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Soil Management for Alfisols in the Semiarid Tropics: Erosion

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Soil Management for Alfisols in the Semiarid Tropics: Erosion 10 Erosion management of Al®sols Soil Use and Management (2002) 18, 10±17 DOI: 10.1079/SUM200194 Soil management for Al®sols in the semiarid tropics: erosion, enrichment ratios and runoff A.L. Cogle2*, K.P.C. Rao1, D.F. Yule2, G.D Smith2, P.J. George1, S.T. Srinivasan1 & L. Jangawad1 Abstract. Continuous cultivation of soils of the semiarid tropics has led to signi®cant land degradation. Soil erosion and nutrient loss caused by high runoff volumes have reduced crop yields and contributed to offsite damage. We compared a number of soil management practices (tillage, mulch and perennial/annual rotational based systems) for their potential to improve crop production and land resource protection in an Al®sol of the semiarid tropics of India. Runoff and soil erosion were monitored and surface soil and sedi- ment were analysed for nitrogen and carbon to determine enrichment ratios. Amelioration of soils with organic additions (farmyard manure, rice straw) or rotating perennial pasture with annual crops increased soil carbon and nitrogen contents and reduced runoff, soil erosion and nutrient loss. Soil erosion totalled less than 7 t ha±1, but enrichment ratios were often greater than 2 resulting in up to 27 kg N ha±1 and 178 kg C ha±1 being lost in sediment. Up to an extra 250 mm of water per year in®ltrated the soil with organic additions and was available for crop water use or percolation to groundwater. The results show that there are good opportunities for reducing degradation and increasing productivity on farms. Keywords: Erosion, runoff, nutrient loss, soil management, Al®sols, semiarid zones, tropics, India INTRODUCTION degradation (Hashim et al. 1998). Enrichment ratios are the common descriptor of such a process and are de®ned as the and degradation affects 166 million ha in the semiarid Ltropics (SAT) of India, with soil erosion by water ratio of nutrient concentration in eroded sediment to that in being the single most important mechanism (Sehgal & Abrol the original soil (Pallis et al. 1990). 1992). A large proportion (33%) of the soils in the SAT are Soil management practices, need to be identi®ed and Al®sols (Kampen & Burford 1980), and they are important implemented that reduce runoff, erosion and nutrient loss, for agricultural production for large numbers of people but which also increase productivity. A range of potential worldwide. Al®sols are subject to low productivity and soil systems exists and can be categorized as tillage and degradation (El-Swaify et al. 1985), and have several biologically based systems. Tillage increases in®ltration by characteristics, which make management dif®cult. These increasing porosity, destroying surface crusts and manip- include low water holding capacity, poor surface soil ulating surface roughness. However, tillage can also degrade stability and high soil strength when dry. Continuous soils. Biologically based options include mulch and pasture cultivation, based on multiple tillage operations over many systems to increase in®ltration (Rao et al. 1992). Mulches are years, has reduced organic matter levels and exacerbated used to protect the soil surface from raindrop impact and these problems causing increased runoff and erosion. subsequent crust formation and to reduce the rate of organic Soil erosion is dependent on the ¯ow of overland water matter decline. In addition to mulching bene®ts, a pasture (or runoff) and its sediment concentration (Hairsine et al. phase also creates root channels and increases organic matter 1992). Reducing soil erosion requires lower runoff volumes throughout the pro®le (Smith et al. 1988). A legume pasture and less opportunity for the soil to become entrained. may contribute soil nitrogen. Smith et al. (1992) outlined an Another concern is that since the ®ne fraction, containing experiment to compare a range of tillage and biological nutrients, is often preferentially eroded, a disproportionate systems; improvements in productivity via additions of loss of the soil nutrients can occur, leading to even greater farmyard manure and plant residues, or pasture/crop rotations were reported (Cogle et al. 1997). The impact of 1ICRISAT, PO Patancheru, 502324, AP, India. 2Present Address: these soil management choices on erosion, nitrogen and Department of Natural Resources and Mines, Peters St, Mareeba. 