Editing IPCC:AR6/SRCCL/Chapter-3 (section)

==== 3.6.1.1 Integrated crop–soil–water management ====

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Forms of integrated cropland management have been practiced in drylands for thousands of years (Knörzer et al. 2009 <sup>[[#fn:r978|978]]</sup> ). Actions include planting a diversity of species including drought-resilient ecologically appropriate plants, reducing tillage, applying organic compost and fertiliser, adopting different forms of irrigation and maintaining vegetation and mulch cover. In the contemporary era, several of these actions have been adopted in response to climate change.

In terms of climate change ''adaptation'' , the resilience of agriculture to the impacts of climate change is strongly influenced by the underlying health and stability of soils as well as improvements in crop varieties, irrigation efficiency and supplemental irrigation, for example, through rainwater harvesting (medium evidence, high agreement) (Altieri et al. 2015 <sup>[[#fn:r979|979]]</sup> ; Amundson et al. 2015 <sup>[[#fn:r980|980]]</sup> ; Derpsch et al. 2010 <sup>[[#fn:r981|981]]</sup> ; Lal 1997 <sup>[[#fn:r982|982]]</sup> ; de Vries et al. 2012 <sup>[[#fn:r983|983]]</sup> ). Desertification often leads to a reduction in ground cover that in turn results in accelerated water and wind erosion and an associated loss of fertile topsoil that can greatly reduce the resilience of agriculture to climate change (medium evidence, high agreement) (Touré et al. 2019 <sup>[[#fn:r984|984]]</sup> ; Amundson et al. 2015 <sup>[[#fn:r985|985]]</sup> ; Borrelli et al. 2017 <sup>[[#fn:r986|986]]</sup> ; Pierre et al. 2017 <sup>[[#fn:r987|987]]</sup> ). Amadou et al. (2011) <sup>[[#fn:r988|988]]</sup> note that even a minimal cover of crop residues (100 kg ha– <sup>1</sup> ) can substantially decrease wind erosion.

Compared to conventional (flood or furrow) irrigation, drip irrigation methods are more efficient in supplying water to the plant root zone, resulting in lower water requirements and enhanced water use efficiency ( ''robust evidence, high agreement'' ) (Ibragimov et al. 2007 <sup>[[#fn:r989|989]]</sup> ; Narayanamoorthy 2010 <sup>[[#fn:r990|990]]</sup> ; Niaz et al. 2009 <sup>[[#fn:r991|991]]</sup> ). For example, in the rainfed area of Fetehjang, Pakistan, the adoption of drip methods reduced water usage by 67–68% during the production of tomato, cucumber and bell peppers, resulting in a 68–79% improvement in water use efficiency compared to previous furrow irrigation (Niaz et al. 2009 <sup>[[#fn:r992|992]]</sup> ). In India, drip irrigation reduced the amount of water consumed in the production of sugarcane by 44%, grapes by 37%, bananas by 29% and cotton by 45%, while enhancing yields by up to 29% (Narayanamoorthy 2010 <sup>[[#fn:r993|993]]</sup> ). Similarly, in Uzbekistan, drip irrigation increased the yield of cotton by 10–19% while reducing water requirements by 18–42% (Ibragimov et al. 2007 <sup>[[#fn:r994|994]]</sup> ).

A prominent response that addresses soil loss, health and cover is altering cropping methods. The adoption of intercropping (inter – and intra-row planting of companion crops) and relay cropping (temporally differentiated planting of companion crops) maintains soil cover over a larger fraction of the year, leading to an increase in production, soil nitrogen, species diversity and a decrease in pest abundance ( ''robust evidence, medium agreement'' ) (Altieri and Koohafkan 2008 <sup>[[#fn:r995|995]]</sup> ; Tanveer et al. 2017 <sup>[[#fn:r996|996]]</sup> ; Wilhelm and Wortmann 2004 <sup>[[#fn:r997|997]]</sup> ). For example, intercropping maize and sorghum with ''Desmodium'' (an insect repellent forage legume) and Brachiaria (an insect trapping grass), which is being promoted in drylands of East Africa, led to a two-to-three-fold increase in maize production and an 80% decrease in stem boring insects (Khan et al. 2014 <sup>[[#fn:r998|998]]</sup> ). In addition to changes in cropping methods, forms of agroforestry and shelterbelts are often used to reduce erosion and improve soil conditions (Section 3.7.2). For example, the use of tree belts of mixed species in northern China led to a reduction of surface wind speed and an associated reduction in soil temperature of up to 40% and an increase in soil moisture of up to 30% (Wang et al. 2008 <sup>[[#fn:r999|999]]</sup> ).

