Browsing by Subject "13C"

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Measuring and modelling resource use competition at the crop-soil-hedge interface on a hillside in Western Thailand
(2015) Hussain, Khalid; Cadisch, Georg
Thailand’s western uplands are facing severe soil loss and runoff problems due to intensive cultivation of cash crops for high food, feed, fiber, and fuel demand by an increasing population. Thus the Land Development Department and the International Board for Soil Research and Management in Thailand are promoting the use of soil conservation measures such as contour hedgerows, grass barriers and agroforestry systems based on fruit trees and annual crops. Although such measures have been shown to be effective in controlling soil erosion, farmers often are reluctant to adopt such practices as inclusion of trees reduces the cropped area and yields competition for available resources with crops. Hence, a better understanding of the underlying processes at the crop-soil-hedge interface is needed to design soil conservation systems that are more attractive for farmers. It was hypothesized that soil conservation systems with hedgerows and intercropping will induce spatial patterns of resource use which can be linked to competition while planting patterns affect canopy characteristics and light distributions. This study focused on the following objectives; (i) to improve understanding of competition at the crop soil hedge interface by combining stable isotope discrimination, electrical resistivity tomography and time domain reflectometry, (ii) to identify the effects of intercropping and hedgerows on maize biomass accumulation, nitrogen concentration and light use efficiency, (iii) to evaluate the competition between maize hedges at crop-soil-hedge interface, (iv) to explore possible mitigating options to cope with competition between hedge and maize by using a modelling approach. A field trial was laid out in randomized complete block design with three replicates at Queen Sirikit research farm, Ban Bo Wi village (13°28´ N and 99°15´ E), Suan Phueng District, Ratchaburi province in western Thailand with 20-25% slope magnitude. The experiment was established in 2009 while the research presented here was carried out during the 2010 and 2011 maize growing seasons. Six cropping treatments with following management practices were investigated: (T1, control) maize [Zea mays L.) monocrop, tillage, with fertilizer application (farmer’s practice; (T2) maize intercropped with chili (Capsicum annuum L. cv. Super Hot), tillage and fertilizer application; (T3) maize intercropped with chili, minimum tillage, fertilizer application, and Jack bean (Canavalia ensiformis (DC) L.) relay cropping; (T4) maize intercropped with chili, minimum tillage, fertilizer application, Jack bean relay cropped, and leucaena (Leucaena leucocephala (Lam.) de Wit) hedgerows; (T5) and (T6) as (T3) and (T4), respectively, but both without fertilizer application. Tillage was carried out manually by hoe to around 0-20 cm depth. Plots were 13 x 4 m. Fertilizer was applied to maize at a rate of 62, 22, 36 kg ha-1 of N, P, and K, respectively. Urea (N) application to maize was done in two splits as 31 kg ha-1 of N one month after sowing maize and another split of 31 kg ha-1 of N two months after sowing maize Chili received 92 kg N ha-1 at the time of transplanting and 92 kg ha-1 N as top dressing one month after transplanting. The impact of competition at the crop-soil-hedge interface was studied in 2011, two years after establishment of soil conservation measures, to exclude the establishment period of leucaena with a potentially weak impact on maize. At this time, highest above ground biomass (AGB) production of maize of 1364 g m-2 was witnessed in T2 being statistically different from all other treatments, except T4 and T3; while lowest above ground biomass production of 1034 g m-2 was observed in T5. In hedgerow treatments, maize rows planted distant to hedges produced 46% and 73% higher AGB than maize growing in rows close to the hedgerow (p≤0.0001) in T4 and T6, respectively. Similar effects were observed for plant height, grain nitrogen concentration and grain yield. Mean grain δ13C was significantly higher in T6 (-9.32‰) than in T4 (-10.49‰) and T1 (-10.55‰). Generally, higher δ13C signals mean higher water availability; however the higher δ13C signals in unfertilized T6 treatment imply that lack of nutrients may have led to increased δ13C values. Similarly in T4, δ13C signals were significantly higher in maize grains originating form rows planted close to hedges (10.33‰, p≤0.0001) than samples obtained from maize rows distant to hedges (-10.64‰). These results point out that competition at the crop-soil-hedge interface was driven by nutrient rather than water limitation. The electrical resistivity tomography (ERT) imaging further supported this finding showing that maize monocrop showed higher soil moisture depletion patterns than hedge intercrop with fertilizer (T4) treatment, while hedge intercrop without fertilization (T6) depleted soil moisture least. Light use efficiency (LUE) for maize above ground biomass production was statistically higher LUEAGB (1.56 g DM MJ-1) in maize and chilli intercrop (T2) than in maize sole cropping LUEAGB (1.23 g DM MJ-1). In T4 and T6 maize rows planted close to hedgerows had lower LUEAGB than rows distant to hedgerows. The land equivalent ratio showed that inclusion of hedgerows with fertilizer application in the intercropping treatment enhanced land utilization by 21%. The Water, Nutrient and Light Capture in Agroforestry (WaNuLCAS) model simulated AGB with R2= 0.83, RMSE=6.3, EF=0.82 and CD=1.4 during calibration while model validation also showed promising results with R2= 0. 76, P<0.001, RMSE=4.6 and EF=0.69. Simulations also pointed to major nutrient limitation between maize rows planted close to hedgerows. Simulations showed that negative impacts of hedgerows on crops can be reduced by managing fertilizer application in hedge adjacent maize rows leading to a successful application of agroforestry systems on a long-term basis not only for soil conservation but also for sustainable crop production in tropical uplands. The study figured out the scope of stable isotopic discrimination, ERT, light use efficiency and modelling approaches for evaluating resource use competition at crop-soil-hedge interface on hillside agriculture. The combination of isotopic discrimination and ERT measurements provided useful information for identification of cause-impact relationships. Spatial LUE patterns provided insights for canopy light harvest under various soil conservation options. Furthermore, light use data was also helpful in validation of WaNuLCAS model which did not only provide multiple options to figure out resource use competition at crop-soil-hedge interface but also allowed to test mitigation options for sustainable crop production in tropical uplands. Model scenarios showed that negative impacts of hedgerows on crops growing close to hedges can be reduced by applying minute additional doses of fertilizer only to the crop rows planted close to hedgerows, leading to a sustainable crop production along with soil conservation. Productivity evaluation of investigated cropping systems showed that inclusion of hedgerows and intercropping in tropical hillside agriculture is promising in enhancing crop production and thus can be adopted by farmers with yield advantage.