Direct effects of nitrogen source on nitrogen yield and recovery 1. Sorghum

There was no effect of crop rotation in 1999, except in terms of grain and TDM yields of sole compared with intercropped sorghum (Table VI). Nitrogen yields, fertilizer N used and consequently the N recoveries in grain and total dry matter were similar in the two cropping systems (Tables VI and VII). Similar trends were observed with sorghum during the second phase of the rotation, proceeded by castor (Tables VIII and IX), except that fertilizer N used and N recovery in grain, and consequently the total fertilizer N used and total N recovery, were greater with the sole crop than the intercrop.

The N options had significant effects on N yield, fertilizer N used and N recovery. In the first year, the total N yield for sorghum, averaged over sole and intercrops, significantly increased with FYM + urea (52.6) over FYM alone (40.9) (Table VI). Application of 60 kg N ha^–1 as urea resulted in significantly higher N yield (69 kg ha^–1) over the FYM + urea treatment. The total N yield of sorghum was significantly greater with application of 60 kg N ha^–1 as urea (80.8 kg N ha^–1), compared to FYM + urea, and both were superior to FYM at 1.5 t ha^–1 (39.0 t ha^–1) under sole crop, whereas in the intercrop all three were similar.

During the second year, higher total-N uptake was observed with urea at 60 kg N ha^–1 (87.7 kg ha^–1) followed by the FYM + urea treatment over FYM alone (43.6 kg ha^–1) (Table VIII). When intercropped, N treatments had no effect on sorghum N yield.

Cropping system had no influence on fertilizer N from different sources in sorghum stalk or chaff (data not shown); for grain and total fertilizer N used during the second year, higher values were obtained for the sole crop than the intercrop (Table IX).

In both years, N yield of sorghum from urea was significantly greater than from FYM (Tables VII and IX). The total fertilizer N used from FYM when applied with urea was similar to that as a sole application. Application at 60 kg N ha^–1 gave higher values for total fertilizer N used over that of urea used in combination with FYM.

Higher recoveries of N were observed in stalk and grain of sorghum compared to that of chaff. In sole-cropped sorghum, the N recovery in grain from FYM varied from 1.7% when used alone to 4.2% in combination with urea during the first year and from 2.4% to 4.0% in the second year, respectively.

The grain N recovery from urea at 60 kg N ha^–1 was lower (14%) compared to that of urea (17%) used at 45 kg N ha^–1 in conjunction with FYM.

Similarly, with intercropping, N recovery from urea at 60 kg N ha^–1 was lower (11%) compared to that from urea used along with FYM (14%). The same was the case with FYM (data not shown).

We estimated total N recoveries of 34% and 23% in sole and intercropped sorghum from 60 kg N ha^–1 as urea, respectively. With FYM + urea, the N recoveries in sole and intercropped sorghum from urea were 34% and 28% during the first year (Table VII).

The N recovered from FYM in sole sorghum ranged between 5.9% with FYM alone to 7.8% in combination with urea (Table VII). Intercropped sorghum recovered 6.2% of the FYM N when combined with urea and 5.4% from FYM alone (Table VII).

During the second year a similar trend was observed in sorghum recoveries when preceded by castor.

However cropping system had a significant effect on N recovery (%) in grain and total N recovery (Table IX).

The grain and total N recoveries (over N treatments) by sole sorghum were higher than those of the intercrop. Higher total N recovery (28%) was obtained when urea was applied in combination with FYM than when applied alone at 60 kg N ha^–1 (23%). The N-recovery percentages from FYM in stalk, chaff and grain (data not shown) and total recovery were similar whether applied alone or in conjunction with urea (Table IX).

The total N recovery from urea was higher in the sole crop (27%) than in the intercrop (19%) at 60 kg N ha^–1. Similarly, in the FYM + urea treatment, the sole-cropped sorghum recorded higher total N recovery (30%) from urea than did the intercrop (27%). The contribution from FYM when used in combination with urea was greater than when applied along to the sole crop (Table IX).

