Potential nutrient contributions of a lakeshore rice-based agroecosystem in Barangay San Antonio, Bay, Laguna to Laguna de Bay, Philippines

Date

1996

Abstract

The study was conducted to determine the flow of nutrients, particularly nitrogen (N), phosphorus (P) and potassium (K) in a lakeshore ric-based agroecosystem in Barangay San Antonio Bay. It also aimed to identify the factors that influences NPK inputs and outputs in the agroecosystem.The flow of NPK to and from the paddy fields and the biophysical and socio-economic environments was determined for the 1994-1995 cropping year using mass-balance approach. The biophysical components of the agroecosystem were represented by natural processes were linked with the natural hydrologic cycle which include rainfall, runoff, leaching and flooding. On the otherhand, the socioeconomic components of the agroecosystem were represented by fertilizer application, irrigation, and cropping practices common in the barangay. Data showed a large part of annual nutrient inputs to the rice fields came from chemical fertilizers which consisted of 135 kg N/ha, 21 kg P/ha and 14 kg K/ha. These amounts accounted for 55 percent of N, 64 percent of P and 5 percent of K of the total inputs. Ratio of dry weights of harvested grain and straw was 1:2.5. This ratio implied an excess supply of NPK in the soil that resulted to the production of more straws than grains to the detriment of farmer's grain yield.The amount of NPK in the drainage waters of the agroecosystem which flowed directly to the lake were the potential nutrient contributions of the agroecosystem to the lake. Based on this study, a total of 35 kg N/ha, 9 kg P/ha and 66 kg K/ha per cropping year were contributed by the paddy fields to the lake via the flow of drainage waters. High volume of water which carried the excess nutrients from the paddy fields were discharged to the lake during heavy rains. More

73 nutrient enrichment of the lake took place during the rainy season. These nutrients which drained from the agroecosystem potentially contributed to the nutrient enrichment of the lake. Previous study showed there are abou 5,700 ha ricelands in the lakeshore of Laguna de Bay. If all farmers practiced the same fertilizer application as those farmers in Brgy. San Antonio, and assuming a 100 percent delivery ratio of drainage water from agroecosystem to the lake, then the potential NPK nutrient contributions of these paddy firlds to Laguna de Bay would be about 199,500 kg N, 51,300 kg P and 376,200 kg K per cropping year. This translates to about 3,990 bags of urea fertilizer, about 7,524 bags of potash fertilizer and 1,026 bags of ammophos fertilizer all drained to the lake.Under current commercial prices a 50 kg bag of complete fertilizer costs P360.00 or P7.20 /kg. Since complete fertilizers contain 14 percent each of N, P, and K would each cost P1.00. Multiplying the amount of NPK lost through drainage by P1.00 meant a cost of P35.0, P9.00, and P66.00 for N, P, and K per ha were lost through drainage waters which flowed to the lake assuming a 100 percent delivery ratio. If there are about 5,700 ha of ricelands in the lakeshores of Laguna de Bay and if all farmers practice the same fertilizer application as those farmers in Brgy. San Antonio, Bay, then the cost of money lost through drainage of N, P, and K would be P199,500.00, P51,300.00 and P376,200.00 respectively or a total of P627,000.00 The lake on the other hand, provided nutrient inputs to the agroecosystem. This was due to inundiation of the paddy fields by lakewater during typhoons. In this study it was shown that flooding provided about 1 percent of the total amount of NPK inputs to the agroecosystem.The total NPK content of the grains harvested were 97 kg N/ha, 11 kg P/ha and 23 kg K/ha. About 4 percent of the harvested grains were consumed by the farmer's families and the rest were sold. Thus the grains consumed amounted to 4 kg N/ha, 1 kg P/ha and 1 kg K/ha. Grains harvested that were sold and exported to other communities represented about 93 kg N/ha, 10 kg P/ha and 22 kg K/ha. For the whole barangay, these add up to about 7.3 tons of N, 0.8 tons of P and 1.7 tons of K.

Document Type

Master Thesis

Degree

Master of Science in Environmental Science

College

School of Environmental Science and Management (SESAM)

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 995 1996 E8 M35

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