The excessive use of nitrogen (N) fertilizers in sustaining high rice yields due to N dynamics in tropical acid soils not only is economically unsustainable but also causes environmental pollution. The objective of this study was to coapply biochar and urea to improve soil chemical properties and productivity of rice. Biochar (5 t ha−1) and different rates of urea (100%, 75%, 50%, 25%, and 0% of recommended N application) were evaluated in both pot and field trials. Selected soil chemical properties, rice plants growth variables, nutrient use efficiency, and yield were determined using standard procedures. Coapplication of biochar with 100% and 75% urea recommendation rates significantly increased nutrients availability (especially P and K) and their use efficiency in both pot and field trials. These treatments also significantly increased rice growth variables and grain yield. Coapplication of biochar and urea application at 75% of the recommended rate can be used to improve soil chemical properties and productivity and reduce urea use by 25%.

Phosphorus is a macronutrient which plays an important role in plant metabolism, growth, and development. However, in tropical acid soils, P fixation is high because of significant amounts of Al and Fe ions. Al and Fe ions can reduce diffusion of P into plant roots. Low absorption of P at initial growth of most plants causes stunting and slow growth of plant leaves. This process reduces photosynthesis. Chicken litter biochar (CLB) had been used on tropical acid soils to improve total P, available P, organic P, and inorganic fractions of P. Moreover, CLB is able to reduce exchangeable acidity, Fe, and Al ions in mineral acid soils because of the reactive surfaces of this organic amendment. However, there is dearth of information on the effects of the right combination of CLB and triple superphosphate (TSP) on the aforementioned soil chemical properties and crop productivity. To this end, the objectives of this study were to improve P: (i) Availability in a mineral acid soil and (ii) uptake, agronomic efficiency, and dry matter yield of Zea mays L. using the right amounts of TSP and CLB. Combinations of 75%, 50%, and 25% CLB (based on recommended 5 t ha−1) and TSP (based on recommended P fertilization for maize) were evaluated in a pot study. Selected soil chemical properties, maize plants nutrient uptake, growth variables, and dry matter yield were determined using standard measures. Results showed that 25% and 50% biochar of 5 t ha−1 with 75% TSP can increase soil P availability, recovery, agronomic use efficiency, and dry matter yield of maize plants. These optimum rates can also reduce P fixation by Al and Fe ions. Therefore, soil and maize productivity can be improved by using CLB (25% and 50% of 5 t ha−1) and TSP (75% of conventional rate) to increase nutrients availability especially P.

The reaction of H2PO4 2-and HPO4-with Al and Fe in acid soils to form a precipitate reduces P availability. Chicken litter biochar has been used to improve soil P availability for maize production but with limited information on optimum rates of biochar and Triple Superphosphate (TSP) to increase P availability. This study determined the optimum amount of chicken litter biochar and TSP that could increase P availability. Different rates of chicken litter biochar and TSP were evaluated in an incubation study for 30, 60, and 90 days. Selected soil chemical properties before and after incubation were determined using standard procedures. Soil pH, total P, available P, and water soluble P increased in treatments with 75% and 50% biochar. Total acidity, exchangeable Al 3+ , and Fe 2+ were significantly reduced by the chicken litter biochar. The chicken litter biochar also increased soil CEC and exchangeable cations (K, Ca, Mg and Na). The use of 75% and 50% of 5 t ha-1 biochar with 25% TSP of the existing recommendation can be used to increase P availability whilst minimizing soil Al and Fe content. This rates can be used to optimize chicken litter biochar and TSP use in acid soils for crop production especially maize and short term vegetables.

The use of N fertilizers on tropical acid soils is increasing because of their low native fertility. Chicken litter biochar was used to improve N use efficiency and rice yield. The objective of this study was to determine the effects of chicken litter biochar on selected chemical properties of a tropical acid soil under rice (MR219) cultivation. Treatments evaluated were in this study were as follows: (1) T1, soil only, (2) T2, existing recommended fertilization, (3) T3, chicken litter biochar alone, and (4) T4, chicken litter biochar + existing recommended fertilization. Plant and soil analyses were conducted using standard procedures. The use of chicken litter biochar increased soil pH, total carbon, total P, available P, total N, and exchangeable N. Also, this practice decreased soil total acidity and exchangeable Al3+. Compared with T2, T4 significantly increased Crop Recovery Efficiency and Agronomic Recovery Efficiency of N. This resulted in a significant increase in the grain yield (11 t ha−1) of MR219 (Malaysia hybrid rice) for T4 compared with the existing rice grain yield of 5.9 t ha−1 (T2). Moreover, application of chicken litter biochar (5 t ha−1) to tropical acid soil suggested that N application can be reduced to 26.67%, 30.03%, 30.15%, and 14.15% of the recommended rates by MADA on days 10, 30, 50, and 70 after transplanting, respectively. Chicken litter biochar can improve the chemical properties of tropical acid soils and rice (MR219) grain yield.

Using muriate of potash (MOP) as a source of potassium (K) is a cost-effective method for crop production in tropical peat soils. However, exchangeable K commonly leaches from tropical peat soils because of high rainfall and a lack of clay to retain this cation. Potassium retention as exchangeable K could inhibit K loss through leaching to increase K availability. Clinoptilolite zeolite (CZ), forest litter compost (FLC), and chicken litter biochar (CLB) can be used to retain K from MOP in tropical peat soils for crop use because of the high affinity of CZ, FLC, and CLB for K ions. These approaches can be used as innovative and sustainable alternatives for the frequently used lime (CaCO3). However, information on using CZ, FLC, and CLB for MOP K retention is limited. Thus, CZ, FLC, and CLB were tested in a leaching study to determine their effects on MOP K retention in tropical peat soil. The use of CZ and FLC at rates of 100% and 75% of the recommended rate for pineapple cultivation (a commonly grown fruit crop in tropical peat soils in Malaysia) improved the K availability, pH, and CEC of the peat soil because of the high CEC of CZ and the humic substances (humic acids, fulvic acids, and humin) of FLC, which have a high affinity for K ions. The CLB did not improve K retention because of the competition between K, Ca, Mg, and Na ions, which are inherently high in this soil amendment. Instead of liming, which only replaces a few of the leached cations, such as calcium, the results of this study suggest an alternative method of retaining peat cations, such as K, that reduce peat acidity. This alternative method of retaining peat soil cations, especially K ions, is a practical and sustainable approach for improving peat soil productivity.