Analysis and evaluation of tillage on an alfisol in a semi-arid tropical region of India

<p>Tillage field experiments were conducted on Alfisols in a semi-arid tropical environment in India. The research was conducted within the framework of the Farming Systems Research Program of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).</p><p>To put the experiments into perspective, a general review is given in chapter 2 on the environment of the semi-arid tropics, its problems and the research related to agricultural production. Rainfed agriculture has failed to provide a stable and sufficient food supply for the populations of many developing countries. An important reason is the severe physical constraint to agricultural production imposed by the harsh climate. Water is the key factor and though the average total precipitation appears to be sufficient for cropping, its distribution is highly erratic. Much of the rain falls in high intensity storms, resulting in uncontrolled runoff and erosion. Thus a high proportion of the water is lost for crop use.<br/>The majority of as much as 500 million people living in the world's semi-arid tropics, depend on agriculture for income, food and shelter. During the last three decades, populations have doubled in many of the 48 countries which are at least partly located in the semi-arid tropics.<br/>Since the indigenous production systems are characterised by stagnant yield levels, hitherto stable forms of agriculture came under immense pressure by the attempt to continue to provide sufficient amounts of food and fiber for the rapidly growing populations. The farmers were compelled increasingly to expand their agricultural activities to more marginal lands.<br/>Consequently, the production potential of the resource base is threatened seriously and vast areas already have been damaged permanently further destabilizing agricultural production.<br/>To improve a situation of recurrent food shortages, governments tended to concentrate their resources on improving agriculture in water- assured areas. With the advent of high yielding varieties of wheat and rice, this strategy proved succesfull.<br/>In India it was realised that continuing such a policy would further widen the gap with dryland farmers, as it creates 'islands of prosperity in a sea of poverty'. Furthermore, there is a physical limit to the area that potentially can be irrigated. A high proportion of the nation's food requirements would still have to be met by rainfed agriculture. So, unless yield levels and stability are improved in this segment of farming, a few poor monsoons in succession would still lead to serious food problems.<br/>Therefore, research on dryland agriculture was revived, but met with limited and varying results. Either too much emphasis was given to genetical improvement of the seeds, or major attention was given to soil and crop management aspects. The proposed technologies did not fit well into the farmers traditional cropping systems, in which crop yield security is important.<br/>In 1972, ICRISAT started to work on the improvement of dryland crops. From the outset, it was recognized that the lack of a suitable technology for soil and water management and crop production systems, was a primary constraint to agricultural development in rainfed farming. A farming systems research program was developed. A so-called watershed based research program evolved, wit' the underlying filosophy that the only water available to the common farmer comes from rain falling on a limited area. Therefore, small natural watersheds comprising several field-scale units, became the testing ground for promising new technologies.<br/>During the first period, attention was focussed on developing improved soil and water conservation and cropping systems suitable for deep Vertisols.</p><p>In Chapter 3, the role of tillage is described generally , and specifically the zonal-tillage concept.<br/>A 'broad bed and furrow' (BBF)-system, based on the zonal-tillage concept, provided a breakthrough for these soils, in which tillage operations are difficult both under wet and dry conditions. The indigenous practice of rainy season fallowing could be replaced by rainy season cropping, as new technology facilitated dry planting at the onset of the monsoon, while primary tillage could be executed after harvest of the second crop. As a result, the rainfall use efficiency increased tremendously and soil erosion was curbed. The BBF-system was fully operable with the use of a multi-purpose tool carrier drawn by a pair of bullocks.<br/>Unfortunately, the system was less succesfull on Alfisols. These soils are structurally weak, the surface becoming smooth and sealing readily due to the impact of rain. At the beginning of the rainy season, substantial portions of the precious water run off even from yet unsaturated soil profiles. Plant establishment proved difficult and crusting was believed to cause poor, spotty plant stands.<br/>Because the BBF-system features many advantages, it was felt worthwhile not to abandon the system, but to try to improve its performance by adapting the tillage component.</p><p>In Chapter 4, the experimental setup of the tillage field experiments is described.</p><p>In Chapter 5, the effects of primary tillage in terms of soil response and its effects on crop growth are discussed. By varying depth and principle of tillage on the beds, infiltration characteristics were expected to be influenced. Different soil surface conditions, in terms of soil surface roughness and storage provided by the increased pore space in the tilled zone, were thus created. In particular, the newly developed tillage treatment (T1) (Fig. 12), in which the whole width of the beds was tilled at the greatest depth, proved superior in intercepting rainfall. The increased soil roughness was shortlived but the effect on pore space lasted throughout the season. The latter aspect, therefore, seems important with respect to water conservation.