Australian Society of Soil Science Inc. {WA Branch) and the Environmental Consultants Association {WA) Inc. Proceedings of Conference Soils 2000 Making our Science More Useable Sponsored by CSBP future farm Muresk Institute of Agriculture Northam, Western Australia 11-13 July 2000 Compiled by C. Tang and D.R. Williamson ------ ----
Australian Society of Soil Science Incorporated (WA Branch) Dr. Mike Wong CSIRO Land and Water Private Bag 5 PO WEMBLEY WA 6913 Environmental Consultants Association (WA) Inc. Ms Michele Northover Post Box 971 WEST PERTH. WA 6872 National Library of Australia Cataloguing-in-Publications Data Western Australian Soil Science Conference (Sttt:, 2000: Northam, WA) Soils 2000: making our science more useable: proceedings of conference Muresk Institute of Agriculture, Northam, Western Australia, 11-13 July 2000. Bibliography. Includes index. ISBN 0 9586595 5 9 1. Soil Science - Western Australia - Congresses. 2. Soil Protection - Western Australia - Congresses. I. Tang, Caixian. II. Williamson, D.R., 1939-. Ill. Australian Society of Soil Science Incorporated (WA Branch) IV. Environmental Consultants Association (W.A.) Incorporated. 631.49941 Published: July 2000 Australian Society of Soil Science Incorporated (WA Branch) Previous Conferences in this Series 1988: Management of Western Australian Soils, Merredin, August 5-6, 1988 1991: Soil Science and the Environment, Albany, September 19-21, 1991. 1994: Soils '94, Busselton, September 7-9, 1994. 1997: Soils '97, Advances in Soil Science for Sustainable Land Use, Geraldton 30 September- 2 October, 1997
Residual effect of phosphorus fertilizer for rice in rainfed lowland soils of cambodia S. PheavA,B' P.F. Whites,c, R. W. Bell A and G.J.D. Kirk 0 A School ofenvironmental Science, Murdoch University, Perth, W.A 6150, Australia. B Department of Agronomy and Cambodia-IRRI-Australia Project, P.O. Box 01, Phnom Penh, Cambodia. cpresent address: Agriculture Western Australia, Baron-Hay Court, S Perth 6151, Australia. 0 Soil and Water Science Division, International Rice Research Institute, Los Banos, Philippines. Abstract Phosphorus (P) deficiency is widespread in Cambodian rice growing soils, and strong responses are generally obtained from P fertilizer application. Since P fertilizer use is expected to increase in Cambodian rice crops, the present study was conducted to examine the residual value of P fertilizer applied to rice. Phosphorus fertilizer at a rate of 16.5 kg P ha- 1 was applied to a wet season rainfed rice crop on a sandy lowland soil (Plinthustalf) in 1997, and the response of rice to this P was quantified in four successive rice crops by reference to yield obtained from a fresh application of 16.5 kg P ha- 1 in each succeeding crop. In crop one, P increased rice yield from 1.5 to 2.8 t. ha- 1, whereas in the crop two, grown with irrigation in the following dry season, the residual P and the freshly applied P, increased grain yield by 62 and 85 %, respectively. In crop three, the residual P from crop one barely increased growth, producing a yield of about 2.0 tlha, whereas the residual P from crop two increased growth by 60%, and freshly applied P increased growth of 70%. In the fourth crop, grain yield responded only weakly or not at all to the residual P from that applied to crop one. These results suggest that P needs to be reapplied every two crops on sandy lowland soils of Cambodia provided grain yields similar to those obtained in the present study are maintained. The mechanisms underlying the decline in residual value of P, including P removal in harvested crop products and long-term reactions of P with soils under alternating waterlogged and dry conditions warrant further investigation. These data will be incorporated into a model of P cycling in the lowland rainfed rice ecosystems of Cambodia. Introduction Phosphorus (P) deficiency is widespread in Cambodian rice growing soils, and strong responses are generally obtained from P fertilizer application (White and Seng 1997). Recommendations have been formulated for the rates of P to be applied on different soil groups of Cambodia, and P fertilizer use is expected to increase in Cambodian rice crops. Increased use of P fertiliser will raise questions about the cycling of P in the rainfed lowland rice ecosystems, and in particular residual value ofp fertilizer applied to rice.
