Introduction
Cereal crops including bread wheat (Triticum aestivum L.) and rice (Oryza sativa L.) are grown in diverse crop rotations worldwide and play a vital role in ensuring food security. As leading food crops, rice and wheat supply 20% and 27% of the dietary energy and protein, respectively, in the developing world (Redona, Reference Redona, Eaglesham, Wildeman and Hardy2004). In conventional rice–wheat rotations, rice seedlings are transplanted in puddled flooded soil to suppress weeds, reduce percolation losses, and improve the availability of certain micronutrients (Nawaz et al., Reference Nawaz, Farooq, Nadeem, Siddique and Lal2019). In contrast, wheat sowing requires well-drained soil of good tilth, which indicates a conflict in soil management practices for rice and the post-rice wheat crop (Farooq et al., Reference Farooq, Basra and Asad2008). Indeed, puddling increases soil compaction by reducing total soil porosity and increasing soil bulk density (Farooq and Nawaz, Reference Farooq and Nawaz2014) and has a detrimental effect on successful wheat establishment due to restricted root growth and aeration stress (Nawaz et al., Reference Nawaz, Farooq, Nadeem, Siddique and Lal2019). In addition, puddling typically results in erratic crop stand establishment due to poor seed–soil contact (Nawaz et al., Reference Nawaz, Farooq, Ahmad, Basra and Lal2016). Several studies on rice–wheat systems have reported lower wheat yield after puddled transplanted flooded rice than after direct-seeded aerobic rice (Nawaz et al., Reference Nawaz, Farooq, Ahmad, Basra and Lal2016, Reference Nawaz, Farooq, Lal and Rehman2017a, b).
Tillage practices affect the pattern of weed emergence, as the weed flora may differ between plow tillage and zero tillage (Nawaz and Farooq, Reference Nawaz and Farooq2016). Conventional tillage helps to suppress weeds during early growth, but late-season weed infestations can be stimulated in this tillage system, which can reduce crop yield and quality (Harker and Clayton, Reference Harker and Clayton2004). Tillage intensity can also affect soil moisture retention and then weed emergence, which has affected the yields of wheat and chickpea (Pradhan et al., Reference Pradhan, Thakur and Sonboir2014). The use of resource conservation technologies including zero tillage in wheat and direct-seeded rice might enhance the productivity and profitability of rice–wheat rotations (Nawaz et al., Reference Nawaz, Farooq, Lal and Rehman2017a, b, Reference Nawaz, Farooq, Nadeem, Siddique and Lal2019) by reducing soil degradation and increasing soil organic matter and soil fertility and finally improving the biological diversity in the rhizosphere (Farooq and Nawaz, Reference Farooq and Nawaz2014; Nawaz et al., Reference Nawaz, Farooq, Ahmad, Basra and Lal2016, Reference Nawaz, Farooq, Lal and Rehman2017a, b, Reference Nawaz, Farooq, Ul-Allah, Gogoi, Lal and Siddique2021). For example, zero tillage in wheat reduces production costs (Hobbs and Gupta, Reference Hobbs, Gupta, Ladha, Hill, Duxbury, Gupta and Buresh2003) and improves soil structure (Mohanty et al., Reference Mohanty, Painuli, Misra and Ghosh2007), soil enzyme activity (Lupwayi et al., Reference Lupwayi, Hanson, Harker, Clayton, Blackshaw, O’Donovan, Johnson, Gan, Irvine and Monreal2007) and microbial biomass carbon by 7–36% (Soon and Arshad Reference Soon and Arshad2005).