Table VI. Effects of cropping system and nitrogen-management options on dry matter and nitrogen yields of sorghum (1999) Grain TDMGrain N Total N Sole crop Inter- crop Mean Sole crop Inter- crop Mean Sole cropInter- crop Mean Sole cropInter- crop Mean N option (kg ha–1 ) FYM ϕ FYM+urea FYM+ϕ urea 60N urea

854 2,259 2,259 2,326

906 1,748 1,748 1,847

880 2,003 2,003 2,087

6,936 8,431 8,431 9,121

6,392 7,072 7,072 6,825

6,664 7,751 7,751 7,973

13.9 13.1 32.0 39.5

15.2 26.4 25.7 30.6

14.5 29.2 29.9 35.1

39.0 57.8 61.1 80.8

42.8 47.4 47.0 57.2

40.9 52.6 54.0 69.0 Mean 1,9241,5628,2306,840 29.424.5 59.748.6 CSa Nb N×CSCS×NCS N N×CSCS×NCS N N×CSCS×NCS N N×CSCS×N F test *c *** ** ** ** *** ** ** NS *** NS NS NS *** ** ** SEM±27.2 52.0 73.5 69.2 72.4 146.4207.1 193.4 1.361.52 2.15 2.31 2.382.02 2.86 3.44 C.D.(0.05) 165 160 226 210 441 451 638 587 – 4.67 – – – 6.23 8.81 11.4 C.V.(%) 7.3 4.8 14 9.1 able VII. Effects of cropping system and nitrogen-management on fertilizer nitrogen used, total nitrogen recovery and soil contribution in sorghum (1999) Fertilizer N used in grain Total fertilizer N used Total N recovery Soil N contribution Sole crop Inter- crop Mean Sole crop Inter- crop Mean Sole crop Inter- crop Mean Sole cropInter- crop Mean N option (kg ha–1 ) (%) (kg ha–1 ) FYM ϕ FYM+urea FYM+ϕ urea 60N urea

0.52 1.25 7.63 8.45

0.55 1.02 6.39 6.68

0.53 1.14 7.01 7.57

1.77 2.35 15.2 20.2

1.65 1.87 12.4 14.0

1.71 2.11 13.8 17.1

5.9 7.8 34 34

5.5 6.2 28 23

5.7 7.0 31 29

37.2 55.5 45.9 60.6

41.2 45.5 34.6 43.2

39.2 50.5 40.2 51.9 Mean 4.46 3.66 9.89 7.48 20 16 49.8 41.1 CSa Nb N×CS CS×NCS N N×CS CS×NCS N N×CS CS×NCS N N×CS CS×N F test NS ***c NS NS NS *** NS NS NS *** NS NS NS ** * * SEM±0.22 0.25 0.34 0.38 0.70 0.83 1.17 1.23 1.3 1.5 2.2 2.3 1.8 2.17 3.07 3.23 C.D.(0.05) – 0.74 – – – 2.55 – – – 4.7 – – – 6.69 9.47 10.09 C.V.(%) 15 23 21 12 Labelled source. a Cropping system. b Nitrogen option. c *, ** and *** denote significance at P= 0.05, 0.01 and 0.001, respectively.

Table VIII. Effects of nitrogen-management options on grain, TDM and nitrogen yields of sorghum preceded by castor (2000) Grain TDMGrain N Total N Sole crop Inter- crop Mean Sole crop Inter- crop Mean Sole cropInter- crop Mean Sole cropInter- Crop Mean N option (kg ha–1 ) FYM ϕ FYM+Urea FYM+ϕ Urea 60N Urea

