Lengths of Time of Rice Husk Biochar Incorporation before Planting Affect Soil Properties and Rice Yield

A factor that causes inconsistencies in rice yield receiving biochar reported in the literature has been identified as the length of time after biochar incorporation into the soil prior to planting. There is limited information on the effect of the varying lengths of time on soil properties and rice growth. This study aimed to determine the effects of the length of time of incorporation of rice husk biochar (RHB) into an acidic paddy soil before rice transplanting on soil properties and rice yield. A greenhouse experiment was conducted using a highly weathered paddy soil subjected to incorporation periods of RHB at various lengths, including 0, 15, 30, and 60 days before rice transplanting (DBT). The RHB incorporation was under a soil moisture content of 70% of the soil water holding capacity. At harvest time (98 days after incorporation), increases in the length of RHB incorporation led to significantly higher Mg, Mn, and Si concentrations, but lower Ca and Fe concentrations in rice whole shoots. Increasing the length of RHB incorporation to 15, 30, and 60 DBT significantly decreased the total rice grain yield to 61.4 g hill−1, 62.5 g hill−1, and 54.4 g hill−1, respectively, compared to 76.0 g hill−1 found at 0 DBT. The depression of rice grain yield with increasing RHB incorporation periods was due to the antagonistic effects of Mg on Ca and Si on Fe. Immediate rice transplanting without a prior RHB incorporation period is recommended for its use as a soil amendment in acidic paddy soils

Effects of Neem Seed Extract on Nitrate and Oxalate Contents in Amaranth Fertilized with Mineral Fertilizer and Cricket Frass

A vegetable’s high antinutrients, nitrate (NO3−) and oxalate, could be remediated by neem seed extract. The combined use of neem seed extract with mineral fertilizer and cricket frass was conducted to evaluate their effects on amaranth’s tissue NO3− and oxalic acid contents by inhibiting nitrification. The effects of five soil amendments were investigated: unamended, mineral fertilizer, and three rates of cricket frass (3.125 Mg ha−1, 6.25 Mg ha−1, and 12.5 Mg ha−1), combined with two rates of neem seed extract: without (−Nm) and with (+Nm) extract. Only the neem extract applied to soils receiving mineral fertilizers decreased soil tissue NO3−−N contents (0.82 g kg−1 for −Nm vs. 0.62 g kg−1 for +Nm). The oxalic acid content of amaranth decreased with mineral fertilizer (0.60 and 0.46 g kg−1 for −Nm and +Nm, respectively), yet increased with the higher rates of cricket frass (1.42–1.52 g kg−1 for −Nm, and 1.23–1.51 g kg−1 for +Nm) compared to the unamended soil (1.05 and 1.00 g kg−1 for −Nm and +Nm). Cations, including K, Ca, Mg, and Na derived from cricket frass, may enhance biosynthesis and the accumulation of oxalic acid. The neem seed extract decreased the tissue’s oxalic contents regardless of soil amendments

Effects of Neem Leaf Extract on the Soil Properties, Growth, Yield, and Inorganic Nitrogen Contents of Lettuce

While lettuce offers essential human nutrients, it also contains anti-nutrients, particularly nitrate (NO3−). The use of neem leaf extract as a natural nitrification inhibitor has proven itself promising to remediate lettuce tissue NO3− content. This study evaluated the effects of neem leaf extract on soil properties, soil nitrification, lettuce growth, yield, and NO3− content. Five nitrification inhibitor treatments were evaluated: (i) no inhibitor (control), (ii) nitrapyrin, and three rates of neem leaf extract based on the dry weight of the raw material: (iii) 1 g kg−1 soil (Neem1), (iv) 2 g kg−1 soil (Neem2), and (v) 4 g kg−1 soil (Neem4). Neem leaf extract generally increased soil concentrations: P (47.6–55.8 mg kg−1), K (45.8–62.7 mg kg−1), Ca (129–164 mg kg−1), and Mg (29.0–35.7 mg kg−1) compared with the control (50.6 mg P kg−1, 35.3 mg K kg−1, 123 mg Ca kg−1, and 24.8 mg Mg kg−1). Neem leaf extracts significantly increased soil NH4+–N concentrations (13.9–30.2 mg kg−1) and nitrification inhibition (12.5–70.5%), but significantly decreased soil NO3−–N concentrations (6.4–13.2 mg kg−1) and net nitrification rates (0.08–0.23 mg N kg−1 day−1) relative to the control (6.6 mg NH4+–N kg−1, 14.7 mg NO3−–N kg−1, 0.26 mg N kg−1 day−1, and 0% nitrification inhibition). The neem leaf extracts significantly decreased shoot fresh weight (13.5–43.1 g plant−1), shoot dry weight (0.84–3.91 g plant−1), and root dry weight (0.14–0.27 g plant−1) compared with the control (52.3 g shoot fresh weight plant−1, 5.36 g shoot dry weight plant−1, and 0.35 g root dry weight plant−1). The significant decreases in the lettuce biomass in the neem extract treatments paralleled the significant decreases in the shoot’s tissue NO3−–N contents and significant increases in tissue NH4+–N content and soil Al concentrations

Land–Use Changes Influencing C Sequestration and Quality in Topsoil and Subsoil

Soil capacity as a major carbon (C) sink is influenced by land use. Estimates of soil organic carbon (SOC) sequestration have mostly focused on topsoils [0–30 cm official Intergovernmental Panel on Climate Change (IPCC) soil depth]. We investigated SOC stocks and their quality as influenced by land-use changes. Soil samples were collected from five soil depths down to 100 cm of three adjacent fields each representing a different land use—forest, cassava, and rice paddy—in Northeast Thailand. Sequestration of SOC in topsoils under all land uses was higher, as indicated by SOC stocks (59.0–82.0 Mg ha−1) than subsoils (30–100 cm) (27.0–33.0 Mg ha−1). The soil profile (0–100 cm) of the forest had higher stocks of SOC and humic acid (115.0 and 6.8 Mg ha−1, respectively) than those of cultivated land uses [paddy (100.0 and 4.8 Mg ha−1, respectively) and cassava (87.0 and 2.3 Mg ha−1, respectively)], which accounted for an average 30% increase in SOC sequestration over those with only topsoil. Topsoils of the forest had higher humic acid content but narrower E4:E6 ratio [the ratio of absorbances at 465 nm (E4) and at 665 nm (E6)] of humic acids (2.8), indicating a higher degree of humification and stabilization than the cultivated soils (3.2–3.6). Subsoil C was higher quality, as indicated by the lower E4:E6 ratio of humic acids than topsoils in all land uses