Mechanized farming in the humid tropics with special reference to soil tillage, workability and timeliness of farm operations : a case study for the Zanderij area of Suriname

The reported investigations concern aspects of mechanized farming for the production of rainfed crops on the loamy soils of the Zanderij formation in Suriname and in particular, the effect of tillage on crop yield and soil properties, workability of field operations and timeliness of field operations. The results were evaluated as to their effect on prospects for mechanized farming in this area.The work was carried out within a joint research project of the Agricultural university Wageningen and the University of Suriname.The soil in the area of investigation is characterized by a low fertility and high acidity. Natural drainage is good but the water holding capacity is low. The climate in the area is classified as Af according to Köppen, the average rainfall is 2234 mm per year.Experiments carried out on the Coebiti experimental farm during a 9 year period, covering 22 cropping cycles, showed that with continued application of conventional tillage consisting of disc ploughing and harrowing, average crop yields were higher than with successive applications of shallow or no tillage. The yield differences varied with crop and conditions, the yield obtained under no tillage was on average about 75 percent of the yield under conventional tillage for maize, sorghum and cowpea. For soya bean this was 85 percent and for groundnuts 90 percent. Shallow tillage like rotavating showed intermediate results. Comparable results were obtained at the Kabo experimental farm covering 4 cropping cycles. Chisel and disc ploughing showed here little difference. With the applied mechanized farming system soil compaction occurs which can be alleviated by soil tillage. The distribution of added fertilizer in the soil reflects the tillage treatments applied. Periodic deep tillage such as ploughing is required to incorporate lime to the appropriate depth to allow deep rooting. From a series of 6 cropping cycles at Coebiti it is concluded that the yield of a no tillage treatment when alternated with conventional tillage can be higher than those obtained under successive application of no tillage. This indicates possibilities for the application of incidental no tillage when workable time for planting is limited. It is concluded that in a mechanized cropping system on these soils, the approach to soil tillage should be flexible. Disc or chisel ploughing, as well as shallow or no tillage can be selected appropriate to crop and prevailing circumstances of field, weather and work progress.The limits for workability of disc ploughing and harrowing were determined by measuring the performance of the operations and relating the results to the moisture content of the 0.0-0.20 m soil layer. The maximum soil moisture content for disc ploughing was found to be 13.9 percent wb and for rotary harrowing 13.2 percent wb. It appeared to be too dry for disc ploughing when the moisture content was lower than 10.3 percent wb.The measured soil moisture contents and pertaining meteorological data were used in development of a soil moisture model formulated with physical proces descriptions from literature. Expectations of workable time for field operations in so far as limited by rain and soil moisture content were calculated with the model on the basis of a 25 year record of meteorological data at Zanderij station.Workability of grain harvesting is governed by the grain moisture status. In field experiments the course of the grain moisture content and attached moisture was determined for maize, groundnut, soya bean, cowpea and sorghum.A practical grain moisture model to calculate the grain moisture status in dependence of the weather was formulated and developed with the experimental data and pertaining meteorological data. The hourly course of grain moisture status after maturity was calculated for the 25 year period, allowing calculations of expectations of workable time for harvesting operations with the appropriate limits for grain moisture content.The timeliness function for maize planting was calculated with an available model of physical crop production (WOFOST). Available data from maize growing experiments in the area were used for calculating site specific parameters and evaluation of the model. With this model yield expectations were calculated on the basis of the 25 year meteorological record.Harvest date experiments were carried out to establish timeliness functions for harvesting of maize, groundnut, soya bean and sorghum. It appeared that crop stand and weather influenced these functions. For maize timelineness costs of up to 100 kg per day were observed under wet conditions in the initial delay period. Under dry conditions timeliness costs were insignificant for the periods considered. For a healthy groundnut crop timeliness costs could be presented by a quadratic function of delay time. Postponement of digging results initially in minor yield reductions per day, the losses per day in the windrow are about four times as high. On a diseased crop losses were much higher. For sorghum observed timeliness costs were between 1.0 and 1.9 percent of initial machine yield per day of postponement of harvesting beyond the date of maturity. The timeliness costs for soya bean harvesting were small in the first two weeks after maturity and increased sharply with further delay.The effect of the results of the investigations on the prospects for mechanized farming in the Zanderij area was evaluated with a linear programming model. The evaluation was done for a farm for the cultivation of maize and groundnuts. This farm, equipped with machinery matching a 55 kW tractor, was operated by the farmer on his own except for harvesting operations. Maximization showed that with p-20 values for workable time an area of 35 ha can be cultivated with a cropping index of 1.9. Workable time is limiting farm operations at opportune times and no tillage planting for maize has to be applied for the long rainy season.The timeliness costs of harvesting had only small effect on the cropping plan. With p-50 values for workable time a cropping index of 2.5 is obtained in the maximization, in this situation workable time is not limiting farm operations and the option for no tillage planting of maize is not used.Workable time is a limiting factor for mechanized farming in the Zanderij area and quantified information is essential for planning. The evaluation provides sufficient indications for strategies to follow to make a mechanized farming system practicable.It is concluded that the model type farm is a practicable proposition, provided socio-economic circumstances allow. A high standard of management is required for the proper planning and timing of the field operations.