Sustaining soil characteristics and nutrients through site-specific nutrient management in cassava production areas for higher yields the Philippines

Increasing demand in the food and the feed industry for cassava has made it first in terms of area harvested among root crops and other staple vegetables in the Philippines (PSA 2017). Yet due to lack of appropriate fertilizer practice, the mean fresh root yield of cassava in country was only 12.51 (tons/ha), way below that of 32.68 of Laos, the highest in South East Asia (FAO, 2018). To increase Philippine cassava yield without undermining soil sustainability, this project aimed to determine the cassava yield responses, to fertilization as influenced by variety while monitoring soil status and crop nutrient removal and to show the efficiency of SSNM (site-specific nutrient management)-based fertilization for cassava. The average exploitable yield gap for cassava across the country was 10.53 +-3.82 t/ha representing significant opportunities to further increase cassava production. Comparing the four fertilization treatments namely, full NPK rate (200-100-350), cassava national fertilizer recommendation/NFR (56-56-56), SSNM prototype (180-70-250), and unfertilized control, data from both on-strain and on-farm trials showed that there is no significant difference in the yield of the full NPK and SSNM treatment as it also surpassed that of the NFR. On-station trials gave a yield of 35.24 t/ha for SSNM and 23 t/ha for the control while on the FPE, SSNM gave 33.39 t/ha for SSNM and 22.61 t/ha for control, across all sites and varieties. Differences in fresh root yield across treatments were influenced by variety and location. Results also confirmed that cassava heavily consumes K, followed by N and then P. Variety also affects N and K removal. Summarizing the results of omission plot trials the amount of fertilizer needed is 17 kg N, 4.5 kg P, and 27 kg K to produce one ton of cassava dry root yield per hectare. Despite the medium to high soil fertility of all sites, cassava still responded to fertilization. The SSNM prototype yield surpassed full NPK and NFR by 3.2% and 13.8% respectively. As such, SSNM-based fertilization is an efficient way of cassava fertilization. By optimizing the SSNM prototype recommendation based upon the influence of variety and site characteristics, appropriate quick fertilizer guides can be developed to increase cassava production in the country.