Previous cultivation of direct-seeded rice improves the soil physical structure by improving soil porosity and reducing soil bulk density (Nawaz et al., Reference Nawaz, Farooq, Ahmad, Basra and Lal2016), resulting in better root penetration by the wheat crop. In rice–wheat rotations, zero tillage suppresses some weeds due to less soil disturbance (Farooq and Nawaz, Reference Farooq and Nawaz2014). Various field experiments have concluded that direct-seeded rice is a better resource conservation technology than puddled transplanted flooded rice for improving soil health. For instance, zero tillage wheat grown after direct-seeded rice helped to sustain productivity in a rice–wheat cropping system (Farooq and Nawaz, Reference Farooq and Nawaz2014; Nawaz et al., Reference Nawaz, Farooq, Ahmad, Basra and Lal2016, Reference Nawaz, Farooq, Lal and Rehman2017a).
Legume incorporation into cropping systems enriches soil organic matter, improves soil nutrient availability (Cupina, Reference Cupina2014) and also soil physical conditions by reducing soil bulk density and enhancing soil aggregation (Mandal et al., Reference Mandal, Singh, Victor and Sharma2003). Previous studies have reported that growing sesbania (Sesbania rostrata Bremek. & Oberm) as an intercrop with direct-seeded rice and residue retention had a positive impact on soil properties and provided a favorable environment for the following crops (Nawaz et al., Reference Nawaz, Farooq, Lal, Rehman, Hussain and Nadeem2017b; Iliger et al., Reference Iliger, Sutar, Chogatapur and Parameshwarareddy2017). Moreover, legume incorporation as a break crop helps to suppress weeds, pests (Jensen et al., Reference Jensen, Peoples and Hauggaard-Nielsen2010), and diseases (Cupina, Reference Cupina2014).
Some studies have compared conventional and conservation tillage systems (Shahzad et al., Reference Shahzad, Farooq and Hussain2016; Nawaz et al., Reference Nawaz, Farooq, Lal and Rehman2017a) and the inclusion of legumes (Lauren et al., Reference Lauren, Shrestha, Sattar and Yadav2001) in rice–wheat systems for their impact on weed dynamics and productivity. However, to the best of our knowledge, there have been no studies on weed dynamics, soil health, productivity and profitability of wheat and chickpea in long-term rice-based conventional and conservation tillage systems. This study evaluated the effect of different rice-based cropping systems (conventional vs. conservation) and legume incorporation on soil physicochemical and biological properties, weed dynamics, productivity, and profitability of both chickpea and wheat grown in plow tillage and zero tillage systems.
Materials and methods
Experimental site
A field study was conducted at the Agronomic Research Area, University of Agriculture, Faisalabad (31°N, 73°E and 184.4 m a.s.l.), Pakistan in 2014/15 and 2015/16. The experimental plots (9.25 m × 15 m) were established in 2012/13. For soil analysis, soil samples were collected before the sowing of wheat and chickpea and after rice harvest from different points in the experimental field. The experimental soil (0–20 cm depth) was a sandy loam with pH 8.2, electrical conductivity (EC) 0.25 dS m–1, and very low organic matter content (0.66%). Available P, total N, and exchangeable K were 7.0 ppm, 330 ppm, and 111 ppm, respectively, at the beginning of the experiment. Weather data during the course of investigation are shown in Supplementary Material Table S1.
Seed material
Seeds of chickpea (Cicer arietinum L.) cultivar ‘Bakhar-2011’ and the bread wheat (Triticum aestivum L.) cultivar ‘Faisalabad-2008’ were sourced from the Pulse Research Institute (Faisalabad, Pakistan) and the Wheat Research Institute (Faisalabad, Pakistan), respectively.
Experimental details and treatments
The experiment comprised the following eight rice–wheat and rice–chickpea systems in a randomized complete block design with 16 plots (with each plot designated as one cropping system); each plot was replicated three times: (1) direct-seeded rice followed by zero tillage wheat or zero tillage chickpea, with no rice residue retention (DR-ZT); (2) direct-seeded rice followed by conventional tillage wheat or conventional tillage chickpea, with no rice residue retention (DR-CT); (3) direct-seeded rice followed by zero tillage wheat or zero tillage chickpea, with rice residue retention (DR-ZTR); (4) direct-seeded rice followed by conventional tillage wheat or conventional tillage chickpea, with rice residue retention (DR-CTR); (5) puddled transplanted flooded rice followed by zero tillage wheat or zero tillage chickpea with no rice residue retention (TR-ZT); (6) puddled transplanted flooded rice followed by conventional tillage wheat or conventional tillage chickpea with no rice residue retention (TR-CT); (7) direct-seeded rice with sesbania brown manuring followed by zero tillage wheat or zero tillage chickpea, with no rice residue retention (DRS-ZT); (8) direct-seeded rice with sesbania brown manuring followed by conventional tillage wheat or conventional tillage chickpea, with no rice residue retention (DRS-CT).
