Eucalyptus biochar application enhances Ca uptake of upland rice, soil available P, exchangeable K, yield, and N use efficiency of sugarcane in a crop rotation system

It was hypothesized that the application of eucalyptus biochar enhances nutrient use efficiencies of simultaneously supplied fertilizer, as well as provides additional nutrients (i.e., Ca, P, and K), to support crop performance and residual effects on subsequent crops in a degraded sandy soil. To test this hypothesis, we conducted an on-farm field experiment in the Khon Kaen province of Northeastern Thailand to assess the effects of different application rates of eucalyptus biochar in combination with mineral fertilizers to upland rice and a succeeding crop of sugarcane on a sandy soil. The field experiment consisted of three treatments: (1) no biochar; (2) 3.1 Mg ha(-1) biochar (10.4 kg N ha(-1), 3.1 kg P ha(-1), 11.0 kg K ha(-1), and 17.7 kg Ca ha(-1)); (3) 6.2 Mg ha(-1) biochar (20.8 kg N ha(-1), 6.2 kg P ha(-1), 22.0 kg K ha(-1), and 35.4 kg Ca ha(-1)). All treatments received the same recommended fertilizer rate (32 kg N ha(-1), 14 kg P ha(-1), and 16 kg K ha(-1) for upland rice; 119 kg N ha(-1), 21 kg P ha(-1), and 39 kg K ha(-1) for sugarcane). At crop harvests, yield and nutrient contents and nitrogen (N) use efficiency were determined, and soil chemical properties and pH(0) monitored. The eucalyptus biochar material increased soil Ca availability (117 +/- 28 and 116 +/- 7 mg kg(-1) with 3.1 and 6.2 Mg ha(-1) biochar application, respectively) compared to 71 +/- 13 mg kg(-1) without biochar application, thus promoting Ca uptake and total plant biomass in upland rice. Moreover, the higher rate of eucalyptus biochar improved CEC, organic matter, available P, and exchangeable K at succeeding sugarcane harvest. Additionally, 6.2 Mg ha(-1) biochar significantly increased sugarcane yield (41%) and N uptake (70%), thus enhancing N use efficiency (118%) by higher P (96%) and K (128%) uptake, although the sugar content was not increased. Hence, the application rate of 6.2 Mg ha(-1) eucalyptus biochar could become a potential practice to enhance not only the nutrient status of crops and soils, but also crop productivity within an upland rice-sugarcane rotation system established on tropical low fertility sandy soils.