Strong responses to P fertilizer have been obtained on a range of Cambodia rice soil, but because many of the soils are sandy and acid (White et al. 1997a,b), it is thought that P fertilizer has little residual, cumulative value. Understanding the residual effects of P fertilizer is critical for managing P on Cambodian rice soils. The objective of the experiment was to examine the residual effects of P fertilizer applied to rice over four consecutive cropping cycles. Methodology The experiment was conducted at the Cambodian Agricultural Research and Development Institute (CARDI) near Phnom Penh. Rice c.v. IR66 was planted on a sandy lowland soil (Plinthustalf) in the wet season, 1997. The response of rice to freshly applied and to residual P was quantified in four successive rice crops (2 wet and 2 dry seasons). Selected chemical properties ofprateah Lang soil (White eta!. 1997a,b) were as follows: ph (1 :1 H 2 0) 5.6 ±0.7; organic carbon 4.0 ±0.2 g/kg; total N 0.4 ±0.2 g/kg; Olsen P 0.4 ±0.5 mg/kg; clay 94 ±47 g/kg; sand 554 ±64 g/kg, and CEC 2.6 ±3.3 cmol(+)/kg. Phosphorus fertilizer, at a rate of 16.5 kg P ha- 1, was first applied basally to a wet season rainfed rice crop on a sandy lowland soil in 1997, and the response of rice to this P was quantified in four successive rice cro~s by reference to yield obtained from a plot receiving a fresh application of 16.5 kg P ha- in each crop (Table 1 ). The residual value of the subsequent applications of P was also determined. Other nutrients; N as urea, K as muriate of potash (KCl) and S as gypsum (CaS0 4.2H 2 0) were applied to all plots for each crop, at the rates of 90 N kg/ha, 30 K kg/ha and 15 S kg/ha to ensure that these nutrients did not limit plant growth. Treatment one (Table 1) received only 30 kg N, 10 kg K and 5 kg S/ha since the yield of this plot was consistently (Table 2). Table 1: The schedule and rates (kg P ha- 1 ) ofp al!j.:!lication in treatments. Treatments Crop 1 Crop2 Crop3 Crop4 {wet season} {dry season} {wet season} {dry season} Nil 0 0 0 0 All crops 16.5 16.5 16.5 16.5 First crop 16.5* R-1 R-2 R-3 Second crop 0 16.5* R-1 R-2 Third crop 0 0 16.5* R-1 Fourth crop 0 0 0 16.5* *:Residual value of previously applied P was measured in each crop by reference to the yield obtained with the freshly applied P. R -1: indicates the second crop after P applied, i.e. the first crop using residual P and so on for R-2 & R-3. A level field, which had no recent history of P fertilizer application, was selected for the trial. Plots were ploughed and harrowed before transplanting. Individual plot size was 5 m x 5 m. The variety sown, IR66, was a modern, photoperiod insensitive variety, recommended for its high yield potential and tolerance to a large range of pests, diseases and low P status soils. It {~5-
is suitable for both rainfed and irrigated dry season cultivation in Cambodia. It has a duration of 110 to 115 days and should be grown in less than 30-cm depth of water. The local practice of rice nursery establishment was adopted. The seedlings were sown at a rate of 100 kg.ha- 1 The seeds were pre-germinated by soaking in a wet sack for 24 to 48 hours prior to broadcasting on the nursery. When the seedlings were 25 days old, healthy seedlings with similar appearance were selected for transplanting with 2 to 3 plants per hill at a spacing between hills of 20 em x 20 em. Missing hills were replaced 5 to 7 days after planting. Weeds were hand-pulled as practiced by farmers to minimize the impact on the plant growth. Pest and diseases were controlled by cultural methods or pesticide application as appropriate. At the maturity, the central 9m 2 portion of every plot was harvested to measure grain weights. The grain was then oven-dried at 70 C for 48 hours to determine dry weight. Results In crop one, P increased rice yield from 1.5 to 2.8 t. ha" 1 (Table 2), whereas in the crop two, grown with irrigation in the following dry season, the residual P and the freshly applied P, increased grain yield by 62 % and 85 %, respectively. In crop three, the residual P from crop one barely increased growth, producing a yield of about 2.0 t. ha- 1, whereas the residual P from crop two increased growth by 60 %, and freshly applied P increased growth by 70 %. In the fourth crop, grain yield responded only weakly or not at all to the residual P from that applied to crop one. Discussion Phosphorus fertilizer nearly doubled