The direct-seeded rice and puddled transplanted flooded rice systems had been maintained as per Nawaz et al. (Reference Nawaz, Farooq, Lal, Rehman, Hussain and Nadeem2017b) for the previous 3 years.
Land preparation and crop husbandry for wheat and chickpea
For conventional tillage wheat and chickpea, the fields after direct-seeded rice were cultivated (up to 20 cm depth) twice with a cultivator followed by leveling while those after puddled transplanted flooded rice were cultivated four times using a cultivator followed by two plankings. In treatment 3 and 4, the rice residues (7 t ha-1) of previous rice crop were retained in the wheat and chickpea plots. In both tillage systems, wheat and chickpea were seeded at 125 and 75 kg ha–1, respectively.
The wheat was sown on 14 November 2014 and 18 November 2015 and chickpea sown on 15 October 2014 and 13 October 2015. The wheat and chickpea were sown using a manually operated single-row drill. For zero tillage wheat and chickpea, the seeds were sown directly into rice stubble. The row-to-row distance was 30 cm for chickpea and 22.5 cm for wheat.
Inorganic fertilizers were applied on the basis of the soil analysis report at 100/90 and 15/50 N/P kg ha–1 in the wheat and chickpea crops, respectively, using urea (46% N) and di-ammonium phosphate (18% N, 46% P). For wheat, the full amount of P and one-third of N was applied as a basal dose, and the remaining two-thirds of N was top dressed equally at the first and second irrigation (flooding method). For chickpea, the full amount of P and N was applied as a basal dose. Two (each of 76 mm) irrigations through flooding method were applied to chickpea, and four (each of 76 mm) to wheat in both tillage systems, in addition to the pre-sowing irrigation of 102 mm.
After recording the weed data at 30 days after sowing, the weed control in wheat fields was achieved through a selective post-emergence herbicide [Atlantas (iodo-mesosulfuron) at 14.4 g a.i. ha−1]. Weeds in chickpea plots were controlled through the manual pulling of weeds at 30 days after sowing. There were no insect pest attacks or diseases in either crop or season. Both crops were harvested on 24 April 2015 and 29 April 2016.
Weed dynamics and soil health
Data on weed density (individual and total) were recorded 45 days after sowing from two random places (each measuring 1 m2) in each plot through visual counting. To determine soil health, the soil was sampled at the harvest of each crop from different positions within the experimental plots using an auger. Soil pH and EC were measured using Thermo Scientific Orion 4-star plus pH/conductivity meter (Thermo Fisher Scientific, Inc., Beverly MA, USA) (Rhoades, Reference Rhoades and Sparks1996; Thomas, Reference Thomas and Sparks1996). Exchangeable K (Richards, Reference Richards1954), available P (Olsen et al., Reference Olsen, Cole, Watanabe and Dean1954), total N (Bremner and Mulvaney, Reference Bremner, Mulvaney, Page, Miller and Keeny1982), soil bulk density (Blake and Hartge, Reference Blake, Hartge and Klute1986), total soil porosity (Vomocil, Reference Vomocil and Blake1965), and total soil organic carbon (Walkley and Black, Reference Walkley and Black1934) were estimated following standard protocols.