<br/>Yield increases were positively related to increasing levels of primary tillage, particularly so when soil moisture was limiting. The T1 tillage method performed best in this respect, thereby contributing in stabilizing yields. The limiting moisture supply was partly due to the growth of weeds. Tillage played a pervasive role in weed control throughout the year. The soil-inverting primary tillage methods facilitated seed bed preparation. Weed regrowth after this type of tillage was delayed compared to the non-inverting methods, thereby providing a temporary advantage. By and large, the effect of primary tillage on the amounts of weeds had disappeared during the plant establishment phase. This is not surprising as all tillage methods were essentially at the minimum tillage level.</p><p>Weed management in the standing crop is essential. Chapter 6 gives a review on the impact of weeds on crop production. It appeared that chemical weed control is not an economically viable option in India for some time to come. Thus, only inter-row cultivation, handweeding and combinations of these were evaluated in the tillage experiments. The potential growth of weeds was tremendous. General weediness levels varied substantially between years and fields, independent from the tillage system. If allowed to grow, the highest measured weediness level at harvest was 6.7 t/ha. Throughout the experiments uncontrolled weeds reduced yields by 10% to 90%. Weed management could greatly reduce weediness levels in the crop. Where inter-row cultivation was practised, inter-row weeds were adequately controlled. However, intra- row weeds developed unchecked and these reduced crop yields considerably, especially in pearl millet. Handweeding proved to be a must for acceptable yields, a supplementary in-the-row weeding after inter-row cultivation being a satisfactory compromise. The effect of weeds on crop yields was partly due to plant population reduction because of competition, but remaining plants also performed less on an individual basis.<br/>The toolbar system allows weeding in tall growing crops for a limited time of 4 to 5 weeks after sowing. When weeds develop after the period in which they affect crop yields, a handweeding may still be desirable; certainly when a sequential crop is considered, but also to prevent the weeds from shedding seeds and to facilitate post-harvest tillage.</p><p>In Chapter 7, plant establishment problems are discussed, as well as various planting method options tested in the field. Poor and uneven stands is one of the major causes of low crop yields in the semi-arid tropics. In Alfisols, crusting was believed an impediment to adequate stands. In the tillage field experiments, plant establishment was given attention but plant establishment was invariably succesfull in all tillage methods. There was no evidence that crusts developed such that crop emergence was hindered. Seed bed compaction by planter press wheels increased crust strength, but apparently it still remained below a harmful] level. In fact, increasing compaction effort increased plant stands and crop yields significantly in a number of cases. An explanation could not be given in terms of improved water supply to germinating seeds and developing seedlings.<br/>But it appears that two aspects of the seed bed are extremely important. Firstly, the presence of weeds affect the proper functioning of the planter furrow opener, making seed placement less consistent. When a dry plant establishment period follows, even small amounts of weeds proved to reduce stands considerably. Secondly, the uniformness of the seedbed is important.<br/>Evaluation of the consistency of seed placement depth following the various tillage methods revealed a high degree of control. Seed depth was normally distributed with standard deviations of less then 1 cm. The importance of placing the seeds exactly was demonstrated in that seedlings from deeper placed seeds were retarded, even within the narrow depth range achieved. As a consequence, in the field inter-row cultivation must be delayed or part of the smaller seedlings must be sacrificed. Also, competition between crop seedlings may prevent the laggards to become productive.<br/>The simulation of the effect of seed placement on emergence showed that the seed bed quality and planting depth have a profound effect not only on total emergence percentage, but also on the uniformity of seedling development.</p><p>In conclusion, the performance of the BBF-system of cultivation in Alfisols can be improved by increasing soil surface roughness and plow layer storage. A new technique of primary tillage, the T1 tillage method, proved best in this respect. In addition, the method features operational advantages as bigger amounts of crop residue and weeds can be handled without clogging the implements. Seed bed preparation is of crucial importance, particularly freedom from weeds and depth uniformity. Compaction of seed beds by planter press wheels contributes positively to plant stands and crop yields. Crusts did not hinder crop emergence at all.<br/>Because none of the evaluated primary tillage methods exceeded the minimum tillage level, weeds developed vigorously soon after planting. For such conditions inter-row cultivation alone proved insufficient to keep weeds in the crop at acceptable levels. Then, supplemental handweeding was absolutely essential for good crop yields.</p>