Evaluation of least limiting water range under different tillage-residue management practices and irrigation regimes in Maize (Zea mays L.)

Tillage-residue management practices significantly affect soil physical properties, crop and water productivity. Least limiting water range (LLWR) expresses the effect of different tillage-residue management systems on improvement and degradation of soil physical quality. Hence, A field study was conducted to evaluate LLWR under four tillage-residue management practices {conventional tillage (CT), no-tillage (NT), no-tillage with residue (NTR) and deep tillage (DT)} and three irrigation regime {IW/PAN-E 1.2, 0.9 and 0.6} in maize (cultivar PMH-1) during kharif 2015 with three replications in split plot design. The soil bulk density (ρb, Mg m -3 ) was found to be significantly higher under NT (1.57) followed by NTR (1.53), CT (1.49) and DT (1.46) at surface layer (0-15 cm). Significant differences were also observed in saturated hydraulic conductivity (Ks, cm hr -1 ) with maximum value in DT (5.36 and 4.63) and minimum in CT (3.93 and 2.80) at 0-7.5 and 7.5-15 cm depth, respectively. The highest mean weight diameter (MWD, mm) and water stable aggregates (WSA >0.25 mm, %) were found under NTR (0.64 and 49.7) and lowest under DT (0.3 and 21.8), respectively. The penetration resistance (PR) varied significantly among various tillage-residue management practices. Significantly, lowest PR was found under DT as it cause physical manipulation at lower soil depths and thus, reduces compaction. Higher volumetric soil water content and soil profile moisture storage was recorded under NTR at different days after sowing due to residue retention. The soil organic carbon content was found to be highest under NTR (4.7g kg -1 ) and lowest in DT (3.93 g kg -1 ). Among different tillage-residue management practices maximum grain yield was observed in DT (6.92 t ha -1 ) and minimum in NT (5.92 t ha -1 ). Among irrigation regimes, the maize grain yield (t ha -1 ) was observed to be maximum under I2 (6.63) and minimum under I3 (6.15). The water productivity (WP) (kg ha -1 mm -1 ) was observed to be highest in DT (10.21) attributing to higher maize grain yield. The WP decreases with increase in irrigation level. To observe the impact of soil physical constraints such as compaction and aeration, the LLWR was calculated for different tillage-residue management practices and found that with increase in tillage intensity the LLWR increases. The mean LLWR (m 3 m -3 ) was found to be highest in DT (0.19) followed by CT (0.16), NTR (0.14) and NT (0.13). Among different tillage-residue management practices the field capacity was the limiting factor for the upper range of LLWR beyond ρb (Mg m -3 ) 1.41, after that 10% air filled porosity become the limiting factor. For the lower range the permanent wilting point was limiting factor beyond ρb (Mg m -3 )1.50 and thereafter PR 2 M Pa become limiting factor for different tillageresidue management practices. There exist a negative relationship between ρb and LLWR. With the increase in LLWR, the maize grain yield increases which attribute to better soil environment for root proliferation and crop growth. Under conditions of poor aeration and compaction DT is the appropriate practice for achieving maximum crop and water productivity.