4880 carbon losses and runoff is discussed in this paper, and Queensland, Australia. *Corresponding author: Fax: 0061±7±40923593. E-mail: [email protected]. recommendations for improving the sustainability of SAT gov.au farms are made. A.L. Cogle et al. 11 MATERIALS AND METHODS maize (Zea mays L.) (Proagro 3448), (1991, 1992) and sorghum (CSH9), (1993). Smith et al. (1992) discussed the Experimental site millet crop, while Cogle et al. (1997) discussed crops The project was established in July 1988 at the International between 1989 and 1993. Crops Research Institute for the Semi Arid Tropics Tillage for T (ICRISAT), Patancheru (18oN, 78oE), 26 km north west of 10 and T20 treatments occurred after the ®rst Hyderabad, Andhra Pradesh, India. Details of the experi- major rain in June and was performed with a tractor- mental site and the 1988 crop season were given by Smith et mounted toolbar using chisel tines. The initial tillage al. (1992). operation was to 10 cm in both treatments, while a second The soil belongs to the Patancheru series, a member of tillage to 10 cm and 20 cm was performed for T10 and T20 the family of Udic Rhodustalfs (Murthy & Swindale 1993), treatments respectively. There were a total of two passes in locally regarded as a crusting, hardsetting soil. The surface tilled plots. In each year, planting was performed as soon as texture is a sandy loam merging to a sandy clay loam or light possible after tillage, but in 1989 and 1990 a delay of several clay at 10±15 cm and then to gravelly sandy loam overlying weeks occurred because of unfavorable weather conditions. murrum (a layer of decomposing parent material); the depth Seeds were sown by hand in a furrow at double the desired of the murrum varies between 30 to 100 cm. ICRISAT has plant population and furrows were ®rmed to promote soil- an average rainfall of 784 mm, with over 80% falling seed contact. Approximately 20 days after planting, seed- between the months of June and October. Average monthly lings were thinned to give the desired population. air temperature in the rainy season range from 25 to 29 0C. Fertilizer was placed in the seed furrow and mixed with soil prior to planting. Nitrogen (N) applications were made Experimental design 2±3 times during the crop season. Fertilizer (diammonium The experimental design was an incomplete randomized phosphate and urea) at a rate of 100 kg N ha±1 and block with an embedded factorial for the tillage by 46 kg P ha±1 was applied over most of the plot and designated amendment comparisons. Each plot was 28 m long (down as the normal fertilizer level. slope) and 5 m wide with a land slope between 1.5±2.0%. After planting, farmyard-manure (15 t ha±1) was applied There were three replications. Fifteen treatments were ±1 to Fm plots and rice straw (5 t ha ) was applied to Rm plots. imposed in the experiment. These were made up of: Both mulches were applied to the surface and not (1) A tillage by amendment factorial for annual crops, incorporated. In 1992 and 1993, rice straw was applied to comprised nine treatments and compared three different all prior-perennial plots, except PCSt. The rationale for tillage depths at 0 cm (T0), 10 cm (T10) and 20 cm (T20) straw application to prior perennials was to prevent the ±1 and three mulches, no mulch (Nm), 15 t ha farmyard- ±1 development of a surface seal/crust and therefore allow a manure (Fm), and 5 t ha rice straw (Rm), which were comparison of the effect of subsurface structural changes. applied annually. The PCSt treatment did not receive straw so as to be able to (2) Perennial species, which were rotated to annual crops measure the effect of a pasture/crop rotation in a non- after four years comprised six treatments : sole perennial mulched situation. The farmyard manure used contained pigeon pea (P) (Cajanus cajan L), sole buffel grass (C) 157 kg N ha±1, 81 kg P ha±1 and 127 kg K ha±1, and the rice (Cenchrus ciliaris L)., sole Verano (St) (Stylosanthes straw contained 35 kg N ha±1, 7 kg P ha±1 and 86 kg K ha±1 hamata L.), and mixtures of these species i.e.. PSt Agronomic management and data collection has pre- (perennial pigeon pea and Stylosanthes hamata), PCSt viously been presented Cogle et al. (1997). (perennial pigeon pea, Cenchrus ciliaris and Stylosanthes hamata) and CSt (Cenchrus ciliaris and Stylosanthes Rainfall and runoff measurement hamata). The perennial species were harvested each Rainfall rate was measured at one minute intervals in a year. Agronomic details and harvest information are tipping bucket pluviometer (0.2 mm tip±1) and recorded on a provided by Cogle et al. (1997). data logger. Runoff from each plot was channeled through a Between 1988 and 1991 the tillage and mulch treatments sediment settling trough (25 cm deep by 22 cm wide), and were cropped annually to cereal crops. In 1992, perennial the ¯ow rate measured by a calibrated tipping bucket crops were removed and in 1992 and 1993 all treatments (approx. 0.05 mm of runoff tip±1) and recorded on the same including those previously under perennial crops were data logger at one minute intervals. Smith & Thomas (1988) planted to a cereal crop to compare the cumulative effects of provide further details. different soil management histories. For discussion of the 1992 and 1993 results, the perennial treatments are referred Annual, preplanting and crop periods to as `prior-perennial' treatments when compared with the To assist data interpretation, the results are presented in treatments that have been cropped to annual crops before 1992, but retain the same abbreviation.
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