Different land use systems improve soil fertility status of sandy soil and increase the yield of rice under rain-fed wet lowland tropical climatic conditions in Papua New Guinea
Abstract
The pratical use of different land use systems(LUS) as a management strategy and the effect of the LUSon soil proprties as an indicator of soil fertility status, and the understanding of the long-term effect of the LUS, are important to maintaining optimal soil fertility and yeild of crops. In the rain-fed wet lowlandtropical soils, studies related to rice production and the associated effectson soil properties are limited to a few studies. In this study, we investigated the effects of four LUS (crop rotation, continuous cropping, manure application and fallow) on soil properties that influence soil fertility status and yield of crops under a rain-fed wet lowland tropical sandy soil conditions.The data were compared with the natural soil data obtained prior to and at the end of the study. All the LUS had no to small effects on bulk density, moisture content, electrical conductivity and pH.Soil organic carbon, total nitrogen, available phosphorus, extractable potassium, and cation exchange capacity were all higher in all the LUS.Crop rotation increased soil organic carbon and cation exchange capacity, fallow increased total nitrogen, and manure application increased available phosphorus and extractable potassium contents, respectively.The LUS had no significant effects on particle composition except that small increases in the silt contentswere observed in the continuous, rotation and fallow systems. In almost all cases, soil organic carbon content influenced the fertility status of the sandy soil and yield of rice. Higher soil organic carbon contentresulted in higher available phosphorous and extarvale potassium,enhence reulted in higher yield of rice but decreased the total nitrogen content.Our results implied that the soil organic carbon content of sandy soils needs to be managed properly for optimal soil fertility and higher yieid.
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Introduction
In agriculture, a good soil in terms of fertility is a soil which is able to deliver to the roots of crops nutrients that are needed for optimum growth and development. A fertile soil required for crop production is an attribute of the biophysical and biochemical composition of the soil [1; 2; 3]. Some of the important physical components of soils are particle size distribution, bulk density, field capacity, and soil color, whereas the chemical components include pH, electrical conductivity, organic matter, cation exchange capacity (CEC), and carbon to nitrogen (C: N) ratio. The third component of the soil system is the biological component, mostly all the living things.
The physical, chemical and biological components of the soil affect several processes important to crop production[4]. For instance, particle size distribution affects infiltration rate and CEC[5], soil pH and redox affect soil nutrient status and availability to crop plants[6; 7; 8].The biological component provides important ecological services in evolution of soil fertility and management of problem soils through decomposition of organic matter [9].In agricultural crop production, it is important properties are managed as their interactions that govern nutrient and availability to crops are affected by on the farm soil use systems [10] and affect farmers who depend on them [11; 12; 13].
The LUS is affected by the economic status of the farming community, the type of crop produced and thelevel of production. Farmers in the developed nations are able to afford farm machineries and farming technologies for intensive crop production. In the poor economies, affordability of farming equipment is a major concern, complicated by lack of investment and technical knowledge to intensify crop production. Regardless of where and how crop is produced, the increase in the human population and too many mouths to feed worldwide means more and more farmland and continuous crop production. In the tropics, continuous farming is solely monocropping of stables; sweet potato (Ipomoea batatas), taro (Colocasia esculenta), cassava (Manihot esculenta) and yam (Discorea sp.) in the tropical and rice (Oryza sativum),maize (Zea mays) and wheat (Triticum assertivum) in the temperate regions are dominating the farms. Continuous farming of sole crops (monocropping) has advantages however loss of soil fertility and the implications on sustainable crop production is a common global issue, calling for a need to manage the soil (physical, chemical and the biological properties) to prevent decline in soil fertility and loss of crop productivity (yield). In PNG, the soils are strongly weathered and poor in soil fertility in some areas, making a few „dominant crops‟(sweet potato, taro, cassava, yam and Irish potato) to be widely grown. Among these staples are the recently introduced cereals – rice, sorghum and maize. Maize is widely cultivated by locals in food gardens, sorghum‟spotentials are yet to be realized and rice production is limited to a few places. In the light of these, rice feeds billions of people worldwide and in PNG is widely consumed in the major towns and cities. The main problems for large-scale production of some of these crops, despite the demand, are poor research for development and non-existence of extension services.
The global literature on soil fertility status, management and rice yield under different cropping systems that are region-specific, e.g. for tropical regions is limited, and where there is information available, cannot be widely adapted because of region-specific variations in climatic and soil conditions[14], local farmers inability to adapt [15] and use them [16]. Therefore, this study was conducted to evaluate the soil fertility status and yield of rice under different LUS in a sandy, mix isohyperthermic, TypicTropo fluvents soil (Soil Survey Staff, 2014) under rain-fed wet lowland tropical conditions.
Conclusion
Crop rotation and addition of DLPM helped improve the poor fertility status of the sandy soil. Consequently, crop rotation and DLPM addition increased yields of rice (both threshed and milled) by a tonne, compared to the yield obtained under continuous cropping and fallow systems. The mechanisms for these appear to be addition of carbon and nutrients (NPK) to the sandy soil and these LUSs‟ potential to increase the CEC facilitated nutrients to be available to the rice plants. High SOC content resulted in low total nitrogen but higher available phosphorus and extractable potassium content. When rice cropping was rotated with peanut as a legume under the same conditions in a similar study, in almost all cases, yield of rice was smaller. These results imply that the main source of soil fertility, hence higher yield of rice on the sandy soil was SOC and not total nitrogen. These findings have implications for management and improvement of sandy soil fertility status to improve the yield of crops under rain-fed wet lowland tropical conditions.