ORGANIC MATTER DECOMPOSITION AND ITS EFFECT ON AVAILABLE  NITROGEN, PHOSPHORUS AND POTASSIUM IN MOUNTAIN CROP FIELD SOILS

Supervisors:

Prof. O.P. Sati, Department of Chemistry, Birla Campus, .HNB Garhwal University, Srinagar 

Dr. G.C.S. Negi GBPIHED, Almora

Summary:

1) In the Western Himalyan mountains 90% agriculture is practiced on sloping cropfields. These cropfields are poor in soil nutrients (organc carbon, N, P, K etc.), and has low crop yield. Soil nutrients get depleted due to rainwater-runoff and soil erosion. Farmers apply massive amounts of farm yard manure (FYM) to replenish the soil fertility at every crop sowing season.

 

2) The FYM consists of either Oak (Quercus spp.) or Pine (Pinus roxburghii) tree leaves. As a result these forests are under heavy stress due to removal of the manuring leaves regularly. Lantana camara, a shrub weed has extensively invaded in these forests and the adjoining cropfields. Therefore, efforts are required to make use of Lantana leaves as a suitable OM to replenish the soil fertility.

 

3) This research was conducted during 1999-2002 to investigate, among the three leaf OM (viz., Oak, Pine and Lantana) which one is superior with regard to soil fertility improvement and whether FYM application practice in traditional agriculture is more beneficial for soil fertility replenishment and crop yield.

 

4) Detailed experimental work for the present research was carried out in rain-fed crop fields at Dobh-Srikot village of Pauri district in Garhwal Himalaya, Uttaranchal State. The study site is located at 1200 m asl. altitude (30o 11' N latitude and 78o 48' E longitude) and falls into sub-tropical climate. This site receive 702 mm rainfall (mean for 1999-2001), two-third of which occurs during rainy season (mid June to mid September). The mean monthly maximum temperature was recorded in September (31.8 0C), and the mean monthly minimum in January (19 0C). The mean annual temperature was 25.8 0C. Pan evaporation was recorded 39% of the annual rainfall.

 

5) In November 1999, 36 experimental plots  (3 rows of 12 plots each) of 10 m2 size were created in the rain-fed crop fields at the study site. Four plots, one each for no-mulch (control), Oak, Pine and Lantana mulch were selected alternatively among a row 12 of these experimental plots. Three sets of four plots each for these OM mulch were maintained thus making a total of nine plots under each mulching treatments. A set of nine was maintained as control (no-mulch). In addition, six plots were maintained for traditional farming practice, which involve twice tilling and use of FYM.

 

6) Tillage operations (digging) (no-tillage, once tillage and twice tillage) were done for each of the mulched plots, thus making different mulch and tillage combinations (Fig. 2.2: Chapter II). Semi-decomposed leaf organic matter of Oak, Pine and Lantana was spread into the experimental plots (Pine = @ 5.27 kg/plot; Oak =  @ 4.13 kg/plot and Lantana = @ 3.87 kg/plot) soon after seed sowing. FYM @ of 3.85 kg/plot was added in the experimental plots maintained for traditional practice. The quantity of mulch material was equated with the N input through FYM in traditional practice.

 

7) Local varieties of staple food crops, wheat and rice were sown in these experimental plots. Each crop was repeated for two cropping seasons starting with wheat sowing in November 1999, followed by rice sowing in June 2000: again wheat sowing in November 2000 and rice sowing in June 2001. Study was thus conducted from wheat crop sowing in November 1999 till the rice crop harvest in September 2001.

 

8) Soil temperature and soil moisture were monitored in all the experimental plots throughout the wheat and rice crop growing seasons at monthly intervals. Mean soil temperature across all the experimental plots was recorded maximum (35 0C) in April 2000, and minimum temperature in December and January (mean= 12 0C). Mean soil temperature across the study period was recorded highest for 2T/FYM (27 0C) and lowest for control (without mulch) plots (23 0C). Analysis of variance (ANOVA) shows that soil temperature was significantly different (P < 0.05) among the experimental plots.

