ABSTRACT
Four levels of N (0, 40, 80, 120 kg ha-1) and P (0, 30, 60, 120 kg ha-1) in all possible combinations as urea and single super phosphate were applied to wheat crop sown after millet, millet green manuring and fallow at two sites in the rainfed areas of Pakistan. The grain yield increased significantly with combined application of N and P fertilizers. A marked interaction of fertilizer N and P on grain yield was observed after fallow and millet. Wheat grain and straw yield responded positively to fertilizers N and P, however all the variations observed in wheat yield are not correlated with extractable values of N and P. The polynomial correlation coefficient between NaHCO3-extractable soil P values and grain yield was fairly high. Out of four experiments response surface model predicting crop yield proved good at two sites only.
PDF Abstract XML References Citation
How to cite this article
DOI: 10.3923/ajps.2002.628.630
URL: https://scialert.net/abstract/?doi=ajps.2002.628.630
INTRODUCTION
Food production in Pakistan is not keeping pace with population growth. The yield of the major crops is stagnated. The farmers of rainfed areas practice low input agriculture because of high risk due to climatic uncertainties (Razzaq et al., 1990). However judicial use is necessary not only for increasing agricultural output but also for realizing maximum return from the investment of fertilizer. Advice to the farming community for levels of fertilizer application is generated from field trials, using different rates of fertilizer nutrients and deriving mean optimum rates from these trials for various agro-climatic zones.
Soil organic matter content or total N is used as a soil test for predicting fertilizer N requirement in Pakistan (Malik et al., 1984). However, the reliability of this method for any crop has not been established. It has been shown that correlation between total soil N, NH4-N and NO3-N is very poor in soils of rainfed areas of Pakistan and that the crop response to fertilizer N is greatly affected by the initial levels of soil NH4-N plus NO3-N (Rice et al., 1986). Use of N in rainfed wheat is 32 kg ha-1 against the optimum use of 71 kg ha-1 and the use of P2O5 is only 9 kg ha-1 against the optimum use of 48 kg ha-1 (Anonymous, 1993).
The study was conducted with the objective of developing fertilizer recommendations for wheat under various cropping sequence of barani conditions in Potohar area, Pakistan.
MATERIALS AND METHODS
The study consisted of four field experiments at two different sites. Three experiments were conducted on Gujranwala soil series, at the National Agricultural Research Centre (NARC), Islamabad and the fourth experiment on Rajar series, in a farmers field at Mandra, Rawalpindi. Some physical and chemical characteristics of these soils are given in Table 1. The methods used for soil analysis have been described by Winkleman et al. (1986).
Table 1: | Chemical and physical properties of the experimental soils |
Nitrogen @ 0, 40, 80, 120 and P @ 0, 30, 60, 120 kg ha-1 in single as well as in all possible combinations were tested using urea and single super phosphate fertilizers. The experiment was laid out with factorial arrangements in a randomized complete block design having four replications. The fertilizers were broadcast and disked into plots of 1.2 x 10 m2 prior to seeding of wheat.
Sodium bicarbonate extractable P was found 20.7, 10.0, 6.8 and 12.9 mg kg-1 at these sites, respectively. While NH4-N and NO3-N were 16.0 and 11.2 mg kg-1 at site-I, 6.6 and 35.6 at site-II, 5.2 and 10.7 at site-III, and 17.1 and 21.4 at site-IV, respectively.
There were six rows in each plot and only the central four rows with a plot size of 8 m2 were harvested at maturity. Weeding was done manually during the growing season. The grain and straw samples were collected, air-dried and weighed.
The data obtained were analyzed using ANOVA (Steel and Torrie, 1980). Response surface curve methodology (multiple regressions using a quadratic model) was adopted to predict the fertilizer response with the equation given below:
Where N and P stand for nitrogen and phosphorus fertilizers, Y for yield of the crop, a and b unknown constants (Khan et al., 1987).
RESULTS AND DISCUSSION
Grain and straw yield: The statistical analysis indicated that treatments effects were significant for straw and biomass (grain plus straw) at all the four sites (Table 2). However, the effect of fertilizers on grain yield was significant only at site-IV. Relatively higher, but non-significant, grain yield was obtained with N80: P30 treatment at sites-I, II and III. In case of site-IV, N40:P60 produced higher grain weight. The highest rate of combined N and P, i.e. N120: P120 produced relatively more grain weight, though differences were non-significant compared to other treatments.
Application of N fertilizer alone tended to depress the grain yield in summer fallow-wheat sequence at sites-II and IV (Fig. 1). Application of P fertilizer at lower rates showed a positive trend on grain yield at all sites except at site-I (Table 2), where native extractable P level was very high (Table 1). Hobbs et al. (1986) observed that on the mera land (soils where sufficient organic manures are not added) N or P fertilizer applied alone had no significant affect on crop yield. Moreover, combined application of N and P was needed for higher yields under rainfed conditions. Arif et al. (1993) observed maximum economic and biological yield of three wheat cultivars with combined application of N and P @ 140: 60 kg ha-1. Similarly, Akhtar et al. (2002) showed that combined application of NP and K was required for the maximum economic yield of wheat in rainfed areas of Pakistan.