Morphological/yield parameters
At final harvest, from each plot, number of spike-bearing tillers were counted from three randomly selected three sampling sites (each of 1 m2) to record the productive tillers. Ten spikes were randomly selected and threshed manually to separate the grains. The grains separated were counted to record number of grains per spike. A subsample of 1000 grains was taken from each plot and weighted to record 1000-grain weight. The crop was harvested, tied into bundles, and sun-dried for a week. Total above-ground wheat biomass of sun-dried samples from each plot were recorded with a spring balance (Kern 281, Inscale, Buckinghamshire, UK). The crop was threshed by a mini-thresher and grain yield for each treatment was recorded by a spring balance (Kern 281, Inscale, Buckinghamshire, UK) in kilograms and later expressed in tons per hectare (t ha−1).
For chickpea, branch and pod number per plant were counted on five plants selected at random in each experimental plot and averaged. Twenty pods of chickpea from each experimental plot were threshed manually to determine the seed number per pod. One hundred seeds were weighed on an electronic balance to record 100-grain weight. To record total grain yield and total biomass of each crop, each plot was harvested in heaps and sun-dried for a week before being weighed on a spring balance (Kern 281, Inscale, Buckinghamshire, UK) to record total above-ground biomass. The bundles were then threshed, and grain yield recorded and expressed in tons per hectare. The harvest index of chickpea was expressed in percentage by dividing grain yield by total above-ground biomass.
Economic analysis
The net benefits for each treatment were calculated by subtracting total cost (fixed cost and variable cost) from the gross income (income from straw and grains) and was converted into (US$ ha−1). The total fixed cost included land rent, seed cost, costs of fertilizer, plant protection, and irrigation. The variable cost included the cost of tillage/seedbed preparation, and harvesting/threshing charges (Table S2). The benefit:cost ratio was computed following CIMMYT (1998).
Statistical analysis
The experimental data were statistically analyzed by analysis of variance (Steel et al., Reference Steel, Torrie and Dicky1997) using the software Statistics MSTAT-C (Crop and Soil Science Department, Michigan University, USA). The treatment means (cropping systems) were compared using the least significant difference at the 5% probability level.
Results
Soil health
At rice harvest, the lowest total soil porosity and the maximum soil bulk density were recorded after harvesting the puddled transplanted flooded rice in both years. The DRS-ZT, DRS-CT, and DR-CR treatments caused the highest total SOC in both years (Table 1).
Table 1. Influence of various rice production systems on soil physical properties before planting wheat or chickpea
Main effects sharing the same letter for a parameter during an experimental year do not differ significantly at p ≤ 0.05.
DSR = direct-seeded rice; DSR + CR = direct-seeded rice + crop residues; SBM = sesbania brown manuring; PuTR = puddled transplanted rice.
The rice–wheat and rice–chickpea cropping systems did not affect soil pH or EC in either year. In both years, the DRS-ZT and DR-ZTR in the rice–chickpea cropping system caused the highest SOC values (Table 2).
Table 2. Influence of various rice–wheat and rice–chickpea cropping systems on different soil properties (ns = non-significant; DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea) Treatments sharing the same letter for a given variable during an experimental year do not differ significantly at p ≤ 0.05
In both years, the direct-seeded rice treatments (except for DR-CT) in the rice–chickpea cropping system had the highest N concentrations (Table 2). In both years, the rice–wheat cropping system had the highest available P in the TR-CT and DRS-ZT treatments. The rice–chickpea cropping system had the highest available P in the transplanted rice treatments in both years. In 2014/15, the maximum exchangeable K was recorded in the rice–chickpea cropping system in the DRS-ZT treatment. In 2015/16, both cropping systems caused the highest exchangeable K in the DRS-ZT treatment (Table 2).