A further measure that can be of increasing importance under climate change is rainwater harvesting (RWH), including traditional ''zai'' (small basins used to capture surface runoff), earthen bunds and ridges (Nyamadzawo et al. 2013 <sup>[[#fn:r1001|1001]]</sup> ), ''fanya juus'' infiltration pits (Nyagumbo et al. 2019 <sup>[[#fn:r1002|1002]]</sup> ), contour stone bunds (Garrity et al. 2010 <sup>[[#fn:r1003|1003]]</sup> ) and semi-permeable stone bunds (often referred to by the French term ''digue filtrante'' ) (Taye et al. 2015 <sup>[[#fn:r1004|1004]]</sup> ). RWH increases the amount of water available for agriculture and livelihoods through the capture and storage of runoff, while at the same time reducing the intensity of peak flows following high-intensity rainfall events. It is therefore often highlighted as a practical response to dryness (i.e., long-term aridity and low seasonal precipitation) and rainfall variability, both of which are projected to become more acute over time in some dryland areas (Dile et al. 2013 <sup>[[#fn:r1005|1005]]</sup> ; Vohland and Barry 2009 <sup>[[#fn:r1006|1006]]</sup> ). For example, for drainage in Wadi Al-Lith, Saudi Arabia, the use of rainwater harvesting was suggested as a key climate change adaptation action (Almazroui et al. 2017 <sup>[[#fn:r1007|1007]]</sup> ). There is ''robust evidence'' and ''high agreement'' that the implementation of RWH systems leads to an increase in agricultural production in drylands (Biazin et al. 2012 <sup>[[#fn:r1008|1008]]</sup> ; Bouma and Wösten 2016 <sup>[[#fn:r1009|1009]]</sup> ; Dile et al. 2013 <sup>[[#fn:r1010|1010]]</sup> ). A global meta-analysis of changes in crop production due to the adoption of RWH techniques noted an average increase in yields of 78%, ranging from –28% to 468% (Bouma and Wösten 2016 <sup>[[#fn:r1011|1011]]</sup> ). Of particular relevance to climate change in drylands is that the relative impact of RWH on agricultural production generally increases with increasing dryness. Relative yield improvements due to the adoption of RWH were significantly higher in years with less than 330 mm rainfall, compared to years with more than 330 mm (Bouma and Wösten 2016 <sup>[[#fn:r1012|1012]]</sup> ). Despite delivering a clear set of benefits, there are some issues that need to be considered. The impact of RWH may vary at different temporal and spatial scales (Vohland and Barry 2009 <sup>[[#fn:r1013|1013]]</sup> ). At a plot scale, RWH structures may increase available water and enhance agricultural production, SOC and nutrient availability, yet at a catchment scale, they may reduce runoff to downstream uses (Meijer et al. 2013 <sup>[[#fn:r1014|1014]]</sup> ; Singh et al. 2012 <sup>[[#fn:r1015|1015]]</sup> ; Vohland and Barry 2009 <sup>[[#fn:r1016|1016]]</sup> ; Yosef and Asmamaw 2015 <sup>[[#fn:r1017|1017]]</sup> ). Inappropriate storage of water in warm climes can lead to an increase in water related diseases unless managed correctly, for example, schistosomiasis and malaria (Boelee et al. 2013 <sup>[[#fn:r1018|1018]]</sup> ).

Integrated crop–soil–water management may also deliver climate change ''mitigation'' benefits through avoiding, reducing and reversing the loss of SOC (Table 6.5). Approximately 20–30 Pg of SOC have been released into the atmosphere through desertification processes, for example, deforestation, overgrazing and conventional tillage (Lal 2004 <sup>[[#fn:r1019|1019]]</sup> ). Activities, such as those associated with conservation agriculture (minimising tillage, crop rotation, maintaining organic cover and planting a diversity of species), reduce erosion, improve water use efficiency and primary production, increase inflow of organic material and enhance SOC over time, contributing to climate change mitigation and adaptation ( ''high confidence'' ) (Plaza-Bonilla et al. 2015 <sup>[[#fn:r1020|1020]]</sup> ; Lal 2015 <sup>[[#fn:r1021|1021]]</sup> ; Srinivasa Rao et al. 2015 <sup>[[#fn:r1022|1022]]</sup> ; Sombrero and de Benito 2010 <sup>[[#fn:r1023|1023]]</sup> ). Conservation agriculture practices also lead to increases in SOC ( ''medium confidence'' ). However, sustained carbon sequestration is dependent on net primary productivity and on the availability of crop-residues that may be relatively limited and often consumed by livestock or used elsewhere in dryland contexts (Cheesman et al. 2016 <sup>[[#fn:r1024|1024]]</sup> ; Plaza-Bonilla et al. 2015 <sup>[[#fn:r1025|1025]]</sup> ). For this reason, expected rates of carbon sequestration following changes in agricultural practices in drylands are relatively low (0.04–0.4 tC ha <sup>–1</sup> ) and it may take a protracted period of time, even several decades, for carbon stocks to recover if lost ( ''medium confidence'' ) (Farage et al. 2007 <sup>[[#fn:r1026|1026]]</sup> ; Hoyle et al. 2013 <sup>[[#fn:r1027|1027]]</sup> ; Lal 2004 <sup>[[#fn:r1028|1028]]</sup> ). This long recovery period enforces the rationale for prioritising the avoidance and reduction of land degradation and loss of C, in addition to restoration activities.

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