The DSSAT cropping system model
The decision support system for agrotechnology transfer (DSSAT) has been in use for the last 15 years by researchers worldwide. This package incorporates models of 16 different crops with software that facilitates the evaluation and application of the crop models for different purposes. Over the last few years, it has become increasingly difficult to maintain the DSSAT crop models, partly due to fact that there were different sets of computer code for different crops with little attention to software design at the level of crop models themselves. Thus, the DSSAT crop models have been re-designed and programmed to facilitate more efficient incorporation of new scientific advances, applications, documentation and maintenance. The basis for the new DSSAT cropping system model (CSM) design is a modular structure in which components separate along scientific discipline lines and are structured to allow easy replacement or addition of modules. It has one Soil module, a Crop Template module which can simulate different crops by defining species input files, an interface to add individual crop models if they have the same design and interface, a Weather module, and a module for dealing with competition for light and water among the soil, plants, and atmosphere. It is also designed for incorporation into various application packages, ranging from those that help researchers adapt and test the CSM to those that operate the DSSAT–CSM to simulate production over time and space for different purposes. In this paper, we describe this new DSSAT–CSM design as well as approaches used to model the primary scientific components (soil, crop, weather, and management). In addition, the paper describes data requirements and methods used for model evaluation. We provide an overview of the hundreds of published studies in which the DSSAT crop models have been used for various applications. The benefits of the new, re-designed DSSAT–CSM will provide considerable opportunities to its developers and others in the scientific community for greater cooperation in interdisciplinary research and in the application of knowledge to solve problems at field, farm, and higher levels.
Resource use at the cropping system level
This paper illustrates the basic ideas of good crop rotations, adequate crop husbandry and high resource-use efficiencies and some relevant ecological approaches. The use of special crops to prevent the need of high inputs of crop protectants or to reduce losses of nutrients at the level of the cropping system deserves special attention in research. Examples are given for the ecological control of soil-borne fungi, parasitic weeds, nitrogen loss and other sustainable techniques to increase the resource-use efficiency at the cropping system level. 
Tillage, Nitrogen, and Cropping System Effects on Soil Carbon Sequestration
Soil C sequestration can improve soil quality and reduce agriculture’s contribution to CO₂ emissions. The long-term (12 yr) effects of tillage system and N fertilization on crop residue production and soil organic C (SOC) sequestration in two dryland cropping systems in North Dakota on a loam soil were evaluated. An annual cropping (AC) rotation [spring wheat (SW) (Triticum aestivum L.)–winter wheat (WW)–sunflower (SF) (Helianthus annuus L.)] and a spring wheat-fallow (SW-F) rotation were studied. Tillage systems included conventional-till (CT), minimum-till (MT), and no-till (NT). Nitrogen rates were 34, 67, and 101 kg N ha⁻¹ for the AC system and 0, 22, and 45 kg N ha⁻¹ for the SW-F system. Total crop residue returned to the soil was greater with AC than with SW-F. As tillage intensity decreased, SOC sequestration increased (NT > MT > CT) in the AC system but not in the SW-F system. Fertilizer N increased crop residue quantity returned to the soil, but generally did not increase SOC sequestration in either cropping system. Soil bulk density decreased with increasing tillage intensity in both systems. The results suggest that continued use of a crop-fallow farming system, even with NT, may result in loss of SOC. With NT, an estimated 233 kg C ha⁻¹ was sequestered each year in AC system, compared with 25 kg C ha⁻¹ with MT and a loss of 141 kg C ha⁻¹ with CT. Conversion from crop-fallow to more intensive cropping systems utilizing NT will be needed to have a positive impact on reducing CO₂ loss from croplands in the northern Great Plains.