Weed dynamics
The weed flora in the different rice-based cropping systems consisted of toothed dock (Rumex dentatus L.), black medick (Medicago lupulina L.), blue pimpernel (Anagallis arvensis L.), common lambsquarter (Chenopodium album L.), swine cress (Cronopus didymus L.), field bindweed (Convolvulus arvensis L.), and littleseed canarygrass (Phalaris minor Retz.). In 2014/15, the wheat crop in the TR-ZT treatment had the highest density of toothed dock. In 2015/16, chickpea and wheat in the DR-ZTR treatment and wheat in the DRS-ZT treatment had the lowest densities of toothed dock. Wheat planted in the TR-ZT treatment had the lowest density of blue pimpernel in 2015/16 (Figure 1). The black medick and blue pimpernel density was highest in DR-CT treatment in both crops in both years (Figures 1 and 2).
Figure 1. Influence of various rice–wheat cropping systems on the density of (a) toothed dock and (b) black medick in wheat and chickpea.
(DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea; Bars are means ± standard error of means. The bars sharing the same letter for a given variable during an experimental year do not differ significantly at p ≤ 0.05)
Figure 2. 720 Influence of various rice–wheat cropping systems on the density of blue pimpernel and common lambsquarters (m–2) in wheat and chickpea.
(DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea; Bars are means ± standard error of means. The bars sharing the same letter for a given variable during an experimental year do not differ significantly at p ≤ 0.05)
The lowest density of common lambsquarter was recorded for both crops in the TR-ZT treatment in 2015/16 (Figure 2). Chickpea planted in the DR-ZT treatment had the lowest density of swine cress in 2015/16. In 2014/15, wheat planted in the DR-CT treatment and chickpea in the TR-CT treatment had the lowest densities of field bindweed (Figure 3). In 2015/16, no emergence of field bindweed was observed in the wheat planted in the DR-CT treatment (Figure 3).
Figure 3. Influence of various rice–wheat cropping systems on (a) the density of swine cress and (b) field bindweed in wheat and chickpea.
(DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea; Bars are means ± standard error of means. The bars sharing the same letter for a given variable during an experimental year do not differ significantly at p ≤ 0.05)
In 2014/15, the DR-CTR and TR-CT treatments caused no emergence of littleseed canary grass in either crop (Figure 4). In 2015/16, chickpea grown in the DR-CT, DR-CTR, and DR-ZTR treatments had the lowest densities of littleseed canary grass (Figure 4). Wheat planted in the TR-ZT treatment in both years and chickpea planted in the DR-ZTR treatment in 2014/15 and 2015/16 had the lowest total broad-leaved weeds (Figure 5). In 2014/15, wheat in the TR-ZT treatment and chickpea in the DR-ZTR and TR-CT treatments had the fewest total weeds (Figure 5). Similarly, in 2015/16, chickpea in the DR-ZTR treatment and wheat in the TR-ZT treatment had the fewest total weeds (Figure 5).
Figure 4. Influence of various rice–wheat cropping systems on the density of littleseed canarygrass in wheat and chickpea.
(DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea; bars are means ± standard error of means. The bars sharing the same letter during an experimental year do not differ significantly at p ≤ 0.05)
Figure 5. Influence of various rice–wheat cropping systems on the densities of (a) broadleaf weeds and (b) total weeds in wheat and chickpea.
(DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea; bars are means ± standard error of means. The bars sharing the same letter for a given variable during an experimental year do not differ significantly at p ≤ 0.05)
Wheat: morphological and yield parameters
The DRS-ZT treatment in both years produced the maximum productive tillers. In both years, the DRS-CT, DR-CTR, and DR-CT treatments had the most grains per spike in the wheat crop (Table 3). The DRS-ZT treatment produced the highest 1000-grain weight in both years (Table 3). The DRS-ZT and DR-ZTR treatments in 2014/15 and the DRS-ZT treatment in 2015/16 had the highest grain yields. In 2014/15, wheat planted in the DRS-CT and DR-ZTR treatments produced the highest biological yields. In 2015/16, the DRS-ZT, DRS-CT, and DR-CTR treatments produced the maximum biological yields. Wheat grown in the DRS-ZT and DR-ZTR treatments in 2014/15 and the TR-CT and DR-ZTR treatments in 2015/16 had the highest harvest indices (Table 3).