rice grain yield in the crop to which it was applied in both the wet and dry season crops. These results support those of White and Seng (1997) who reported that rice responds strongly to P fertiliser on the Prateah Lang soil. Prateah Lang soil occupies about 25-30% of the total lowland rice growing areas of Cambodia (White et al. 1997b ), so P responses of this magnitude are to be expected over large areas of Cambodia, provided similar rates of P as used here were applied, and other basal fertilisers especially N, K and S are applied at adequate rates. Phosphorus in the present study was applied at 16.5 kg P/ha, which is above the rate recommended for Prateah Lang soils (10-13 kg Plha: White et al. 1998b). Increased yields can be obtained with higher rates up to 20 kg/ha (White et al. 1999), although the repeated application of 16.5 kg Plha did not increase grain yield above that achieved with a single application of 16.5 kg Plha (Fig. 1). However, repeated applications of the recommended rate is not advisable since the P clearly has significant residual value, and higher rates are not likely to be adopted by resource-poor Cambodian rice farmers. The recommended rate is for soils that have not been previously fertilised. The key question of the present study was to determine the residual value of the applied fertiliser P and to determine how long this application would remain effective in correcting P deficiency. The related question was to determine how frequently P fertiliser should be applied in order to maintain adequate rice yields. The applied P is effective for two successive crops; it was only partially effective in the third crop which produced grain yields of about 75 % of maximum, and ineffective in crop four which yielded that same amount of grain as crops receiving no added P. These results suggest that P needs to be reapplied every two crops on sandy lowland
i Table 2: The response of rice grain yields to phosphorus fertilizer application on a lowland sandy soil in Cambodia over four successive cropping cycles (2 wet and 2 dry seasons). Values are means of four replicates. Treatments Crop 1 Crop 2 (wet season) (dry season) Nil 1.86 1.70 All crops 3.00 2.41 First crop 2.89 2.22 Second crop 1.53 2.37 Third crop 1.55 1.28 Fourth crop 1.66 1.25 LSD (5%) 0.28 0.30 Crop 3 (wet season) 1.52 3.00 2.01 2.74 3.00 1.40 0.29 Crop4 (dry season) 0.33 LSD (5%): least significant different at five percents; See table 1 for a detailed explanation of the treatments. 0.77 2.08 0.88 1.55 2.21 2.26... ns.c...; -"C Ci) > r:: ~ (!) 3.0 ILSD tm Nil An crops Fresh-P DR-1 R-2 IElR-3 Nil All crops Fresh..P R-1 R-2 R-3 Residual P response Figure 1: Rice yields response to freshly applied and to residual phosphorus fertilizer. See Table 1 for a description of P treatments used to obtain the above mean yields. IS'7
Prateah Lang soils of Cambodia provided grain yields similar to those obtained in the present study are maintained. The mechanisms underlying the decline in residual value of P, including P removal in harvested crop products, and long-term reactions of P with soils under alternating waterlogged and dry conditions warrant further investigation. In addition the dynamics of the cycling of the residual P, especially between wet and dry seasons needs to be examined. Comparative studies of P residual value in other Cambodian rice soils will also be needed so that this data can be incorporated into a general model of P cycling in the lowland rainfed rice ecosystems of Cambodia. References White, P.F. and Seng, V. 1997. Responses of rainfed lowland rice to phosphorus fertiliser application in Cambodia. p. 202-208. In: Breeding Strategies for Rainfed Lowland Rice in Drought-ProneEnvironments. ACIAR Proceeding no. 77, Australian Centre for InternationalAgricultural Research, Canberra, Australia. White P F, Oberthur T and Pheav S. 1997a Soil and rice. In Rice Production in Cambodia. Ed. H J Nesbitt. International Rice Research Institute. pp 21-29. Los Banos, Philippines. White P F, Oberthur T and Pheav S. 1997b The Soil Used for Rice Production in Cambodia: A manual for their identification and management. International Rice Research Institute. Los Banos, Philippines. 70 p. White P F, Nesbitt, H. J., Ros, C., Seng, V. and Lor, B. 1999. Local rock phosphate deposits are a good source of phosphorus fertilizer for rice production in Cambodia. Soil Sci. Plant Nutr. 45: 51-63.