flowering or grain filling stage. By doing so, farmers can increase their yield by up to 0.28 t/ha.
Most Filipino farmers use fertilizers from inorganic sources while a few use organic and bio-inoculants. Green manuring, on the other hand, is not practiced. To increase nutrient uptake, the speaker recommended combining green manure, organic, and inorganic fertilizers, which would also improve biological nitrogen fixation. In addition, bio-inoculant technologies will aid nutrient absorption by facilitating microorganism activity in the soil. Furthermore, the use of slow-release fertilizers to improve recovery as well as the use of rice straw as residue recycling will increase nutrient input in lowland production systems. Each intervention could increase yield from 0.21 t/ha by as much as 1.00 t/ha and 2.63 t/ha when combined.
Therefore, with the application of the three main recommended nutrition management practices above, lowland rice farmers can increase their yield (from mean yield of 3.68 t/ha) to a range of 3.89- 4.68 t/ha depending on the adopted intervention. Combinations (>2) of the interventions under field condition may raise yields from 4.15 t/ha to as high as 6.31 t/ha. Dr. Sta. Cruz emphasized however, that all these must be done hand-in-hand with good crop management.
Finally, the speaker suggested that site-specific decision-aided tools in nutrient management, such as IRRI’s Nutrient Manager or PhilRice’s Palay Check should be promoted to reach Filipino farmers. (Avril Adrianne D. Madrid)