Optimal fertilizer requirement of rainfed sunflower based on varying soil moisture stress indices on semi-arid vertisols of India

Abstract

Six field experiments were conducted on sunflower with treatments comprising of 4 dates of sowing (sown during different standard meteorological weeks viz., 28 (9-15 July), 30 (23-29 July), 32 (6-12 August) and 34 (21-26 August), 3 moisture conservation methods (ridge & furrow, skip row with furrow and flat bed) and 3 levels of fertilizer NP (40-20, 50-25 and 60-30 kg/ha) during kharif 1999 to 2004 at Solapur on semi-arid vertisols. Based on daily rainfall (RF), daily runoff (RO) and crop soil moisture stress index (MSI) were measured for each combination of date of sowing (DOS) and moisture conservation (MC) method in each season. Correlation analysis indicated a positive relation of seed yield with rainfall in all 4 DOS. The relation was relatively higher for flat bed in 1st DOS, ridge & furrow in 2nd DOS, skip row with furrow in 3rd and 4th DOS. It was negatively related with RO in 1st DOS, but positively related with the other 3 DOS. The relation was higher under ridge & furrow system in 1st DOS (negative) and 4th DOS (positive), while under flat bed in 2nd and 3rd DOS. Negative relation of MSI was found with yield under all the 12 combinations of DOS and MC indicating a higher relation under skip row with furrow in 1st, 2nd and 4th DOS, and flat bed in 3rd DOS. The relation between RF and RO was positive, while MSI had negative relation with both RF and RO. Regression models of seed yield through RF, RO, SMI, fertilizer N and P, along with fertilizer x MSI interaction were calibrated. The predictability ranged from 0.12 (ridge and furrow in 3rd DOS) to 0.91 (flat bed in 1st DOS). A ready reckon of optimal N and P doses at varying MSI levels (0.15 to 0.75) indicated that ridge and furrow method is efficient in 1st DOS with an optimal N and P ranging from 51 to 53 kg/ha and 26 to 27 kg/ha, respectively. Skip row with furrow method was efficient when crop was sown in any of the other DOS with an optimal N ranging from 38 to 66 kg/ha (2nd DOS), 44 to 73 kg/ha (3rd DOS) and 47 to 74 kg/ha (4th DOS). The optimal P ranged from 19 to 33 kg/ha (2nd DOS), 22 to 36 kg/ha (3rd DOS) and 24 to 37 kg/ha (4th DOS) for attaining maximum productivity of sunflower on semi-arid vertisols.