 

9) Mean soil moisture across all the treatment plots was found maximum during rainy season (16% in July 2000). Soil temperature dropped critically to all time low (mean = 0.77 %) in March 2001. Across all the experimental plots and study period mean soil moisture was found almost equal (9% under 2T/FYM and control plots to 10% under Oak and Pine mulched plots). ANOVA shows that the soil moisture was significantly different (P<0.05) among the experimental plots. Both soil moisture and soil temperature were closely related (P<0.05). The higher the soil moisture the higher the soil temperature and vice-versa.

 

10) Leaf OM of all the three species was studied for decomposition and nutrient release pattern. The rate of decomposition was found different for the three species. Decomposition in Pine was comparatively slower than Oak and Lantana. During the whole study period (450 days from placement of litter for decomposition) only 43.2% Pine leaf OM was decomposed, which was found 48.8% in Oak. Lantana leaf OM decomposed at a faster rate and recorded 93.3% decomposition in 300 days. In all the three species leaf OM decomposed at a faster rate during rainy season.

11) Rate of decomposition (expressed as mg dry matter loss per gram of OM per day) was found maximum for Lantana (3.1 mg/g), followed by Oak (1.1 mg/g) and Pine (0.96 mg/g). Considering this rate of OM loss, Pine may take 1042 days, Oak 926 days and Lantana 323 days for total OM decomposition. Turnover rate (K) for Lantana was found highest (0.68), followed by Oak (0.54) and Pine (0.46).

 

12) Initial N, P, and K concentrations in Lantana leaves was found highest among other two leaf OM studied. On an average, the N concentration in Lantana leaves was three times higher than Pine, and P and K concentrations were 6.5 and 8 times higher than Oak leaves.

 

13) Concentration of N in residual OM markedly increased both for Pine and Oak for the initial six to seven months but declined substantially in Oak afterwards. In Lantana, an initial decline in N concentration was recorded during winters, which increased marginally at the end of winter season and stabilized thereafter.

 

14) P concentration in the decomposing leaf OM was also found variable for all the three plant species. Concentration of P in residual OM of Pine decreased initially and increased thereafter. Oak showed marginal increase in P concentration throughout the study period. In contrast to Oak, a marginal decline in P concentration was observed in Lantana throughout the study period.

 

15) Different from the pattern of N and P concentrations in decomposing OM, an initial decline in K concentration was observed for all the three species, which increased during rainy season for Oak and Pine, and throughout the study period for Lantana. In both Pine and Oak leaf OM, concentration of P and K was found higher at the end of the study period as compared to the initial, and the reverse was true for Lantana.

 

16) Significant negative relationship was found between nutrient concentration in residual OM and weight of OM remaining in litter bags for Pine and Oak, whereas this relationship was positive for Lantana. Lantana OM having high nutrient concentration decomposed at a faster rate and released nutrients rapidly than the other two species.

 

17) Soil organic carbon (OC) was low  (0.96%) in the experimental plots at the start of the experiment in November 1999. Subsequent to application of mulch (Oak, Pine and Lantana) leaf OM and FYM the soil OC increased in all the experimental plots till following rainy season, and declined thereafter. Mean concentration of OC was recorded highest (1.06%) for Lantana OM mulched plots and lowest (0.97%) for control. Across all the experimental plots and study period maximum OC was recorded for 2T/L (1.20%) in July and minimum for NT/C (0.79% in January). Mean OC concentration across all the experimental plots at the end of the study period was found in the order: Lantana (1.06%) > 2T/FYM (1.05%) > Oak (1.03%) > Pine (0.99) > Control-no mulch (0.97%).

 

18) Mean values of soil pH across all the experimental plots for the entire study period were found ranging between 5.77 (NT/C) and 6.29 (1T/L). In general, soil pH was high under Lantana mulched plots (mean= 6.22) and low under Oak mulched plots (mean= 5.86). A common belief that Pine mulch makes soil acidic was not found true in this experiment.

 

19) Organic N concentration in soil was found variable (ANOVA significant at P<0.05) across the study period for all the experimental plots. Across all the experimental plots the highest concentration of N was recorded under 2T/L (0.31%) in March 2000 and minimum for 2T/FYM (0.18%) in September 2001. The peak concentration of N in soil was recorded in March for all the treatments, and minimum in September.