Effects of Time of Weed Removal and Cropping system on Weed Control and Crop Performance in Okra/Amaranthus Intercrop
A field trial was conducted during the late wet seasons of 2011 and 2012 at the Research Farm of the Federal University of Agriculture, Alabata, Abeokuta (7015’N, 3025’E) in the forest savanna- transition zone of Ogun State, South Western Nigeria. The objective was to evaluate the effect of time of weed removal and cropping system on weed control and crop performance in okra/amaranthus intercrop. The experiment was laid out in a Randomized Complete Block Design (RCBD) in a Split- plot arrangement. The treatments consisted of three main plots and five sub plots replicated three times. The main plot treatments were single hoe- weeding at 3 weeks after planting (WAP), double weeding at 3 & 6 WAP and no weeding, while the sub plots consisted of okra intercropped with amaranthus at 0.5g/m2or 1.0g/m2, okra sole and amaranthus sole at 0.5g/m2 or 1.0g/m2. Results from the study showed that intercropping of okra with amaranthus reduced weed infestation significantly (p<0.05) compared to sole okra. Weed control treatments significantly (p<0.05) reduced weed infestation in the intercrop while cropping system did not have any significant effect (p<0.05) on the weed biomass, plant height, pod length, number of pods and pod fresh weight. Uncontrolled weed infestation led to 50.7% yield loss in okra. It is therefore concluded that intercropping of okra with amaranthus is an effective means of reducing weed pressure in okra production as well as increasing land productivity. 
Influence of Tillage Practice and Cropping System on Growth Attributes and Grain Yield of Maize [Zea mays L.] in the Forest Agro-ecological Zone of Ghana
Tillage is one of the most important practices in agricultural production due to its influence on the physical, chemical, and biological properties of the soil environment. Field experiments were conducted to find out the effects of tillage practice and cropping system on the growth attributes and grain yield of maize within the Forest agro-ecological zone of Ghana from 2011 to 2014. The experimental design was a randomized complete block, arranged in a split plot with four replications. Minimum tillage [MT] and Full tillage [FT] were the main treatments. Maize intercropped with mucuna [Maize/M]; maize intercropped with pigeon pea [Maize/Pp]; maize intercropped with cowpea [Maize/C]; sole maize with recommended rate of mineral fertilizer [Maize/F] and sole maize with minimum mineral fertilizer application [Maize] were the subplot treatments. In the first year all the treatments received 30-20-20 kg N-P2O5-K2Oha-1 [F1] except Maize/F which received 60-40-40 kg N-P2O5-K2Oha-1 [F2]. Interaction between tillage and cropping system showed a similar pattern of plant growth during the first and second years. However, grain yield for the second year was at least 50% less than the first year even though plant growth and grain yield were similar for most of the interactions. In the third year grain yield, Maize/Pp + F1 [3.34 t/ha] under MT produced significantly higher grain yield than most other treatment combinations except Maize/M + F1 [3.12 tha-1] and Maize/Pp + F1 [3.31 tha-1] both under FT. In the fourth year grain yield for Maize/Pp + F1 [3.41 tha-1] under MT and Maize/Pp + F1 [3.45 tha-1] under FT were similar but significantly higher than all the other treatment combinations. All other combinations recorded grain yields below 2.50 tha-1. From this study, Maize intercropped with Pigeon pea showed the highest potential under both minimum and full tillage practices. For increased and sustainable maize production within the forest agro-ecology in Ghana, this system is therefore recommended for maize farmers, particularly the poorly resourced farmers. 
 Jones, J.W., Hoogenboom, G., Porter, C.H., Boote, K.J., Batchelor, W.D., Hunt, L.A., Wilkens, P.W., Singh, U., Gijsman, A.J. and Ritchie, J.T., 2003. The DSSAT cropping system model. European journal of agronomy, 18(3-4), pp.235-265.
 Struik, P.C. and Bonciarelli, F., 1997. Resource use at the cropping system level. In Developments in Crop Science (Vol. 25, pp. 179-189). Elsevier.
 Halvorson, A.D., Wienhold, B.J. and Black, A.L., 2002. Tillage, nitrogen, and cropping system effects on soil carbon sequestration.
 Adeyemi, O.R., Fabunmi, T.O., Adedeji, V.O. and Adigun, J.A., 2014. Effects of time of weed removal and cropping system on weed control and crop performance in okra/Amaranthus intercrop. Journal of Experimental Agriculture International, pp.1697-1707.
 Issaka, R.N., Buri, M.M., Dugan, E., Omae, H. and Nagumo, F., 2016. Influence of Tillage Practice and Cropping System on Growth Attributes and Grain Yield of Maize [Zea mays L.] in the Forest Agro-ecological Zone of Ghana. International Journal of Plant & Soil Science, pp.1-9.
The DSSAT cropping system model