Table 3. Influence of various rice–wheat cropping systems on grain yield and related parameters of wheat (DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea)
Treatments sharing the same letter for a given variable during an experimental year do not differ significantly at p ≤ 0.05.
Chickpea: morphological and yield parameters
In both years, the DRS-ZT and DR-ZTR treatments produced the most branches per chickpea plant. The DRS-ZT treatment produced the most pods per plant in both years and the DRS-ZT and DRS-CT treatments produced the most grains per pod (Table 4). In both years, the DRS-ZT and DR-ZT/CT treatments produced the highest 100-grain weights. In 2014/15, the DRS-ZT, DRS-CT, and DR-CTR treatments presented the highest grain yields. In 2015/16, the DRS-ZT and DRS-CT treatments had the highest grain yields (Table 4). In 2014/15, the DRS-CT, DRS-ZT, DR-CTR, and DR-ZTR treatments produced the most biological yield. In 2015/16, the DRS-CT and DRS-ZT treatments produced the highest biological yield. The DRS-ZT treatment had the highest harvest index in 2015/16 (Table 4).
Table 4. Influence of various rice–wheat cropping systems on grain yield and related parameters of chickpea (DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea) Treatments sharing the same letter for a given variable during an experimental year do not differ significantly at p ≤ 0.05
Economics
For both wheat and chickpea, the DRS-ZT treatment produced the highest net benefits and benefit:cost ratio (averaged over 2 years), while crop growth after TR-CT had the lowest (Table 5).
Table 5. Economic analysis of wheat and chickpea grown in different rice-based cropping systems (DR-ZT = direct-seeded rice followed by zero tillage wheat or chickpea; DR-CT = direct-seeded rice followed by conventional tillage wheat or chickpea; DR-ZTR = direct-seeded rice followed by zero tillage wheat or chickpea with residue mulch from previous rice crop; DR-CTR = direct-seeded rice followed by conventional tillage wheat or chickpea with residue mulch from previous rice crop; TR-ZT = puddled transplanted rice followed by zero tillage wheat or chickpea; TR-CT = puddled transplanted rice followed by conventional tillage wheat or chickpea; DRS-ZT = sesbania incorporation in direct-seeded rice followed by zero tillage wheat or chickpea; DRS-CT = sesbania incorporation in direct-seeded rice followed by conventional tillage wheat or chickpea; wheat grain = $12.38/40 kg; chickpea grain = $34.28/40 kg; wheat straw = $1.45/40 kg; chickpea straw = $0.57/40 kg; $ 1 = 105 PKR; For economic analysis, the grain and straw yields are reduced as recommended by CIMMYT. (1988)]
Discussion
The rice-based cropping systems and different tillage practices used in this study for wheat and chickpea crops significantly affected weed dynamics, soil physio-chemical properties, grain yield, and profitability. Soil analysis after rice harvest indicated that the rice production systems (TR and DR) triggered a series of changes in soil quality (Table 1). Puddling enhanced soil bulk density and reduced soil porosity (Table 1). Indeed, puddling deteriorates soil physical properties (McDonald et al., Reference McDonald, Riha, Duxbury, Steenhuis and Lauren2006) due to the formation of hardpan that causes subsurface compaction (Saharawat et al., Reference Saharawat, Gathala, Ladha, Malik, Singh, Jat, Gupta, Pathak, Singh, Ladha, Yadvinder-Singh, Erenstein and Hardy2010) and increases soil bulk density (Farooq and Nawaz, Reference Farooq and Nawaz2014; Nawaz et al., Reference Nawaz, Farooq, Nadeem, Siddique and Lal2019). Puddling-induced compaction reduces soil porosity by changing pore size distribution and aggregate stability (Behera et al., Reference Behera, Varshney and Goel2009) and adversely affects the soil carbon stock (Ladha et al., Reference Ladha, Dawe, Pathak, Padre, Yadav, Bijay, Yadvinder, Singh, Singh, Kundu, Sakal, Ram, Regmi, Gami, Bhandari, Amin, Yadav, Bhattarai, Das, Aggarwal, Gupta and Hobbs2003), thus resulting in poor soil quality as observed in this study. In contrast, direct-seeded rice improves soil structure, which is attributed to low soil bulk density, increased soil porosity, and improved SOC (Prasad and Balanagoudar, Reference Prasad and Balanagoudar2017). Moreover, sesbania brown manuring in direct-seeded rice improves soil quality by enhancing SOC and improving soil physical properties (Tables 1 and 2; Maitra and Zaman, Reference Maitra and Zaman2017; Nawaz et al., Reference Nawaz, Farooq, Lal, Rehman, Hussain and Nadeem2017b).