 

20) Across all the experimental plots and entire study period the mean concentration of soil N was recorded maximum for plots mulched with Lantana (0.261%) and minimum (0.225%) in the plots without any mulch. N concentration was found an all time minimum at the end of the study period (i.e. at the harvest of rice crop in September 2001) for all the experimental plots (mean= 0.22%).

 

21) Mean soil N concentration across the wheat and rice crops separately (0.247 Vs 0.242%) across all the experimental plots was significantly different (t= 3.85, P < 0.01). For both the crops Lantana mulched plots had higher soil N concentration. In terms of N kg ha-1 the values range from a minimum of 1800 kg ha-1 for 2T/FYM in September 2001 and 6200 kg ha-1 for 2T/L in March 2000.

 

22) NO3-N concentration in soil was also found variable (ANOVA significant at P<0.05) for all the experimental plots. Mean value of NO3-N concentration across the entire study period and experimental plots was highest for 2T/O (8.40 µg/g) in July 2000 and lowest for NT/C (1.45 µg/g) in January 2000.  At the end of the study period the mean concentration of soil NO3-N was recorded maximum for plots mulched with Pine (5.71 µg/g) and minimum (3.72 µg/g) for control plots. NO3-N concentration followed an increasing trend for all the experimental plots throughout the study period, starting from a minimum concentration (1.13 µg/g) initially in November 1999.

 

23) Mean NO3-N concentration across for all the experimental plots during rice crop was significantly higher (t=7.54; P < 0.01) than it was under the wheat crop (5.71 Vs 4.63 µg/g). Across both the crops NO3-N concentration was found maximum under Pine mulched plots.

 

24) NH4-N concentration in soil of all the experimental plots was also found variable across the study period (ANOVA significant at P<0.05). Across the entire study period and experimental plots the highest concentration of NH4-N was recorded under 2T/L (8.0 µg/g) in March 2000 and minimum for NT/C (2.80 µg/g) in January 2000. Mean NH4-N concentration in soil across all the treatment and study period was found in the following order: Lantana (6.17) > Oak (5.07) > Pine (4.98) > FYM (4.69) > Control (3.78).

 

25) Mean NH4-N concentration across all the experimental plots during rice crop (5.38 µg/g) was significantly greater (t= 9.24; P<0.01) than the mean across wheat crop (4.71 µg/g). In terms of kg ha-1 the NH4-N value range from 2.46 (initially in November 1999) to 16 kg ha-1 for 2T/L in March 2000.

 

26) Mean C: N ratio in soil across all the experimental plots fall in a narrow range of 3.9-4.5 for wheat crop (mean = 4.13), and from 3.9-4.7 for rice crop (mean = 4.33).

 

27) Exchangeable P concentration in soil of the experimental plots was variable across the study period (ANOVA significant at P<0.05). Across the entire study period and experimental plots the highest concentration of P was recorded under 1T/L (0.097 ppm) in July and May 2001 and minimum for NT/O (0.005 ppm) in September 2000. A high mean concentration of P was found for rice under Lantana OM treated soils and for wheat crops under 2T/FYM. For the other OM treated soils (oak and pine) the soil P concentration for both the wheat and rice crop season was almost the same.

 

28) In general, Lantana mulched plots recorded highest P concentration (mean = 0.047 ppm) for the entire study period and this value was found lowest (0.027 ppm) for Oak mulched plots. P concentration was found an all time minimum at the end of the study period (i.e. at the harvest of rice crop in September 2001).

 

29) Exchangeable K concentration in soil of the experimental plots was found variable across the study period (ANOVA significant at P<0.05). Mean K concentration across the entire study period and experimental plots was recorded maximum under 2T/L (1.37 ppm) in May 2001 and minimum under 2T/C (0.33 ppm) in September 2001. In general, mean values of soil K across the whole study period was maximum (1.01 ppm) for plots mulched with Lantana and minimum for control plots (0.76 ppm).

