Variation in soil quality in tropical dryland agroecosystem: Impact of different crop sequences

Role of crop diversification on productivity has been studied widely but its impact on soil carbon dynamics is least studied. The present study was designed to compare the effects of crop diversification in terms of rice‐based mixed crops viz. wheat (RW), chickpea (RC), and flaxseed (RF) and mono‐crops viz. pigeonpea (PP) and mustard (MU) on major soil quality including physical, chemical and biological parameters, total crop biomass, and carbon input (CI) in a tropical rainfed dryland agroecosystem. Trend of total crop biomass observed was: pigeonpea > rice > wheat > mustard > flaxseed > chickpea. Across all the crop sequences, CI into the soil through crop residues including stubbles and root biomass varied considerably and followed the trend: PP > RW > RF > RC > MU. Levels of soil organic carbon (SOC), humic acid, fulvic acid, water holding capacity (WHC), macro‐aggregate fraction, microbial biomass carbon and phosphorus, enzyme activities of alkaline phosphatase, and β‐glucosidase were higher whereas bulk density, meso‐, and micro‐aggregate fractions were lower in the mixed crops than mono‐crops. SOC was positively correlated to all the attributes except bulk density, meso‐, and micro‐aggregate fractions. Lower values of the various soil quality attributes in PP despite the highest CI into the soil as compared to all the mixed crops might be due to the soil carbon priming effect. This study indicated that the quantity of CI through mixed crops had less impact in sustaining soil fertility and productivity of agroecosystems and suggests that the quality of CI play vital role. Mixed cropping sequence especially rice‐wheat was found to be the better option for the dry tropics.