In this study, switching from a conventional tillage system to a zero tillage system in rice-based cropping affected total N, available P, exchangeable K, and total SOC. The DRS-ZT treatment had the highest SOC, total N, available P, and exchangeable K followed by the DRS-CT, DR-ZTR, DR-CTR, and DR-ZT treatments in the rice–wheat and rice–chickpea cropping systems (Table 2). Sesbania brown manuring in direct-seeded rice improved soil fertility, possibly due to the rapid decomposition of sesbania surface mulch which enhanced the available N, P, and K and substantially improved the SOC (Nawaz et al., Reference Nawaz, Farooq, Lal, Rehman, Hussain and Nadeem2017b; Iliger et al., Reference Iliger, Sutar, Chogatapur and Parameshwarareddy2017). Sesbania is the fast-growing legume that forms a symbiotic relationship with gram-negative bacteria to develop nitrogen-fixing nodules in the stem and roots (Capoen et al., Reference Capoen, Oldroyd, Goormachtig and Holsters2010) and thus increase the soil nutrient pool. Moreover, manuring with legume crops enhances soil porosity and improves soil aggregation and soil water holding capacity, thereby improving soil quality.
In this study, residue retention of the rice crop in post-rice wheat or chickpea improved the SOC in the wheat and chickpea crops, which is attributed to the accelerated activities of soil microbes that hasten residue decomposition (Das et al., Reference Das, Ghosh, Lal, Saha and Ngachan2017). Increases in N, P, and K concentrations with zero tillage may be due to the release of nutrients as the residue decomposes. Less soil disturbance in zero tillage and the decomposition of surface-retained residues enhanced the nutrient pool in the rhizosphere (Bertol et al., Reference Bertol, Engel, Mafra, Bertol and Ritter2007), resulting in better root uptake of these nutrients. Further, zero tillage followed by sesbania brown manuring in direct-seeded rice increased the concentration of available N, P, and K nutrients (Table 2) in the root zone, and is known to improve SOC, and reduce soil bulk density to improve soil health (Maitra and Zaman, Reference Maitra and Zaman2017). Soil fertility was improved more with chickpea than wheat in the DRS-ZT, DR-ZT, and DR-ZTR treatments (Table 2) because chickpea is a leguminous crop that can fix biological N to help restore the N balance, maintain soil fertility, and increase soil SOC (Mohammadi et al., Reference Mohammadi, Ghalavand and Aghaalikhani2010).