1,454 2,814 2,814 2,666

1,196 2,210 2,210 2,056

1,325 2,512 2,512 2,361

7,603 11,339 11,339 11,412

7,658 8,532 8,532 8,456

7,631 9,936 9,936 9,934

16.3 34.5 34.9 32.9

16.3 25.5 24.6 25.7

16.3 30.0 29.8 29.3

43.6 79.6 84.9 87.7

57.8 57.8 58.4 60.4

50.7 68.7 71.6 74.0 Mean 2,437 1,91810,423 8,29529.6 23.0 73.9 58.6 CSa Nb N×CS CS×NCS N N×CS CS×NCS N N×CS CS×NCS N N×CS CS×N F test NS ***c NS NS NS ***** ** NS *** * * NS ** ** ** SEM±149 91 129 186 541 325 207 193 3.3 1.1 1.6 3.6 9.3 4.0 5.7 10.5 C.D.(0.05) – 281 – – – 1,002638 5867 – 3.5 5.0 17.2 – 12.4 17.5 45.3 C.V.(%) 10 8.5 11 15 Table IX: Effects nitrogen-management options on fertilizer nitrogen used, total nitrogen recovery and soil contribution in sorghum preceded by castor (2000) Fertilizer N in grain Total fertilizer N used Total N recovered Soil contribution Sole cropInter- crop Mean Sole cropInter- crop Mean Sole cropInter- crop Mean Sole cropInter- crop Mean N option (kg ha–1 ) (%) (kg N ha–1 ) FYM ϕ FYM+Urea FYM+ϕ Urea 60N Urea

0.71 1.20 5.48 5.91

0.50 0.81 4.50 4.93

0.60 1.00 4.99 5.42

2.00 2.86 13.4 15.9

1.94 1.86 11.9 11.7

1.97 2.36 12.7 13.8

6.7 9.5 30 27

6.5 6.2 27 19

6.6 7.9 28 23

41.6 76.7 71.5 71.8

55.9 56.0 46.4 48.7

48.8 66.3 58.9 60.2 Mean 3.33 2.68 8.54 6.84 18 15 65.4 51.8 CSa Nb N×CSCS×N CS N N×CSCS×N CS N N×CSCS×N CS N N×CSCS×N F test *c *** NS NS ** *** NS NS * *** NS NS NS NS * * SEM±0.10 0.38 0.54 0.48 0.06 0.59 0.83 0.72 0.40 1.3 1.8 1.6 9.21 3.98 5.63 10.42 C.D.(0.05) 0.62 1.18 – – 0.36 1.81 – – 2.4 4.0 – – – – 17.3 45.0 C.V.(%) 31 19 19 17 ϕ Labelled source. a Cropping system. b Nitrogen option.c *, ** and *** denote significance at P= 0.05, 0.01 and 0.001, respectively.

3.2.2. Castor

The total N yield in the aboveground parts at harvest during the first year increased from 60.5 kg ha^–1 with FYM to 78.3 kg ha^–1 at 60 kg N ha^–1 as urea. The N yield from urea (76.2 kg ha^–1) used along with FYM was similar to that obtained with urea at 60 kg N ha^–1(Table X). A similar trend was seen with regard to N yield in grain (Table X).

The N used from FYM (3.11 kg ha^–1) and consequently the manure-N recovery (10%) were slightly higher when applied in combination with urea at 45 kg N ha^–1 over FYM applied alone (2.18 kg ha^–1; 7.3%). The total N recovered from urea was significantly greater (27%) when used along with FYM over that when urea was applied alone (22%) (Table XI).

Grain-N and total-N accumulations by castor averaged over N treatments were higher in 2000 when preceded by sorghum/pigeon pea (38.5; 57.1 kg ha^–1) compared to those preceded by sole sorghum (35.0; 52.3 kg ha^–1), although the differences were not significant (Table XII). Similar trends were seen in N yield of stalk and chaff (data not shown). The N-management options combining organic and chemical sources had a significant influence on N yield, fertilizer N used and fertilizer N recovery values (Table XII and XIII). Significantly greater values for urea N used were obtained for grain as well as for total fertilizer-N when applied alone at 60 kg N ha^–1 over those obtained when applied with FYM. However, the N recoveries were similar in both treatments.

3.2.3. Pigeon pea

The pigeon pea crop took little N (<1.0%) from either urea or from FYM. The %N derived from fixation (%Ndfa) determined using the ¹⁵N-dilution method (using a long-duration sorghum as the reference crop) was estimated as 43% and 65% in sole and intercropped pigeon pea, respectively (data not shown).