Root growth, water potential, nutrient uptake and grain yield of upland rice as affected by soil moisture deficit and compaction [Philippines]

Soil compaction increased soil penetration resistance. High soil penetration resistance decreased root growth in deeper soil profiles (15- to 40-cm soil depths). With sufficient water (300 mm) and nutrient supply, soil compaction increased nutrient (NPK) uptake and upland rice yield. Otherwise, at 30 mm water, it decreased root growth and, consequently, reduced yield. Potassium at 75 kg/ha reduced the ill-effects of drought and soil compaction. Drought stress also increased soil penetration resistance, more in compacted than in noncompacted soils, and bulk density. It decreased shoot and root growth, NPK uptake, leaf water potential and grain yield more than did soil compaction. Total root nutrient uptake, however, was influenced more by soil compaction than by drought stress. Soil compaction and drought stress both decreased root respiration rate. Potassium application in nutrient-deficient acid soils increased root growth in deeper soil profiles, resulting in increased nutrient uptake and grain yield. Root growth decreased with soil depth due to increasing soil penetration resistance. Available nutrients also decreased with soil depth. However, root growth at various soil depths was positively correlated with grain yield. Varietal differences in K response was observed in Leyte. Crop yield was twice of the control (0 kg K/ha) with 25 kg K/ha. At 50 kg K/ha, yield of UPLRi-7 during the second cropping increased four times. Root growth and grain yield in Leyte [Philippines] are improved by K nutrition. Higher grain yield was observed in Batangas compared to Leyte site because of more fertile soil and higher weekly solar radiation. Under favorable conditions, genetic characteristics can be well expressed, thus, significant varietal differences in grain yield was observed in Batangas. Results at farmers' field experiments suggest that upland rice yield was influenced by site, variety, and K fertilizer. Grain yield can be increased by planting varieties with high yield potential and which are highly responsive to applied nutrient, and by proper timing of cropping season