**3. Conclusions**

highest P were 9.18, 8.00, and 7.96 ppm, respectively, when biochar was applied at 20 t/ha, and lowest P were 7.49, 7.48, and 7.44 ppm, respectively, when no biochar was applied. The initial K was 0.16 meq/100 g soil, and after crop harvest under control condition (80% of FC), 60% of field capacity, and 40% of field capacity, highest K were 0.18 meq/100 g soil, 0.18 meq/100 g soil, and 0.17 meq/100 g soil, respectively, when biochar was applied at 20 t/ha, and lowest K were 0.17 meq/ 100 g soil, 0.17 meq/100 g soil, and 0.17 meq/100 g soil, respectively, when no biochar was applied. [53] reported biochar increased plant available nutrient in soil. [54] reported drought reduced N, P, and K levels in soil. [55] observed that the addition of biochar to soils increased soil phosphorus (P), soil potassium (K), and

**2.16 Effect of rice husk biochar on Zn, pH, and organic carbon (OC) in soil**

Drought stress adversely affected soil chemical properties such as Zn, pH, and OC. Application of rice husk biochar increased Zn, pH, and OC in soil. Zn and soil pH varied significantly with different doses of rice husk biochar under drought conditions, but OC varied insignificantly (**Table 12**).The initial Zn content was 17.4 meq/100 g soil, and after crop harvest under control condition (80% of FC), 60% of field capacity, and 40% of field capacity, highest Zn were 17.4 meq/100 g soil, 15.3 meq/100 g soil, and 14.9 meq/100 g soil, respectively, when biochar was applied at 20 t/ha, and lowest Zn were 13.9 meq/100 g soil, 13.2 meq/100 g soil, and 12.6 meq/100 g soil, respectively, when no biochar was applied. The initial pH was 6.1, and after crop harvest under control condition (80% of FC), 60% of field capacity, and 40% of field capacity, highest pH were 7.0, 6.9, and 6.7, respectively, when biochar was applied at 20 t/ha, and lowest pH were 6.7, 6.7, and 6.6, respectively, when no biochar was applied. The initial OC was 1.4%, and after crop harvest under control condition (80% of FC), 60% of field capacity, and 40% field capacity, highest OC were 0.7, 0.7, and 0.6%, respectively, when biochar was applied at 20 t/ha, and lowest OC were 0.54, 0.53, and 0.52%, respectively, when no biochar was applied. Similar result was reported by [56]. [57] marked biochar improved soil chemical properties of saline soil and biochar increased organic carbon. [58] found that biochar increased soil pH, thus reducing lime requirements.

> **Zn (meq/100 g soil) pH OC (%) 17.49 6.18 1.45**

> > **Control 60% of FC**

**40% of FC**

**Control 60% of FC**

**40% of FC**

**After harvest**

 13.9b–e 13.2de 12.6e 6.7ab 6.7b 6.6b 0.5a 0.5a 0.5a 14.3b–e 14.0b–e 13.2de 6.7ab 6.7ab 6.7ab 0.5a 0.5a 0.5a 15.7ab 14.8b–d 13.9c–e 6.9a 6.7ab 6.7ab 0.6a 0.6a 0.59a 17.4a 15.3bc 14.9b–d 7.0a 6.9a 6.7ab 0.7a 0.7a 0.6a

CV (%) 7.4 2.9 6.8

*Effect of rice husk biochar on Zn, pH, and organic carbon in soil under drought conditions.*

**40% of FC**

total soil nitrogen (N).

*Maize - Production and Use*

**Before sowing**

**Table 12.**

**72**

**Biochar doses (t/ha)**

**Control 60% of FC**

*Figure having similar letter did not vary significantly.*

**under drought stress**

Application of rice husk biochar increased plant height, days to maturity, total dry weight, chlorophyll content, plant water relations, SPAD value, exudation rate and reduced proline content, and days to flowering of maize under drought conditions. In maize plant drought stress tolerance ameliorate rice husk biochar and increased cob diameter, cob length, 100 grain weight of cob, seed /cob and finally maize yield at drought conditions.
