Potassium fertilization and soil diagnostic criteria for forage corn (Zea mays L.) production contributing to lower potassium input in regional fertilizer recommendation

Abstract

Effective soil diagnostic criteria for exchangeable potassium (Ex-K) combined with inorganic potassium (K) application rates were developed to lower K input in forage corn (Zea mays L.) production using experimental fields with different application rates and histories of cattle manure compost. Two corn varieties, ‘Cecilia’ as a low K uptake variety and ‘Yumechikara’ as a high K uptake variety, were selected from among 20 varieties and tested to make diagnostic criteria for K fertilization applicable to varieties with different K uptakes. The K uptakes increased from 96 to 303 kg K ha−1 for ‘Cecilia’ and from 123 to 411 kg K ha−1 for ‘Yumechikara’ with increasing Ex-K content on a dry soil basis from 0.11 to 0.92 g kg−1 with no inorganic K fertilizer application. The K uptake by corn for achieving the target dry matter yield of 18 Mg ha−1 was estimated to be approximately 200 kg K ha−1 in common between the two varieties. Yields of both varieties achieved the target yield at an Ex-K content of approximately 0.30 g kg−1 with no K fertilization, although ‘Yumechikara’ reached the target yield at a lower Ex-K content. At the low Ex-K content of 0.1 g kg−1, inorganic K fertilizer application at 83 kg K ha−1 was needed to gain the target yield, and apparent K recovery rate for K fertilizer was calculated to be 70% for both varieties. The K uptakes for gaining the target yield by the K fertilization were lower than that by soil K supply. Based on these results, diagnostic criteria of Ex-K and inorganic K application rates were set up as follows: at an Ex-K content of < 0.15 g kg−1, inorganic K fertilizer is applied at 83 kg K ha−1 (100 kg ha−1 as potassium oxide (K2O) equivalent); at an Ex-K content of 0.15–0.30 g kg−1, the application rate is reduced to 33 kg K ha−1 (40 kg K2O ha−1); at an Ex-K content of ≥ 0.30 g kg−1, inorganic K fertilizer is not applied because of sufficient K in the soil. Additionally, we propose that cattle manure compost be used to supplement soil K fertility.