Wheat-Maize Intercropping With Reduced Tillage and Straw Retention: A Step Towards Enhancing Economic and Environmental Benefits in Arid Areas.

Intercropping is considered a promising system for boosting crop productivity. However, intercropping usually requires higher inputs of resources that emit more CO2. It is unclear whether an improved agricultural pattern could relieve this issue and enhance agricultural sustainability in an arid irrigation area. A field experiment using a well-designed agricultural practice was carried out in northwest China; reduced tillage, coupled with wheat straw residue retention measures, was integrated with a strip intercropping pattern. We determined the crop productivity, water use, economic benefits, and carbon emissions (CEs). The wheat-maize intercropping coupled with straw covering (i.e., NTSI treatment), boosted grain yield by 27-38% and 153-160% more than the conventional monoculture of maize and wheat, respectively, and it also increased by 9.9-11.9% over the conventional intercropping treatment. Similarly, this pattern also improved the water use efficiency by 15.4-22.4% in comparison with the conventional monoculture of maize by 45.7-48.3% in comparison with the conventional monoculture of wheat and by 14.7-15.9% in comparison with the conventional intercropping treatment. Meanwhile, NTSI treatment caused 7.4-13.7% and 37.0-47.7% greater solar energy use efficiency than the conventional monoculture of maize and wheat, respectively. Furthermore, the NTSI treatment had a higher net return (NR) by 54-71% and 281-338% and a higher benefit per cubic meter of water (BPW) by 35-51% and 119-147% more than the conventional monoculture of maize and wheat, respectively. Similarly, it increased the NR and BPW by 8-14% and 14-16% in comparison with the conventional intercropping treatment, respectively. An additional feature of the NTSI treatment is that it reduced CEs by 13.4-23.8% and 7.3-17.5% while improving CE efficiency by 62.6-66.9% and 23.2-33.2% more than the conventional monoculture maize and intercropping treatments, respectively. We can draw a conclusion that intercropping maize and wheat, with a straw covering soil surface, can be used to enhance crop production and NRs while effectively lowering CO2 emissions in arid oasis irrigation region.

Enhancing the systems productivity and water use efficiency through coordinated soil water sharing and compensation in strip-intercropping.

In arid areas, water shortage is threating agricultural sustainability, and strip-intercropping may serve as a strategy to alleviate the challenge. Here we show that strip-intercropping enhances the spatial distributions of soil water across the 0-110 cm rooting zones, improves the coordination of soil water sharing during the co-growth period, and provides compensatory effect for available soil water. In a three-year (2009-2011) experiment, shorter-season pea (Pisum sativum L.) was sown in alternate strips with longer-season maize (Zea mays L.) without or with an artificially-inserted root barrier (a solid plastic sheet) between the strips. The intercropped pea used soil water mostly in the top 20-cm layers, whereas maize plants were able to absorb water from deeper-layers of the neighboring pea strips. After pea harvest, the intercropped maize obtained compensatory soil water from the pea strips. The pea-maize intercropping without the root barrier increased grain yield by 25% and enhanced water use efficiency by 24% compared with the intercropping with the root barrier. The improvement in crop yield and water use efficiency was partly attributable to the coordinated soil water sharing between the inter-strips and the compensatory effect from the early-maturing pea to the late-maturing maize.

Interspecies Interactions in Relation to Root Distribution Across the Rooting Profile in Wheat-Maize Intercropping Under Different Plant Densities.