 

30) Across the two crop seasons (wheat and rice) the mean concentration of soil K was recorded maximum for plots mulched with Lantana (0.95 ppm) and minimum (0.67 ppm) under control (no-mulch) plots. Concentration of K was found declining in the initial stage of crop growth and which increased there after towards the end of the crop season.

 

31) During wheat crop growing season (20 November 1999 to 20 April 2000) mean N-concentration in the leached soil was found maximum for 2T/O and 1T/C (0.52%) and minimum for 1T/P and 2T/FYM (0.30%). In general, the mean N concentration was found maximum (0.42%) for plots without mulch (control) and minimum for pine OM mulched plots (0.28%). ANOVA indicates that the mean N-concentration in silt was significantly different (P < 0.05) across all the experimental plots and runoff events.

 

32) Mean N-concentration in the runoff water across the wheat crop growing season was found highest in NT/C (0.12%) and lowest in 2T/FYM (0.04%) and 2T/P (0.04%). ANOVA showed that the mean N-concentration in runoff across all the experimental plots was significantly different (P<0.05).

 

33) During rice crop growing season (14 June 2000 -10 October 2000) mean N-concentration in leached soil was found maximum for 2T/FYM (1.52%) and minimum for NT/C (0.92%). In general, the mean N-concentration in silt fall in a narrow range (1.08-1.12%) for all the OM mulched treatment plots, except for 2T/FYM plots (1.52%). Analysis of variance showed that mean N-concentration in silt was significantly different (P < 0.05) across all the experimental plots and runoff events.

 

34) Mean N-concentration in the runoff water during rice crop was found highest in 2T/FYM (0.125%) and lowest in 2T/L (0.065%). In general, N-concentration in runoff water from Oak mulched plots was poor in N (0.074%) and that collected from 2T/FYM plots was rich in N (0.125%). ANOVA showed that the mean N-concentration in runoff water across all the experimental plots and runoff events was significantly different (P<0.05).

 

35) During the wheat crop season the total amount of N (g/plot) lost through silt loss was recorded minimum for NT/P  (0.012) and maximum for 2T/FYM (2.4). Quantity of N lost through runoff water was found maximum for 2T/FYM (1.43 g/plot) and minimum for 1T/L (0.198 g/plot). The total N loss through these two components  (silt loss+ runoff) was recorded maximum for 2T/FYM (3.82 g/plot) and minimum for NT/P (0.216 g/plot). In general, Pine OM mulched plots lost a minimum amount of N through silt loss and runoff (0.357 g/plot) and 2T/FYM plots lost about 11 times more N (g/plot) than this minimum. Lantana mulched plots lost lower amounts of N through leaching (0.419 g/plot).

 

36) During the rice crop season the total amount of N (g/plot) lost through silt loss was recorded minimum again for 1T/P  (0.264) and maximum for 1T/O (1.86). Quantity of N lost through runoff water was found maximum for 2T/FYM (0.140 g/plot) and minimum for 2T/O (0.066) and NT/O (0.068 g/plot). The total N loss through these two components  (silt loss + runoff) was recorded maximum for 1T/C (1.96 g/plot) and minimum for 1T/P (0.37 g/plot). In general, Pine OM mulched plots lost lowest N (0.60 g/plot) and 2T/FYM plots the highest (1.50 g/plot). Lantana mulched plots lost intermediate amounts of N through leaching (1.10 g/plot).

 

37) The total annual loss of N through leaching (silt loss + runoff, kg ha-1) summed up for wheat and rice crop season was found in the following order: 2T/FYM (5.02) > control (2.43) > Oak mulch (0.91) > Lantana mulch (0.62) > Pine mulch (0.48).

 

38) Mean N-enrichment ratio across the wheat crop growing season was found ranging between 0.72 (NT/O and 2T/P) to 1.39 (1T/C). This ratio was found in the range of 2.0 (1T/L)-3.52 (2T/FYM) for rice crop. When mean value of ER was calculated across the annual crop cycle (wheat + rice crops) the maximum value was recorded for 2T/FYM (2.14) and the minimum for 1T/L (1.42). In general, across the three organic mulch materials lowest ER ratio was recorded for Pine (1.56) and Lantana (1.57).

