Soil hydraulic response to conservation agriculture under irrigated intensive cereal-based cropping systems in a semiarid climate

Assessment of soil hydraulic response to conservation agriculture (CA) practices may assist in better management decisions in agriculturally sensitive and environmentally fragile agroecosystems. Although, the potential of management induced temporal changes of soil hydraulic properties (SHPs) has been studied particularly in relation to tillage, few studies have evaluated combined effects of tillage, crop residue retention and cropping sequence, which are essential components of CA, on near-saturated SHPs under field conditions. The objective of this study was thus to evaluate the long-term effect after eight years of CA practices and short-term effect of crops on near-saturated soil hydraulic conductivity, k(h), and water transmission properties under irrigated intensive cereal-based cropping systems in a semiarid climate (NW Indo-Gangetic Plains, India). There were four treatments: (1) conventionally tilled rice-wheat cropping system, (2) reduced till CA-based rice-wheat-mungbean system, (3) no-till CA-based rice-wheat-mungbean system and (4) no-till CA-based maize-wheat-mungbean system. Steady state infiltration rates were obtained at four pressure heads by hood infiltrometer consecutively over two cropping seasons, ie., during harvest season of rice/maize (October 2017) and maximum crop growth stage of wheat (February 2018). Data were analysed in terms of k(h), flow weighted mean pore radius (r(0)), hydraulically active porosity (epsilon) and threshold pore radius (r(bp)), a new pore measure indicative of macropore stability derived by substituting soil's bubble pressure in the capillary equation. Our results showed that no tillbased CA enhanced k(h) as compared with conventional cultivation practice. Although the interaction effect of treatments with crop seasons were statistically non-significant (p < 0.05), considerable changes of soil hydraulic properties were observed over crop seasons under CA treatments. Transition from maize to wheat in the crop sequence reduced k(h) values by about 55, 44, 34 and 40% at pressure heads of 0, - 1, - 2 and - 4 cm, respectively. In contrast, transition from rice to wheat in rice-based no till CA increased k(h) values by 129, 164, 124 and 24% in the same pressure head ranges. Irrespective of crop seasons, higher k(h) was observed under CA due to formation of macropores with better continuity, greater size and numbers as compared with conventional intensive tillage treatment. Reduced till-based CA showed an intermediate effect with respect to the different soil hydraulic characteristics in both crop seasons. Moreover, higher rp values were observed for a given k(h) for CA treatments suggesting that interaggregate pores are the dominant pathways of infiltration flux in CA. A relatively smaller temporal variation of r(bp) was indicative of a more stable macropore system established by rice-based CA as compared with maize-based CA. CA also enhanced hydraulically active macropores as compared with intensive tillage based conventional agriculture. Overall, the results revealed that the potential impacts of CA on near-saturated SHPs are largely governed by characteristic changes in macro- and interaggregate pores.