Micronutrient application for improved yield and quality in purple yam

Tulin (PhilRoot crops) conducted a study to assess the effects of the addition of different levels of micronutrient fertilizers to NPK fertilizers on the growth and yield of purple yam variety VU-2 from 2002-2007. Effects on plant tissue, tuber quality, and soil chemical properties were also evaluated. Biozome-200, a commercially available micronutrient soil conditioner, was used. Biozome-200 contains a rich source of micronutrients such as manganese, zinc, iron, copper, boron, chlorine, molybdenum, cobalt, and other macronutrients such as magnesium and sulfur. Findings of the study revealed the following: Addition of 4 kg/ha, 8 kg/ha, and 16 kg/ha of Biozome-200 and 150-50-150 kg/ha NPK fertilizers produced significantly higher yields (15.72-18.52 t/ha) compared to unfertilized plots (11.32 t/ha) and those applied with NPK only (12.88 t/ha). A progressive increase in yield was noted as the micronutrient fertilizer rates increased from 4 kg/ha. The highest yield obtained was 270% higher than the national average yield of 5 t/ha and 64% higher than the yield in unfertilized plots. As in other crops, the positive effect on yield was attributed to the enhanced efficiency of macronutrient fertilizers due to micronutrients addition. The same trend was observed in net income (P 130,930-185,870) as the micronutrient fertilizer rates increased from 4 kg/ha to 16 kg/ha compared with unfertilized plots (P 58,400) and those applied with NPK only (P 75,930). The small investment on micronutrient fertilizer addition of about P 800 - P 1,800 gave a highly significant increase in net income from P 55,000 to as much as P 109,940 per cropping. These results supported previous findings that fertilizer application increased dry matter production in yam. Using 50 g and 100 g tuber setts for the same set of treatments showed that the use of 100 g tuber setts gave higher tuber yields (8.6 - 19 t/ha) and net incomes (P 68,950 - 258,080). In both experiments, the highest tuber yields were obtained from 16 kg/ha of Biozome-200 + 150-50-150 kg/ha NPK. Although cost of production was relatively lower using 50 g tuber setts (73,050 - 91,920) compared with 100 g tuber setts (P 103,050 - P 121,920), the P 30,000 additional cost in using 100 g tuber setts was offset by an increase in net income from P 96,200 to as much as P 107,200. These results showed the importance of choosing the right tuber sett sizes in yam because bigger tuber setts had relatively higher amounts of stored food which can be used by yam in its growth and development. Application of micronutrients coupled with the use of bigger tuber setts further boost the yield of purple yam. This showed that right combination of cultural management practices or component technologies leads to higher yield and income. When micronutrient fertilizers were reduced from 150-50-150 kg/ha NPK in previous experiments to 75-25-75 kg/ha NPK, significant reduction in total tuber yield (11.01-14.77 t/ha) and net income (PhP 44,865 to PhP 116,665) was observed even with the use of 100 g tuber setts. These results validated previous findings that yam requires high amounts of NPK fertilizers for tuber development. Micronutrients especially Cu, Mn, Zn, and B were particularly involved in the reproductive phase of plant growth and development. Thus bigger tubers were obtained in NPK treatments with 8 kg/ha and 16 kg/ha Biozome-200. Plant tissue analysis showed that the addition of micronutrient fertilizers increased the amount of total N and K in yam leaves. K is one of the limiting nutrients affecting root development or tuberization of rootcrops. Aside from N and K, the amount of total P, Fe, Mn, Zn, and Cu likewise increased with the addition of macro and micronutrients. Purple yam from Visayas State University applied with micronutrients were compared with purple yam from Bohol without micronutrients. Results showed that the purple yam from Bohol addition of micronutrients resulted in higher amounts of total Mg, Ca, Na, Fe, Cu, and Zn, which improved the nutritional content of purple yam. The addition of micronutrients also increased the amounts of organic matter, available P, exchangeable acidity due to slight reduction in soil pH and exchangeable Zn in the soil. This improvement in the nutrient supplying capacity of the soil directly enhanced the growth and yield of purple yam. Another important contribution of micronutrient addition was the slight reduction in soil pH value which was critical in the development of purple coloration in yam. Previous findings showed that acid soils produced dark colored yams than alkaline soils. The darker the purple coloration, the greater the market demand for purple yam because of high anthocyanin and micronutrient contents which produce very attractive health and food products.