Different tillage systems in rice-based cropping systems significantly affect weed dynamics. Overall, the TR-ZT, DR-ZTR, and DRS-ZT treatments had less weed flora. The DR-CT treatment had the highest densities of toothed dock and blue pimpernel, and the DR-CTR and DRS-ZT treatments had the highest densities of common lambsquarter, swine cress, and field bindweed (Figures 1 to 4). Surface residue retention in zero tillage acts as a physical barrier to the germination of weed seeds. Further, allelochemicals released from the residue of rice mulch may inhibit weed seed germination (Afridi et al., Reference Afridi, Khan, Gul and Daud2014), which may explain the reduced weed infestation in the DR-ZTR treatment (Figures 1 to 5). Surface residue acts as a mulch and induces changes in the soil micro-environment that minimize soil temperature variations and prevent light stimulus (Franke et al., Reference Franke, Singh, McRoberts, Nehra, Godara, Malik and Marshall2007) and substantially reduce weed emergence and density, as observed in this study. Reduced weed infestations in zero tillage systems followed by transplanted rice may be due to a reduction in weed seed viability under flooding conditions, for example, common lambsquarter (Farooq and Nawaz, Reference Farooq and Nawaz2014). Seed viability of littleseed canarygrass and toothed dock declines when exposed to light and fluctuating temperature (Farooq and Nawaz, Reference Farooq and Nawaz2014), which may have reduced its germination in the wheat and chickpea crops, as observed in conventional tillage (Figure 4). Conventional tillage followed by direct-seeded rice enhanced the emergence of weed seeds as the plow tillage disturbs the soil and brings weed seeds to shallower depths, exposing them to temperature and sunlight (Figures 1 to 5; Singh et al., Reference Singh, Kaur, Kang and Singh2012), which facilitates their germination.
The DRS-ZT and DRS-CT treatments had the highest grain yields for wheat and chickpea (Tables 3 and 4). Indeed, sesbania brown manuring in direct-seeded rice improved soil physical conditions, such as increased SOC, improved soil porosity, and reduced soil bulk density (Table 1) and N, P, and K concentrations in the rhizosphere (Table 2), which enhanced growth, yield-related traits, and ultimately grain yield. Sesbania reportedly improves the soil organic matter (SOM) pool and macro- and micro-nutrient uptake (N, P, K, Zn, and Cu) in the root zone (Iliger et al., Reference Iliger, Sutar, Chogatapur and Parameshwarareddy2017), which may explain the improved performance of both wheat and chickpea in this study (Tables 3 and 4). Furthermore, zero tillage provides a favorable soil environment by increasing soil storage pores (0.5–50 mm; Pagliai et al., Reference Pagliai, Vignozzi and Pellegrini2004) and improving soil aggregation, soil organic carbon (SOC) (Jacobs et al., Reference Jacobs, Rauber and Ludwig2009), and soil microbial activity (Singh and Kaur, Reference Singh and Kaur2012), which finally enhances soil productivity and grain yield. In this study, zero tillage after sesbania brown manuring reduced the frequency of soil disturbance and damage to the soil structure. As soil surface remained covered with straw, we noticed nutrient enrichment in the plow layer by decreasing nutrient losses and adding surface SOM. Crop residues are rich in high-carbon compounds such as lignin and cellulose, sources of SOM. Upon decomposition of these residues, carbon is released that promotes soil microbial immobilization and mineralizes inorganic nutrients (Devevre and Horwath, Reference Devêvre and Horwáth2000), thus enhancing soil productivity and improving grain yield. The DRS-ZT treatment for both wheat and chickpea produced the maximum net benefit and benefit:cost ratio, due to high grain yields and cost-savings in terms of tillage in this treatment.
Conclusion
Puddling and flooding in rice deteriorate the soil structure by increasing soil bulk density and decreasing soil porosity and SOC contents. While the transplanted flooded rice systems had the lowest weed flora; sesbania brown manuring, and the retention of rice crop residues in zero tillage also helped to suppress weeds. Moreover, sesbania brown manuring in direct-seeded rice and rice straw mulch in zero tillage systems improved soil properties as evidenced by the increased total N, available P, exchangeable K, and SOC, reduced soil bulk density, and increased total soil porosity. Thus, weed suppression and the better soil environment with sesbania brown manuring and zero tillage improved crop productivity, profitability, and overall performance of wheat and chickpea grown in rice-based systems. Legume incorporation in existing rice–wheat systems will improve soil health and productivity in the long term.
Conflicts of interest
The authors declare no conflicts of interest.
Funding
This research did not receive any specific funding.
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/S0014479721000090
