Optimization of fertilizer performances in long-term garlic cropping soils

Continuous cropping is a common pattern of modern agriculture that takes regional advantages for crop yield profits. Along the progress of mono-cropping continuously supported by intensive fertilizer inputs, such a cropping pattern often undergoes serious problems with low fertilizer use efficiencies and unsustainable crop production. In this study, we dealt with a > 25-year continuous garlic cropping system as an example for a problem-solving investigation. These garlic cropping soils underwent problems characterized by loss of soil organic matter, dramatic retention of NH₄⁺-N, and excess accumulation of phosphate and potash chemicals. Through hydroponic simulations, we revealed that the presence of NH₄⁺-N inhibited the root uptake of NO₃^--N and K by 68% and 88%, respectively. Despite the traditionally emphasized importance of K, we observed the negative effect of high K on the growth of garlic roots. Further field experiments demonstrated that P and K applications can be reduced by 60% and 50%, respectively, without loss of yield. We thus developed a high-performance fertilization strategy by integrating a recomposed NPK fertilizer formulation to reduce unnecessary P and K inputs, a supplementary application of long-lasting C of woody peat to compensate for the soil C loss, and a foliar K approach to strengthen the stomatal function improvement with K. This strategy allowed a 15% increase of garlic yield and a seasonal soil C profit of ca. 1.8 Mg ha^-1 even at ca. 30% lower fertilizer cost. This study would be helpful in managing garlic fertilization and developing compound fertilizers, with broader significance for other long-term cropping soils.