Nitrogen fertilizer application did not affect grain and straw yields at site-II, i.e fallow-wheat sequence on Gujranwala soil series (Table 3). Whereas, on sites-I and III of the same soil series but with different cropping sequence at NARC, i.e. wheat after millet green manuring and after millet harvest, had a marked response to N fertilizer.
Table 2: | Wheat grain yield response to different N and P fertilizer rates at different sites |
Table 3: | Significance of N and P treatment responses on growth parameters of wheat |
* : P < 0.1 | ** : P < 0.05 |
Response to N fertilizer on the site-IV with fallow-wheat sequence, i.e., Rajar series at Mandra was significant despite mineral N contents of this site being almost equal to that of site-II, where no response to fertilizer N was observed. Rice et al. (1986) also observed high build-up applied levels of NO3-N+NH4- N in fallow field of the rainfed area and wheat response to N fertilizer N was greatly affected by the initial levels of NO3-N + NH4-N. The grain and straw yield response to P fertilizer was observed at two sites, i.e. site-II and IV (Table 4). At sites-II and III non-significant treatment effects were observed. At site-IV all P levels tested produced similar results but higher than the control. It indicates that the requirements for vegetative growth and grain production were met with lower rates of P fertilizer application.
The levels of extractable P at site-I were quite high and these levels are generally considered adequate for wheat (Olsen and Somers, 1982; Pala and Matat, 1987), hence no response was observed to the applied P fertilizer. Soil extractable P levels at sites-II and III were low and a marked response to P fertilizer was observed only at site-II, however a little response at site-III. This indicates that large heterogeneity occurred in the soil and profile characteristics other than NP levels that affected the crop response to applied fertilizers. A marked interaction of fertilizers N and P was observed at sites-III and IV for grain yield and for straw weight only at site-IV.
Soil test values and crop response: An attempt was made to relate soil test values with relative crop yield. The extractable P levels and grain yield response to P fertilizer followed a typical response pattern; with low levels of soil test values a high response and vice versa (Fig. 1A). However, the response patterns were markedly influenced by the application of varying levels of N fertilizer (Fig. 1B). In contrast to P response, it was difficult to correlate clearly soil test values of mineral N (NH4-N + NO3-N) with grain yield (Fig. 2A); addition of graded levels of fertilizer P rendered these relationships more intricate (Fig. 2B).
Fig. 1A: | Wheat grain yield response (%) as related to extractable P in soil |
Fig. 1B: | Wheat grain yield response (%) in relation to extractable-P in soil at various levels of N fertilizer |
Fig. 2A: | Wheat grain yield response (%) as related to mineral N in soil |
Fig. 2B: | Wheat grain yield response (%) as related to mineral-N in soils with addition of graded levels of P fertilizer |
Table 4: | Response equations for grain and straw yield at different sites |
Similarly, Pala and Matar (1987) could not develop relationship between soil test values of mineral N with wheat grain yield.
Response surface equations for grain yield: In order to obtain fertilizer response relationship, the quadratic response surface (multiple regressions) model was used. The characteristic of the multiple regression equations suggested that the predictability of this model is reliable only in the case of site-IV experiment (high R2 value), followed by site-III (Table 4). In case of sites-I and II, the R2 values were too low and thus of the limited use for fertilizer response predication. Bhatti and Khan (1999) also tested regression models for predicting the response of wheat to N fertilizer and developed site-specific N requirements both for irrigated and rainfed conditions. These models successfully predicted the fertilizer requirements. The trials conducted by Bhatti and Khan (1999) were simple as the studied a single variable i.e., nitrogen fertilizer as compared to results of the present set of experiments where two variable (N&P) and their different levels were tested.
The cropping sequence and crop management practices affect soil N and P levels and the crop response to applied N and P fertilizer. The relationship between soil P test values and grain yield was predictable to a large extent, whereas it was difficult to correlate mineral N values with grain yield.
ACKNOWLEDGMENTS
Authors gratefully acknowledge Dr. M. I. Khan and Mr. N. A. Khan, Computer and Statistical Section and Mr. M. Zameer Khan and Mr. Sagheer Ahmad, Potash Research Programme, National Agricultural Research Centre, Islamabad, for their technical assistance.
REFERENCES
- Akhtar, M.E., M.Z. Khan, S. Ahmad and M. Akhtar, 2002. Response of wheat to different N, P and K rates of applied fertilizers under rainfed conditions of Pakistan. Asian J. Plant Sci., 1: 337-339.
CrossRefDirect Link