In wheat-maize intercropping systems, the maize is often disadvantageous over the wheat during the co-growth period. It is unknown whether the impaired growth of maize can be recovered through the enhancement of the belowground interspecies interactions. In this study, we (i) determined the mechanism of the belowground interaction in relation to root growth and distribution under different maize plant densities, and (ii) quantified the "recovery effect" of maize after wheat harvest. The three-year (2014-2016) field experiment was conducted at the Oasis Agriculture Research Station of Gansu Agricultural University, Wuwei, Northwest China. Root weight density (RWD), root length density (RLD), and root surface area density (RSAD), were measured in single-cropped maize (M), single-cropped wheat (W), and three intercropping systems (i) wheat-maize intercropping with no root barrier (i.e., complete belowground interaction, IC), (ii) nylon mesh root barrier (partial belowground interaction, IC-PRI), and (iii) plastic sheet root barrier (no belowground interaction, IC-NRI). The intercropped maize was planted at low (45,000 plants ha-1) and high (52,000 plants ha-1) densities. During the wheat/maize co-growth period, the IC treatment increased the RWD, RLD, and RSAD of the intercropped wheat in the 20-100 cm soil depth compared to the IC-PRI and IC-NRI systems; intercropped maize had 53% lower RWD, 81% lower RLD, and 70% lower RSAD than single-cropped maize. After wheat harvest, the intercropped maize recovered the growth with the increase of RWD by 40%, RLD by 44% and RSAD by 11%, compared to the single-cropped maize. Comparisons among the three intercropping systems revealed that the "recovery effect" of the intercropped maize was attributable to complete belowground interspecies interaction by 143%, the compensational effect due to root overlap by 35%, and the compensational effect due to water and nutrient exchange (CWN) by 80%. The higher maize plant density provided a greater recovery effect due to increased RWD and RLD. Higher maize plant density stimulated greater belowground interspecies interaction that promoted root growth and development, strengthened the recovery effect, and increased crop productivity.

Integrated double mulching practices optimizes soil temperature and improves soil water utilization in arid environments.

Water shortage threatens agricultural sustainability in many arid and semiarid areas of the world. It is unknown whether improved water conservation practices can be developed to alleviate this issue while increasing crop productivity. In this study, we developed a "double mulching" system, i.e., plastic film coupled with straw mulch, integrated together with intensified strip intercropping. We determined (i) the responses of soil evaporation and moisture conservation to the integrated double mulching system and (ii) the change of soil temperature during key plant growth stages under the integrated systems. Experiments were carried out in northwest China in 2009 to 2011. Results show that wheat-maize strip intercropping in combination with plastic film and straw covering on the soil surface increased soil moisture (mm) by an average of 3.8 % before sowing, 5.3 % during the wheat and maize co-growth period, 4.4 % after wheat harvest, and 4.9 % after maize harvest, compared to conventional practice (control). The double mulching decreased total evapotranspiration of the two intercrops by an average of 4.6 % (P < 0.05), compared to control. An added feature was that the double mulching system decreased soil temperature in the top 10-cm depth by 1.26 to 1.31 °C in the strips of the cool-season wheat, and by 1.31 to 1.51 °C in the strips of the warm-season maize through the 2 years. Soil temperature of maize strips higher as 1.25 to 1.94 °C than that of wheat strips in the top 10-cm soil depth under intercropping with the double mulching system; especially higher as 1.58 to 2.11 °C under intercropping with the conventional tillage; this allows the two intercrops to grow in a well "collaborative" status under the double mulching system during their co-growth period. The improvement of soil moisture and the optimization of soil temperature for the two intercrops allow us to conclude that wheat-maize intensification with the double mulching system can be used as an effective farming model in alleviating water shortage issues experiencing in water shortage areas.

[Effects of different conservation tillage measures on winter wheat water use in Wuwei oasis irrigated area].

Field experiments were conducted in 2006-2008 to study the effects different conservation tillage measures, including conventional tillage with stubble incorporating (TS), no-tillage without stubble retention (NT), no-tillage with stubble standing (NTSS), no-tillage with stubble retention (NTS), on the soil moisture profile, soil water storage, water use efficiency (WUE), and grain yield of winter wheat in Wuwei oasis irrigated area. Comparing with conventional tillage, NTS and NTSS could significantly increase the water storage in 0-30 cm soil layer from returning green to jointing stage, and increase this storage in 30-150 cm soil layer from returning green till maturity. NTS, NTSS, and NT increased the water storage in whole soil profile (0-150 cm) by 29.55-34.69 mm, 17.32-21.79 mm, and 0.89-15.68 mm at sowing, and 37.59-38.35 mm, 5.70-22.14 mm, and 4.61-13.93 mm at harvesting, respectively. The difference in water storage became more significant with increasing soil depth. NTS, NTSS, NT and TIS increased the grain yield of winter wheat by 15.65%-16.84%, 6.98%-12.75%, 5.88%-11.74%, and 3.92%-8.16%, and the WUE by 17.15%-17.52%, 7.75%-9.65%, 8.24%-10.00%, and 4.17%-9.91%, respectively. NTS and NTSS improved the rain water use efficiency and grain yield, being the efficient conservative tillage measures to alleviate the lack of water resource in the study area.