 

39) Grain yield for wheat was recorded maximum under 2T/L (0.669 kg/plot) and minimum for NT/L (0.308 kg/plot). In general, mean grain yield for plots mulched with Lantana OM was highest (0.522 kg/plot) and for 2T/FYM (0.386 kg/plot) was the lowest. Yield of straw was recorded maximum (1.34 kg/plot) for control and (1.33 kg/plot) Oak mulched plots and minimum (0.95 kg/plot) for Pine mulched plots. ANOVA indicates that both grain yield (P<0.05) and straw yield (P<0.05) were significantly different among the experimental plots mulched with different OM in this experiment.

 

40) Total crop yield (grain + straw) was recorded maximum for Oak mulched plots (1.83 kg/plot) and minimum for Pine mulched plots (1.28 kg/plot). Across all the experimental plots rice yield was recorded maximum under 1T/P (0.513 kg/plot) and minimum under 2T/FYM (0.049 kg/plot).

 

41) Wheat grain produced under Lantana OM mulch was high in N (1.86%), P (0.20%) and K (0.18%) concentration. The wheat grain produced under control (no-mulch) had the lowest concentration (N= 1.48%, P= 0.16% and K= 0.14%). Highest concentration of these nutrients was also recorded for wheat straw grown under Lantana mulch. ANOVA indicates that this difference in nutrient concentration in both grain (P<0.05) and straw (P<0.05) across all the experimental plots was significant.

 

42) Rice grain produced under Lantana mulch was high in N (0.996%), P (0.278%) and K (0.315%) concentration, and that produced under no-mulch (control) had the lowest concentration (N= 0.79%; P= 0.251% and K= 0.248%). Highest concentration for all these three nutrients was also recorded for rice straw grown under Lantana mulch. The rice straw grown under control (no-mulch) was poorer in all these three nutrients. ANOVA indicates that this difference in nutrient concentration in both grain (P<0.05) and straw (P <0.05) was significant. Corresponding to the N status of grain, the proportion of protein was also found maximum in Lantana mulched plots (13.03%) and minimum in control (no-mulch) plots (10.73%).

 

43) In wheat crop concentration of both soluble sugar (0.335%) and reducing sugar (0.265%) were found highest in grain produced under Lantana mulch. The non-reducing sugar was found highest in grain produced in Pine mulched plots. The minimum concentration of all these three forms of sugars were found in grain produced under control (no-mulch) plots.

 

44) The soluble sugar and reducing sugar content in grain were positively correlated (r = 0.853; P < 0.01), whereas the reducing sugar and non-reducing sugar were unrelated (r = 0.230), and soluble sugar and non-reducing sugar were weakly negatively related (r = -0.204).

 

45) Concentration of both soluble (0.548%) and non-reducing sugar (0.330%) were found highest in rice grain produced under Lantana mulched plots, but the reducing sugar was found highest (0.267%) under traditional farming. The concentration of soluble sugar and reducing sugar (r=0.354; P<0.01) were positively correlated, and soluble sugar and non-reducing sugar (r=0.128) were found unrelated. However, significant positive correlation was found between reducing sugar and non-reducing sugar (r=0.966; P < 0.01).

 

46) In conclusion, this research has found out that traditional ways of crop cultivation using FYM is non-remunerative, as it neither yields good crop harvests, nor restores soil fertility. Soil and water conservation effects of this practice is also minimal. Lantana weed due to its fast decomposition and release of nutrients improves soil fertility, boosts the cropyield and conserves soil and water from erosion loss. The two commonly used OM materials (Oak and Pine) were inferior compared to Lantana in one way or another. Therefore, Lantana leaf OM can suitably be used as a mulch in the mountain rain-fed farming.

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K.D. Kandpal  

Subject : ORGANIC CHEMISTRY

Ph. D - Chemistry HNB Garhwal University, Srinagar

Correspondence Address:    K.D. Kandpal, LWRM/GBPIHED, Kosi-Katarmal, Almora,Uttaranchal-263 643

Work Title

Organic matter decomposition and its effect on available nitrogen, phosphorus and potassium in mountain crop field soils