This paper presents various studies on the effects of macro- and micronutrient fertilization on the productivity (growth and yield), profitability, and quality of root crops such as purple yam (Dioscorea
alata) and sweetpotato (Ipomoea batatas),1 and vegetables such as tomato (Lycopersicon esculentum), pechay (Brassica napus), and cabbage (Brassica oleracea).
Most of the results presented here were taken from the findings of various research projects conducted by the author. Some of these projects were done in pot experiments (i.e., sweetpotato and pechay) and field experiments (i.e., purple yam, purple sweetpotato, cabbage, and tomato). The use of protected cultivation for tomato was also presented in comparison with the normal production in the open field. In all of the studies presented here, different combinations of macro- and micronutrients were used to determine the levels of nutrients that would enhance productivity, profitability, and quality. Results showed that for purple yam and purple sweetpotato, growth was greatly enhanced by the addition of macro- and micronutrient fertilizers. This is evident in the production of bigger leaves and longer vines. In terms of profitability, results showed that the application of higher levels of macro and micronutrient fertilizers significantly affected the yield of purple yam.
The highest net income was obtained using a combination of 150-50-150 kilograms per hectare (kg/ha) nitrogen, phosphate, and potassium (N-P2O5-K2O, also N-P-K) + 8 kg/ha Biozome-200, which produced a net income of PHP 185,685.71 per hectare; more than 400 percent increase over the control, which posted a net income of only PHP 38,800. Results in purple sweetpotato, meanwhile, indicated that the highest yield (21.8 tons per hectare [ton/ ha]) was obtained using a combination of 45-45-45 kg/ha N-P-K + 8 kg/ha
Biozome-200, amounting to an income of PHP 114,409 compared with the yield and income of the control (16.2 ton/ha, net income of PHP 89,866).
Considering the low cost of production for sweetpotato compared with that for yam, and the added health benefits that we can derive from the former, it is highly profitable to invest in producing sweetpotatoes. In terms of tuber quality, macro- and micronutrient fertilization enhanced the intensity of purple coloration and anthocyanin content in yam and sweetpotato. The effects are more pronounced in acid soil than in neutral soil. In the case of tomatoes, growth and yield were significantly affected by a protective structure and increasing potassium levels. Tomatoes grew much better, had greater yield, and better fruit quality under a protective structure than in the open field. Further, growth and yield were increased by addition of 50 kg/ha potassium (applied as K2O), indicating the beneficial effects of potassium biofortification on tomatoes. Higher antioxidant activity was determined in all tomato samples as affected by different potassium levels,whether under a protective structure or in the open field. The highest antioxidant activity was observed in tomatoes grown in the open field using 50 kg/ha K2O. For pechay, the addition of 8 kg/ha iron significantly increased growth performance, yield, and quality. With cabbage, a fertilizer level of 88-110-60 kg/ha N-P-K was found to be more productive and sustainable for production during the wet season. This gave a yield of about 12 tons/ha at a fertilizer cost of more than PHP 16,000, equivalent to 40 percent of what farmers normally spend. During the dry season, a fertilizer level of 90-90-60 kg/ha N-P-K was found to be more sustainable for cabbage production. This gave a yield of about 12 tons/ha at a fertilizer cost of PHP 6,123, which is only 20 percent of a farmer’s typical expenditure. Relatively higher levels of fertilizers were needed during the wet season. Results further showed that reducing the amount of fertilizer from 444-93-142 kg/ha N-P-K to 88-110-60 kg/ha N-P-K and from 335-258-396 kg/ha N-P-K to 90-90-60 kg/ha N-P-K
gave a sustainable yield aside from significantly cutting the cost of fertilizer and improving the balance of nutrients.
It is evident from the results of these studies that plant nutrition and proper fertilization play an important role in improving the yield of crops. These are necessary in attaining food security, especially in the Philippines, which faces the problem of land deterioration due to declining soil fertility. Establishing the right combinations of both macro- and micronutrients is therefore vital in more efficient and sustainable crop production.