Data from sowing-date and other experiments conducted for nine cultivars at three locations ranging from 1830 H S to 27815 H N were analysed for photoperiod response. All cultivars were found to have a qualitative response to photoperiod. The results of the analysis show that cultivars previously reported to be``relatively insensitive'' to photoperiod were, in fact, highly sensitive. Flowering in short-duration cultivars was delayed by up to a 100 days when daylength in the photoperiod-inductive phase exceeded a critical value. Medium-and long-duration cultivars delayed¯owering by over 150 days in response to photoperiod. A model was able to predict this wide range in¯owering dates.
SU MMARYWhen exposed to hot (22-35 xC) and dry climatic conditions in the field during the final 4-6 weeks of pod filling, peanuts (Arachis hypogaea L.) can accumulate highly carcinogenic and immunosuppressing aflatoxins. Forecasting of the risk posed by these conditions can assist in minimizing preharvest contamination. A model was therefore developed as part of the Agricultural Production Systems Simulator (APSIM) peanut module, which calculated an aflatoxin risk index (ARI) using four temperature response functions when fractional available soil water was <0 . 20 and the crop was in the last 0 . 40 of the pod-filling phase. ARI explained 0 . 95 (Pf0 . 05) of the variation in aflatoxin contamination, which varied from 0 to c. 800 mg/kg in 17 large-scale sowings in tropical and four sowings in sub-tropical environments carried out in Australia between 13 November and 16 December 2007. ARI also explained 0 . 96 (Pf0 . 01) of the variation in the proportion of aflatoxincontaminated loads (>15 mg/kg) of peanuts in the Kingaroy region of Australia during the period between the 1998/99 and 2007/08 seasons. Simulation of ARI using historical climatic data from 1890 to 2007 indicated a three-fold increase in its value since 1980 compared to the entire previous period. The increase was associated with increases in ambient temperature and decreases in rainfall. To facilitate routine monitoring of aflatoxin risk by growers in near real time, a web interface of the model was also developed. The ARI predicted using this interface for eight growers correlated significantly with the level of contamination in crops (r=0 . 95, Pf0 . 01). These results suggest that ARI simulated by the model is a reliable indicator of aflatoxin contamination that can be used in aflatoxin research as well as a decision-support tool to monitor pre-harvest aflatoxin risk in peanuts.
Continuous adoption of rice-wheat cropping system (RWCS) has led to depletion of inherent soil fertility resulting in a serious threat to its sustainability in the Indo-Gangetic plain region (IGPR) of India. The inclusion of legumes in RWCS assumes a great significance to restore soil fertility. But farmers in the IGPR rarely grow legumes in the system. We, therefore, carried out farmers' participatory diagnostic survey in the Upper Gangetic plain zone (UGP) to understand farmers' fertilizer management practices for wheat (Trititicum aestivum L. Emend Fiori & Paol) following rice (Oryza sativa L.) or pigeonpea (Cajanus cajan(L.)Millsp). The survey indicated that most of the farmers in UGP grew pigeonpea in place of rice under RWCS as only a break crop at a 2-3 year interval. The farmers applied, on average, 11 kg N ha À1 and 24 kg P ha À1 to wheat sown after rice, and 12 kg N ha À1 and 19 kg P ha À1 to wheat sown after pigeonpea. Wheat yields, however, were lower (3.3 t ha À1) when sown after pigeonpea than after rice (3.7 t ha À1). The survey was followed by a field experiment at Modipuram (298 4 0 N), Meerut, India that continued during the three consecutive years (1998-1999 to 2000-2001) to examine the effect of inclusion of pigeonpea in place of rice on soil fertility, N and P use efficiency and yields of wheat. In 1998-1999, wheat yields after pigeonpea were lower than after rice, but improved significantly (p < 0.05) by 11.4-15.1% in pigeonpea plots compared with those in rice plots during 1999-2000 and 2000-2001, respectively. The use efficiency of applied N and P fertilizers in wheat, measured as agronomic efficiency and apparent recovery, was increased with combined use of fertilizer N and P at recommended rate, and also with inclusion of pigeonpea in place of rice. The post-wheat harvest NO 3-N in soil profile beyond 45 cm depth was significantly greater under rice-wheat system than under pigeonpea-wheat system, suggesting that inclusion of pigeonpea may help in minimizing NO 3-N leaching to deeper profile layers beyond root zone. Similarly, in the treatments receiving both 120 kg N and 26 kg P ha À1 , NO 3-N beyond 45 cm soil depth was lower compared to those receiving N or P alone. Inclusion of pigeonpea in place of rice enhanced carbon accumulation in the soil profile. The available P content was, however, invariably low under pigeonpea plots as compared to that under rice. With continuous rice-wheat cropping, the bulk density (BD) of soil was www.elsevier.com/locate/fcr Field Crops Research 92 (2005) 85-105
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